bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒06‒21
twenty-nine papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS One. 2020 ;15(6): e0234572
    Yougang AP, Kamgang B, Tedjou AN, Wilson-Bahun TA, Njiokou F, Wondji CS.
      The Asian mosquito, Aedes albopictus (Skuse), is an invasive mosquito which has become one of the most important vectors of dengue, Zika, and chikungunya viruses worldwide. This species was reported for the first time in Cameroon in early 2000s and became the dominant Aedes species in the urban areas in the southern part of Cameroon but remain poorly characterized. Here, we assessed the susceptibility profile of A. albopictus collected throughout Cameroon and investigated the potential resistance mechanisms involved. Immature stages of A. albopictus were collected between March and July 2017 in 15 locations across Cameroon and reared until G1/G2 generation. Larval, adult bioassays, and synergists [piperonyl butoxide (PBO) and diethyl maleate (DEM)] assays were carried out according to WHO recommendations. F1534C mutation was genotyped in field collected adults (Go) using allele specific PCR. All tested populations were susceptible to both larvicides, temephos and Bacillus thuringiensis israelensis (Bti), after larval bioassays. Adult bioassays revealed a high level of resistance of A. albopictus to 4% DDT with mortality rates ranging from 12.42% in Bafang to 75.04% in Kumba. The resistance was reported also in 0.05% deltamethrin, 0.25% permethrin, and 0.1% propoxur in some locations. A loss of susceptibility to 0.1% bendiocarb was found in one of three populations analysed. A full susceptibility to 1% fenitrothion were observed across the country. A full recovery or partial of susceptibility was observed in A. albopictus when pre-exposed to PBO or DEM and then to DDT and permethrin, respectively. The F1534C kdr mutation was not detected in A. albopictus. This study showed that the susceptibility profile of A. albopictus to insecticide vary according to the sampling location and insecticides used. These findings are useful to planning vector control program against arbovirus vectors in Cameroon and can be used as baseline data for further researches.
  2. PLoS Negl Trop Dis. 2020 Jun 19. 14(6): e0008362
    Heath CJ, Grossi-Soyster EN, Ndenga BA, Mutuku FM, Sahoo MK, Ngugi HN, Nbakaya JO, Siema P, Kitron U, Zahiri N, Hortion J, Waggoner JJ, King CH, Pinsky BA, LaBeaud AD.
      Arboviruses are among the most important emerging pathogens due to their increasing public health impact. In Kenya, continued population growth and associated urbanization are conducive to vector spread in both urban and rural environments, yet mechanisms of viral amplification in vector populations is often overlooked when assessing risks for outbreaks. Thus, the characterization of local arbovirus circulation in mosquito populations is imperative to better inform risk assessments and vector control practices. Aedes species mosquitoes were captured at varying stages of their life cycle during different seasons between January 2014 and May 2016 at four distinct sites in Kenya, and tested for chikungunya (CHIKV), dengue (DENV) and Zika (ZIKV) viruses by RT-PCR. CHIKV was detected in 45 (5.9%) and DENV in 3 (0.4%) mosquito pools. No ZIKV was detected. Significant regional variation in prevalence was observed, with greater frequency of CHIKV on the coast. DENV was detected exclusively on the coast. Both viruses were detected in immature mosquitoes of both sexes, providing evidence of transovarial transmission of these arboviruses in local mosquitoes. This phenomenon may be driving underlying viral maintenance that may largely contribute to periodic re-emergence among humans in Kenya.
  3. Trans R Soc Trop Med Hyg. 2020 Jun 15. pii: traa045. [Epub ahead of print]
    Goodyer L, Grootveld M, Deobhankar K, Debboun M, Philip M.
      BACKGROUND: Characterisation of mosquito repellents using arm-in-cage tests are performed by assessing the 95% effective dose (ED95), half-life and complete protection time (CPT). This study fully characterizes these properties for p-menthane-3,8-diol (PMD), which has not been widely studied, and a long-acting formulation containing a PMD-vanillin composite.METHODS: A series of arm-in-cage tests against Aedes aegypti (Diptera: Culicidae) mosquitoes were devised using 6 volunteers to estimate CPT or 10 to estimate the ED95 and half-lives for three repellents: 20% N,N-diethyl-3-methylbenzamide (DEET), 30% PMD and a novel 30% PMD-vanillin formulation. Non-linear regression analysis was used to characterize the relationship between applied dose and CPT.
    RESULTS: PMD and DEET showed a very similar log dose relationship to CPT; however, the PMD-vanillin formulation exhibited a sigmoidal 'S-shaped' relationship. This resulted in a 1.5-fold higher CPT for PMD-vanillin compared with that of 20% DEET when applied at a dose of 1.6 mg/cm2, but little difference was observed at lower doses of 0.8-1 mg/cm2. The ED95 value for the 30% PMD and PMD-vanillin formulations were 0.25 and 0.24 mg/cm2, respectively, these being higher than that for 20% DEET (0.09 mg/cm2). The half-lives for 30% PMD and 20% DEET were similar (2.23 vs. 2.74 h), but longer for the PMD-vanillin formulations (3.8 h).
    CONCLUSIONS: A full characterisation for other repellent formulations, particularly those claiming extended longevity, should be conducted in order to identify differences at various applied doses.
    Keywords:  DEET; PMD; half-life; longevity; mosquito; repellent
  4. Parasit Vectors. 2020 Jun 15. 13(1): 310
    Mayton EH, Tramonte AR, Wearing HJ, Christofferson RC.
      BACKGROUND: Transmission dynamics of arboviruses like Zika virus are often evaluated by vector competence (the proportion of infectious vectors given exposure) and the extrinsic incubation period (EIP, the time it takes for a vector to become infectious), but vector age is another critical driver of transmission dynamics. Vectorial capacity (VC) is a measure of transmission potential of a vector-pathogen system, but how these three components, EIP, vector competence and vector age, affect VC in concert still needs study.METHODS: The interaction of vector competence, EIP, and mosquito age at the time of infection acquisition (Ageacquisition) was experimentally measured in an Aedes aegypti-ZIKV model system, as well as the age-dependence of probability of survival and the willingness to bite. An age-structured vectorial capacity framework (VCage) was then developed using both EIPMin and EIPMax, defined as the time to first observed minimum proportion of transmitting mosquitoes and the time to observed maximum proportion of transmitting mosquitoes.
