bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒12‒06
eighteen papers selected by
Richard Halfpenny
Staffordshire University


  1. J Vector Borne Dis. 2019 Oct-Dec;56(4):56(4): 308-314
    Filali OB, Faraj C, Kabine M, Debboun M, Sarih M.
      BACKGROUND & OBJECTIVES: Prior to their elimination in 1974 and 2004, respectively, Plasmodium falciparum and P. vivax were the main native malaria parasites involved in disease transmission in Morocco. Imported cases of human malaria are still reported from the country. Anopheles labranchiae in northern Morocco and An. sergentii in the southern regions are the main malaria vectors. The bionomics and insecticide susceptibility of An. sergentii are poorly understood and need to be further studied to enhance the epidemiological surveillance of this important malaria vector.METHODS: The adults and larvae of Anopheles sergentii were collected during the mosquito breeding season in 2015 and 2016 and environmental characteristics of their breeding sites were recorded. Blood meals were analyzed using PCR-RFLP. Alongside, the WHO routine susceptibility tests with DDT (4%) and malathion (5%) were conducted and An. sergentii specimens were screened for knockdown resistance (kdr) and acetyl cholinesterase encoding (ace-1) gene mutations.
    RESULTS: Anopheles sergentii was observed during the summer and autumn seasons, feeding mainly on sheep, cows and also on humans. The WHO bioassays revealed complete susceptibility to DDT and malathion. Analysis of the sequences of the voltage-gated sodium channel gene revealed the absence of the kdr "Leu-Phe" mutation and PCR-RFLP revealed the absence of the G119S mutation in the ace-1.
    INTERPRETATION & CONCLUSION: With the increasing number of imported cases of human malaria in Morocco, the indiscriminate feeding behavior of this species may pose an infectious medical threat. Fortunately, the absence of insecticide resistance can ensure, for now, the efficiency of insecticides, as a part of the vector control program in controlling An. sergentii in Morocco.
    Keywords:  Blood meal; breeding site; insecticide susceptibility; insecticide-resistant gene; vector
    DOI:  https://doi.org/10.4103/0972-9062.302033
  2. J Med Entomol. 2020 Dec 01. pii: tjaa262. [Epub ahead of print]
    Rothman SE, Jones JA, LaDeau SL, Leisnham PT.
      The temperate United States has experienced increasing incidence of mosquito-borne diseases. Recent studies conducted in Baltimore, MD have demonstrated a negative relationship between abundances of Aedes albopictus (Skuse) and Culex mosquitoes and mean neighborhood income level, but have not looked at the presence of pathogens. Mosquitoes collected from five socioeconomically variable neighborhoods were tested for infection by West Nile, chikungunya, and Zika viruses in 2015 and 2016, and again from four of the neighborhoods in 2017. Minimum infection rates of pooled samples were compared among neighborhoods for each year, as well as among individual blocks in 2017. West Nile virus was detected in both Ae. albopictus and Culex pools from all neighborhoods sampled in 2015 and 2017. No infected pools were detected in any year for chikungunya or Zika viruses, and none of the target viruses were detected in 2016. Infection rates were consistently higher for Culex than for Ae. albopictus. Minimum infection rate was negatively associated with mean neighborhood income for both species in 2015. Although earlier work has shown a positive association between block-level abandonment and mosquito abundance, no association was detected in this study. Still, we demonstrate that viral infection in mosquito pools can differ substantially across adjacent urban neighborhoods that vary by income. Though trap security and accessibility often inform city sampling locations, detecting and managing arboviral risk requires surveillance across neighborhoods that vary in socioeconomics, including lower income areas that may be less accessible and secure but have higher infection rates.
    Keywords:  arbovirus; city; income; mosquito
    DOI:  https://doi.org/10.1093/jme/tjaa262
  3. PLoS Negl Trop Dis. 2020 Dec 03. 14(12): e0008941
    Gutiérrez-Bugallo G, Boullis A, Martinez Y, Hery L, Rodríguez M, Bisset JA, Vega-Rúa A.
