Culex Species Research Articles

Benefits and limitations of emerging techniques for mosquito vector control

Benefits and limitations of emerging techniques for mosquito vector control

Fine-scale spatial and temporal variations in insecticide resistance in Culex pipiens complex mosquitoes in rural south-eastern Tanzania

BackgroundCulex mosquitoes cause considerable biting nuisance and sporadic transmission of arboviral and filarial diseases.MethodsUsing standard World Health Organization procedures, insecticide resistance profiles and underlying mechanisms were investigated during dry and wet seasons of 2015 and 2016 in Culex pipiens complex from three neighbouring administrative wards in Ulanga District, Tanzania. Synergist tests with piperonyl butoxide, diethyl maleate, and triphenyl phosphate, were employed to investigate mechanisms of the observed resistance phenotypes. Proportional biting densities of Culex species, relative to other taxa, were determined from indoor surveillance data collected in 2012, 2013, and 2015.ResultsInsecticide resistance varied significantly between wards and seasons. For example, female mosquitoes in one ward were susceptible to bendiocarb and fenitrothion in the wet season, but resistant during the dry season, while in neighbouring ward, the mosquitoes were fully susceptible to these pesticides in both seasons. Similar variations occurred against bendiocarb, DDT, deltamethrin, and lambda-cyhalothrin. Surprisingly, with the exception of one ward in the wet season, the Culex populations were susceptible to permethrin, commonly used on bednets in the area. No insecticide resistance was observed against the organophosphates, pirimiphos-methyl and malathion, except for one incident of reduced susceptibility in the dry season. Synergist assays revealed possible involvement of monooxygenases, esterases, and glutathione S-transferase in pyrethroid and DDT resistance. Morphology-based identification and molecular assays of adult Culex revealed that 94% were Cx. pipiens complex, of which 81% were Cx. quinquefasciatus, 2% Cx. pipiens, and 3% hybrids. About 14% of the specimens were non-amplified during molecular identifications. Female adults collected indoors were 100% Cx. pipiens complex, and constituted 79% of the overall biting risk.ConclusionsThe Cx. pipiens complex constituted the greatest biting nuisance inside people’s houses, and showed resistance to most public health insecticides possible. Resistance varied at a fine geographical scale, between adjacent wards, and seasons, which warrants some modifications to current insecticide resistance monitoring strategies. Resistance phenotypes are partly mediated by metabolic mechanisms, but require further evaluation through biochemical and molecular techniques. The high densities and resistance in Culex could negatively influence the acceptability of other interventions such as those used against malaria mosquitoes.

Size of Openings in Water-Holding Containers: Impact on Oviposition by Culex (Culex) Mosquitoes.

To assess how a grate covering a catch basin impacts oviposition by Culex mosquitoes, a field study was conducted in south Florida using containers with two types of covers, with openings of equal area, but different configurations. One opening mimicked a catch basin grate with 16 small openings, while the other cover had just one large opening. The number and presence of egg rafts in six of each container and cover combination was recorded over 18 nights at two field sites, consisting of a wastewater management facility area and residential subdivision. Three mosquito species, all belonging to the subgenus Culex accounted for more than 99% of total egg rafts collected: Culex nigripalpus (n = 1766), Culex quinquefasciatus (n = 754) and Culex coronator (n = 526). Approximately 90% of Cx. nigripalpus and Cx. coronator egg rafts were deposited in the containers with the large opening cover; whereas more Cx. quinquefasciatus egg rafts were laid in the containers with small opening covers than those of Culex nigripalpus and Culex coronator combined. Similar patterns of egg laying activity were noted at each sampling stations. These results suggest that for locating oviposition sites Culex quinquefasciatus may rely more on olfactory clues, while other Culex species depend more on visual clues.

Crossover Dynamics of Culex (Diptera: Culicidae) Vector Populations Determine WNV Transmission Intensity.