    RESULTS: The within-mosquito dynamics of vector competence/EIP were not significant among treatments where mosquitoes were exposed at different ages. However, VCage revealed: (i) age-dependence in vector-virus interactions is important for transmission success; (ii) lower vector competence but at shorter EIPs was sufficient for transmission perpetuation; and (iii) R0 may be overestimated by using non-age-structured VC.
    CONCLUSIONS: The results indicate that ultimately the temporal component of the virus-vector dynamics is most critical, especially when exposure occurred at advanced mosquito age. While our study is limited to a single virus-vector system, and a multitude of other factors affect both vector competence and mosquito mortality, our methods can be extrapolated to these other scenarios. Results indicate that how 'highly' or 'negligibly' competent vectors are categorized may need adjustment.
    Keywords:  Aedes aegypti; Arbovirus; Biting rate; EIP; Extrinsic incubation period; Mortality; Vector competence; Vectorial capacity; Zika
  5. Acta Virol. 2020 ;64(2): 187-200
    Korytár Ľ, Peňazziová K, Pistl J, Tichá E, Čabanová V, Csank T.
      West Nile virus (WNV) is a mosquito-borne flavivirus (the genus Flavivirus) representing a medical and veterinary public health concern. Birds are the most important reservoirs. Culicine mosquitoes transmit WNV to vertebrate hosts (including horses and humans) and migratory birds play role in its long-distance transport. Slovakia is geographically localised at the crossroad of migration routes connecting South Europe and Africa with breeding localities in the Western, Northern, Central and Eastern Europe and Siberia. This review summarizes historical and present knowledge on WNV in Slovakia during a period of more than fifty years. Five European mosquito species capable to transmit WNV are native in Slovakia. Based on recent research results, the major role in the WNV transmission is attributed to Culex mosquitoes, which are also the most abundant species. Virus isolates from birds that succumbed to WNV infection are genetically close to Central European strains. Historical and recent results point out, that WNV circulates in the population of vectors, reservoirs and hosts for decades. Although West Nile fever epidemics in Slovakia were not reported yet, virus isolation, molecular detection and serological findings in reservoirs and hosts confirm that sporadic cases occur. Furthermore, the first autochthonous human case may indicate favourable conditions for WNV transmission to humans. The climate change and precipitation anomalies may favour to increase vector abundance, hence increase the chance of WNV epidemics. This review highlights an urgent need of a countrywide surveillance program aimed on the WNV occurrence in vectors and reservoirs in Slovakia. Keywords: West Nile virus; flavivirus; vector-borne pathogen; arbovirus.
  6. Malar J. 2020 Jun 16. 19(1): 207
    Monroe A, Moore S, Okumu F, Kiware S, Lobo NF, Koenker H, Sherrard-Smith E, Gimnig J, Killeen GF.
      BACKGROUND: Effective targeting and evaluation of interventions that protect against adult malaria vectors requires an understanding of how gaps in personal protection arise. An improved understanding of human and mosquito behaviour, and how they overlap in time and space, is critical to estimating the impact of insecticide-treated nets (ITNs) and determining when and where supplemental personal protection tools are needed. Methods for weighting estimates of human exposure to biting Anopheles mosquitoes according to where people spend their time were first developed over half a century ago. However, crude indoor and outdoor biting rates are still commonly interpreted as indicative of human-vector contact patterns without any adjustment for human behaviour or the personal protection effects of ITNs.MAIN TEXT: A small number of human behavioural variables capturing the distribution of human populations indoors and outdoors, whether they are awake or asleep, and if and when they use an ITN over the course of the night, can enable a more accurate representation of human biting exposure patterns. However, to date no clear guidance is available on what data should be collected, what indicators should be reported, or how they should be calculated. This article presents an integrated perspective on relevant indicators of human-vector interactions, the critical entomological and human behavioural data elements required to quantify human-vector interactions, and recommendations for collecting and analysing such data.
    CONCLUSIONS: If collected and used consistently, this information can contribute to an improved understanding of how malaria transmission persists in the context of current intervention tools, how exposure patterns may change as new vector control tools are introduced, and the potential impact and limitations of these tools. This article is intended to consolidate understanding around work on this topic to date and provide a consistent framework for building upon it. Additional work is needed to address remaining questions, including further development and validation of methods for entomological and human behavioural data collection and analysis.
    Keywords:  Exposure; Human-vector contact; Human-vector interaction; Insecticide-treated nets; Outdoor biting; Outdoor transmission; Residual malaria transmission
  7. J Med Entomol. 2020 Jun 19. pii: tjaa111. [Epub ahead of print]
    Kang DS, Cunningham JM, Lovin DD, Chadee DD, Severson DW.
      Efforts directed at genetic modification of mosquitoes for population control or replacement are highly dependent on the initial mating success of transgenic male mosquitoes following their release into natural populations. Adult mosquito phenotypes are influenced by the environmental conditions experienced as larvae. Semifield studies conducted to date have not taken that under consideration when testing male mating fitness, and have compared mating success of males reared under identical environmental conditions. We performed pairwise mating challenges between males from a genetically modified laboratory strain (BF2) versus males from a recent Trinidad field isolate of Aedes aegypti (L.), a major vector of multiple arboviruses. We utilized larval density and nutrition to simulate environmental stress experienced by the Trinidad males and females. Our results indicated that environmental stress during larval development negatively influenced the competitiveness and reproductive success of males from the Trinidad population when paired with optimum reared BF2 males. Small (0.027 m3) and large (0.216 m3) trials were conducted wherein stressed or optimum Trinidad males competed with optimum BF2 males for mating with stressed Trinidad females. When competing with stress reared Trinidad males, optimum reared BF2 males were predominant in matings with stress reared Trinidad females, and large proportions of these females mated with males of both strains. When competing with optimum reared Trinidad males, no difference in mating success was observed between them and BF2 males, and frequencies of multiple matings were low. Our results indicate that future mating competition studies should incorporate appropriate environmental conditions when designing mating fitness trials of genetically modified males.
    Keywords:  competition; fitness; genetically modified organism; transgenic
  8. J Vis Exp. 2020 May 31.
    Azar SR, Weaver SC.
