bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒11‒15
twenty-five papers selected by
Richard Halfpenny
Staffordshire University


  1. Malar J. 2020 Nov 09. 19(1): 396
    Marcombe S, Maithaviphet S, Bobichon J, Phommavan N, Nambanya S, Corbel V, Brey PT.
      BACKGROUND: In Laos, the malaria burden remains high despite a significant reduction of cases during the last decade. In the context of the disease elimination by 2030, a nationwide entomological survey was conducted to better understand the distribution, abundance and behaviour of major malaria vectors (Anopheles spp.) in the country.METHODS: Mosquito collections were implemented in ten villages from ten provinces during the rainy and dry seasons of 2014 and 2015 by using human landing catch (HLC) and cow bait collection (CBC) methods. After morphological identification in the field, molecular identification of the sibling species of Anopheles mosquitoes from the Funestus, Leucosphyrus, and Maculatus groups were determined using PCR specific alleles. A screening of Plasmodium falciparum and Plasmodium vivax infections in the vectors was carried out by quantitative PCR assays.
    RESULTS: A total of 14,146 adult mosquitoes representing 25 different Anopheles species were collected and morphologically identified. Molecular identification revealed the presence of 12 sibling species within the main primary vector groups, including Anopheles maculatus, Anopheles rampae, Anopheles sawadwongporni, Anopheles pseudowillmori, Anopheles dravidicus, Anopheles minimus, Anopheles aconitus, Anopheles pampanai, Anopheles harrisoni, Anopheles dirus, Anopheles baimaii, Anopheles nemophilous. Anopheles maculatus and An. minimus were predominant during both the dry and rainy seasons, but showed highly zoophilic preferences (Zoophilic index of 98% and 95%, respectively). Overall, 22% of the total malaria vectors were collected between 10:00 PM and 5:00 AM indoors when people are sleeping. Twenty-seven percent of primary and secondary vectors were collected outdoors before 10:00 PM or after 5:00 AM, times when people are usually awake and outdoors. Only two specimens were positive for P. falciparum, one An. aconitus from Phongsaly and one An. minimus from Vientiane Province CONCLUSIONS: The results indicate that people living in rural areas in Laos are constantly exposed to malaria vectors throughout the year and specifically outdoors. The use of LLINs/IRS remains important but innovative tools and new strategies are needed to address locally, the early and outdoor malaria transmission. Lack of expertise in general entomological methods may further exacerbate the situation.
    Keywords:  Anopheles dirus; Anopheles maculatus; Anopheles minimus; Biting preferences; Laos; Malaria; Plasmodium infection; Primary and secondary vectors
    DOI:  https://doi.org/10.1186/s12936-020-03453-9
  2. Parasit Vectors. 2020 Nov 11. 13(1): 574
    Sumruayphol S, Chaiphongpachara T, Samung Y, Ruangsittichai J, Cui L, Zhong D, Sattabongkot J, Sriwichai P.
      BACKGROUND: Anopheles sawadwongporni Rattanarithikul & Green, Anopheles maculatus Theobald and Anopheles pseudowillmori (Theobald) of the Anopheles maculatus group (Diptera: Culicidae) are recognized as potential malaria vectors in many countries from the Indian subcontinent through Southeast Asia to Taiwan. A number of malaria vectors in malaria hotspot areas along the Thai-Myanmar border belong to this complex. However, the species distribution and dynamic trends remain understudied in this malaria endemic region.METHODS: Mosquitoes of the Maculatus group were collected using CDC light traps every other week from four villages in Tha Song Yang District, Tak Province, Thailand from January to December 2015. Adult female mosquitoes were morphologically identified on site using taxonomic keys. Molecular species identification was performed by multiplex PCR based on the internal transcribed spacer 2 (ITS2) region of ribosomal DNA (rDNA) and sequencing of the cox1 gene at a DNA barcoding region in a subset of 29 specimens.
    RESULTS: A total of 1328 An. maculatus (sensu lato) female mosquitoes were captured with An. maculatus, An. sawadwongporni and An. pseudowilmori accounting for 75.2, 22.1 and 2.7% respectively. The field captured mosquitoes of the Maculatus group were most abundant in the wet season and had a preferred distribution in villages at higher elevations. The phylogenetic relationships of 29 cox1 sequences showed a clear-cut separation of the three member species of the Maculatus group, with the An. pseudowillmori cluster being separated from An. sawadwongporni and An. maculatus.
    CONCLUSIONS: This study provides updated information for the species composition, seasonal dynamics and microgeographical distribution of the Maculatus group in malaria-endemic areas of western Thailand. This information can be used to guide the planning and implementation of mosquito control measures in the pursuance of malaria transmission.
    Keywords:  Anopheles maculatus; Anopheles pseudowillmori; Anopheles sawadwongporni; Cytochrome c oxidase subunit 1; Internal transcribed spacer 2; Seasonal dynamic; Species complex
    DOI:  https://doi.org/10.1186/s13071-020-04452-0
  3. Sci Data. 2020 Nov 11. 7(1): 382
    Vasconcelos D, Nunes NJ, Gomes J.
