bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒03‒15
thirty-five papers selected by
Richard Halfpenny
Staffordshire University


  1. Vector Borne Zoonotic Dis. 2020 Mar 05.
    Musa AA, Muturi MW, Musyoki AM, Ouso DO, Oundo JW, Makhulu EE, Wambua L, Villinger J, Jeneby MM.
      Background: Zoophilic mosquitoes play an important role in the transmission of arboviruses of medical importance at human-wildlife interfaces, yet arbovirus surveillance efforts have been focused mostly on anthropophilic mosquitoes. Understanding the diversity of zoophilic mosquitoes and their associated feeding patterns and arboviruses can inform better vector control strategies. Materials and Methods: We morphologically identified mosquitoes collected from two game reserves in Kenya, the Maasai Mara National Reserve (MMNR) and locations near the Shimba Hills National Reserve (SHNR). Representative mosquitoes were also identified by cytochrome c oxidase subunit 1 (COI) barcode sequencing. In addition, we identified the vertebrate hosts of mosquito blood meals from the contents of each mosquito's abdomen by high-resolution melting (HRM) analysis and sequencing of COI, 16S ribosomal RNA, and cytochrome b gene PCR products. Similarly, mosquito arbovirus infections were identified by HRM analysis and sequencing of Alphavirus- and Flavivirus-specific RT-PCR products. Results: Of 2858 mosquitoes collected, 51 were engorged with blood meals from seven different vertebrate hosts, including humans, birds, domestic, and peridomestic animals and wildlife. Culex was the most abundant mosquito genus, with Culex pipiens being the most abundant species in both study regions. Among MMNR samples, we detected dengue serotype-2 virus (DENV-2) for the first time in Aedes tarsalis and Aedes tricholabis, as well as Sindbis virus in male Cx. pipiens. We also detected DENV-2 in Aedes aegypti sampled from locations near the SHNR. Human and diverse wildlife blood meals were identified, including bushbuck blood in the dengue-infected Ae. tarsalis and both human and hippopotamus blood in a single Eretmapodites chrysogaster mosquito. Conclusions: Our findings highlight the potential risk of sylvatic dengue and Sindbis transmission to humans by zoophilic mosquitoes at human-wildlife interfaces in Africa. Of specific importance, we provide evidence of sylvatic DENV-2 in Ae. tarsalis and Ae. tricholabis, representing potential new dengue vectors.
    Keywords:  Aedes; Eretmapodites; Sindbis virus; dengue virus; mosquito blood meal; zoophilic mosquitoes
    DOI:  https://doi.org/10.1089/vbz.2019.2563
  2. Parasitol Int. 2020 Mar 10. pii: S1383-5769(20)30049-0. [Epub ahead of print] 102099
    Vivekanandhan P, Bedini S, Shivakumar MS.
      The repeated usage of chemical insecticides, responsible for insecticide resistance in mosquitoes and environmental toxicity. Currently effective and environmental-safe control strategies are needed for the control disease-vector mosquitoes. Entomopathogens can be an effective alternative to chemical insecticide. Herein we isolated and tested 46 soil-borne entomopathogenic fungi belonging to six genera, namely Beauveria sp., Metarhizium sp., Fusarium sp., Aspergillus sp., Trichoderma sp., and Verticillium sp., fungi conidia were tested on Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus larvae. Bioassays results show that M. anisopliae fungal isolate causes a 100%, 98.6% and 92% mortality within six days, on Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus, respectively. M. anisopliae treated three mosquito larvae have lower lifetime with LT50 values in A. stephensi, 2.931 days; A. aegypti, 2.676 days and C. quinquefasciatus, 3.254 days. 18 s rDNA sequence analysis confirmed that the isolated fungus are belonging to the genus of M. anisopliae-VKKH3, B. bassiana-VKBb03, and V. lecanii-VKPH1. Our results clearly show that M. anisopliae has good potential, as a low-cost, environmentally safe tool for the control of A. aegypti, A. stephensi, and C. quinquefasciatus mosquitoes.
    Keywords:  Aedes aegypti; Anopheles stephensi; Culex quinquefasciatus; Eco-friendly; Entomopathogenic fungus; Larval bioassay; Microbial pesticide
    DOI:  https://doi.org/10.1016/j.parint.2020.102099
  3. J Med Entomol. 2020 Mar 11. pii: tjaa031. [Epub ahead of print]
    Yang F, Schildhauer S, Billeter SA, Hardstone Yoshimizu M, Payne R, Pakingan MJ, Metzger ME, Liebman KA, Hu R, Kramer V, Padgett KA.
      Insecticide resistance in Aedes aegypti mosquitoes poses a major threat to public health worldwide. There are two primary biological mechanisms that can lead to insecticide resistance, target site and metabolic resistance, both of which confer resistance to specific classes of insecticides. Due to the limited number of chemical compounds available for mosquito control, it is important to determine current enzymatic profiles among mosquito populations. This study assessed resistance profiles for three metabolic pathways, α-esterases, β-esterases, and mixed-function oxidases (MFOs), as well as insensitivity of the acetylcholinesterase (iAChE) enzyme in the presence of propoxur, among Ae. aegypti from the Central Valley and southern California. All field-collected Ae. aegypti demonstrated elevated MFOs and iAChE activity, indicating potential development of pyrethroid and organophosphate resistance, respectively. Although regional variations were found among α-esterase and β-esterase activity, levels were generally elevated, further suggesting additional mechanisms for developing organophosphate resistance. Furthermore, mosquito samples from southern California exhibited a higher expression level to all three metabolic enzymes and iAChE activity in comparison to mosquitoes from the central region. These results could help guide future mosquito control efforts, directing the effective use of insecticides while limiting the spread of resistance.
    Keywords:   Aedes aegypti ; California; insecticide resistance
    DOI:  https://doi.org/10.1093/jme/tjaa031
  4. PLoS Negl Trop Dis. 2020 Mar 10. 14(3): e0007926
    Mancini MV, Herd CS, Ant TH, Murdochy SM, Sinkins SP.
      The global incidence of arboviral diseases transmitted by Aedes mosquitoes, including dengue, chikungunya, yellow fever, and Zika, has increased dramatically in recent decades. The release of Aedes aegypti carrying the maternally inherited symbiont Wolbachia as an intervention to control arboviruses is being trialled in several countries. However, these efforts are compromised in many endemic regions due to the co-localization of the secondary vector Aedes albopictus, the Asian tiger mosquito. Ae. albopictus has an expanding global distribution following incursions into a number of new territories. To date, only the wMel and wPip strains of Wolbachia have been reported to be transferred into and characterized in this vector. A Wolbachia strain naturally infecting Drosophila simulans, wAu, was selected for transfer into a Malaysian Ae. albopictus line to create a novel triple-strain infection. The newly generated line showed self-compatibility, moderate fitness cost and complete resistance to Zika and dengue infections.
    DOI:  https://doi.org/10.1371/journal.pntd.0007926
  5. BMC Biol. 2020 Mar 12. 18(1): 26
    Redmond SN, Sharma A, Sharakhov I, Tu Z, Sharakhova M, Neafsey DE.