      The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine the rate of infection, disseminated infection, and potential transmission of the virus in the mosquito population in question. These procedures are widely utilized with various modifications in vector competence evaluations globally. They are important in determining the potential role that a given mosquito (i.e., species, population, individual) may play in the transmission of a given agent.
  9. PLoS One. 2020 ;15(6): e0234399
    Madewell ZJ, López MR, Espinosa-Bode A, Brouwer KC, Sánchez CG, McCracken JP.
      BACKGROUND: Dengue, chikungunya, and Zika viruses are increasingly important public health problems. Burning vegetation, leaves, and other plant products have been shown to be effective mosquito repellents for their vector, Aedes spp., but there has been scant research on whether firewood cooking smoke in households influences mosquito populations or mosquito-borne diseases. About 2.9 billion people worldwide use biomass fuel for household cooking and heating, resulting in an estimated 1.6 million deaths annually from household air pollution (HAP)-related diseases. Global health agencies now encourage households to transition from biomass to clean fuels, but it is unclear whether such interventions may actually increase risk for mosquito-borne diseases. This retrospective case-control study evaluated associations between arboviral infections and cooking with firewood in Santa Rosa, Guatemala.METHOD: Vigilancia Integrada Comunitaria (VICo) was a prospective public health surveillance system for bacterial, parasitic, and viral causes of diarrheal, neurological, respiratory, and febrile illnesses in hospitals and clinics in the department of Santa Rosa, Guatemala. Enrolled VICo in-patients and out-patients during 2011-2018 were interviewed using standardized questionnaires on demographics and household characteristics. Blood and stool specimens were collected and tested to identify the etiologies presenting symptoms. Cases were defined as laboratory-positive for dengue, chikungunya, or Zika virus infections. Controls were laboratory-positive for bacterial and viral diarrheal illnesses (e.g., Salmonella, Shigella, Campylobacter, Escherichia coli, rotavirus, norovirus, sapovirus, or astrovirus). Cooking with firewood, kitchen location, stove type, and firewood cooking frequency were the independent exposure variables. Logistic regression models were used to analyze unadjusted and adjusted associations between arboviral infections and exposures of interest.
    RESULT: There were 311 arboviral cases and 1,239 diarrheal controls. Arboviral infections were inversely associated with cooking with firewood in the main house (AOR: 0.22; 95% CI: 0.08-0.57), cooking with firewood on an open hearth (AOR: 0.50; 95% CI: 0.33-0.78), and cooking with firewood ≥5 times per week (AOR: 0.54; 95% CI: 0.36-0.81), adjusting for age, sex, ethnicity, socioeconomic status index, number of people per household, community population density, community elevation, recruitment location, season, and admission year.
    CONCLUSION: Several primary determinants of HAP exposure were inversely associated with arboviral infections. Additional studies are needed to understand whether interventions to reduce HAP might actually increase risk for mosquito-borne infectious diseases, which would warrant improved education and mosquito control efforts in conjunction with fuel interventions.
  10. Virology. 2020 Aug;pii: S0042-6822(20)30092-1. [Epub ahead of print]547 35-46
    Jaeger AS, Weiler AM, Moriarty RV, Rybarczyk S, O'Connor SL, O'Connor DH, Seelig DM, Fritsch MK, Friedrich TC, Aliota MT.
      Spondweni virus (SPONV) is the most closely related known flavivirus to Zika virus (ZIKV). Its pathogenic potential and vector specificity have not been well defined. SPONV has been found predominantly in Africa, but was recently detected in a pool of Culex quinquefasciatus mosquitoes in Haiti. Here we show that SPONV can cause significant fetal harm, including demise, comparable to ZIKV, in a mouse model of vertical transmission. Following maternal inoculation, we detected infectious SPONV in placentas and fetuses, along with significant fetal and placental histopathology, together suggesting vertical transmission. To test vector competence, we exposed Aedes aegypti and Culex quinquefasciatus mosquitoes to SPONV-infected bloodmeals. Aedes aegypti could efficiently transmit SPONV, whereas Culex quinquefasciatus could not. Our results suggest that SPONV has the same features that made ZIKV a public health risk.
    Keywords:  Aedes aegypti; Arbovirus; Congenital zika syndrome; Flavivirus; Spondweni virus; Vector competence; Zika virus
  11. Health Place. 2020 May;pii: S1353-8292(19)31148-7. [Epub ahead of print]63 102339
    Desjardins MR, Casas I, Victoria AM, Carbonell D, Dávalos DM, Delmelle EM.
      Dengue fever (DENF), chikungunya (CHIK), and Zika are responsible for the majority of the burden caused by vector-borne diseases (VBDs); which are produced by viruses primarily transmitted by the Aedes mosquito. Aedes have become prolific in urban areas due to a combination of climate change, rapid urbanization, increased human mobility, and globalization, causing the three VBDs to emerge in novel regions. Community knowledge can provide detailed insights about the spatial heterogeneity of disease risk and rates within a particular region, improving public health interventions. Knowledge, Attitude, and Practice (KAP) surveys are used to shed light on at-risk communities' understanding of the vector, the pathogen, prevention and treatment strategies. Little is known how KAP varies among diseases, and among neighborhoods within a city. Understanding KAP variation among co-circulating VBDs at a fine-level, especially differences between endemic and emerging diseases, can improve targeted interventions, education programs, and health policy. We administered KAP surveys to 327 individuals in healthcare centers and selected neighborhoods in Cali, Colombia in June 2019. We utilized generalized linear models (GLMs) to identify significant predictors of KAP. Our findings suggest that knowledge is related to community characteristics (e.g. strata), while attitudes and practices are more related to individual-level factors. Access to healthcare also forms significant predictor of residents participating in preventative practices. The results can be leveraged to inform public health officials and communities to motivate at-risk neighborhoods to take an active role in vector surveillance and control, while improving educational and surveillance resources in Cali, Colombia.
    Keywords:  Chikungunya; Community surveys; Dengue; Vector-borne disease; Zika
  12. J Med Entomol. 2020 Jun 19. pii: tjaa110. [Epub ahead of print]
    Oduwole OA, Oringanje CM, Oduola AO, Nwachuku NS, Meremikwu MM, Alaribe AAA.