      As vectors of malaria, dengue, zika, and yellow fever, mosquitoes are considered one of the more severe worldwide health hazards. Widespread surveillance of mosquitoes is essential for understanding their complex ecology and behaviour, and also for predicting and formulating effective control strategies against mosquito-borne diseases. One technique involves using bioacoustics to automatically identify different species from their wing-beat sounds during flight. In this dataset, we collect sounds of three species of mosquitoes: Aedes Aegypti, Culex Quinquefasciatus & Pipiens, and Culiseta. These species were collected and reproduced in the laboratory of the Natural History Museum of Funchal, in Portugal, by entomologists trained to recognize and classify mosquitoes. For collecting the samples, we used a microcontroller and a mobile phone. The dataset presents audio samples collected with different sampling rates, where 34 audio features characterize each sound file, making it is possible to observe how mosquito populations vary heterogeneously. This dataset provides the basis for feature extraction and classification of flapping-wing flight sounds that could be used to identify different species.
    DOI:  https://doi.org/10.1038/s41597-020-00725-6
  4. Acta Trop. 2020 Nov 04. pii: S0001-706X(20)31648-X. [Epub ahead of print] 105735
    Noden BH, Bradt DL, Sanders JD.
      Vector-borne diseases in the United States have recently increased as a result of the changing nature of vectors, hosts, reservoirs, parasite/pathogens, and the ecological and environmental conditions. While most focus has been on mosquito-borne pathogens affecting humans, little is known regarding parasites of companion animal, livestock and wildlife and their potential mosquito hosts in the United States. This study assessed the prevalence of mature infections of Dirofilaria immitis and avian malaria parasites (Haemosporida) within urban mosquito (Diptera, Culicidae) communities in Oklahoma. 2,620 pools consisting of 12,686 mosquitoes from 13 species collected over two summers were tested for the presence of filarioid and haemosporidian DNA. Dirofilaria immitis-infected mosquitoes were detected only in Aedes albopictus (MIR=0.18-0.22) and Culex pipiens complex (MIR=0.12) collected in cities in central and southern Oklahoma. Two other filarioid nematode species with 91-92% similarity with Onchocerca spp. and Mansonella spp. were also detected. Haemosporidian DNA was detected in 13 mosquito pools (0.9% of pools tested) from seven mosquito species out of 13 species tested. Plasmodium DNA in four species (Cx. coronator, Cx. pipiens complex, Cx. tarsalis, and Psorophora columbiae) had high homology with published sequences of avian Plasmodium species while DNA in four other species (Cx. nigripalpus, Ps. columbiae, Anopheles quadrimaculatus, and An. punctipennis) were closely related to Plasmodium species from deer. One pool of Cx. tarsalis was positive with a 100% sequence identity of Haemoproteus sacharovi. This study provides a baseline concerning the diversity of parasites in different mosquito species present in the southern Great Plains. These studies provide important information for understanding the factors of transmission involving the mosquito community, potential hosts, and different mosquito-borne parasites in this important region involved in livestock management and wildlife conservation.
    Keywords:  Dirofilaria; Haemoproteus; Oklahoma; Plasmodium; Surveillance; south central United States; urban
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105735
  5. Parasit Vectors. 2020 Nov 10. 13(1): 558
    Torres R, Hernandez E, Flores V, Ramirez JL, Joyce AL.
      BACKGROUND: Wolbachia bacteria are widely distributed throughout terrestrial arthropod species. These bacteria can manipulate reproduction and influence the vector competence of their hosts. Recently, Wolbachia have been integrated into vector control programmes for mosquito management. A number of supergroups and strains exist for Wolbachia, and they have yet to be characterized for many mosquito species. In this study, we examined Wolbachia prevalence and their phylogenetic relationship to other Wolbachia, using mosquitoes collected in Merced County in the Central Valley of California.METHODS: Adult mosquitoes were collected from 85 sites in Merced County, California in 2017 and 2018. Traditional and quantitative PCR were used to investigate the presence or absence and the density of Wolbachia, using Wolbachia-specific 16S rRNA and Wolbachia-surface protein (wsp) genes. The supergroup of Wolbachia was determined, and Multilocus Sequence Typing (MLST) by sequencing five housekeeping genes (coxA, gatB, ftsZ, hcpA and fbpA) was also used to determine Wolbachia supergroup as well as strain.
    RESULTS: Over 7100 mosquitoes of 12 species were collected: Aedes melanimon, Ae. nigromaculis, Ae. vexans, Ae. aegypti, Culex pipiens, Cx. stigmatosoma, Cx. tarsalis, Anopheles franciscanus, An. freeborni, An. punctipennis, Culiseta incidens and Cs. inornata. Eight showed evidence of Wolbachia. To our knowledge, this study is the first to report detection of Wolbachia in five of these species (Ae. melanimon, Cx. stigmatosoma, Cx. tarsalis, Cs. incidens and Cs. inornata). Culex pipiens and Cx. stigmatosoma had a high frequency and density of Wolbachia infection, which grouped into supergroup B; Cs. inornata clustered with supergroup A. MLST comparisons identified Cx. pipiens and Cx. stigmatosoma as wPip strain type 9 supergroup B. Six species had moderate to low (< 14%) frequencies of Wolbachia. Four species were negative, Ae. nigromaculis, An. franciscanus, An. freeborni and Ae. aegypti.
    CONCLUSIONS: New records of Wolbachia detection were found in mosquitoes from Merced County, California. Culex stigmatosoma and Cs. inornata were new records for Wolbachia supergroup B and A, respectively. Other species with Wolbachia occurred with low frequency and low density. Detection of Wolbachia in mosquitoes can be used to inform potential vector control applications. Future study of Wolbachia within Cx. stigmatosoma and Cs. inornata in California and through the range of these species could further explore Wolbachia infection in these two species.