      BACKGROUND: Like many countries from the Americas, Cuba is threatened by Aedes aegypti-associated arboviruses such as dengue (DENV), Zika (ZIKV), and chikungunya (CHIKV) viruses. Curiously, when CHIKV was actively circulating in the region in 2013-2014, no autochthonous transmission of this virus was detected in Havana, Cuba, despite the importation of chikungunya cases into this city. To investigate if the transmission ability of local mosquito populations could explain this epidemiological scenario, we evaluated for the first time the vector competence of two Ae. aegypti populations (Pasteur and Párraga) collected from Havana for dengue virus type 1 (DENV-1), CHIKV, and ZIKV.METHODOLOGY/PRINCIPAL FINDINGS: Mosquito populations were fed separately using blood containing ZIKV, DENV-1, or CHIKV. Infection, dissemination, and transmission rates, were estimated at 3 (exclusively for CHIKV), 7, and 14 days post exposure (dpe) for each Ae. aegypti population-virus combination. Both mosquito populations were susceptible to DENV-1 and ZIKV, with viral infection and dissemination rates ranging from 24-97% and 6-67% respectively. In addition, CHIKV disseminated in both populations and was subsequently transmitted. Transmission rates were low (<30%) regardless of the mosquito population/virus combination and no ZIKV was detected in saliva of females from the Pasteur population at any dpe.
    CONCLUSIONS/SIGNIFICANCE: Our study demonstrated the ability of Ae. aegypti from Cuba to transmit DENV, ZIKV, and CHIKV. These results, along with the widespread distribution and high abundance of this species in the urban settings throughout the island, highlight the importance of Ae. aegypti control and arbovirus surveillance to prevent future outbreaks.
    DOI:  https://doi.org/10.1371/journal.pntd.0008941
  4. Insects. 2020 Nov 29. pii: E848. [Epub ahead of print]11(12):
    Cebrián-Camisón S, Martínez-de la Puente J, Figuerola J.
      Aedes invasive mosquitoes (AIMs) play a key role as vectors of several pathogens of public health relevance. Four species have been established in Europe, including Aedes aegypti, Aedesalbopictus, Aedes japonicus and Aedes koreicus. In addition, Aedes atropalpus has been repeatedly recorded although it has not yet been established. In spite of their importance in the transmission of endemic (e.g., heartworms) and imported pathogens (e.g., dengue virus), basic information of parameters affecting their vectorial capacity is poorly investigated. The aim of this study is to review the blood feeding patterns of these invasive mosquito species in Europe, summarizing available information from their native and introduced distribution ranges. The feeding patterns of mosquitoes constitute a key parameter affecting the contact rates between infected and susceptible hosts, thus playing a central role in the epidemiology of mosquito-borne pathogens. Our results highlight that these mosquito species feed on the blood of different vertebrate groups from ectotherms to birds and mammals. However, humans represent the most important source of blood for these species, accounting for 36% and 93% of hosts identified for Ae. japonicus and Ae. aegypti, respectively. In spite of that, limited information has been obtained for some particular species, such as Ae. koreicus, or it is restricted to a few particular areas. Given the high vector competence of the four AIM species for the transmission of different emerging arboviruses such as dengue, Chikungunya, Zika or Yellow fever viruses and their high feeding rates on humans, these AIM species may have an important impact on the vectorial capacity for such pathogens on urban and periurban areas. Finally, we propose directions for future research lines based on identified knowledge gaps.
    Keywords:  Asian tiger mosquito; alien species; dengue; feeding behavior; feeding pattern; hosts; vectors; yellow fever; zika
    DOI:  https://doi.org/10.3390/insects11120848
  5. Sci Total Environ. 2021 Feb 01. pii: S0048-9697(20)35949-0. [Epub ahead of print]754 142420
    Soh S, Aik J.