      The study was carried out to determine relative abundance, species diversity, of Anopheles species (Diptera: Culicidae) in selected forested areas in Cross River State, Nigeria and the prevalence of malaria infection in the specimens. Mosquitoes were collected using pyrethrum spray catch and Centre for Disease Control light traps modified with yeast and sugar to generate carbon dioxide (CO2) and identified using morphological identification keys. We used a multiplex polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP) to simultaneously distinguish sibling species of the An. gambiae s.l, including separation of An. gambiae s.s. and An. coluzzii (Diptera: Culicidae). The samples were also screened for Plasmodium infection using the enzyme-linked immunosorbent assay. One hundred and four Anopheles specimens were collected during the study of which 97% was An. gambiae complex and 3% was An. rufipes (Diptera: Culicidae). Only 77% of the An. gambiae s.l. was identify to species level. The result shows that 41.6% was An. gambiae s.s. and 34.6% was An. coluzzii. No sporozoite of Plasmodium was detected in the Anopheles species. The study also found a hybrid form of An. gambiae s.s. and An. coluzzii. These findings suggest the first documented evidence of hybrid forms of An. gambiae s.s./An. coluzzii in South Eastern Nigeria although its epidemiological implication is still not clear.
    Keywords:  Nigeria; malaria; mosquitoes; tourists; vectors
  13. Enferm Clin. 2020 Jun;pii: S1130-8621(20)30253-9. [Epub ahead of print]30 Suppl 4 473-476
    Suriami , Ishak H, Syafar M, Mallongi A, Rauf AU.
      OBJECTIVE: Dengue hemorrhagic fever (DHF) is an infectious disease caused by the dengue virus which results in acute fever.METHODS: Design of this study was a survey method with short duration Quasi-Experimental. The sample in this study was 240 houses.
    RESULTS: Results showed that intervention by giving abathion in the village of Rhino I natural gas, Salo Palai and Muara Badak Ilir villages was effective in eliminating larvae with value Z=4.750, p=0.000.
    CONCLUSION: Aedes aegypti larvae are suggested to need cross-sectoral cooperation, providing data on the presence of Aedes aegypti larvae and increasing efforts to eradicate mosquito nests.
    Keywords:  Abatization; Aedes; Larva
  14. Enferm Clin. 2020 Jun;pii: S1130-8621(20)30201-1. [Epub ahead of print]30 Suppl 4 294-297
    Ishak H, Aisyah AS, Mallongi A, Astuti RDP.
      OBJECTIVE: This study aims to analyze the relationship between the use of screen in ventilation, the use of anti-mosquitoes, the habit of hanging clothes and the effectiveness of fogging on the incidence of DHF in the Pontap Community Health Center, Palopo City.METHOD: The study design was a case-control study. The study type was quasi-experimental using the non-randomized one group pretest-posttest with control design. The statistical test used Chi-square and logistic regression test.
    RESULT: There was a relationship between the use of anti-mosquito repellent and the incidence of DHF with a p-value=0.000; OR=7.222; 95% CI: 2.515-20.736. Habits of hanging clothes with a p-value=0.000; OR=10.545; 95% CI: 3.399-32.719.
    CONCLUSION: The use of screen in home ventilation did not have a significant correlation with the incidence of DHF. While the fogging is still quite effective decreasing the density of the Aedes aegypti.
    Keywords:  Aedes aegypti; DHF; Fogging; Mosquito density; Risk factors
  15. Ecol Evol. 2020 Jun;10(11): 5079-5088
    Bataillard D, Christe P, Pigeault R.
      Glyphosate is the world's most widely used herbicide. The commercial success of this molecule is due to its nonselectivity and its action, which would supposedly target specific biosynthetic pathways found mainly in plants. Multiple studies have however provided evidence for high sensitivity of many nontarget species to glyphosate and/or to formulations (glyphosate mixed with surfactants). This herbicide, found at significant levels in aquatic systems through surface runoffs, impacts life history traits and immune parameters of several aquatic invertebrates' species, including disease-vector mosquitoes. Mosquitoes, from hatching to emergence, are exposed to aquatic chemical contaminants. In this study, we first compared the toxicity of pure glyphosate to the toxicity of glyphosate-based formulations for the main vector of avian malaria in Europe, Culex pipiens mosquito. Then we evaluated, for the first time, how field-realistic dose of glyphosate interacts with larval nutritional stress to alter mosquito life history traits and susceptibility to avian malaria parasite infection. Our results show that exposure of larvae to field-realistic doses of glyphosate, pure or in formulation, did not affect larval survival rate, adult size, and female fecundity. One of our two experimental blocks showed, however, that exposure to glyphosate decreased development time and reduced mosquito infection probability by malaria parasite. Interestingly, the effect on malaria infection was lost when the larvae were also subjected to a nutritional stress, probably due to a lower ingestion of glyphosate.
    Keywords:  Plasmodium relictum; diet; glyphosate‐based herbicides; vector
  16. Virus Res. 2020 Jun 16. pii: S0168-1702(20)30151-9. [Epub ahead of print] 198060
    Oderinde BS, Mora-Cárdenas E, Carletti T, Baba MM, Marcello A.
      The burden of Arboviral infections is largely underestimated in Africa, particularly in North-Eastern Nigeria. A total of 200 serum samples were collected from patients exhibiting febrile illness who visited the State Specialist Hospital in Maiduguri for medical attention between March and April 2018. Sera were tested for Flavivirus RNA by a pan-flaviviral primer set using hemi-nested RT PCR. Twenty-six samples were positive for flaviviral RNA and sequence analysis indicated a high number of West Nile virus infections and one case of Zika virus. In-house recombinant NS1-based IgM ELISA indicated 47% of WNV and 22% of ZIKV infections. These data were also compared to commercially available assays for West Nile and Zika virus. Finally, NS1 IgG ELISA was conducted for Dengue, Zika, West Nile and Usutu viruses. For serum samples detected by at least one flavivirus, 94,5% tested positive by NS1 IgG antibodies, while only 5.5% of the patients were negative for all. To conclude, there is a high prevalence rate of arbovirus infections in the region, including Zika and Usutu viruses that were not previously detected. Interestingly, the analysis was conducted using in-house tools to allow the implementation of a sustainable surveillance protocol locally.
    Keywords:  Africa; Dengue virus; Nigeria; Usutu virus; West Nile virus; Zika virus; diagnosis; flavivirus; serology
  17. PLoS One. 2020 ;15(6): e0234557
    Milali MP, Kiware SS, Govella NJ, Okumu F, Bansal N, Bozdag S, Charlwood JD, Maia MF, Ogoma SB, Dowell FE, Corliss GF, Sikulu-Lord MT, Povinelli RJ.