    Keywords:  16S rRNA; Aedes aegypti; Aedes melanimon; Culex pipiens; Culex stigmatosoma; Culiseta inornata; Multilocus sequence typing (MLST); Strain characterization; Supergroup; Vector control; Wolbachia
    DOI:  https://doi.org/10.1186/s13071-020-04429-z
  6. Int J Environ Res Public Health. 2020 Nov 10. pii: E8300. [Epub ahead of print]17(22):
    Manica M, Riello S, Scagnolari C, Caputo B.
      The distribution of mosquitos and their corresponding hosts is critical in public health to determine the risk of transmission for vector-borne diseases. In this pilot study conducted in the small Mediterranean island of Ventotene, a known stopover site for migratory birds, the spatio-temporal distribution of two major mosquito vectors is analyzed from the natural to urban environment. The results show that Aedes albopictus aggregates mostly near areas with a human presence and the urban landscape, while Culex pipiens is more spatio-temporally spread, as it can also be found in wilder and less anthropized areas where the availability of human hosts is limited. Culex pipiens is also active earlier in the year. From a microgeographical perspective, our results confirm the anthropophilic spatial distribution of Ae. Albopictus, while suggesting that the circulation of bird zoonosis, such as West Nile, could be favored by the Cx. pipiens distribution. The results highlight the different ecology of the vectors and the interplay with their hosts, even at a small scale. The current evidence may help in forecasting the risk of pathogen transmission and surveillance planning.
    Keywords:  Aedes albopictus; Culex pipiens; Ventotene island; natural to urban gradient; pathogen transmission; public health; spatial distribution; urban ecology; zoonoses
    DOI:  https://doi.org/10.3390/ijerph17228300
  7. PLoS One. 2020 ;15(11): e0241688
    Muhammad NAF, Abu Kassim NF, Ab Majid AH, Abd Rahman A, Dieng H, Avicor SW.
      Urbanization could potentially modify Aedes albopictus' ecology by changing the dynamics of the species, and affecting their breeding sites due to environmental changes, and thus contribute to dengue outbreaks. Thus, this study was conducted to evaluate the biting rhythm, fecundity and longevity of adult female Ae. albopictus in relation to urbanization strata; urban, suburban and rural areas in Penang Island, Malaysia. The experiments were done in comparison to a laboratory strain. Twenty-four hours biting activity of all the mosquito strains showed a clear bimodal biting activity, with morning and evening twilight peaks. The interaction effect between biting time and mosquito strains was not significant. Meanwhile, differences in fecundity among mosquito strains were statistically significant (F(3,442) = 10.559, P < 0.05) with urban areas having higher mean number of eggs (mean = 107.69, standard error = 3.98) than suburban (mean = 94.48, standard error = 5.18), and rural areas (mean = 72.52, standard error = 3.87). Longevity of adult females were significantly higher (F(3,441) = 31.259, P < 0.05) for mosquito strains from urban areas compared to the other strains. These findings would provide crucial information for the planning of control programs in Malaysia, particularly Penang.
    DOI:  https://doi.org/10.1371/journal.pone.0241688
  8. Int J Environ Res Public Health. 2020 Nov 06. pii: E8196. [Epub ahead of print]17(21):
    Buxton M, Machekano H, Gotcha N, Nyamukondiwa C, Wasserman RJ.
      Mosquitoes account for a significant burden of morbidity and mortality globally. Despite evidence of (1) imminent anthropogenic climate and environmental changes, (2) vector-pathogen spatio-temporal dynamics and (3) emerging and re-emerging mosquito borne infections, public knowledge on mosquito bio-ecology remain scant. In particular, knowledge, attitude and practices (KAPs) on mosquitoes are often neglected despite otherwise expensive remedial efforts against consequent infections and other indirect effects associated with disease burden. To gather baseline KAPs that identify gaps for optimising vector-borne disease control, we surveyed communities across endemic and non-endemic malaria sub-districts (Botswana). The study revealed limited knowledge of mosquitoes and their infections uniformly across endemic and non-endemic areas. In addition, a significant proportion of respondents were concerned about mosquito burdens, although their level of personal, indoor and environmental protection practices varied significantly across sub-districts. Given the limited knowledge displayed by the communities, this study facilitates bridging KAP gaps to minimise disease burdens by strengthening public education. Furthermore, it provides a baseline for future studies in mosquito bio-ecology and desirable control practices across differential spheres of the rural-urban lifestyle, with implications for enhanced livelihoods as a consequence of improved public health.
    Keywords:  Central district Botswana; emerging-re-emerging diseases; knowledge attitude practice (KAP), mosquito-borne infection; vector-borne diseases
    DOI:  https://doi.org/10.3390/ijerph17218196
  9. J Med Entomol. 2020 Nov 12. pii: tjaa242. [Epub ahead of print]
    Swan T, Russell TL, Burkot TR, Liu J, Ritchie SA, Staunton KM.