      Culex mosquitoes are important vectors of West Nile Virus (WNV), St. Louis Encephalitis Virus (SLEV) and Japanese Encephalitis Virus (JEV). Climate change is expected to alter their ability to spread diseases in human populations. Studies examining the influence of climate variability on Culex mosquitoes in South East Asia are scarce. We examined the influence of climate variability on reported Culex mosquito larval habitats from 2009 to 2018 in Singapore. We analysed the non-linear immediate and lagged weather dependence of Culex habitats over 5 weeks in negative binomial regression models using nationally representative data. We adjusted for the effects of long-term trend, seasonality, public holidays and autocorrelation. There were 41,170 reported Culex larval habitats over the study period. Non-residential premises were associated with more reports of habitats compared to residential premises [Rate Ratio (RR): 113.9, 95% CI: 110.9, 116.9]. Larvae in more than 90% of these habitats were entomologically identified as Culex quinquefasciatus. In residences, every 10 mm increase in rainfall above a 90 mm threshold was associated with a 10.1% [Incidence Rate Ratio (IRR): 0.899, 95% CI: 0.836, 0.968] cumulative decline in larval habitats. Public holidays were not significantly included in the model analysing larval habitats in residences. In non-residences, a 1 °C increase in the ambient air temperature with respect to the mean was associated with a 36.0% (IRR: 1.360, 95% CI: 1.057, 1.749) cumulative increase in Culex larval habitats. Public holidays were associated with a decline in Culex larval habitats in the same week. Our study provides evidence of how ambient air temperature and rainfall variability influences the abundance of Culex mosquito larval habitats. Our findings support the utility of using weather data in predictive models to inform the timing of vector control measures aimed at reducing the risk of WNV and other Culex-borne flavivirus transmission in urban areas.
    Keywords:  Climate variability; Culex; Singapore; Time series; West Nile Virus
    DOI:  https://doi.org/10.1016/j.scitotenv.2020.142420
  6. Parasit Vectors. 2020 Dec 01. 13(1): 604
    Buxton M, Nyamukondiwa C, Dalu T, Cuthbert RN, Wasserman RJ.
      BACKGROUND: Predators play a critical role in regulating larval mosquito prey populations in aquatic habitats. Understanding predator-prey responses to climate change-induced environmental perturbations may foster optimal efficacy in vector reduction. However, organisms may differentially respond to heterogeneous thermal environments, potentially destabilizing predator-prey trophic systems.METHODS: Here, we explored the critical thermal limits of activity (CTLs; critical thermal-maxima [CTmax] and minima [CTmin]) of key predator-prey species. We concurrently examined CTL asynchrony of two notonectid predators (Anisops sardea and Enithares chinai) and one copepod predator (Lovenula falcifera) as well as larvae of three vector mosquito species, Aedes aegypti, Anopheles quadriannulatus and Culex pipiens, across instar stages (early, 1st; intermediate, 2nd/3rd; late, 4th).
    RESULTS: Overall, predators and prey differed significantly in CTmax and CTmin. Predators generally had lower CTLs than mosquito prey, dependent on prey instar stage and species, with first instars having the lowest CTmax (lowest warm tolerance), but also the lowest CTmin (highest cold tolerance). For predators, L. falcifera exhibited the narrowest CTLs overall, with E. chinai having the widest and A. sardea intermediate CTLs, respectively. Among prey species, the global invader Ae. aegypti consistently exhibited the highest CTmax, whilst differences among CTmin were inconsistent among prey species according to instar stage.
    CONCLUSION: These results point to significant predator-prey mismatches under environmental change, potentially adversely affecting natural mosquito biocontrol given projected shifts in temperature fluctuations in the study region. The overall narrower thermal breadth of native predators relative to larval mosquito prey may reduce natural biotic resistance to pests and harmful mosquito species, with implications for population success and potentially vector capacity under global change.
    Keywords:  Biological control; Climate change; Critical thermal limits; Pest mosquitoes; Predator-prey interactions; Thermal tolerance
    DOI:  https://doi.org/10.1186/s13071-020-04479-3
  7. Malar J. 2020 Dec 02. 19(1): 447
    Mishra AK, Bharti PK, Vishwakarma A, Nisar S, Rajvanshi H, Sharma RK, Saha KB, Shukla MM, Jayswar H, Das A, Kaur H, Wattal SL, Lal AA.
      BACKGROUND: Understanding of malaria vector density, distribution, insecticide resistance, vector incrimination, infection status, and identification of sibling species are some of the essential components of vector control measures for achieving malaria elimination goals.METHODS: As part of the malaria elimination demonstration project, entomological surveillance was carried out from October 2017 to October 2019 by collecting indoor resting mosquitoes using hand catch method. Susceptibility test was done for determining the insecticide resistance status of vector mosquito Anopheles culicifacies using standard protocols by the World Health Organization. The cone bioassay method was used for determining the efficacy and quality of insecticide sprayed. Mosquitoes collected from different ecotypes were identified and processed for parasite identification, vector incrimination and sibling species determination.