First introduced into the United States in 1999, West Nile virus (WNV) has become endemic and has established itself as the predominant mosquito-borne arbovirus in North America. Transmitted by mosquitoes of the genus Culex, regional landscapes influence local vector species abundance, creating different mosquito ecologies that drive local transmission dynamics. In central Iowa, two mosquito species, Culex restuans Theobald and Culex pipiens Linnaeus, serve as the predominant mosquito vectors. Importantly, these mosquito populations are influenced by seasonal patterns in their abundance, with Cx. restuans preferring cool, early spring temperatures, while Cx. pipiens prefer the warmer, mid- to late-summer months. The point of the season at which Cx. pipiens becomes the dominant species is generally referred to as a 'crossover' period. To better understand the influence of crossover dynamics on WNV transmission, we examined environmental and mosquito abundance data, as well as mosquito infection rates and human disease cases from 2016 to 2018. We demonstrate that temperature influences the timing and duration of the crossover period, influencing mosquito abundance and human disease transmission. Together, these results suggest that Culex species crossover is an important variable of WNV transmission dynamics, which may provide an early warning indicators of increased WNV transmission.

A Study on the Identification of Five Arboviruses from Hematophagous Mosquitoes and Midges Captured in Some Parts of Northern Turkey

Whether zoonotic or not, arboviral infections are continuing to be a major threat to human health as well as the livestock industry all around the world. This project presented the results of the identification study on five arboviruses, including West Nile virus (WNV), Bovine ephemeral fever virus, Akabane virus, Bluetongue virus, and Epizootic hemorrhagic disease virus, in mosquitos and midges from eight provinces of the Black Sea Region. During 2011 and 2012, 3193 mosquitoes were captured around natural streams, rivers, lakes, and ponds using dry-baited miniature light-traps. Identification studies were concluded by employing molecular methods. According to the morphological identification, blood-sucking mosquitoes and biting-midges belonged to Aedes (44.69%), Anopheles (28.34%), Culex (22.14%) and Culicoides (4.83%) species. Overall, 146 pools were made up of captured mosquitos and midges. None of the five viruses were directly identified by mosquitoes. Mosquitoes and midges have got a crucial role in the transmission of arboviruses. The risk of occurrence for the investigated arboviruses will continue depending upon many factors including the presence of these viruses in Turkey and its neighboring countries, uncontrolled livestock movements, global warming and climate changes.

Morphological Identification, Species Composition and Distribution of Mosquitoes in Kosti region, White Nile State, Central Sudan

Mosquitoes are a large diverse group of insects, with members being most important as vectors of diseases. The correct identification of mosquitoes is crucial to the control of the mosquito-borne diseases. This study was designed to provide baseline data on the species composition and distribution of members of the Anophelines and Culicines genera in ten selected localities in Kosti region, White Nile State, Central Sudan. Global Positioning System (GPS) was used to select collection sites. Adult mosquitoes were collected by pyrethrum spray catch (PSC) from randomly selected houses in Allia, Alnsr, Alskahdeed, Almrabie, Alshati, Althwrat, Alraba, Block 26, Block 32 and Khadugli in Kosti region during September 2014-August 2015. The Anophelines and Culicines mosquitoes were identified using standard morphological keys. Two Anopheles species and three Culex species were morphologically identified. These were An. gambiae s.s.; An. pharoensis; Cx. quinquefasciatus; Cx. univittatus and Cx. pipiens. This is the first report of An. pharoensis in the study area. The Highest mosquito abundance was observed in the September followed by October, while the lowest mosquito abundance was in July. An. gambiae s.s and Cx. quinquefasciatus were the predominant species which has importance as they indicate the presence of Malaria and arboviral infections in the study areas; respectively. These findings are of importance in the planning and implementation of vector control strategy in the Kosti region, White Nile state.