      The global distribution of Aedes albopictus (Skuse) is rapidly expanding which has contributed to the emergence and re-emergence of dengue and chikungunya outbreaks. Improvements in vector surveillance are necessary to facilitate optimized, evidence-based vector control operations. Current trapping technology used to target Ae. albopictus and other Aedes species for vector surveillance are limited in both scale and scope, thus novel tools are required. Here, we evaluated the Male Aedes Sound Trap (MAST) for its capacity to sample male Ae. albopictus. Aims of this study were twofold: 1) to determine the most effective frequency for capturing male Ae. albopictus and 2) to investigate fine-scale variations in male Ae. albopictus abundance. MASTs which produced sound lure frequencies between 500 and 650 Hz captured significantly more male Ae. albopictus than those with sound lure frequencies set to 450 Hz. Further, the higher sound lure frequency of 700 Hz significantly reduced catches relative to 650 Hz. MASTs placed in woodland habitats captured significantly more male Ae. albopictus than MASTs placed near houses. These results provide baseline information for optimizing sound lure frequencies and placement of the MAST to sample male Ae. albopictus in remote areas.
    Keywords:   Aedes albopictus ; male; mosquito surveillance; sound lure; wing beat frequency
    DOI:  https://doi.org/10.1093/jme/tjaa242
  10. Malar J. 2020 Nov 11. 19(1): 408
    Pinda PG, Eichenberger C, Ngowo HS, Msaky DS, Abbasi S, Kihonda J, Bwanaly H, Okumu FO.
      BACKGROUND: Long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) have greatly reduced malaria transmission in sub-Saharan Africa, but are threatened by insecticide resistance. In south-eastern Tanzania, pyrethroid-resistant Anopheles funestus are now implicated in > 80% of malaria infections, even in villages where the species occurs at lower densities than the other vector, Anopheles arabiensis. This study compared the insecticide resistance phenotypes between the two malaria vectors in an area where pyrethroid-LLINs are widely used.METHODS: The study used the World Health Organization (WHO) assays with 1×, 5× and 10× insecticide doses to assess levels of resistance, followed by synergist bioassays to understand possible mechanisms of the observed resistance phenotypes. The tests involved adult mosquitoes collected from three villages across two districts in south-eastern Tanzania and included four insecticide classes.
    FINDINGS: At baseline doses (1×), both species were resistant to the two candidate pyrethroids (permethrin and deltamethrin), but susceptible to the organophosphate (pirimiphos-methyl). Anopheles funestus, but not An. arabiensis was also resistant to the carbamate (bendiocarb). Both species were resistant to DDT in all villages except in one village where An. arabiensis was susceptible. Anopheles funestus showed strong resistance to pyrethroids, surviving the 5× and 10× doses, while An. arabiensis reverted to susceptibility at the 5× dose. Pre-exposure to the synergist, piperonyl butoxide (PBO), enhanced the potency of the pyrethroids against both species and resulted in full susceptibility of An. arabiensis (> 98% mortality). However, for An. funestus from two villages, permethrin-associated mortalities after pre-exposure to PBO only exceeded 90% but not 98%.
    CONCLUSIONS: In south-eastern Tanzania, where An. funestus dominates malaria transmission, the species also has much stronger resistance to pyrethroids than its counterpart, An. arabiensis, and can survive more classes of insecticides. The pyrethroid resistance in both species appears to be mostly metabolic and may be partially addressed using synergists, e.g. PBO. These findings may explain the continued persistence and dominance of An. funestus despite widespread use of pyrethroid-treated LLINs, and inform new intervention choices for such settings. In short and medium-term, these may include PBO-based LLINs or improved IRS with compounds to which the vectors are still susceptible.
    Keywords:  Anopheles funestus; Ifakara health institute; Insecticide resistance; PBO; Tanzania
    DOI:  https://doi.org/10.1186/s12936-020-03483-3
  11. Pathog Glob Health. 2020 Nov 08. 1-13
    Widmar NJO, Bir C, Long E, Ruple A.
      Mosquito-borne illnesses present a public health threat. This analysis quantifies general online mosquito media, and the Zika virus [ZIKV) specifically, from 7-20-2016 to 10-20-2018 in five U.S. geographies. The ZIKV sub-search comprised a shrinking share of online media about mosquitoes over time. Net sentiment, numerical scoring of search result positivity/negativity bounded between -100 and +100, was assessed. Mean net sentiment for the general mosquitoes search was -51; -55 for ZIKV. The ZIKV search revealed more variation in weekly net sentiment with a standard deviation of 14, compared to 10 for mosquitoes. Seventy-seven percent of the weeks had a net sentiment for the mosquito search that was more positive than the ZIKV search. For the 23% of the time the ZIKV search net sentiment was more positive than the general mosquito search, there were mentions of scientific advances, such as the potential for vaccine development associated with the post. Greater emphasis on public health threats from mosquitoes may be necessary to stimulate public action on mosquito-borne illness control. This analysis serves as an illustration of the potential for online/social media analysis to inform health officials of public interest/focus, and perhaps inform effective communication campaigns to combat public health threats.
    Keywords:  Public health; Zika virus; mosquito; public perceptions; social media listening
    DOI:  https://doi.org/10.1080/20477724.2020.1842641
  12. J Med Entomol. 2020 Nov 12. pii: tjaa235. [Epub ahead of print]
    Bellini R, Carrieri M, Balestrino F, Puggioli A, Malfacini M, Bouyer J.