      BACKGROUND: Aedes aegypti is the principal mosquito vector of Zika, dengue, and yellow fever viruses. Two subspecies of Ae. aegypti exhibit phenotypic divergence with regard to habitat, host preference, and vectorial capacity. Chromosomal inversions have been shown to play a major role in adaptation and speciation in dipteran insects and would be of great utility for studies of Ae. aegypti. However, the large and highly repetitive genome of Ae. aegypti makes it difficult to detect inversions with paired-end short-read sequencing data, and polytene chromosome analysis does not provide sufficient resolution to detect chromosome banding patterns indicative of inversions.RESULTS: To characterize chromosomal diversity in this species, we have carried out deep Illumina sequencing of linked-read (10X Genomics) libraries in order to discover inversion loci as well as SNPs. We analyzed individuals from colonies representing the geographic limits of each subspecies, one contact zone between subspecies, and a closely related sister species. Despite genome-wide SNP divergence and abundant microinversions, we do not find any inversions occurring as fixed differences between subspecies. Many microinversions are found in regions that have introgressed and have captured genes that could impact behavior, such as a cluster of odorant-binding proteins that may play a role in host feeding preference.
    CONCLUSIONS: Our study shows that inversions are abundant and widely shared among subspecies of Aedes aegypti and that introgression has occurred in regions of secondary contact. This library of 32 novel chromosomal inversions demonstrates the capacity for linked-read sequencing to identify previously intractable genomic rearrangements and provides a foundation for future population genetics studies in this species.
    Keywords:  Aedes aegypti; Chromosomal inversions; Introgression; Structural variation
    DOI:  https://doi.org/10.1186/s12915-020-0757-y
  6. Front Bioeng Biotechnol. 2020 ;8 102
    Campos EVR, de Oliveira JL, Abrantes DC, Rogério CB, Bueno C, Miranda VR, Monteiro RA, Fraceto LF.
      Arboviruses such as yellow fever, dengue, chikungunya and zika are transmitted mainly by the mosquito vector Aedes aegypti. Especially in the tropics, inefficacy of mosquito control causes arboviruses outbreaks every year, affecting the general population with debilitating effects in infected individuals. Several strategies have been tried to control the proliferation of A. aegypti using physical, biological, and chemical control measures. Other methods are currently under research and development, amongst which the use of nanotechnology has attracted a lot of attention of the researchers in relation to the production of more effective repellents and larvicides with less toxicity, and development of rapid sensors for the detection of virus infections. In this review, the utilization of nano-based formulations on control and diagnosis of mosquito-borne diseases were discussed. We also emphasizes the need for future research for broad commercialization of nano-based formulations in world market aiming a positive impact on public health.
    Keywords:  Aedes aegypti; arboviruses; biosensors; larvicides; nanobiotechnology; vector control
    DOI:  https://doi.org/10.3389/fbioe.2020.00102
  7. PLoS One. 2020 ;15(3): e0229847
    Ricas Rezende H, Malta Romano C, Morales Claro I, Santos Caleiro G, Cerdeira Sabino E, Felix AC, Bissoli J, Hill S, Rodrigues Faria N, Cardoso da Silva TC, Brioschi Santos AP, Cerutti Junior C, Vicente CR.
      In Brazil, Dengue (DENV) and Zika (ZIKV) viruses are reported as being transmitted exclusively by Aedes aegypti in urban settings. This study established the vectors and viruses involved in an arbovirus outbreak that occurred in 2019 in a rural area of Espírito Santo state, Brazil. Mosquitoes collected were morphologically identified, sorted in samples, and submitted to molecular analysis for arboviruses detection. Phylogenetic reconstruction was performed for the viral sequence obtained. All 393 mosquitoes were identified as Aedes albopictus. DENV-1 genotype V was present in one sample and another sample was positive for ZIKV. The DENV-1 clustered with viruses that have circulated in previous years in large urban centers of different regions in Brazil. This is the first report of A. albopictus infected by DENV and ZIKV during an outbreak in a rural area in Brazil, indicating its involvement in arboviral transmission. The DENV-1 strain found in the A. albopictus was not new in Brazil, being involved previously in epidemics related to A. aegypti, suggesting the potential to A. albopictus in transmitting viruses already circulating in the Brazilian population. This finding also indicates the possibility of these viruses to disperse across urban and rural settings, imposing additional challenges for the control of the diseases.
    DOI:  https://doi.org/10.1371/journal.pone.0229847
  8. Sci Rep. 2020 Mar 11. 10(1): 4518
    Abong'o B, Gimnig JE, Torr SJ, Longman B, Omoke D, Muchoki M, Ter Kuile F, Ochomo E, Munga S, Samuels AM, Njagi K, Maas J, Perry RT, Fornadel C, Donnelly MJ, Oxborough RM.
      Indoor residual spraying (IRS) of insecticides is a major vector control strategy for malaria prevention. We evaluated the impact of a single round of IRS with the organophosphate, pirimiphos-methyl (Actellic 300CS), on entomological and parasitological parameters of malaria in Migori County, western Kenya in 2017, in an area where primary vectors are resistant to pyrethroids but susceptible to the IRS compound. Entomological monitoring was conducted by indoor CDC light trap, pyrethrum spray catches (PSC) and human landing collection (HLC) before and after IRS. The residual effect of the insecticide was assessed monthly by exposing susceptible An. gambiae s.s. Kisumu strain to sprayed surfaces in cone assays and measuring mortality at 24 hours. Malaria case burden data were extracted from laboratory records of four health facilities within the sprayed area and two adjacent unsprayed areas. IRS was associated with reductions in An. funestus numbers in the intervention areas compared to non-intervention areas by 88% with light traps (risk ratio [RR] 0.12, 95% CI 0.07-0.21, p < 0.001) and 93% with PSC collections (RR = 0.07, 0.03-0.17, p < 0.001). The corresponding reductions in the numbers of An. arabiensis collected by PSC were 69% in the intervention compared to the non-intervention areas (RR = 0.31, 0.14-0.68, p = 0.006), but there was no significant difference with light traps (RR = 0.45, 0.21-0.96, p = 0.05). Before IRS, An. funestus accounted for over 80% of Anopheles mosquitoes collected by light trap and PSC in all sites. After IRS, An. arabiensis accounted for 86% of Anopheles collected by PSC and 66% by CDC light trap in the sprayed sites while the proportion in non-intervention sites remained unchanged. No sporozoite infections were detected in intervention areas after IRS and biting rates by An. funestus were reduced to near zero. Anopheles funestus and An. arabiensis were fully susceptible to pirimiphos-methyl and resistant to pyrethroids. The residual effect of Actellic 300CS lasted ten months on mud and concrete walls. Malaria case counts among febrile patients within IRS areas was lower post- compared to pre-IRS by 44%, 65% and 47% in Rongo, Uriri and Nyatike health facilities respectively. A single application of IRS with Actellic 300CS in Migori County provided ten months protection and resulted in the near elimination of the primary malaria vector An. funestus and a corresponding reduction of malaria case count among out-patients. The impact was less on An. arabiensis, most likely due to their exophilic nature.
    DOI:  https://doi.org/10.1038/s41598-020-61350-2
  9. Malar J. 2020 Mar 10. 19(1): 109
    Masalu JP, Finda M, Killeen GF, Ngowo HS, Pinda PG, Okumu FO.
      BACKGROUND: Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. This compromises effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacy against mosquitoes of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin, and fitted to chairs and outdoor kitchens, respectively.METHODS: Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of 28 households in dry and wet seasons, using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24 h-mortality. Finally, The World Health Organization insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages.
    RESULTS: Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and only one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-85%, while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 77-81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl and bendiocarb), but resistant to pyrethroids commonly used on LLINs (deltamethrin and permethrin).