Outline-based geometric morphometric analysis to identify two Anopheles and three Culex mosquitoes in Thailand

Abstract. Chaiphongpachara T. 2019. Outline-based geometric morphometric analysis to identify two Anopheles and three Culex mosquitoes in Thailand. Biodiversitas 20: 1866-1872. Geometric morphometric (GM) techniques have become popular for applications in entomology studies, especially mosquitoes. Outline-based methods (OTLs) are one such form of GM technique used to analyze pseudo-landmarks on contours or boundary outlines. This study investigated the efficacy of an OTL to distinguish two species of Anopheles mosquitoes including An. epiroticus and An. subpictus s.l. and three species of Culex mosquitoes, including Cx. quinquefasciatus, Cx. visnui and Cx. whitmorei in Thailand and compared outlines, including internal outline 1 (IOL1), internal outline 2 (IOL2) and external outline (EOL) within the mosquito wing to assess the optimal outline for analysis. The results indicated that OTLs were highly effective with certain species and each outline had the potential difference for identification. For size analysis, An. epiroticus had a mean perimeter length of IOL2 and EOL length larger than An. subpictus. Different sizes between species was found in IOL1, which was statistically significant after Bonferroni test (p < 0.05). Culex size analysis of IOL2 and EOL demonstrated a statistical difference for all species while size difference patterns between outlines found that IOL1 differed from other outlines. While shapes in two Anopheles of all cells were different between species, there was statistical significance based on Mahalanobis distances (p < 0.05). Almost all pairwise Mahalanobis distances between Culex species of IOL1, IOL2 and EOL established statistical differences, except for pairs of Cx. visnui and Cx. whitmorei via IOL2 analysis.

Identification, abundance, and diversity of mosquitoes in Akure South Local Government Area, Ondo State, Nigeria

BackgroundMosquitoes are known to be notorious for their ability to constitute a nuisance as well as transmit disease-causing organisms (pathogens) to hosts. This study was aimed to determine the species distribution, abundance, and diversity of mosquitoes in Akure South Local Government Area, Ondo State, Nigeria.ResultsA total number of 100 sites (20 sites from each location) were randomly sampled in the five locations (Alagbaka, FUTA, Oja-Oba, Ondo road, and Seebi). These larvae were identified to species level using × 20 magnification of a dissecting microscope and identification keys. Thirteen species of mosquitoes including 5 Aedes species, 6 Culex species, and a species of Anopheles and Toxorhynchites belonging to four genera were recorded. The abundance of the four mosquito genera varied significantly (p < 0.05) with Culex having the highest abundance (2151) and Toxorhynchites having the lowest abundance (23). Also, the distribution and abundance of the mosquito species varied significantly (p < 0.05) with Culex andersoni being the most abundant species encountered (709) and Culex striatipes being the least abundant (8). The favorable physico-chemical parameters that favor breeding include pH range of 7.14–7.30, temperature range of 27.3–29 °C, electrical conductivity range of 65.6–98.0 μs, and dissolved oxygen range of 2.43–3.84 mg/l. Also, FUTA (1400) and Oja-Oba (994) had higher mosquito abundance than other locations (Alagbaka—124, Seebi—198, and Ondo road—224).ConclusionsThe persistent occurrence of Aedes, Culex, and Anopheles species pose a serious epidemiological concern to the inhabitants of Akure South Local Government Area. Therefore, public enlightenment on vector control is of paramount importance.