      Vector-borne diseases account for 17% of infectious diseases, leading to more than one million deaths each year. Mosquitoes are responsible for 90% of the casualties and alternative control methods to insecticides are urgently needed, especially against Aedes vectors. Aedes albopictus is a particularly important species, causing major public health problems because it is a vector of several arboviruses and has a strong invasive behavior. Various genetic control methods have been proposed to be integrated into the management strategies of Aedes species, among which the sterile insect technique (SIT), which proved efficient against various insect pests and vectors. However, the ability of released irradiated sterile male mosquitoes to compete with their wild counterparts and induce sterility in wild females, which is critical to the success of this strategy, remained poorly defined. Here, we assessed the field competitiveness of Ae. albopictus irradiated male using data from eight release trials implemented in Northern Italy for 3 yr. Sterile males were capable of inducing a good level of sterility in the wild female population, however, with high variability in time and space. The field competitiveness of the released males was strongly negatively correlated with the ratio of sterile to wild males. This should be taken into consideration when designing future programs to suppress field populations of Aedes mosquitoes.
    Keywords:  competitiveness; control; gamma-ray; genetic; suppression
    DOI:  https://doi.org/10.1093/jme/tjaa235
  13. Malar J. 2020 Nov 10. 19(1): 402
    Kasinathan G, Sahu SS, Krishnamoorthy N, Baig MM, Thankachy S, Dash S, Subramanian S, Jambulingam P.
      BACKGROUND: The success of malaria control using long-lasting insecticidal nets (LLINs) is threatened by pyrethroid resistance developed by the malaria vectors, worldwide. To combat the resistance, synergist piperonyl butoxide (PBO) incorporated LLINs is one of the available options. In the current phase II hut trial, the efficacy of Veeralin®LN (an alpha-cypermethrin and PBO-incorporated net) was evaluated against Anopheles culicifacies, a pyrethroid resistant malaria vector.METHODS: The performance of Veeralin®LN was compared with MAGNet®LN and untreated net in reducing the entry, induced exit, mortality and blood feeding inhibition of target vector species.
    RESULTS: The performance of Veeralin was equal to MAGNet in terms of reducing hut entry, inhibiting blood feeding and inducing exophily, and with regard to causing mortality Veeralin was better than MAGNet. When compared to untreated net, a significant reduction in hut entry and blood feeding and an increase in exophily and mortality were observed with Veeralin. In cone bioassays, unwashed Veeralin caused > 80% mortality of An. culicifacies.
    CONCLUSIONS: Veeralin performed equal to (entry, exit, feeding) or better than (mortality in huts and cone bioassays) MAGNet and could be an effective tool against pyrethroid resistant malaria vectors.
    Keywords:  Alpha-cypermethrin; Anopheles culicifacies; Experimental huts; Piperonyl butoxide; Veeralin
    DOI:  https://doi.org/10.1186/s12936-020-03480-6
  14. PLoS One. 2020 ;15(11): e0240743
    Sandeu MM, Mulamba C, Weedall GD, Wondji CS.
      BACKGROUND: Insecticide resistance is challenging the effectiveness of insecticide-based control interventions to reduce malaria burden in Africa. Understanding the molecular basis of insecticides resistance and patterns of gene flow in major malaria vectors such as Anopheles funestus are important steps for designing effective resistance management strategies. Here, we investigated the association between patterns of genetic structure and expression profiles of genes involved in the pyrethroid resistance in An. funestus across Uganda and neighboring Kenya.METHODS: Blood-fed mosquitoes An. funestus were collected across the four localities in Uganda and neighboring Kenya. A Microarray-based genome-wide transcription analysis was performed to identify the set of genes associated with permethrin resistance. 17 microsatellites markers were genotyped and used to establish patterns of genetic differentiation.
    RESULTS: Microarray-based genome-wide transcription profiling of pyrethroid resistance in four locations across Uganda (Arua, Bulambuli, Lira, and Tororo) and Kenya (Kisumu) revealed that resistance was mainly driven by metabolic resistance. The most commonly up-regulated genes in pyrethroid resistance mosquitoes include cytochrome P450s (CYP9K1, CYP6M7, CYP4H18, CYP4H17, CYP4C36). However, expression levels of key genes vary geographically such as the P450 CYP6M7 [Fold-change (FC) = 115.8 (Arua) vs 24.05 (Tororo) and 16.9 (Kisumu)]. In addition, several genes from other families were also over-expressed including Glutathione S-transferases (GSTs), carboxylesterases, trypsin, glycogenin, and nucleotide binding protein which probably contribute to insecticide resistance across Uganda and Kenya. Genotyping of 17 microsatellite loci in the five locations provided evidence that a geographical shift in the resistance mechanisms could be associated with patterns of population structure throughout East Africa. Genetic and population structure analyses indicated significant genetic differentiation between Arua and other localities (FST>0.03) and revealed a barrier to gene flow between Arua and other areas, possibly associated with Rift Valley.
    CONCLUSION: The correlation between patterns of genetic structure and variation in gene expression could be used to inform future interventions especially as new insecticides are gradually introduced.
    DOI:  https://doi.org/10.1371/journal.pone.0240743
  15. Curr Treat Options Infect Dis. 2020 Nov 06. 1-12
    Bifani AM, Ong EZ, de Alwis R.