      After mating, female mosquitoes need animal blood to develop their eggs. In the process of acquiring blood, they may acquire pathogens, which may cause different diseases in humans such as malaria, zika, dengue, and chikungunya. Therefore, knowing the parity status of mosquitoes is useful in control and evaluation of infectious diseases transmitted by mosquitoes, where parous mosquitoes are assumed to be potentially infectious. Ovary dissections, which are currently used to determine the parity status of mosquitoes, are very tedious and limited to few experts. An alternative to ovary dissections is near-infrared spectroscopy (NIRS), which can estimate the age in days and the infectious state of laboratory and semi-field reared mosquitoes with accuracies between 80 and 99%. No study has tested the accuracy of NIRS for estimating the parity status of wild mosquitoes. In this study, we train an artificial neural network (ANN) models on NIR spectra to estimate the parity status of wild mosquitoes. We use four different datasets: An. arabiensis collected from Minepa, Tanzania (Minepa-ARA); An. gambiae s.s collected from Muleba, Tanzania (Muleba-GA); An. gambiae s.s collected from Burkina Faso (Burkina-GA); and An.gambiae s.s from Muleba and Burkina Faso combined (Muleba-Burkina-GA). We train ANN models on datasets with spectra preprocessed according to previous protocols. We then use autoencoders to reduce the spectra feature dimensions from 1851 to 10 and re-train the ANN models. Before the autoencoder was applied, ANN models estimated parity status of mosquitoes in Minepa-ARA, Muleba-GA, Burkina-GA and Muleba-Burkina-GA with out-of-sample accuracies of 81.9±2.8 (N = 274), 68.7±4.8 (N = 43), 80.3±2.0 (N = 48), and 75.7±2.5 (N = 91), respectively. With the autoencoder, ANN models tested on out-of-sample data achieved 97.1±2.2% (N = 274), 89.8 ± 1.7% (N = 43), 93.3±1.2% (N = 48), and 92.7±1.8% (N = 91) accuracies for Minepa-ARA, Muleba-GA, Burkina-GA, and Muleba-Burkina-GA, respectively. These results show that a combination of an autoencoder and an ANN trained on NIR spectra to estimate the parity status of wild mosquitoes yields models that can be used as an alternative tool to estimate parity status of wild mosquitoes, especially since NIRS is a high-throughput, reagent-free, and simple-to-use technique compared to ovary dissections.
  18. Lancet. 2020 Jun 11. pii: S0140-6736(20)31048-5. [Epub ahead of print]
    Manning JE, Oliveira F, Coutinho-Abreu IV, Herbert S, Meneses C, Kamhawi S, Baus HA, Han A, Czajkowski L, Rosas LA, Cervantes-Medina A, Athota R, Reed S, Mateja A, Hunsberger S, James E, Pleguezuelos O, Stoloff G, Valenzuela JG, Memoli MJ.
      BACKGROUND: In animal models, immunity to mosquito salivary proteins protects animals against mosquito-borne disease. These findings provide a rationale to vaccinate against mosquito saliva instead of the pathogen itself. To our knowledge, no vector salivary protein-based vaccine has been tested for safety and immunogenicity in humans. We aimed to assess the safety and immunogenicity of Anopheles gambiae saliva vaccine (AGS-v), a peptide-based vaccine derived from four A gambiae salivary proteins, in humans.METHODS: In this randomised, placebo-controlled, double-blind, phase 1 trial, participants were enrolled at the National Institutes of Health Clinical Center in Bethesda, MD, USA. Participants were eligible if they were healthy adults, aged 18-50 years with no history of severe allergic reactions to mosquito bites. Participants were randomly assigned (1:1:1), using block randomisation and a computer-generated randomisation sequence, to treatment with either 200 nmol of AGS-v vaccine alone, 200 nmol of AGS-v with adjuvant (Montanide ISA 51), or sterile water as placebo. Participants and clinicians were masked to treatment assignment. Participants were given a subcutaneous injection of their allocated treatment at day 0 and day 21, followed by exposure to feeding by an uninfected Aedes aegypti mosquito at day 42 to assess subsequent risk to mosquito bites in a controlled setting. The primary endpoints were safety and immunogenicity at day 42 after the first immunisation. Participants who were given at least one dose of assigned treatment were assessed for the primary endpoints and analysis was by intention to treat. The trial was registered with, NCT03055000, and is closed for accrual.
    FINDINGS: Between Feb 15 and Sept 10, 2017, we enrolled and randomly assigned 49 healthy adult participants to the adjuvanted vaccine (n=17), vaccine alone (n=16), or placebo group (n=16). Five participants did not complete the two-injection regimen with mosquito feeding at day 42, but were included in the safety analyses. No systemic safety concerns were identified; however, one participant in the adjuvanted vaccine group developed a grade 3 erythematous rash at the injection site. Pain, swelling, erythema, and itching were the most commonly reported local symptoms and were significantly increased in the adjuvanted vaccine group compared with both other treatment groups (nine [53%] of 17 participants in the adjuvanted vaccine group, two [13%] of 16 in the vaccine only group, and one [6%] of 16 in the placebo group; p=0·004). By day 42, participants who were given the adjuvanted vaccine had a significant increase in vaccine-specific total IgG antibodies compared with at baseline than did participants who were give vaccine only (absolute difference of log10-fold change of 0·64 [95% CI 0·39 to 0·89]; p=0·0002) and who were given placebo (0·62 [0·34 to 0·91]; p=0·0001). We saw a significant increase in IFN-γ production by peripheral blood mononuclear cells at day 42 in the adjuvanted vaccine group compared with in the placebo group (absolute difference of log10 ratio of vaccine peptide-stimulated vs negative control 0·17 [95% CI 0·061 to 0·27]; p=0·009) but we saw no difference between the IFN-γ production in the vaccine only group compared with the placebo group (0·022 [-0·072 to 0·116]; p=0·63).
    INTERPRETATION: AGS-v was well tolerated, and, when adjuvanted, immunogenic. These findings suggest that vector-targeted vaccine administration in humans is safe and could be a viable option for the increasing burden of vector-borne disease.