    RESULTS: The two known malaria vector species (Anopheles culicifacies and Anopheles fluviatilis) were found in the study area, which have been previously reported in this and adjoining areas of the State of Madhya Pradesh. The prevalence of An. culicifacies was significantly higher in all study villages with peak in July while lowest number was recorded in May. Proportion of vector density was observed to be low in foothill terrains. The other anopheline species viz, Anopheles subpictus, Anopheles annularis, Anopheles vagus, Anopheles splendidus, Anopheles pallidus, Anopheles nigerrimus and Anopheles barbirostris were also recorded in the study area, although their prevalence was significantly less compared to the An. culicifacies. In 2017, An. culicifacies was found to be resistant to dichloro-diphenyl-trichloroethane (DDT) and malathion, with possible resistance to alphacypermethrin and susceptible to deltamethrin. However, in 2019, the species was found to be resistant to alphacypermethrin, DDT, malathion, with possible resistance to deltamethrin. The bioassays revealed 82 to > 98% corrected % mortality of An. culicifacies on day-one post-spraying and 35 to 62% on follow-up day-30. Anopheles culicifacies sibling species C was most prevalent (38.5%) followed by A/D and E while B was least pre-dominant (11.9%). Anopheles fluviatilis sibling species T was most prevalent (74.6%) followed by U (25.4%) while species S was not recorded. One An.culicifacies (sibling species C) was found positive for Plasmodium falciparum by PCR tests in the mosquitoes sampled from the test areas.
    CONCLUSION: Based on the nine entomologic investigations conducted between 2017-2019, it was concluded that An. culicifacies was present throughout the year while An. fluviatilis had seasonal presence in the study areas. Anopheles culicifacies was resistant to alphacypermethrin and emerging resistance to deltamethrin was observed in this area. Anopheles culicifacies was confirmed as the malaria vector. This type of information on indigenous malaria vectors and insecticide resistance is important in implementation of vector control through indoor residual spraying (IRS) and use of insecticide-impregnated bed nets for achieving the malaria elimination goals.
    DOI:  https://doi.org/10.1186/s12936-020-03517-w
  8. Genes (Basel). 2020 Nov 25. pii: E1403. [Epub ahead of print]11(12):
    Gueye OK, Tchouakui M, Dia AK, Faye MB, Ahmed AA, Wondji MJ, Nguiffo DN, Mugenzi LMJ, Tripet F, Konaté L, Diabate A, Dia I, Gaye O, Faye O, Niang EHA, Wondji CS.
      The emergence and spread of insecticide resistance among the main malaria vectors is threatening the effectiveness of vector control interventions in Senegal. The main drivers of this resistance in the Anopheles gambiae complex (e.g., An. gambiae and Anopheles coluzzii) remains poorly characterized in Senegal. Here we characterized the main target site and metabolic resistances mechanisms among the An. gambiae and An. coluzzii populations from their sympatric and allopatric or predominance area in Senegal. Larvae and pupae of An. gambiae s.l. were collected, reared to adulthood, and then used for insecticides susceptibility and synergist assays using the WHO (World Health Organisation) test kits for adult mosquitoes. The TaqMan method was used for the molecular characterization of the main target site insecticide resistance mechanisms (Vgsc-1014F, Vgsc-1014S, N1575Y and G119S). A RT-qPCR (Reverse Transcriptase-quantitative Polymerase Chaine Reaction) was performed to estimate the level of genes expression belonging to the CYP450 (Cytochrome P450) family. Plasmodium infection rate was investigated using TaqMan method. High levels of resistance to pyrethroids and DDT and full susceptibility to organophosphates and carbamates where observed in all three sites, excepted a probable resistance to bendiocarb in Kedougou. The L1014F, L1014S, and N1575Y mutations were found in both species. Pre-exposure to the PBO (Piperonyl butoxide) synergist induced a partial recovery of susceptibility to permethrin and full recovery to deltamethrin. Subsequent analysis of the level of genes expression, revealed that the CYP6Z1 and CYP6Z2 genes were over-expressed in wild-resistant mosquitoes compared to the reference susceptible strain (Kisumu), suggesting that both the metabolic resistance and target site mutation involving kdr mutations are likely implicated in this pyrethroid resistance. The presence of both target-site and metabolic resistance mechanisms in highly pyrethroid-resistant populations of An. gambiae s.l. from Senegal threatens the effectiveness and the sustainability of the pyrethroid-based tools and interventions currently deployed in the country. The Kdr-west mutation is widely widespread in An. coluzzii sympatric population. PBO or Duo nets and IRS (Indoor Residual Spraying) with organophosphates could be used as an alternative measure to sustain malaria control in the study area.