      At the turn of the nineteenth century, yellow fever (YF) was considered the most dangerous infectious disease with high case fatality. Subsequent, mass vaccination campaigns coupled with widespread elimination of the YF mosquito vector significantly decreased YF cases and reduced outbreaks to the tropical and subtropical forested regions of Africa and South America. However, recent (2016) large outbreaks in Angola, Democratic Republic of Congo (DRC), and South-Eastern Brazil, where previously had been demarcated as low-risk regions, have highlighted the possibility of a rapidly changing epidemiology and the potential re-emergence of yellow fever virus (YFV). Furthermore, the first-ever importation of YFV into Asia has highlighted the potential fear of YFV emerging as a global threat. In this review, we describe the changing epidemiology of YF outbreaks, and highlight the use of public health policies, therapeutics, and vaccination as tools to help eliminate future YFV outbreaks.
    Keywords:  Epidemiology; Immunity; Outbreak control; Therapeutics; Vaccination; Yellow fever
    DOI:  https://doi.org/10.1007/s40506-020-00237-2
  16. Parasit Vectors. 2020 Nov 07. 13(1): 550
    Silva MR, Lugão PHG, Chapiro G.
      BACKGROUND: The Aedes aegypti mosquito is the primary vector for several diseases. Its control requires a better understanding of the mosquitoes' live cycle, including the spatial dynamics. Several models address this issue. However, they rely on many hard to measure parameters. This work presents a model describing the spatial population dynamics of Aedes aegypti mosquitoes using partial differential equations (PDEs) relying on a few parameters.METHODS: We show how to estimate model parameter values from the experimental data found in the literature using concepts from dynamical systems, genetic algorithm optimization and partial differential equations. We show that our model reproduces some analytical formulas relating the carrying capacity coefficient to experimentally measurable quantities as the maximum number of mobile female mosquitoes, the maximum number of eggs, or the maximum number of larvae. As an application of the presented methodology, we replicate one field experiment numerically and investigate the effect of different frequencies in the insecticide application in the urban environment.
    RESULTS: The numerical results suggest that the insecticide application has a limited impact on the mosquitoes population and that the optimal application frequency is close to one week.
    CONCLUSIONS: Models based on partial differential equations provide an efficient tool for simulating mosquitoes' spatial population dynamics. The reduced model can reproduce such dynamics on a sufficiently large scale.
    Keywords:  Aedes aegypti; Modeling; Spatial Population Dynamics
    DOI:  https://doi.org/10.1186/s13071-020-04426-2
  17. Heliyon. 2020 Oct;6(10): e05003
    Nair K, Al-Thani R, Ginibre C, Chandre F, Alsafran M, Jaoua S.
      Bacillus thuringiensis (Bt) is a Gram-positive soil bacterium that has been recognized as an effective bioinsecticide active against plant, animal and human pathogenic and disease vector insects. During its sporulation phase, Bt produces crystals consisting of δ-endotoxins, which upon ingestion kill specifically insect larvae. Bt subsp. israelensis (Bti) is very active against dipteran insects. Bti based bioinsecticides are considered as a sustainable solution to control the Dipteran insects responsible of plant, animal and human diseases. In this study, Bti strains isolated from Qatar soil were analyzed for their insecticidal activities against the dipteran insect Aedes aegypti Bora Bora (Culicidae, Diptera) and for their δ-endotoxins yields per cell. Among the local Bti strains, four exceptional strains producing spherical crystals, were found to be more insecticidal than the reference strain Bti H14. When tested for their δ-endotoxin yield, the Bti QBT217 strain, producing typical spherical crystals and having the best insecticidal activity, was recognized as the best candidate strain for potential bioinsecticide production and biological control of dipteran insects, particularly the disease vector insect A. aegypti.
    Keywords:  Aedes aegypti Bora Bora; Agricultural science; Bacillus thuringiensis subsp. israelensis; Bioassay; Environmental science; Epidemiology; Food safety; Infectious disease; Insecticidal; Microbiology; δ-endotoxin production
    DOI:  https://doi.org/10.1016/j.heliyon.2020.e05003
  18. Acta Trop. 2020 Nov 04. pii: S0001-706X(20)31655-7. [Epub ahead of print]213 105742
    Maekawa Y, Pemba D, Kumala J, Gowelo S, Higa Y, Futami K, Sawabe K, Tsuda Y.
      We conducted a nationwide survey of mosquito distribution in Malawi from November 2011 to April 2012, and from July to September 2012. Using dried specimens of mosquito adults collected during the survey, we analyzed their cytochrome c oxidase subunit I (COI) gene sequences, prepared specimens, and registered the genetic information (658 bp) of 144 individuals belonging to 51 species of 10 genera in GenBank. Using the obtained genetic information, we analyzed the degree of intraspecific variation and investigated the various species from morphological and genetic perspectives. Moreover, we conducted phylogenetic analysis of the medically important species distributed from Africa to Asia and explored their geographical differentiation. Results showed that individuals morphologically classified as Culex univittatus complex included a individual of Cx. perexiguus which, to date, have not been reported in southern Africa. Furthermore, Mansonia uniformis, distributed in Africa and Asia, was revealed to belong to genetically distinct populations, with observed morphological differences of the samples suggesting that they are separate species. The results of genetic analysis further suggested that Cx. ethiopicus is not a synonym of Cx. bitaeniorhynchus, but that it is an independent species; although, in this study, the only definite morphological difference observed was in the shape of the wing scales. Further morphological and genetic investigation of individuals of these species, including larvae, is highly recommended.