    FUNDING: Office of the Director and the Division of Intramural Research at the National Institute of Allergy and Infectious Diseases, and National Institutes of Health.
  19. ScientificWorldJournal. 2020 ;2020 8938309
    Kessy ST, Nyundo BA, Mnyone LL, Lyimo IN.
      Despite the considerable progress made so far, the effectiveness and mass application of odour-baited outdoor mosquito control devices in pipelines is limited by several factors. These include the design and size of the devices, optimal placement of attractive blends, and nature of materials into which the blends are impregnated. The primary aim of this study was to manipulate these factors to improve the attractiveness of our recently developed passive outdoor host seeking device (POHD) to outdoor biting Anopheles arabiensis. Specifically, the study aimed to determine optimal placement of odour blends and killing bioactives in POHD for maximum attraction and killing of An. arabiensis and to assess the effects of blend types, formulation, and residual activity on attractiveness of the POHD to An. arabiensis. The POHDs baited with attractive blends, carbon dioxide (CO2), and bendiocarb-treated electrostatic netting were placed either towards the top or bottom openings, and other modifications were exposed to An. arabiensis under the semifield system at Ifakara Health Institute (IHI). Each night, a total of 100 starved female, 3-7-day-old, semifield reared An. arabiensis mosquitoes were released, collected the next morning (alive or dead), counted, and recorded. Live mosquitoes were maintained in the semifield insectary and monitored for 24 hours mortality. Each treatment combination of the POHD was tested in three replicates. Overall, the results indicated that the proportion of mosquitoes attracted to and killed in the POHD varied with position of attractants and killing agent (bendiocarb). The POHD with bottom placed attractants and bendiocarb attracted and killed higher proportion of mosquitoes compared to the POHD with top placed attractants and bendiocarb. The highest mortalities were observed when the POHD was baited with a combination of attractive blends and CO2. Moreover, the residual activity of attractive blends applied inside POHD varied with type and formulation of attractive blend. The POHD packed with Mbita and Ifakara blend in microencapsulated pellets (granules) attracted higher proportion of mosquitoes than that baited with soaked nylon-strip formulation of either blends. Interestingly, POHD baited with Mbita blend in microencapsulated pellets (granules) formulation attracted and killed higher proportion of mosquitoes (>90%) than that baited with Ifakara blend even 9 months after application. Conclusively, the POHD remained effective for a relatively longer period of time when baited with bottom placed synthetic blends and CO2 combination, thus warranting further trials under real life situations.
  20. Int Health. 2020 Jun 20. pii: ihaa033. [Epub ahead of print]
    Omatola CA, Onoja AB, Moses E, Mahmud M, Mofolorunsho CK.
      BACKGROUND: Dengue virus (DENV) is spreading to parts of the world where it had not been previously reported. Increased international travel has led to intercontinental importation of dengue by visitors returning from countries in sub-Saharan Africa. Although dengue is well documented in the rain forest region of Nigeria, there is a dearth of information in the Guinea Savannah region, which is a major transit point for local and international visitors in the most populous nation in Africa. We provide preliminary evidence of dengue activity in the Guinea Savannah and highlight the risk factors.METHODS: Blood was collected from a cross-section of 200 patients attending four hospitals in Anyigba, Kogi State. Anti-dengue antibody was identified using DENV immunoglobulin G (IgG) immunoassays. Questionnaires were used to obtain sociodemographic variables and risk factors. Data were analysed with SPSS version 16.0 for Windows.
    RESULTS: Forty-two (20.5%) participants had anti-DENV IgG antibodies. Persons within the 45-59 y age group were more seropositive, with a rate of 35%. Males were more seropositive compared with females. Marriage, formal education, involvement in business activities and the presence of grasses around homes were associated with higher IgG seropositivity. The presence of open water containers around human dwellings and a lack of mosquito net use are predisposing factors.
    CONCLUSIONS: This study identified past exposure to DENV among people in Anyigba, located in the Guinea Savannah region. Proper diagnosis of febrile episodes is required to improve case management and curtail off-target treatment. The high rate of previous exposure of patients to dengue indicates the need to strengthen vector control and dengue surveillance programs.
    Keywords:  Guinea Savannah; IgG; Nigeria; dengue
  21. Salud Publica Mex. 2020 Jul-Aug;62(4):62(4): 388-401
    Villarreal-Treviño C, Ríos-Delgado JC, Penilla-Navarro RP, Rodríguez AD, López JH, Nettel-Cruz JA, Moo-Llanes DA, Fuentes-Maldonado G.
      OBJECTIVE: To determine the abundance and geographic distribution of the main malaria vectors, which are influenced by habitat characteristics and ecological factors that directly impact adult density and the dynamics of malaria transmission in Mexico.MATERIALS AND METHODS: Samples of larvae were collected from 19 states in Mexico. Each larval habitat was characterized in situ determining the following parameters: water depth, turbidity, percentage of vegetation cover, amount of detritus, presence of algae, light intensity, type of vegetation, amount of predators, habitat stability, altitude, and hydrologic type.
    RESULTS: A total of 21 687 larvae corresponding to 13 anopheline species were obtained from 149 aquatic habitats. The most abundant species were Anopheles pseudopunctipennis (52.91%), An. albimanus (39.14%) and An. franciscanus (5.29%). The multiple logistic regression analysis showed a negative association between An. pseudopunctipennis and water turbidity (ß=-1.342; Wald=6.122; p=0.013) and the amount of detritus (ß=-2.206; Wald=3.642; p=0.050). While in An. albimanus, there was a significant positive association with water turbidity (ß=1.344; Wald=4.256; p=0.039), a negative correlation was found with the altitude (ß=-3.445; Wald=5.407; p =0.020). The highest mosquito species diversity index was found in Chiapas (Fisher's α=1.20) and the lowest diversity in Chihuahua (Fisher's α=0.26). The greatest richness was found in streams (n=11).
    CONCLUSIONS: The two most abundant species were: An. albimanus and An. pseudopunctipennis. Detailed knowledge of the distribution and characteristics of their larval habitats will be useful for the effective implementation of control strategies in Mexico.
    Keywords:  Anopheles; Mexico; larval habitat; malaria
  22. Comput Methods Programs Biomed. 2020 Jun 05. pii: S0169-2607(20)31418-8. [Epub ahead of print]196 105585
    Abidemi A, Aziz NAB.