    Keywords:  An. coluzzii; An. gambiae; N1575Y; Senegal; kdr; malaria; metabolic resistance; pyrethroid
    DOI:  https://doi.org/10.3390/genes11121403
  9. Mol Ecol. 2020 Nov 30.
    Tennessen JA, Ingham VA, Toé KH, Guelbéogo WM, Sagnon N, Kuzma R, Ranson H, Neafsey DE.
      The Anopheles gambiae complex consists of multiple morphologically indistinguishable mosquito species including the most important vectors of the malaria parasite Plasmodium falciparum in sub-Saharan Africa. Nine cryptic species have been described so far within the complex. The ecological, immunological, and reproductive differences among these species will critically impact population responses to disease control strategies and environmental changes. Here we examine whole-genome sequencing data from a longitudinal study of putative A. coluzzii in western Burkina Faso. Surprisingly, many specimens are genetically divergent from A. coluzzii and all other Anopheles species and represent a new taxon, here designated Anopheles TENGRELA (AT). Population genetic analysis suggests that the cryptic GOUNDRY subgroup, previously collected as larvae in central Burkina Faso, represents an admixed population descended from both A. coluzzii and AT. AT harbors low nucleotide diversity except for the 2La inversion polymorphism which is maintained by overdominance. It shows numerous fixed differences with A. coluzzii concentrated in several regions reflecting selective sweeps, but the two taxa are identical at standard diagnostic loci used for taxon identification and thus AT may often go unnoticed. We present an amplicon-based genotyping assay for identifying AT which could be usefully applied to numerous existing samples. Misidentified cryptic taxa could seriously confound ongoing studies of Anopheles ecology and evolution in western Africa, including phenotypic and genotypic surveys of insecticide resistance. Reproductive barriers between cryptic species may also complicate novel vector control efforts, for example gene drives, and hinder predictions about evolutionary dynamics of Anopheles and Plasmodium.
    Keywords:   Anopheles ; admixture; cryptic taxa; reproductive barrier; selective sweep; vector
    DOI:  https://doi.org/10.1111/mec.15756
  10. J Vector Borne Dis. 2019 Oct-Dec;56(4):56(4): 380-382
    Debnath F, Provash CS, Chakraborty A, Dutta S.
      A dengue outbreak struck Baranagar municipality area of North 24 Parganas district, West Bengal in July 2016. This study presents the epidemiological and virology findings of this outbreak. The outbreak started from 17 July and continued until 17th December. Total 1660 dengue cases (overall attack rate: 7/1000) and two deaths (case fatality rate: 1/1000) were reported. All age groups were affected. Out of the 213 blood samples collected from probable dengue cases and tested at Virus Unit, ICMR-National Institute of Cholera & Enteric Diseases (NICED), Kolkata, 163 (76%) tested seropositive through NS1 / IgM ELISA confirming dengue infection. DENV 1 was the predominant (53%, 44/83) serotype followed by DENV 2 (23%, 19/83), DENV 4 (15.6%, 13/83), DENV 3 (8.4%,7/ 83). Coexistence of dengue and chikungunya virus infection was detected. Major presentation of the confirmed dengue cases was fever with headache (95%), followed by arthralgia, myalgia, retro-orbital pain, abdominal pain, diarrhoea, and rash. Abundance of vector breeding spaces was observed in the area. Accordingly the health authorities were suggested to conduct frequent mass awareness campaigns involving community to reduce breeding sources during pre-monsoon and monsoon months. Further, adult mosquito control measures were also suggested throughout the year and inter-departmental coordination was recommended for prevention of such outbreaks in future.