    Keywords:  COI; GenBank; mosquitoes; neighbor-joining; phylogenetics; taxonomy
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105742
  19. Acta Trop. 2020 Nov 04. pii: S0001-706X(20)31652-1. [Epub ahead of print]213 105739
    Pagac BB, Spring AR, Stawicki JR, Dinh TL, Lura T, Kavanaugh MD, Pecor DB, Justi SA, Linton YM.
      Routine biosurveillance efforts at the Naval Station Guantanamo Bay, Cuba, on 18 June 2019, detected two unusual mosquitos in a CO2-baited CDC light trap. Morphological and molecular analysis confirmed the presence of Aedes (Fredwardsius) vittatus (Bigot, 1861) - the first record of the Old World dengue, chikungunya, Zika and yellow fever virus vector into the Americas - and provides evidence for its establishment in Cuba. Newly submitted GenBank sequences from Dominican Republic further evidence its establishment in the Caribbean, and a median-joining network analysis using mitochondrial COI gene sequences clearly supports multiple introductions of Ae. vittatus into the Caribbean from the Indian subcontinent. It was determined that many Ae. vittatus COI barcode sequences in GenBank are currently misidentified as Aedes (Fredwardsius) cogilli Edwards, 1922.
    Keywords:  Caribbean; Cuba; Dominican Republic; Zika; chikungunya; dengue; invasive species; network analysis; new record
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105739
  20. Trans R Soc Trop Med Hyg. 2020 Nov 09. pii: traa125. [Epub ahead of print]
    Juhairiyah J, Andiarsa D, Indriyati L, Ridha MR, Prasodjo RS, Dhewantara PW.
      BACKGROUND: Malaria remains a significant public health concern in Indonesia. Knowledge about spatial patterns of the residual malaria hotspots is critical to help design elimination strategies in Kotabaru district, South Kalimantan, Indonesia.METHODS: Laboratory-confirmed malaria cases from 2012 to 2016 were analysed to examine the trend in malaria cases. Decomposition analysis was performed to assess seasonality. Annual spatial clustering of the incidence and hotspots were identified by Moran's I and the local indicator for spatial association, respectively.
    RESULTS: The annual parasite incidence of malaria was significantly reduced by 87% from 2012 to 2016. Plasmodium vivax infections were significantly much more prevalent over time, followed by Plasmodium falciparum infections (p<0.001). The monthly seasonality of P. vivax and P. falciparum was distinct. High incidence was spatially clustered identified in the north, west and parts of south Kotabaru. Two persistent and four re-emerging high-risk clusters were identified during the period. Despite the significant reduction in the incidence of malaria, the residual high-risk villages remained clustered in the northern part of Kotabaru.
    CONCLUSIONS: A spatially explicit decision support system is needed to support surveillance and control programs in the identified high-risk areas to succeed in the elimination goal of 2030.
    Keywords:  Indonesia; Kalimantan; epidemiology; malaria; spatial analysis
    DOI:  https://doi.org/10.1093/trstmh/traa125
  21. Parasit Vectors. 2020 Nov 07. 13(1): 549
    González MA, Dilger E, Ronderos MM, Spinelli GR, Courtenay O, Hamilton JGC.
      BACKGROUND: We assessed the impact of two sand fly insecticide interventions (insecticide spraying and insecticide-impregnated dog collars) on the peridomestic abundance and distribution of mosquitoes (Culicidae) and biting midges (Ceratopogonidae) in western São Paulo (Brazil) in a long-term (42-month) evaluation. Both of these dipteran groups are vectors of diseases of medical and veterinary relevance to humans and domestic animals in Brazil.METHODS: The interventions in the 3-arm stratified randomised control trial were: pheromone + insecticide (PI) (chicken roosts were sprayed with microencapsulated lambda-cyhalothrin; pheromone lure has no effect on the Diptera pests studied here); dog-collars (DC) (dogs fitted with deltamethrin-impregnated collars); and control (C) (unexposed to pyrethroids) were extended by 12 months. During that time, adult mosquitoes and midges were sampled along 280 households at three household locations (inside human dwellings, dog sleeping sites and chicken roosts).
    RESULTS: We collected 3145 culicids (9 genera, 87.6% Culex spp.) distributed relatively uniformly across all 3 arms: 41.9% at chicken roosts; 37.7% inside houses; and 20.3% at dog sleeping sites. We collected 11,464 Culicoides (15 species) found mostly at chicken roosting sites (84.7%) compared with dog sleeping sites (12.9%) or houses (2.4%). Mosquitoes and Culicoides were most abundant during the hot and rainy season. Increased daytime temperature was marginally associated with increased mosquito abundance (Z = 1.97, P = 0.049) and Culicoides abundance (Z = 1.71, P = 0.087). There was no significant association with daily average rainfall for either group. Household-level mosquito and midge numbers were both significantly reduced by the PI intervention 56% [incidence rate ratio, IRR = 0.54 (95% CI: 0.30-0.97), P ≤ 0.05] and 53% [IRR = 0.47 (95% CI: 0.26-0.85), P ≤ 0.05], respectively, compared to the control intervention. The abundance of both dipteran groups at dog sleeping sites was largely unaffected by the PI and DC interventions. The PI intervention significantly reduced abundance of mosquitoes inside houses (41%) and at chicken roosting sites (48%) and reduced midge abundance by 51% in chicken roosting sites.