    CONCLUSION: Most houses had actively-used peri-domestic outdoor spaces where exposure to mosquitoes occurred. The transfluthrin-treated chairs and ribbons reduced outdoor-biting malaria vectors in these peri-domestic spaces, and also elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two new prototype formats for transfluthrin emanators, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne pathogens in areas where peri-domestic human activities are common.
    Keywords:  Eave ribbons; Ifakara Health Institute; Malaria vectors; Outdoor-biting; Peri-domestic spaces; Spatial repellents; Transfluthrin; Transfluthrin-treated chairs
    DOI:  https://doi.org/10.1186/s12936-020-03180-1
  10. Acta Trop. 2020 Mar 07. pii: S0001-706X(19)31763-2. [Epub ahead of print] 105440
    Silva R, Mavridis K, Vontas J, Rodrigues A, Osório H.
      Despite reduction in the prevalence of malaria, Guinea-Bissau (GB) is still widely affected by the disease that is primarily vectored by Anopheles gambiae s.l. mosquitoes. Monitoring mosquito susceptibility and investigating the insecticide resistance status is an integral part of malaria control actions. Here, mosquito populations from five regions of GB: Bafatá, Bissau, Buba, Cacheu and Gabu were monitored for species ID and insecticide resistance, using diagnostic and intensity WHO bioassays, as well as molecular assays. Phenotypic and molecular identification of species showed the presence of An. gambiae s.s. (S form), An. coluzzii (M form) and An. arabiensis, as well as rare An. arabiensis/ An. gambiae hybrids. Resistance to permethrin and deltamethrin was found in all Anopheles populations assayed, with the intensity of resistance for permethrin being moderate to high, as confirmed by bioassays performed at concentration intensities of 5X and 10X. Consistent to these findings, molecular analysis showed a higher frequency of knock-down resistance (kdr) mutations (L1014F, L1014S, reaching > 90% in some areas) compared to previous studies in the same region, as well as detected for the first time the presence of the super kdr mutation (N1575Y) in GB. The "iAche" (G119S) resistance mutation was also found in GB in low frequencies (up to 12.41%). Additionally, the synergistic PBO-permethrin bioassays suggested partial involvement of non target (metabolic and/or reduced penetration) resistance mechanism. Expression analysis of known pyrethroid metabolisers indicated the slight overexpression and possible association of the cytochrome P450s CYP6Z1, CYP4G16 with the pyrethroid resistance phenotype. The findings should guide future evidence-based resistance management strategies in GB.
    Keywords:  Ace-1; Anopheles gambiae; Detoxification enzymes; Guinea-Bissau; IAChe; Insecticide resistance; Kdr; Malaria; Mosquitoes; P450s
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105440
  11. Insects. 2020 Mar 11. pii: E178. [Epub ahead of print]11(3):
    Shoukat RF, Zafar J, Shakeel M, Zhang Y, Freed S, Xu X, Jin F.
      Dengue fever is one of the most rapidly spreading arthropod-borne diseases. Diurnal vectorial properties of Aedes albopictus contribute to the dispersion of the dengue viruses. Frequent and injudicious use of synthetic insecticides led to the evolution of resistant phenotypes in Ae. albopictus which necessitates the search for an alternative of current control strategies. Developing a long-lasting and environmentally safe tactic based on knowledge of ecology and population dynamics of Ae. albopictus is critical. Therefore, with a view towards biological control and ecology, the effect of entomopathogenic fungi (EPF) Beauveria bassiana on filial and first filial generations of Ae. albopictus were studied. Investigations showed 87.5% adulticidal activity leading to altered fecundity and adult longevity in a filial generation. The lethal (LC50) and sublethal (LC20) concentrations of B. bassiana were applied to filial generation (F0) to study demographic parameters in the first filial generation (F1). Results showed reduced net reproductive rates (Ro) intrinsic rate of increase (r), and mean generation time (T) compared to uninfected controls. Prolonged larval and pupal duration were observed followed by reduced longevity of male and female adults. Fecundity in the first filial generation was significantly changed with the lethal and sublethal concentrations of B. bassiana. Thus, it is concluded that B. bassiana has the potential to play a vital role in integrated mosquito management strategies.
    Keywords:  Asian tiger; Beauveria bassiana; demography; entomopathogenic fungi; mosquito
    DOI:  https://doi.org/10.3390/insects11030178
  12. J Med Entomol. 2020 Mar 11. pii: tjaa035. [Epub ahead of print]
    Saeung M, Ngoen-Klan R, Thanispong K, Muenworn V, Bangs MJ, Chareonviriyaphap T.
      Aedes-borne virus disease control relies on insecticides to interrupt transmission. Temephos remains a key chemical for control of immature stage Aedes in Thailand and much of Southeast Asia. However, repeated use of insecticides may result in selection for resistance in vector populations, thus compromising operational intervention. Herein, the phenotypic response to temephos by Aedes aegypti (L.) and Aedes albopictus (Skuse) collected in Thailand and surrounding countries is presented. Data from 345 collection sites are included: 283 from literature review (244 sites with Ae. aegypti, 21 with Ae. albopictus, and 18 having both species sampled), plus 62 locations with Ae. aegypti in Thailand conducted between 2014 and 2018. Susceptibility assays followed WHO guidelines using the recommended discriminating dose of temephos (0.012 mg/liter) against late third to early fourth instar Ae. aegypti. Findings revealed 34 locations with susceptible Ae. aegypti, 13 with suspected resistance, and 15 indicating resistance. Published data between 1999 and 2019 in Thailand found Ae. aegypti resistant in 73 of 206 collection sites, whereas 3 locations from 11 sampled with low-level resistant in Ae. albopictus. From surrounding countries conducting temephos assays (Cambodia, Lao PDR, Myanmar, Malaysia, and Singapore), resistance is present in Ae. aegypti and Ae. albopictus from 27 of 56 and 19 of 28 locations, respectively. Routine insecticide susceptibility monitoring should be an operational requirement in vector control programs. Given the wide distribution and apparent increase in temephos-resistance, alternative larvicidal compounds must be considered if chemical control is to remain a viable vector control strategy.
    Keywords:   Aedes aegypti ; Aedes albopictus ; Thailand; resistance; temephos susceptibility
    DOI:  https://doi.org/10.1093/jme/tjaa035
  13. Zoonoses Public Health. 2020 Mar 12.
    Wöhnke E, Vasic A, Raileanu C, Holicki CM, Tews BA, Silaghi C.
      West Nile virus (WNV), a zoonotic arbovirus, has recently established an autochthonous transmission cycle in Germany. In dead-end hosts like humans and horses the WNV infection may cause severe symptoms in the central nervous system. In nature, WNV is maintained in an enzootic transmission cycle between birds and ornithophilic mosquitoes. Bridge vector species, such as members of the Culex pipiens complex and Aedes spp., also widely distributed in Germany, might transmit WNV to other vertebrate host species. This study determined and compared the vector competence of field-collected northern-German Cx. pipiens biotype pipiens and laboratory-reared Ae. vexans Green River (GR) for WNV lineage 1 (strain: Magpie/Italy/203204) and WNV lineage 2 (strain: "Austria") under temperatures typical for northern Germany in spring/summer and autumn. For assessment of vector competence, 7- to 14-day-old female mosquitoes were offered a WNV containing blood meal via Hemotek membrane feeding system or cotton-stick feeding. After incubation at 18°C respectively 24°C for 14 days engorged female mosquitoes were salivated and dissected for determination of infection, dissemination and transmission rates by reverse transcriptase quantitative real-time PCR (RT-qPCR). Both Ae. vexans GR and Cx. pipiens biotype pipiens were infected with both tested WNV strains and tested 14 days post-inoculation. Disseminated infections were detected only in Ae. vexans GR incubated at 18°C and in Cx. pipiens pipiens incubated at 24°C after infection with WNV lineage 1. Transmission of WNV lineage 1 was detected in Cx. pipiens pipiens incubated at 24°C. These results indicate that Cx. pipiens pipiens from Northern Germany may be involved in the transmission of WNV, also to dead-end hosts like humans and horses.