    Keywords:  Chikungunya co-infection; DENV 1; DENV 2; IgM ELISA; NS1 ELSA; dengue fever
    DOI:  https://doi.org/10.4103/0972-9062.302043
  11. Rev Soc Bras Med Trop. 2020 ;pii: S0037-86822020000100384. [Epub ahead of print]53 e20200502
    Silva-Inacio CL, Paiva AAP, Araújo JMG, Ximenes MFFM.
      INTRODUCTION: Haemagogus are mosquitoes with diurnal habits that live preferentially in forest areas. In Brazil, they are considered the primary vectors of wild yellow fever.METHODS: The ecological relationships between Haemagogus spegazzinii, the environment, and some of its activities in the semiarid region of Rio Grande do Norte were analyzed by collecting eggs with ovitraps, actively searching in tree holes, capturing adults in Shannon traps, and conducting an investigation for viral infections.
    RESULTS: A total of 2420 eggs, 271 immature specimens (larvae and pupae), and 206 adults were collected. Egg collection depended on rainfall and relative humidity, with oviposition occurring between January and May. Larvae were found in five plant species, including Tabebuia aurea (craibeira), with 160 larvae collected. We observed shared breeding sites between Hg. spegazzinii and the following species: Aedes albopictus, Aedes terrens, Culex spp., and Toxorhynchites theobaldi. Adults exhibited greater activity between 5 pm and 6 pm, when 191 (92.7%) specimens were captured, while only 1 (0.5%) was collected between 7 pm and 8 pm. The relationship between Hg. spegazzinii and rainfall was significant, with positive correlations with accumulated rainfall 5, 10, 15, 20, and 30 days before mosquito collection. We found that the species was infected with the DENV-2 virus.
    CONCLUSIONS: This work contributes new information on the bioecology of Hg. spegazzinii, with data on the main reproduction periods, oviposition, breeding sites, activity times, and the relationship between the species and meteorological variables in the Caatinga of northeastern Brazil.
    DOI:  https://doi.org/10.1590/0037-8682-0502-2020
  12. PLoS Genet. 2020 Nov 30. 16(11): e1008946
    de Melo ES, Wallau GL.
      Transposable elements (TEs) are mobile genetic elements that parasitize basically all eukaryotic species genomes. Due to their complexity, an in-depth TE characterization is only available for a handful of model organisms. In the present study, we performed a de novo and homology-based characterization of TEs in the genomes of 24 mosquito species and investigated their mode of inheritance. More than 40% of the genome of Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus is composed of TEs, varying substantially among Anopheles species (0.13%-19.55%). Class I TEs are the most abundant among mosquitoes and at least 24 TE superfamilies were found. Interestingly, TEs have been extensively exchanged by horizontal transfer (172 TE families of 16 different superfamilies) among mosquitoes in the last 30 million years. Horizontally transferred TEs represents around 7% of the genome in Aedes species and a small fraction in Anopheles genomes. Most of these horizontally transferred TEs are from the three ubiquitous LTR superfamilies: Gypsy, Bel-Pao and Copia. Searching more than 32,000 genomes, we also uncovered transfers between mosquitoes and two different Phyla-Cnidaria and Nematoda-and two subphyla-Chelicerata and Crustacea, identifying a vector, the worm Wuchereria bancrofti, that enabled the horizontal spread of a Tc1-mariner element among various Anopheles species. These data also allowed us to reconstruct the horizontal transfer network of this TE involving more than 40 species. In summary, our results suggest that TEs are frequently exchanged by horizontal transfers among mosquitoes, influencing mosquito's genome size and variability.
    DOI:  https://doi.org/10.1371/journal.pgen.1008946
  13. PLoS Negl Trop Dis. 2020 Nov 30. 14(11): e0008920
    Ye G, Wang Y, Liu X, Dong Q, Cai Q, Yuan Z, Xia H.