      Background Dengue is a vector-borne viral disease endemic in Malaysia. The disease is presently a public health issue in the country. Hence, the use of mathematical model to gain insights into the transmission dynamics and derive the optimal control strategies for minimizing the spread of the disease is of great importance. Methods A model involving eight mutually exclusive compartments with the introduction of personal protection, larvicide and adulticide control strategies describing dengue fever transmission dynamics is presented. The control-induced basic reproduction number (R˜0) related to the model is computed using the next generation matrix method. Comparison theorem is used to analyse the global dynamics of the model. The model is fitted to the data related to the 2012 dengue outbreak in Johor, Malaysia, using the least-squares method. In a bid to optimally curtail dengue fever propagation, we apply optimal control theory to investigate the effect of several control strategies of combination of optimal personal protection, larvicide and adulticide controls on dengue fever dynamics. The resulting optimality system is simulated in MATLAB using fourth order Runge-Kutta scheme based on the forward-backward sweep method. In addition, cost-effectiveness analysis is performed to determine the most cost-effective strategy among the various control strategies analysed. Results Analysis of the model with control parameters shows that the model has two disease-free equilibria, namely, trivial equilibrium and biologically realistic disease-free equilibrium, and one endemic equilibrium point. It also reveals that the biologically realistic disease-free equilibrium is both locally and globally asymptotically stable whenever the inequality R˜0<1 holds. In the case of model with time-dependent control functions, the optimality levels of the three control functions required to optimally control dengue disease transmission are derived. Conclusion We conclude that dengue fever transmission can be curtailed by adopting any of the several control strategies analysed in this study. Furthermore, a strategy which combines personal protection and adulticide controls is found to be the most cost-effective control strategy.
    Keywords:  Basic reproduction number; Dengue fever model; Johor dengue outbreak; Optimal control strategies; Parameter estimation
  23. Med Vet Entomol. 2020 Jun 18.
    Cohen S, Silberbush A.
      Predator-released kairomones indicating the presence of predatory fish are known to alter the behaviour and life-history traits of several aquatic herbivores. Culex mosquitoes (Diptera: Culicidae) respond to such cues by altering oviposition habitat selection and larval development time. These responses differ among fish species indicating composition differences among fish-released cues, but the recognition pattern is not clear. This study tested the dependence of fish recognition to co-evolution and the level of threat to larvae. We compared Culex responses to three fish, the invasive larvivorous Gambusia affinis (Cyprinodontiformes: Poeciliidae), the native larvivorous Aphanius mento (Cyprinodontiformes: Cyprinodontidae) and the native algivorous Garra rufa (Cypriniformes: Cyprinidae). The effects of cues released by the three fish on Culex oviposition and life-history shifts were compared in field mesocosms and lab tests. Our results showed that ovipositing females were significantly repelled only by cues originated from G. affinis, while developing larvae response was a more general one. Our results support the idea that fish-released kairomones differ in composition or quantities among different species.
    Keywords:  Aphanius mento; Culex spp.; Gambusia affinis; Garra rufa; kairomones; life-history; oviposition
  24. Parasite. 2020 ;27 43
    Mamai W, Maiga H, Somda NSB, Wallner T, Konczal A, Yamada H, Bouyer J.
      The production of a large number of mosquitoes of high biological qualities and reliable sex sorting before release are key challenges when applying the sterile insect technique as part of an area-wide integrated pest management approach. There is a need to fully evaluate the production capacity of the equipment developed in order to plan and maintain a daily production level for large-scale operational release activities. This study aimed to evaluate the potential use of the FAO/IAEA larval rearing unit for Aedes aegypti and the subsequent female contamination rate after sex sorting with a Fay-Morlan glass separator. Trays from each rack were tilted and their contents sorted either for each individual tray or after mixing the content of all trays from the rack. The pupal production and the female contamination rate were estimated with respect to day of collection, position of the tray, type of pupae collection, and sorting operator. Results showed significant daily variability of pupal production and female contamination rate, with a high male pupal production level achieved on the second day of collection and estimated female contamination of male pupae reached around 1%. Neither tray position nor type of pupae collection affected the pupal production and female contamination rate. However, the operator had a significant effect on the female contamination rate. These results highlight the need to optimize pupal production at early days of collection and to develop a more effective and automated method of sex separation.
    Keywords:  Fay–Morlan glass plate separator; Female contamination; Mosquitoes; Pupal production; Sterile insect technique; Vectors
  25. R Soc Open Sci. 2020 May;7(5): 191951
    Voloshin V, Kröner C, Seniya C, Murray GPD, Guy A, Towers CE, McCall PJ, Towers DP.
      Robust imaging techniques for tracking insects have been essential tools in numerous laboratory and field studies on pests, beneficial insects and model systems. Recent innovations in optical imaging systems and associated signal processing have enabled detailed characterization of nocturnal mosquito behaviour around bednets and improvements in bednet design, a global essential for protecting populations against malaria. Nonetheless, there remain challenges around ease of use for large-scale in situ recordings and extracting data reliably in the critical areas of the bednet where the optical signal is attenuated. Here, we introduce a retro-reflective screen at the back of the measurement volume, which can simultaneously provide diffuse illumination, and remove optical alignment issues while requiring only one-sided access to the measurement space. The illumination becomes significantly more uniform, although noise removal algorithms are needed to reduce the effects of shot noise, particularly across low-intensity bednet regions. By systematically introducing mosquitoes in front of and behind the bednet in laboratory experiments, we are able to demonstrate robust tracking in these challenging areas. Overall, the retro-reflective imaging set-up delivers mosquito segmentation rates in excess of 90% compared to less than 70% with backlit systems.
    Keywords:  entomology; mosquito tracking; retro-reflective screen
  26. BMC Infect Dis. 2020 Jun 17. 20(1): 425
    Siya A, Kalule BJ, Ssentongo B, Lukwa AT, Egeru A.