    Keywords:   Aedes vexans ; Culex pipiens pipiens ; West Nile virus; vector competence
    DOI:  https://doi.org/10.1111/zph.12700
  14. Insects. 2020 Mar 06. pii: E169. [Epub ahead of print]11(3):
    Fernando HSD, Hapugoda M, Perera R, Iv WCB, De Silva BGDNK.
      In Sri Lanka, dengue is the most serious arboviral disease. Recent increases in dengue cases suggest a higher infection rate and spread of the disease to new areas. The present study explores gene flow patterns of Ae. aegypti, the main vector of dengue disease, among 10 collection sites including major ports and inland cities using variations at 11 microsatellite loci. Discriminant analysis of principal components (DAPC) and k-means clustering estimated eight genetic clusters. Analysis of Molecular Variance (AMOVA) estimated equal variances among cities and among collections in Colombo, Sri Lanka. Significant evidence, although weak, was detected for isolation by distance. Analysis of gene flow rates and directions using MIGRATE-n indicated that populations throughout the island served as a source of immigrants for Colombo with abundant gene flow among major commercial cities in Sri Lanka, which appear to receive migrant mosquitoes from throughout Sri Lanka. The observed patterns probably arise through human movement of Ae. aegypti during commerce from throughout Sri Lanka into Colombo increasing the risk of spread. The patterns uncovered in this study are significant for global health as Sri Lanka is situated along a key international shipping route.
    Keywords:  Aedes aegypti; Sri Lanka; gene flow patterns; population structure
    DOI:  https://doi.org/10.3390/insects11030169
  15. PLoS One. 2020 ;15(3): e0221838
    Benedict MQ, Hunt CM, Vella MG, Gonzalez KM, Dotson EM, Collins CM.
      Larval mosquitoes are aquatic omnivorous scavengers which scrape food from submerged surfaces and collect suspended food particles with their mouth brushes. The composition of diets that have been used in insectaries varies widely though necessarily provides sufficient nutrition to allow colonies to be maintained. Issues such as cost, availability and experience influence which diet is selected. One component of larval diets, essential fatty acids, appears to be necessary for normal flight though deficiencies may not be evident in laboratory cages and are likely more important when mosquitoes are reared for release into the field in e.g. mark-release-recapture and genetic control activities. In this study, four diets were compared for rearing Anopheles gambiae and Aedes aegypti, all of which provide these essential fatty acids. Two diets were custom formulations specifically designed for mosquitoes (Damiens) and two were commercially available fish foods: Doctors Foster and Smith Koi Staple Diet and TetraMin Plus Flakes. Development rate, survival, dry weight and adult longevity of mosquitoes reared with these four diets were measured. The method of presentation of one diet, Koi pellets, was additionally fed in two forms, pellets or a slurry, to determine any effect of food presentation on survival and development rate. While various criteria might be selected to choose 'the best' food, the readily-available Koi pellets resulted in development rates and adult longevity equal to the other diets, high survival to the adult stage and, additionally, this is available at low cost.
    DOI:  https://doi.org/10.1371/journal.pone.0221838
  16. J Biol Res (Thessalon). 2020 Dec;27 5
    Kazmi SS, Ali W, Bibi N, Nouroz F.
      Zika virus (ZIKV) is a newly emergent relative of the Flaviviridae family and linked to dengue (DENV) and Chikungunya (CHIVKV). ZIKV is one of the rising pathogens promptly surpassing geographical borders. ZIKV infection was characterized by mild disease with fever, headache, rash, arthralgia and conjunctivitis, with exceptional reports of an association with Guillain-Barre syndrome (GBS) and microcephaly. However, since the end of 2015, an increase in the number of GBS associated cases and an astonishing number of microcephaly in fetus and new-borns in Brazil have been related to ZIKV infection, raising serious worldwide public health concerns. ZIKV is transmitted by the bite of infected female mosquitoes of Aedes species. Clarifying such worrisome relationships is, thus, a current unavoidable goal. Here, we extensively described the current understanding of the effects of ZIKV on heath, clinical manifestation, diagnosis and treatment options based on modern, alternative and complementary medicines regarding the disease.
    Keywords:  Aedes mosquito; Epidemiology; Guillain–Barré syndrome; Microcephaly; Treatment; Zika virus
    DOI:  https://doi.org/10.1186/s40709-020-00115-4
  17. Am J Trop Med Hyg. 2020 Mar 09.
    Vongsouvath M, Bharucha T, Seephonelee M, de Lamballerie X, Newton PN, Dubot-Pérès A.
      Recent expansions of vector-borne diseases highlight the need for improved surveillance, especially in resource-poor settings. Dengue virus (DENV), chikungunya virus (CHIKV), and Zika virus (ZIKV) share the same vectors as well as similar clinical presentations, suggesting that combined surveillance would be useful. We hypothesized that blood spotted on dengue rapid diagnostic tests (RDTs) could be harnessed for sample collection in remote areas for subsequent detection of DENV, CHIKV, and ZIKV by reverse transcription real-time polymerase chain reaction (RT-qPCR). CHIKV and ZIKV dilutions were spotted on dengue RDTs (SD BIOLINE Dengue DUO), dried, and extracted. As reference, aliquots of each viral dilution were directly extracted. Using specific RT-qPCR tests, both viruses were successfully detected from RDT extracts. However, the limit of detection was slightly lower in comparison to direct extracts, two logfold for CHIKV and one logfold for ZIKV. For analysis of temperature stability, DENV dilutions were spotted on RDTs and stored for up to 2 months at -80°C, 4°C, or 35°C before testing. Storage of RDTs for 2 months at 35°C did not jeopardize detection of RNA by RT-qPCR; only minimal degradation was observed. This proof-of-principle study demonstrates the potential of using dengue RDTs for DENV/CHIKV/ZIKV combined surveillance in areas without access to laboratory facilities. Further investigations are needed for evaluation of tri-viral surveillance under field conditions using patient samples. Large-scale implementation of surveillance for these viruses is of crucial public health importance for the early detection of epidemics. This method also has important implications for improving understanding of the molecular epidemiology of the three viruses.
    DOI:  https://doi.org/10.4269/ajtmh.19-0881
  18. J Med Entomol. 2020 Mar 12. pii: tjaa045. [Epub ahead of print]
    Parker AT, McGill K, Allan BF.