      Advances in technology have greatly stimulated the understanding of insect-specific viruses (ISVs). Unfortunately, most of these findings are based on sequencing technology, and laboratory data are scarce on the transmission dynamics of ISVs in nature and the potential effects of these viruses on arboviruses. Mesonivirus is a class of ISVs with a wide geographical distribution. Recently, our laboratory reported the isolation of a novel strain of mesonivirus, Yichang virus (YCV), from Culex mosquitoes, China. In this study, the experimental infection of YCV by the oral route for adult and larvae mosquitoes, and the vertical transmission has been conducted, which suggests that YCV could adopt a mixed-mode transmission. Controlled experiments showed that the infectivity of YCV depends on the mosquito species, virus dose, and infection route. The proliferation curve and tissue distribution of YCV in Cx. quinquefasciatus and Ae. albopictus showed that YCV is more susceptible to Ae. albopictus and is located in the midgut. Furthermore, we also assessed the interference of YCV with flaviviruses both in vitro and in vivo. YCV significantly inhibited the proliferation of DENV-2 and ZIKV, in cell culture, and reduced transmission rate of DENV-2 in Ae. albopictus. Our work provides insights into the transmission of ISVs in different mosquito species during ontogeny and their potential ability to interact with mosquito-borne viruses.
    DOI:  https://doi.org/10.1371/journal.pntd.0008920
  14. Emerg Top Life Sci. 2020 Dec 01. pii: ETLS20200187. [Epub ahead of print]
    Sacchetto L, Drumond BP, Han BA, Nogueira ML, Vasilakis N.
      Yellow fever virus (YFV) is the etiological agent of yellow fever (YF), an acute hemorrhagic vector-borne disease with a significant impact on public health, is endemic across tropical regions in Africa and South America. The virus is maintained in two ecologically and evolutionary distinct transmission cycles: an enzootic, sylvatic cycle, where the virus circulates between arboreal Aedes species mosquitoes and non-human primates, and a human or urban cycle, between humans and anthropophilic Aedes aegypti mosquitoes. While the urban transmission cycle has been eradicated by a highly efficacious licensed vaccine, the enzootic transmission cycle is not amenable to control interventions, leading to recurrent epizootics and spillover outbreaks into human populations. The nature of YF transmission dynamics is multifactorial and encompasses a complex system of biotic, abiotic, and anthropogenic factors rendering predictions of emergence highly speculative. The recent outbreaks in Africa and Brazil clearly remind us of the significant impact YF emergence events pose on human and animal health. The magnitude of the Brazilian outbreak and spillover in densely populated areas outside the recommended vaccination coverage areas raised the specter of human - to - human transmission and re-establishment of enzootic cycles outside the Amazon basin. Herein, we review the factors that influence the re-emergence potential of YFV in the neotropics and offer insights for a constellation of coordinated approaches to better predict and control future YF emergence events.
    Keywords:  arbovirus; epizootics; outbreak; re-emergence; transmission cycles; yellow fever virus
    DOI:  https://doi.org/10.1042/ETLS20200187
  15. Trends Parasitol. 2020 Nov 26. pii: S1471-4922(20)30296-8. [Epub ahead of print]
    Smith DL, Musiime AK, Maxwell K, Lindsay SW, Kiware S.
      
    Keywords:  dynamics and control; malaria; mosquito ecology; vector control
    DOI:  https://doi.org/10.1016/j.pt.2020.10.011
  16. Malar J. 2020 Nov 30. 19(1): 441
    Ekawati LL, Johnson KC, Jacobson JO, Cueto CA, Zarlinda I, Elyazar IRF, Fatah A, Sumiwi ME, Noviyanti R, Cotter C, Smith JL, Coutrier FN, Bennett A.
      BACKGROUND: Following a dramatic decline of malaria cases in Aceh province, geographically-based reactive case detection (RACD) was recently evaluated as a tool to improve surveillance with the goal of malaria elimination. While RACD detected few cases in households surrounding index cases, engaging in forest work was identified as a risk factor for malaria and infections from Plasmodium knowlesi-a non-human primate malaria parasite-were more common than expected. This qualitative formative assessment was conducted to improve understanding of malaria risk from forest work and identify strategies for targeted surveillance among forest workers, including adapting reactive case detection.METHODS: Between June and August, 2016, five focus groups and 18 in-depth interviews with forest workers and key informants were conducted in each of four subdistricts in Aceh Besar and Aceh Jaya districts. Themes included: types of forest activities, mobility of workers, interactions with non-human primates, malaria prevention and treatment-seeking behaviours, and willingness to participate in malaria surveys at forest work sites and using peer-referral.