      BACKGROUND: Malaria remains a major tropical vector-borne disease of immense public health concern owing to its debilitating effects in sub-Saharan Africa. Over the past 30 years, the high altitude areas in Eastern Africa have been reported to experience increased cases of malaria. Governments including that of the Republic of Uganda have responded through intensifying programs that can potentially minimize malaria transmission while reducing associated fatalities. However, malaria patterns following these intensified control and prevention interventions in the changing climate remains widely unexplored in East African highland regions. This study thus analyzed malaria patterns across altitudinal zones of Mount Elgon, Uganda.METHODS: Times-series data on malaria cases (2011-2017) from five level III local health centers occurring across three altitudinal zones; low, mid and high altitude was utilized. Inverse Distance Weighted (IDW) interpolation regression and Mann Kendall trend test were used to analyze malaria patterns. Vegetation attributes from the three altitudinal zones were analyzed using Normalized Difference Vegetation Index (NDVI) was used to determine the Autoregressive Integrated Moving Average (ARIMA) model was used to project malaria patterns for a 7 year period.
    RESULTS: Malaria across the three zones declined over the study period. The hotspots for malaria were highly variable over time in all the three zones. Rainfall played a significant role in influencing malaria burdens across the three zones. Vegetation had a significant influence on malaria in the higher altitudes. Meanwhile, in the lower altitude, human population had a significant positive correlation with malaria cases.
    CONCLUSIONS: Despite observed decline in malaria cases across the three altitudinal zones, the high altitude zone became a malaria hotspot as cases variably occurred in the zone. Rainfall played the biggest role in malaria trends. Human population appeared to influence malaria incidences in the low altitude areas partly due to population concentration in this zone. Malaria control interventions ought to be strengthened and strategically designed to achieve no malaria cases across all the altitudinal zones. Integration of climate information within malaria interventions can also strengthen eradication strategies of malaria in such differentiated altitudinal zones.
    Keywords:  Altitude; Climate change; Ecohealth; Infectious diseases; Malaria; Patterns; Time series
  27. Sci Rep. 2020 Jun 16. 10(1): 9689
    Salami D, Sousa CA, Martins MDRO, Capinha C.
      The geographical spread of dengue is a global public health concern. This is largely mediated by the importation of dengue from endemic to non-endemic areas via the increasing connectivity of the global air transport network. The dynamic nature and intrinsic heterogeneity of the air transport network make it challenging to predict dengue importation. Here, we explore the capabilities of state-of-the-art machine learning algorithms to predict dengue importation. We trained four machine learning classifiers algorithms, using a 6-year historical dengue importation data for 21 countries in Europe and connectivity indices mediating importation and air transport network centrality measures. Predictive performance for the classifiers was evaluated using the area under the receiving operating characteristic curve, sensitivity, and specificity measures. Finally, we applied practical model-agnostic methods, to provide an in-depth explanation of our optimal model's predictions on a global and local scale. Our best performing model achieved high predictive accuracy, with an area under the receiver operating characteristic score of 0.94 and a maximized sensitivity score of 0.88. The predictor variables identified as most important were the source country's dengue incidence rate, population size, and volume of air passengers. Network centrality measures, describing the positioning of European countries within the air travel network, were also influential to the predictions. We demonstrated the high predictive performance of a machine learning model in predicting dengue importation and the utility of the model-agnostic methods to offer a comprehensive understanding of the reasons behind the predictions. Similar approaches can be utilized in the development of an operational early warning surveillance system for dengue importation.
  28. Malar J. 2020 Jun 17. 19(1): 210
    Kamau A, Mtanje G, Mataza C, Mwambingu G, Mturi N, Mohammed S, Ong'ayo G, Nyutu G, Nyaguara A, Bejon P, Snow RW.
      BACKGROUND: Malaria transmission has recently fallen in many parts of Africa, but systematic descriptions of infection and disease across all age groups are rare. Here, an epidemiological investigation of parasite prevalence, the incidence of fevers associated with infection, severe hospitalized disease and mortality among children older than 6 months and adults on the Kenyan coast is presented.METHODS: A prospective fever surveillance was undertaken at 6 out-patients (OPD) health-facilities between March 2018 and February 2019. Four community-based, cross sectional surveys of fever history and infection prevalence were completed among randomly selected homestead members from the same communities. Paediatric and adult malaria at Kilifi county hospital was obtained for the 12 months period. Rapid Diagnostic Tests (CareStart™ RDT) to detect HRP2-specific to Plasmodium falciparum was used in the community and the OPD, and microscopy in the hospital. Crude and age-specific incidence rates were computed using Poisson regression.
    RESULTS: Parasite prevalence gradually increased from childhood, reaching 12% by 9 years of age then declining through adolescence into adulthood. The incidence rate of RDT positivity in the OPD followed a similar trend to that of infection prevalence in the community. The incidence of hospitalized malaria from the same community was concentrated among children aged 6 months to 4 years (i.e. 64% and 70% of all hospitalized and severe malaria during the 12 months of surveillance, respectively). Only 3.7% (12/316) of deaths were directly attributable to malaria. Malaria mortality was highest among children aged 6 months-4 years at 0.57 per 1000 person-years (95% CI 0.2, 1.2). Severe malaria and death from malaria was negligible above 15 years of age.
    CONCLUSION: Under conditions of low transmission intensity, immunity to disease and the fatal consequences of infection appear to continue to be acquired in childhood and faster than anti-parasitic immunity. There was no evidence of an emerging significant burden of severe malaria or malaria mortality among adults. This is contrary to current modelled approaches to disease burden estimation in Africa and has important implications for the targeting of infection prevention strategies based on chemoprevention or vector control.
    Keywords:  Adults; Age-pattern; Immunity; Infection; Malaria; Mortality; Severe disease
  29. Am J Trop Med Hyg. 2020 Jun 16.
    Beshir KB, Grignard L, Hajissa K, Mohammed A, Nurhussein AM, Ishengoma DS, Lubis IND, Drakeley CJ, Sutherland CJ.
      Rapid diagnostic tests (RDTs) play a critical role in malaria diagnosis and control. The emergence of Plasmodium falciparum parasites that can evade detection by RDTs threatens control and elimination efforts. These parasites lack or have altered genes encoding histidine-rich proteins (HRPs) 2 and 3, the antigens recognized by HRP2-based RDTs. Surveillance of such parasites is dependent on identifying false-negative RDT results among suspected malaria cases, a task made more challenging during the current pandemic because of the overlap of symptoms between malaria and COVID-19, particularly in areas of low malaria transmission. Here, we share our perspective on the emergence of P. falciparum parasites lacking HRP2 and HRP3, and the surveillance needed to identify them amid the COVID-19 pandemic.