      Larvae of container-breeding mosquitoes develop in a wide range of container habitats found in residential neighborhoods. Different mosquito species may exhibit preference for different container types and sizes. Due to phenological differences, species composition in container habitats may change over time. We first conducted weekly neighborhood container surveys to determine the types of container habitats found in residential neighborhoods, and to determine mosquito species composition over time within these habitats. We then conducted an oviposition choice field assay to determine whether female mosquitoes of different species preferentially oviposit in different container types commonly found in neighborhoods. Halfway through the experiment, the largest container was removed at half the sites to test the hypothesis that incomplete source reduction alters oviposition preference among the remaining containers. In the neighborhood surveys, large containers had the greatest mosquito densities and the highest species richness. Aedes albopictus (Skuse), the most commonly collected mosquito, was found in all container types. The oviposition experiment indicated that Culex spp. females preferentially oviposit in large containers. When the largest container was removed, the total number of egg rafts decreased. Aedes spp. females preferred to oviposit in large- and medium-sized containers, but the total number of eggs laid did not change when the large container was removed. These results confirm that understanding habitat preferences of container-breeding mosquitoes is important to control efforts targeting vector species and that incomplete removal of container habitats may have unpredictable consequences for the distribution of juveniles among remaining habitats.
    Keywords:  container type; mosquito; oviposition choice
    DOI:  https://doi.org/10.1093/jme/tjaa045
  19. Geohealth. 2018 Dec;2(12): 395-409
    Hess A, Davis JK, Wimberly MC.
      Understanding the geographic distribution of mosquito-borne disease and mapping disease risk are important for prevention and control efforts. Mosquito-borne viruses (arboviruses), such as West Nile virus (WNV), are highly dependent on environmental conditions. Therefore, the use of environmental data can help in making spatial predictions of disease distribution. We used geocoded human case data for 2004-2017 and population-weighted control points in combination with multiple geospatial environmental data sets to assess the environmental drivers of WNV cases and to map relative infection risk in South Dakota, USA. We compared the effectiveness of (1) land cover and physiography data, (2) climate data, and (3) spectral data for mapping the risk of WNV in South Dakota. A final model combining all data sets was used to predict spatial patterns of disease transmission and characterize the associations between environmental factors and WNV risk. We used a boosted regression tree model to identify the most important variables driving WNV risk and generated risk maps by applying this model across the entire state. We found that combining multiple sources of environmental data resulted in the most accurate predictions. Elevation, late-season humidity, and early-season surface moisture were the most important predictors of disease distribution. Indices that quantified interannual variability of climatic conditions and land surface moisture were better predictors than interannual means. We suggest that combining measures of interannual environmental variability with static land cover and physiography variables can help to improve spatial predictions of arbovirus transmission risk.
    Keywords:  climate; disease map; land cover; mosquito‐borne disease; remote sensing; spatial model
    DOI:  https://doi.org/10.1029/2018GH000161
  20. Front Physiol. 2019 ;10 1591
    Senthil-Nathan S.
      Mosquitoes are a serious threat to the society, acting as vector to several dreadful diseases. Mosquito management programes profoundly depend on the routine of chemical insecticides that subsequently lead to the expansion of resistance midst the vectors, along with other problems such as environmental pollution, bio magnification, and adversely affecting the quality of public and animal health, worldwide. The worldwide risk of insect vector transmitted diseases, with their associated illness and mortality, emphasizes the need for effective mosquitocides. Hence there is an immediate necessity to develop new eco-friendly pesticides. As a result, numerous investigators have worked on the development of eco-friendly effective mosquitocidal compounds of plant origin. These products have a cumulative advantage of being cost-effective, environmentally benign, biodegradable, and safe to non-target organisms. This review aims at describing the current state of research on behavioral, physiological, and biochemical effects of plant derived compounds with larvicidal effects on mosquitoes. The mode of physiological and biochemical action of known compounds derived from various plant families as well as the potential of plant secondary metabolites, plant extracts, and also the essential oils (EO), as mosquitocidal agents are discussed. This review clearly indicates that the application of vegetal-based compounds as mosquito control proxies can serve as alternative biocontrol methods in mosquito management programes.
    Keywords:  biopesticide; enzyme; physiology; phytochemical; secondary metabolites; toxicity; vector
    DOI:  https://doi.org/10.3389/fphys.2019.01591
  21. Vector Borne Zoonotic Dis. 2020 Mar 09.
    James SL, Marshall JM, Christophides GK, Okumu FO, Nolan T.
      Mosquitoes containing gene drive systems are being developed as complementary tools to prevent transmission of malaria and other mosquito-borne diseases. As with any new tool, decision makers and other stakeholders will need to balance risks (safety) and benefits (efficacy) when considering the rationale for testing and deploying gene drive-modified mosquito products. Developers will benefit from standards for judging whether an investigational gene drive product meets acceptability criteria for advancing to field trials. Such standards may be formalized as preferred product characteristics and target product profiles, which describe the desired attributes of the product category and of a particular product, respectively. This report summarizes discussions from two scientific workshops aimed at identifying efficacy and safety characteristics that must be minimally met for an investigational gene drive-modified mosquito product to be deemed viable to move from contained testing to field release and the data that will be needed to support an application for first field release.
    Keywords:  biosafety; efficacy; gene drive; malaria; mosquito
    DOI:  https://doi.org/10.1089/vbz.2019.2606
  22. Parasit Vectors. 2020 Mar 12. 13(1): 126
    Mihreteab S, Lubinda J, Zhao B, Rodriguez-Morales AJ, Karamehic-Muratovic A, Goitom A, Shad MY, Haque U.
      BACKGROUND: The present study focuses on both long- and short-term malaria transmission in Eritrea and investigates the risk factors. Annual aggregates of information on malaria cases, deaths, diagnostics and control interventions from 2001 to 2008 and monthly reported data from 2009 to 2017 were obtained from the National Malaria Control Programme. We used a generalized linear regression model to examine the associations among total malaria cases, death, insecticide-treated net coverage, indoor residual spraying and climatic parameters.RESULTS: Reduction in malaria mortality is demonstrated by the milestone margins of over 97% by the end of 2017. Malaria incidence likewise declined during the period (from 33 to 5 per 1000 population), representing a reduction of about 86% (R2 = 0.3) slightly less than the decline in mortality. The distribution of insecticide treated nets generally declined between 2001 and 2014 (R2 = 0.16) before increasing from 2015 to 2017, while the number of people protected by indoor residual spraying slightly increased (R2 = 0.27). Higher rainfall was significantly associated with an increased number of malaria cases. The covariates rainfall and temperature are a better pair than IRS and LLIN to predict incidences. On the other hand, IRS and LLIN is a more significant pair to predict mortality cases.
    CONCLUSIONS: While Eritrea has made significant progress towards malaria elimination, this progress should be maintained and further improved. Distribution, coverage and utilization of malaria control and elimination tools should be optimized and sustained to safeguard the gains made. Additionally, consistent annual performance evaluation of malaria indicators would ensure a continuous learning process from gains/threats of epidemics and resurgence in regions already earmarked for elimination.
    Keywords:  Control; Elimination; Eritrea; Malaria; Public health; Vector-borne diseases
    DOI:  https://doi.org/10.1186/s13071-020-3974-x
  23. Med Vet Entomol. 2020 Mar 11.
    Lilja T, Eklöf D, Jaenson TGT, Lindström A, Terenius O.
      Four species of the Anopheles maculipennis complex have previously been recorded in Sweden. A recent addition to the complex is Anopheles daciae, which is considered to be closely related to, but distinct from Anopheles messeae. The original designation of An. daciae was based on five genetic differences (161, 165, 167, 362 and 382) in the second internal transcribed spacer (ITS) 2 of the ribosomal RNA. Further studies have shown that only two nucleotide differences (362 and 382) robustly separate the species. Thirty-three An. maculipennis complex mosquitoes were collected in the province of Uppland, Sweden. All were An. daciae but showed double peaks for three variable positions (161, 165 and 167). When cloned, the intra-individual nucleotide variation was almost exclusively fixed with either TTC or AAT, originally diagnostic for An. messae and An. daciae, respectively. To further investigate the intra-individual variation, nine An. daciae and 11 An. messeae were collected in southern Sweden and their ITS2 fragments were amplified and sequenced using Illumina MiSeq sequencing (Illumina, Inc., San Diego, CA, USA). For the diagnostic nucleotide 382 no intra-individual variation could be detected. However, although each An. daciae specimen carried several ITS2 sequence variants for the four other nucleotides, there was no intra-individual variation in the An. messeae specimens.