    CONCLUSIONS: Sprayed insecticide at chicken roosting sites reduced the abundance of mosquitoes and midges at the peridomestic level while dog collars had no effect on numbers for any group.
    Keywords:  Abundance; Brazil; Chickens; Culicidae; Culicoides; Distribution; Insecticide intervention; Lambda-cyhalothrin; Species composition
    DOI:  https://doi.org/10.1186/s13071-020-04427-1
  22. Transbound Emerg Dis. 2020 Nov 10.
    Tchouassi DP, Torto B, Sang R, Riginos C, Ezenwa VO.
      Loss of biodiversity can affect transmission of infectious diseases in at least two ways: by altering host and vector abundance or by influencing host and vector behavior. We used a large herbivore exclusion experiment to investigate the effects of wildlife loss on the abundance and feeding behavior of mosquito vectors and to explore consequences for vector-borne disease transmission. Large herbivore loss affected both mosquito abundance and blood-feeding behavior. For Aedes mcintoshi, the dominant mosquito species in our study and a primary vector of Rift Valley Fever Virus (RVFV), abundance decreased with large herbivore loss, while blood-feeding on humans increased. Despite an elevated human biting rate in the absence of large herbivores, we estimated that the potential for RVFV transmission to humans doubles in the presence of large herbivores. These results demonstrate that multiple effects of biodiversity loss on vectors can lead to counterintuitive outcomes for human disease risk.
    Keywords:  arbovirus; biodiversity; mosquito-borne disease; vector; vectorial capacity
    DOI:  https://doi.org/10.1111/tbed.13918
  23. Acta Trop. 2020 Nov 06. pii: S0001-706X(20)31664-8. [Epub ahead of print] 105751
    Nagaki SS, Chaves LSM, López RVM, Bergo ES, Laporta GZ, Conn JE, Sallum MAM.
      Nyssorhynchus darlingi (Root) is the dominant malaria vector in the Brazilian Amazon River basin, with additional Anophelinae Grassi species involved in local and regional transmission. Mosquito blood-feeding behavior is an essential component to define the mosquito-human contact rate and shape the transmission cycle of vector-borne diseases. However, there is little information on the host preferences and blood-feeding behavior of Anophelinae vectors in rural Amazonian landscapes. The barrier screen sampling (BSS) method was employed to sample females from 34 peridomestic habitats in 27 rural communities from 11 municipalities in the Brazilian Amazon states of Acre, Amazonas, Pará and Rondônia, from August 2015 to November 2017. Nyssorhynchus darlingi comprised 97.94% of the females collected resting on barrier screens, and DNA sequence comparison detected 9 vertebrate hosts species. The HBI index ranged from 0.03-1.00. Results revealed the plasticity of Ny. darlingi in blood-feeding on a wide range of mainly mammalian hosts. In addition, the identification of blood meal sources using silica-dried females is appropriate for studies of human malaria vectors in remote locations.
    Keywords:  Amazon; Human blood index; blood-feeding behavior; malaria; rural communities
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105751
  24. Parasit Vectors. 2020 Nov 11. 13(1): 569
    Eastwood G, Shepard JJ, Misencik MJ, Andreadis TG, Armstrong PM.
      BACKGROUND: La Crosse virus (LACV) (genus Orthobunyavirus, family Peribunyaviridae) is a mosquito-borne virus that causes pediatric encephalitis and accounts for 50-150 human cases annually in the USA. Human cases occur primarily in the Midwest and Appalachian regions whereas documented human cases occur very rarely in the northeastern USA.METHODS: Following detection of a LACV isolate from a field-collected mosquito in Connecticut during 2005, we evaluated the prevalence of LACV infection in local mosquito populations and genetically characterized virus isolates to determine whether the virus is maintained focally in this region.
    RESULTS: During 2018, we detected LACV in multiple species of mosquitoes, including those not previously associated with the virus. We also evaluated the phylogenetic relationship of LACV strains isolated from 2005-2018 in Connecticut and found that they formed a genetically homogeneous clade that was most similar to strains from New York State.
    CONCLUSION: Our analysis argues for local isolation and long-term persistence of a genetically distinct lineage of LACV within this region. We highlight the need to determine more about the phenotypic behavior of these isolates, and whether this virus lineage poses a threat to public health.
    Keywords:  Arbovirus; Genetic distinction; La Crosse virus; Mosquito species; Pathogen persistence; Public health risk; Vector
    DOI:  https://doi.org/10.1186/s13071-020-04440-4
  25. Molecules. 2020 Nov 06. pii: E5175. [Epub ahead of print]25(21):
    Benelli G, Petrelli R, Canale A.
      Discovering and validating effective drugs to manage arthropod-borne diseases (ABD) is a timely and important research challenge with major impacts on real-world control programs at the time of quick resistance development in the targeted pathogens. This editorial highlights major research advances in the development of drugs for the control of vector-borne diseases, with a significant focus on malaria, Chagas disease, dengue, human African trypanosomiasis, leishmaniasis, and Zika. Broad reviews providing new insights on ABD recently published in Molecules have also been covered in "The Editors' pick" section.
    Keywords:  Chagas disease; Japanese encephalitis; West Nile fever; Zika virus; chikungunya; dengue; human African trypanosomiasis; leishmaniasis; lymphatic filariasis; malaria; yellow fever
    DOI:  https://doi.org/10.3390/molecules25215175