    RESULTS: Reported forest activities included mining, logging, and agriculture in the deep forest and along the forest fringe. Forest workers, particularly miners and loggers, described often spending weeks to months at work sites in makeshift housing, rarely utilizing mosquito prevention and, upon fever, self-medicating and seeking care from traditional healers or pharmacies rather than health facilities. Non-human primates are frequently observed near work sites, and most forest work locations are within a day's journey of health clinics. Employers and workers expressed interest in undertaking malaria testing and in participating in survey recruitment by peer-referral and at work sites.
    CONCLUSIONS: Diverse groups of forest workers in Aceh are potentially exposed to malaria through forest work. Passive surveillance and household-based screening may under-estimate malaria burden due to extended stays in the forest and health-seeking behaviours. Adapting active surveillance to specifically target forest workers through work-site screening and/or peer-referral appears promising for addressing currently undetected infections.
    Keywords:  Aceh; High risk population; Malaria; Socio-behavioural surveillance
    DOI:  https://doi.org/10.1186/s12936-020-03511-2
  17. Viruses. 2020 11 25. pii: E1349. [Epub ahead of print]12(12):
    Kuno G.
      Since the recent epidemics of yellow fever in Angola and Brazil as well as the importation of cases to China in 2016, there has been an increased interest in the century-old enigma, absence of yellow fever in Asia. Although this topic has been repeatedly reviewed before, the history of human intervention has never been considered a critical factor. A two-stage literature search online for this review, however, yielded a rich history indispensable for the debate over this medical enigma. As we combat the pandemic of COVID-19 coronavirus worldwide today, we can learn invaluable lessons from the historical events in Asia. In this review, I explore the history first and then critically examine in depth major hypotheses proposed in light of accumulated data, global dispersal of the principal vector, patterns of YF transmission, persistence of urban transmission, and the possibility of YF in Asia. Through this process of re-examination of the current knowledge, the subjects for research that should be conducted are identified. This review also reveals the importance of holistic approach incorporating ecological and human factors for many unresolved subjects, such as the enigma of YF absence in Asia, vector competence, vector dispersal, spillback, viral persistence and transmission mechanisms.
    Keywords:  Aedes aegypti; Asia; hypothesis; international sanitary convention; medical enigma; spillback; transmission cycle; vector dispersal; yellow fever
    DOI:  https://doi.org/10.3390/v12121349
  18. Pathogens. 2020 Nov 30. pii: E1005. [Epub ahead of print]9(12):
    Constant O, Bollore K, Clé M, Barthelemy J, Foulongne V, Chenet B, Gomis D, Virolle L, Gutierrez S, Desmetz C, Moares RA, Beck C, Lecollinet S, Salinas S, Simonin Y.
      West Nile virus (WNV) and Usutu virus (USUV) are zoonotic arboviruses. These flaviviruses are mainly maintained in the environment through an enzootic cycle involving mosquitoes and birds. Horses and humans are incidental, dead-end hosts, but can develop severe neurological disorders. Nevertheless, there is little data regarding the involvement of other mammals in the epidemiology of these arboviruses. In this study, we performed a serosurvey to assess exposure to these viruses in captive birds and mammals in a zoo situated in the south of France, an area described for the circulation of these two viruses. A total of 411 samples comprising of 70 species were collected over 16 years from 2003 to 2019. The samples were first tested by a competitive enzyme-linked immunosorbent assay. The positive sera were then tested using virus-specific microneutralization tests against USUV and WNV. USUV seroprevalence in birds was 10 times higher than that of WNV (14.59% versus 1.46%, respectively). Among birds, greater rhea (Rhea Americana) and common peafowl (Pavo cristatus) exhibited the highest USUV seroprevalence. Infections occurred mainly between 2016-2018 corresponding to a period of high circulation of these viruses in Europe. In mammalian species, antibodies against WNV were detected in one dama gazelle (Nanger dama) whereas serological evidence of USUV infection was observed in several Canidae, especially in African wild dogs (Lycaon pictus). Our study helps to better understand the exposure of captive species to WNV and USUV and to identify potential host species to include in surveillance programs in zoos.
    Keywords:  arbovirus; flavivirus; seroprevalence; usutu virus; west nile virus; zoological garden
    DOI:  https://doi.org/10.3390/pathogens9121005