    Keywords:  Anopheles maculipennis complex; haplotypes; intra-individual variation; polymorphic; species diagnosis
    DOI:  https://doi.org/10.1111/mve.12436
  24. Med Vet Entomol. 2020 Mar 10.
    Kamber T, Koekemoer LL, Mathis A.
      Species of the genus Anopheles vary with regard to their vector capacity for Plasmodium spp., the causative agent of malaria, and their accurate identification is often required. Loop-mediated isothermal amplification (LAMP) is a rapid, simple and low-cost method for specific DNA amplification. Primers for LAMP assays specific for the Anopheles funestus group and Anopheles gambiae complex species as well as for the species Anopheles arabiensis, An. funestus, An. gambiae s.s/Anopheles coluzzii (major vectors) and Anopheles rivulorum (minor vector) were designed targeting specific genome or rDNA internal transcribed spacer regions. Reaction conditions (buffer composition, primer concentrations, incubation time) were evaluated and the specificities of the assays confirmed with DNA from non-target Anopheles species. DNA release from the mosquitoes is achieved simply by heating them for 5 min in water. An aliquot of the DNA solutions is transferred to the reaction tube using disposable inoculation loops. The outcome of the LAMP amplifications after 1 h incubation at 65 °C can easily be visualized by a colour change visible to the naked eye. The assays are operable under field conditions requiring only basic equipment (portable heat block programmable at 65 and 80 °C, cooler for master mixes).
    Keywords:  Anopheles spp.; field identification; malaria; vector
    DOI:  https://doi.org/10.1111/mve.12437
  25. Proc Natl Acad Sci U S A. 2020 Mar 12. pii: 201919709. [Epub ahead of print]
    Ukegbu CV, Giorgalli M, Tapanelli S, Rona LDP, Jaye A, Wyer C, Angrisano F, Blagborough AM, Christophides GK, Vlachou D.
      After being ingested by a female Anopheles mosquito during a bloodmeal on an infected host, and before they can reach the mosquito salivary glands to be transmitted to a new host, Plasmodium parasites must establish an infection of the mosquito midgut in the form of oocysts. To achieve this, they must first survive a series of robust innate immune responses that take place prior to, during, and immediately after ookinete traversal of the midgut epithelium. Understanding how parasites may evade these responses could highlight new ways to block malaria transmission. We show that an ookinete and sporozoite surface protein designated as PIMMS43 (Plasmodium Infection of the Mosquito Midgut Screen 43) is required for parasite evasion of the Anopheles coluzzii complement-like response. Disruption of PIMMS43 in the rodent malaria parasite Plasmodium berghei triggers robust complement activation and ookinete elimination upon mosquito midgut traversal. Silencing components of the complement-like system through RNAi largely restores ookinete-to-oocyst transition but oocysts remain small in size and produce a very small number of sporozoites that additionally are not infectious, indicating that PIMMS43 is also essential for sporogonic development in the oocyst. Antibodies that bind PIMMS43 interfere with parasite immune evasion when ingested with the infectious blood meal and significantly reduce the prevalence and intensity of infection. PIMMS43 genetic structure across African Plasmodium falciparum populations indicates allelic adaptation to sympatric vector populations. These data add to our understanding of mosquito-parasite interactions and identify PIMMS43 as a target of malaria transmission blocking.
    Keywords:  complement-like response; malaria transmission; mosquito innate immunity; mosquito population replacement; transmission blocking vaccines
    DOI:  https://doi.org/10.1073/pnas.1919709117
  26. Parasit Vectors. 2020 Mar 12. 13(1): 125
    Graves PM, Sheridan S, Fuimaono S, Lau CL.
      BACKGROUND: Prevalence of lymphatic filariasis (LF) antigen in American Samoa was 16.5% in 1999. Seven rounds of mass drug administration (MDA) programmes between 2000 and 2006 reduced antigen prevalence to 2.3%. The most efficient methods of surveillance after MDA are not clear, but testing specific at-risk groups such as adults may provide earlier warning of resurgence. The role of migration from LF endemic countries in maintaining transmission also needs investigation. Few studies have investigated knowledge about LF and how that relates to infection risk. This study aims to investigate associations between socio-demographics, population mobility, disease knowledge and LF infection risk.METHODS: In 2014, we surveyed 670 adults aged 16-68 years (62% female) at two worksites in American Samoa. Sera were tested for LF antigen and antibodies (Bm14 and Wb123) by rapid test and/or ELISA. Multivariate logistic regression was used to assess association between seromarkers and demographic factors, household socioeconomic status (SES), residence, travel history, and knowledge of LF.
    RESULTS: Overall, 1.8% of participants were positive for antigen, 11.8% for Bm14, 11.3% for Wb123 and 17.3% for at least one antibody. Recent travel outside American Samoa was not associated with positivity for any seromarker. Men had higher seroprevalence than women for all outcomes (any antibody: adjusted odds ratio (aOR) = 3.49 (95% CI: 2.21-5.49). Those aged over 35 years (compared to 15-24 years) had higher prevalence of Bm14 antibody (aOR = 3.75, 3.76 and 4.17 for ages 35-44, 45-54 and ≥ 55 years, respectively, P < 0.05). Lower SES was associated with seropositivity (antigen: aOR = 2.89, 95% CI: 1.09-7.69; either antibody: aOR = 1.51, 95% CI: 1.12-2.05). Those who knew that mosquitoes transmitted LF had lower Wb123 antibody prevalence (aOR = 0.55, 95% CI: 0.32-0.95).
    CONCLUSIONS: Opportunistic sampling of adults at worksites provided an efficient and representative way to assess prevalence and risk factors for LF in American Samoa and in hindsight, foreshadowed the resurgence of transmission. Risk of LF infection, detected by one or more serological markers, was not related to recent travel history, but was strongly associated with male gender, older age, lower SES, and lack of knowledge about mosquito transmission. These results could guide future efforts to increase MDA participation.
    Keywords:  American Samoa; Disease knowledge; Lymphatic filariasis; Mosquito; Population mobility; Sero-epidemiology; Socioeconomic status; Surveillance
    DOI:  https://doi.org/10.1186/s13071-020-3996-4
  27. PLoS Negl Trop Dis. 2020 Mar 09. 14(3): e0008072
    Rougeron V, Elguero E, Arnathau C, Acuña Hidalgo B, Durand P, Houze S, Berry A, Zakeri S, Haque R, Shafiul Alam M, Nosten F, Severini C, Gebru Woldearegai T, Mordmüller B, Kremsner PG, González-Cerón L, Fontecha G, Gamboa D, Musset L, Legrand E, Noya O, Pumpaibool T, Harnyuttanakorn P, Lekweiry KM, Mohamad Albsheer M, Mahdi Abdel Hamid M, Boukary AOMS, Trape JF, Renaud F, Prugnolle F.
      More than 200 million malaria clinical cases are reported each year due to Plasmodium vivax, the most widespread Plasmodium species in the world. This species has been neglected and understudied for a long time, due to its lower mortality in comparison with Plasmodium falciparum. A renewed interest has emerged in the past decade with the discovery of antimalarial drug resistance and of severe and even fatal human cases. Nonetheless, today there are still significant gaps in our understanding of the population genetics and evolutionary history of P. vivax, particularly because of a lack of genetic data from Africa. To address these gaps, we genotyped 14 microsatellite loci in 834 samples obtained from 28 locations in 20 countries from around the world. We discuss the worldwide population genetic structure and diversity and the evolutionary origin of P. vivax in the world and its introduction into the Americas. This study demonstrates the importance of conducting genome-wide analyses of P. vivax in order to unravel its complex evolutionary history.
    DOI:  https://doi.org/10.1371/journal.pntd.0008072
  28. Geohealth. 2018 Mar;2(3): 104-115
    Endo N, Eltahir EAB.
      New dam construction is known to exacerbate malaria transmission in Africa as the vectors of malaria-Anopheles mosquitoes-use bodies of water as breeding sites. Precise environmental mechanisms of how reservoirs exacerbate malaria transmission are yet to be identified. Understanding of these mechanisms should lead to a better assessment of the impacts of dam construction and to new prevention strategies. Combining extensive multiyear field surveys around the Koka Reservoir in Ethiopia and rigorous model development and simulation studies, environmental mechanisms of malaria transmission around the reservoir were examined. Most comprehensive and detailed malaria transmission model, Hydrology, Entomology, and Malaria Transmission Simulator, was applied to a village adjacent to the reservoir. Significant contributions to the dynamics of malaria transmission are shaped by wind profile, marginal pools, temperature, and shoreline locations. Wind speed and wind direction influence Anopheles populations and malaria transmission during the major and secondary mosquito seasons. During the secondary mosquito season, a noticeable influence was also attributed to marginal pools. Temperature was found to play an important role, not so much in Anopheles population dynamics, but in malaria transmission dynamics. Change in shoreline locations drives malaria transmission dynamics, with closer shoreline locations to the village making malaria transmission more likely. Identified environmental mechanisms help in predicting malaria transmission seasons and in developing village relocation strategies upon dam construction to minimize the risk of malaria.
    Keywords:  environmental conditions; malaria transmission; water resource reservoirs
    DOI:  https://doi.org/10.1002/2017GH000108
  29. Prev Med Rep. 2020 Jun;18 101059
    Schoch-Spana M, Watson C, Ravi S, Meyer D, Pechta LE, Rose DA, Lubell KM, Podgornik MN, Sell TK.
      Aerial spraying of products to kill larvae or adult mosquitoes is a public health measure used to control vector-borne diseases. In some outbreaks, the intervention has evoked controversy and community resistance. This study evaluated how local opinion leaders in US localities affected by Zika think about community engagement in public health policies for outbreak response. In December 2017 through March 2018, 4 focus groups were convened in Houston, TX, New Orleans, LA, Miami, FL, and Brooklyn, NY. They discussed a hypothetical scenario that featured vector control by aerial spraying. Participants (N = 20) more readily accepted this vector control method under 4 conditions: They were informed of alternatives, benefits, and risks for human health and the environment. Public health claims were backed by objective evidence and an authority figure genuinely working in the community's interests. They received timely notice about how to mitigate toxin exposure. And, aerial spraying helped to protect vulnerable individuals. The community engagement requirements of the local opinion leaders resonate with core principles of recent public health ethics frameworks: namely, personal autonomy, transparency, reasonableness, and solidarity. Participants foresaw problems with community consent in an era of growing social media use and mistrust in governmental and scientific authority. They also debated whether health authorities should use moral-based arguments, in addition to science-based ones, to communicate aerial spraying's risks and benefits.
    Keywords:  Community engagement; Disease outbreak; Ethics; Public health; Vector control; Zika
    DOI:  https://doi.org/10.1016/j.pmedr.2020.101059
  30. BMC Infect Dis. 2020 Mar 12. 20(1): 208
    Polwiang S.
      BACKGROUND: In Thailand, dengue fever is one of the most well-known public health problems. The objective of this study was to examine the epidemiology of dengue and determine the seasonal pattern of dengue and its associate to climate factors in Bangkok, Thailand, from 2003 to 2017.METHODS: The dengue cases in Bangkok were collected monthly during the study period. The time-series data were extracted into the trend, seasonal, and random components using the seasonal decomposition procedure based on loess. The Spearman correlation analysis and artificial neuron network (ANN) were used to determine the association between climate variables (humidity, temperature, and rainfall) and dengue cases in Bangkok.
    RESULTS: The seasonal-decomposition procedure showed that the seasonal component was weaker than the trend component for dengue cases during the study period. The Spearman correlation analysis showed that rainfall and humidity played a role in dengue transmission with correlation efficiency equal to 0.396 and 0.388, respectively. ANN showed that precipitation was the most crucial factor. The time series multivariate Poisson regression model revealed that increasing 1% of rainfall corresponded to an increase of 3.3% in the dengue cases in Bangkok. There were three models employed to forecast the dengue case, multivariate Poisson regression, ANN, and ARIMA. Each model displayed different accuracy, and multivariate Poisson regression was the most accurate approach in this study.
    CONCLUSION: This work demonstrates the significance of weather in dengue transmission in Bangkok and compares the accuracy of the different mathematical approaches to predict the dengue case. A single model may insufficient to forecast precisely a dengue outbreak, and climate factor may not only indicator of dengue transmissibility.
    Keywords:  ARIMA; Artificial neuron network; Dengue fever; Poisson regression
    DOI:  https://doi.org/10.1186/s12879-020-4902-6
  31. Acta Trop. 2020 Mar 09. pii: S0001-706X(19)30921-0. [Epub ahead of print] 105438
    Vianna RAO, Rua EC, Fernandes AR, Dos Santos TCS, Dalcastel LAB, Dos Santos MLB, de Paula PDS, de Carvalho FR, Pache de Faria AO, Almeida PL, Sales LF, Riley LW, de Oliveira SA, Cardoso CAA.
      INTRODUCTION: Typical symptoms of primary Zika virus infection are not specific and share similarities with other arbovirus infections such as dengue fever and chikungunya. As acute infection can be asymptomatic in up to 73% of cases, infants with microcephaly represent a diagnostic challenge for pediatricians. We describe the frequency of congenital Zika syndrome (CZS) in Brazilian children born to asymptomatic pregnant mothers and its differential diagnosis.METHODS: This longitudinal, observational study was conducted on children with suspected CZS whose mothers did not report rash during pregnancy, referred to the reference hospital in a metropolitan area of ​ Rio de Janeiro, Brazil. The diagnosis of suspected CZS was based on Brazilian Ministry of Health protocol.
    RESULTS: Forty-three (17%) of 246 referred children were born to mothers without rash history during pregnancy. Thirteen (30%) of 43 children met the Brazilian Ministry of Health criteria for CZS, all with microcephaly (two post-natal). The other children included 11 cases with post-natal microcephaly due to hypoxic-ischemic encephalopathy (6), non-progressive encephalopathy of unknown etiology (2), microcephaly under investigation (2) and congenital toxoplasmosis (1); 17 children were misdiagnosed with microcephaly and progressed with normal head circumference during the follow-up period; one child was included because of epidemiological link and one was loss to follow-up. All children who underwent laboratory investigation for ZIKV infection during neonatal period had negative RT-qPCR tests.
    CONCLUSION: We emphasize the increasing importance of CZS in differential diagnosis of microcephaly at birth or post-natal period. Detailed clinical investigation assisted by neuroimaging tests may clarify the diagnosis of CZS when laboratory tests are not available during the acute phase of the disease.
    Keywords:  Congenital Zika syndrome; Microcephaly at birth; Post-natal microcephaly; RT-PCR; Zika virus
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105438
  32. PLoS One. 2020 ;15(3): e0230274
    Salami D, Capinha C, Martins MDRO, Sousa CA.
      The spread of dengue through global human mobility is a major public health concern. A key challenge is understanding the transmission pathways and mediating factors that characterized the patterns of dengue importation into non-endemic areas. Utilizing a network connectivity-based approach, we analyze the importation patterns of dengue fever into European countries. Seven connectivity indices were developed to characterize the role of the air passenger traffic, seasonality, incidence rate, geographical proximity, epidemic vulnerability, and wealth of a source country, in facilitating the transport and importation of dengue fever. We used generalized linear mixed models (GLMMs) to examine the relationship between dengue importation and the connectivity indices while accounting for the air transport network structure. We also incorporated network autocorrelation within a GLMM framework to investigate the propensity of a European country to receive an imported case, by virtue of its position within the air transport network. The connectivity indices and dynamical processes of the air transport network were strong predictors of dengue importation in Europe. With more than 70% of the variation in dengue importation patterns explained. We found that transportation potential was higher for source countries with seasonal dengue activity, high passenger traffic, high incidence rates, high epidemic vulnerability, and in geographical proximity to a destination country in Europe. We also found that position of a European country within the air transport network was a strong predictor of the country's propensity to receive an imported case. Our findings provide evidence that the importation patterns of dengue into Europe can be largely explained by appropriately characterizing the heterogeneities of the source, and topology of the air transport network. This contributes to the foundational framework for building integrated predictive models for bio-surveillance of dengue importation.
    DOI:  https://doi.org/10.1371/journal.pone.0230274
  33. Geohealth. 2019 Aug;3(8): 202-217
    Ogashawara I, Li L, Moreno-Madriñán MJ.
      Dengue fever, a disease caused by a vector-borne flavivirus, is endemic to tropical countries, but its occurrence has been reported worldwide. This study aimed to understand important factors contributing to the spatial and temporal patterns of dengue occurrence in São Paulo, the largest municipality of Brazil. The temporal assessment of dengue occurrence covered the 2011-2016 time period and was based on climatological data, such as the El Niño indices and time series statistical tools such as the continuous wavelet transformation. The spatial assessment used Landsat 8 data for years 2014-2016 to estimate land surface temperature and normalized indices for vegetation, urban areas, and leaf water. Results from a cross correlation for the temporal analysis found a relationship between the sea surface temperature anomalies index and the number of reported dengue cases in São Paulo (r = 0.5) with a lag of +29 (weeks) between the climatic event and the response on the dengue incidence. This relationship, initially nonlinear, became linear after correcting for the lag period. For the spatial assessment, the linear stepwise regression model detected a low relationship between dengue incidence and minimum surface temperature (r = 0.357) and no relationship with other environmental parameters. The poor relationship might be due to confounding effects of socioeconomic factors as these seem to influence the spatial dynamics of dengue incidence. More testing is needed to validate these methods in other locations. Nevertheless, we presented possible tools to be used for the improvement of dengue control programs.
    Keywords:  El Niño; Landsat 8; continuous wavelet transformation; dengue; land surface temperature; remote sensing indices
    DOI:  https://doi.org/10.1029/2019GH000186
  34. Malar J. 2020 Mar 14. 19(1): 110
    Musa JJ, Moore SJ, Moore J, Mbuba E, Mbeyela E, Kobe D, Swai JK, Odufuwa OG.
      BACKGROUND: Long-lasting insecticidal nets (LLINs) are the most sustainable and effective malaria control tool currently available. Global targets are for 80% of the population living in malaria endemic areas to have access to (own) and use a LLIN. However, current access to LLINs in endemic areas is 56% due to system inefficiencies and budget limitations. Thus, cost-effective approaches to maximize access to effective LLINs in endemic areas are required. This study evaluated whether LLINs that had been stored for 5 years under manufacturer's recommended conditions may be optimally effective against Anopheles mosquitoes, to inform malaria control programmes and governments on the periods over which LLINs may be stored between distributions, in an effort to maximize use of available LLINs.METHODS: Standard World Health Organization (WHO) bioassays (cone and tunnel test) were used to evaluate the bio-efficacy and wash resistance of Olyset® and DawaPlus® 2.0 (rebranded Tsara® Soft) LLINs after 5 years of storage at 25 °C to 33.4 °C and 40% to 100% relative humidity. In addition, a small scale Ifakara Ambient Chamber test (I-ACT) was conducted to compare the bio-efficacy of one long stored LLINs to one new LLIN of the same brand, washed or unwashed. LLINs were evaluated using laboratory reared fully susceptible Anopheles gambiae sensu stricto (s.s.) (Ifakara strain) and pyrethroid resistant Anopheles arabiensis (Kingani strain).
    RESULTS: After 5 years of storage, both unwashed and washed, Olyset® and DawaPlus® 2.0 (Tsara® Soft) LLINs passed WHO bio-efficacy criteria on knockdown (KD60) ≥ 95%, 24-h mortality ≥ 80% and ≥ 90% blood-feeding inhibition in WHO assays against susceptible An. gambiae s.s. DawaPlus® 2.0 LLINs also passed combined WHO bioassay criteria against resistant An. arabiensis. Confirmatory I-ACT tests using whole nets demonstrated that long-stored LLINs showed higher efficacy than new LLINs on both feeding inhibition and mortality endpoints against resistant strains.
    CONCLUSIONS: Even after long-term storage of around 5 years, both Olyset® and DawaPlus® 2.0 LLINs remain efficacious against susceptible Anopheles mosquitoes at optimal storage range of 25 °C to 33.4 °C for temperature and 40% to 100% relative humidity measured by standard WHO methods. DawaPlus® 2.0 (Tsara® Soft) remained efficacious against resistant strain.
    Keywords:  ITN; LLIN; Long lasting insecticidal nets; Long storage nets; Malaria; Tanzania
    DOI:  https://doi.org/10.1186/s12936-020-03183-y
  35. Rev Bras Epidemiol. 2020 ;pii: S1415-790X2020000100416. [Epub ahead of print]23 e200018
    Wolfarth-Couto B, Filizola N, Durieux L.
      INTRODUCTION: Malaria is an infectious disease of high transmission in the Amazon region, but its dynamics and spatial distribution may vary depending on the interaction of environmental, socio-cultural, economic, political and health services factors.OBJECTIVE: To verify the existence of malaria case patterns in consonance with the fluviometric regimes in Amazon basin.
    METHOD: Methods of descriptive and inferential statistics were used in malaria and water level data for 35 municipalities in the Amazonas State, in the period from 2003 to 2014.
    RESULTS: The existence of a tendency to modulate the seasonality of malaria cases due to distinct periods of rivers flooding has been demonstrated. Differences were observed in the annual hydrological variability accompanied by different patterns of malaria cases, showing a trend of remodeling of the epidemiological profile as a function of the flood pulse.
    CONCLUSION: The study suggests the implementation of regional and local strategies considering the hydrological regimes of the Amazon basin, enabling municipal actions to attenuate the malaria in the Amazonas State.
    DOI:  https://doi.org/10.1590/1980-549720200018