Integrated West Nile Virus Surveillance in Harris County, Texas, 2003 to 2018

ObjectiveThis abstract aims to: 1) describe human WNV infections in Harris County excluding the City of Houston, Texas, 2003 to 2018; 2) explore geographical distributions of WNV positive mosquito pools in relation to human cases; 3) provide a brief overview of the county’s rigorous multidisciplinary WNV surveillance and control in mosquitoes and humans.IntroductionWest Nile virus (WNV) is the leading cause of autochthonous arboviral disease in the United States1. The virus is primarily spread to people through the bite of infected Culex species of mosquitos. WNV was first identified in Harris County, Texas, in 20022. Since then, the mosquito-borne virus has become endemic in the region, with surges in 2012 and 2014. Although majority of individuals infected are asymptomatic, WNV induced neuroinvasive infections often result in hospitalizations and adverse outcomes3-7, thus may pose a significant concern in public health and healthcare. The Harris County Public Health (HCPH) Surveillance and Epidemiology Unit (SEU) conducts surveillance of WNV in humans, in collaboration with Mosquito and Vector Control Division (MVCD) that monitors the virus in mosquito populations and birds. Mosquito abatement activities are implemented in areas where positive mosquitoes and human cases are identified. In this integrated model, clusters of WNV positive mosquito pools in relation with human cases provide comprehensive surveillance data to guide targeted efforts of mosquito control, disease prevention, and community education.MethodsSurveillance data of human WNV cases and WNV tested mosquito pools 2003 to 2018 in Harris County excluding the City of Houston were used for the analysis. Human cases included were confirmed and probable cases. Frequencies, percentages, age-adjusted annual average rates were used to describe the data. Geographical locations of WNV positive mosquito pools and human cases were mapped and analyzed using ESRI ArcGIS to determine the spatial relationship between the positive mosquito pools and human cases. Space-Time analysis was performed on 16 years of human disease data using Scan statistics in SatScan™ to test the effect of time and identify significant geographical clusters of WNV cases over time, which revealed a statistically significant cluster in 2012 to 2014 in northwest of Harris County. Subsequently, human cases and WNV positive mosquito pools of 2012 to 2014 were selected for hotspot analysis to verify the results from Satscan analysis and visualize the geographical cluster. Human cases were aggregated into census tracts and analyzed by optimized hotspot method; the positive mosquito pools were geocoded using their intersection locations and analyzed by ESRI Getis-Ord Gi hotspot method.ResultsFrom 2003 to 2018, a total of 295 confirmed and probable human WNV cases were identified, including 217 neuroinvasive and 78 fever cases. The median age of patients was 58 years old; 64.8% were male. The onset of majority of the cases (80.7%) concentrated in July to September. Among case-patients, 72.9% were hospitalized, and 3.4% died. The annual average age-adjusted incidence rate of WNV was 0.7 per 100,000 during 2003 to 2018. However, the rate was 1.8 and 2.7 per 100,000 in 2012 and 2014, respectively. Over 68% of the cases clustered in west and northwest of the county.The annual WNV positive mosquito pools ranged from 0.2% to 10.2% amongst the years. The number of WNV positive mosquito pools in 2014 was more than 4 times higher than the average number during those years, the highest record in the County.Hot spots of human cases and the positive mosquito pools were both identified in northwest Harris County. There was a significant geographical overlap between human cases and the positive mosquito pools.The space-time analysis for the 16 years detected a significant high-risk cluster in 2012 to 2014 in northwest Harris County. Findings from optimized hotspot analysis on human cases are consistent with the results from SatScan analysis. Statistically significant hot spots of positive mosquito pools identified by Getis-Ord Gi hotspot analysis displayed highly overlay with the statistically significant cluster of human cases detected by Satscan space-time analysis.ConclusionsWNV infection is underestimated. Studies suggest that every one case identified represent five infections 8-9. Therefore, the actual number of cases is likely substantially higher. Clinicians should be alerted in WNV season and consider testing and reporting as early as possible, especially in neuroinvasive patients. The public should be encouraged to utilize personal protection, particularly during peak seasons. This analysis shows that GIS mapping and optimized hotspot analysis of WNV human cases in relation to positive mosquito pools can provide statistical evidences of areas most affected, thus inform targeted mosquito control, prevention and education strategies in people living in areas with high virus activitie

Culex torrentium: A Potent Vector for the Transmission of West Nile Virus in Central Europe.

The continuous circulation of West Nile virus (WNV) in Central, South and East Europe and its recent detection in several dead birds and two horses in Germany highlights the need for information on WNV vector competence of mosquitoes from Central Europe. Therefore, three common Culex species (Culex pipiens biotype pipiens, Culex pipiens biotype molestus and Culex torrentium) from Germany were orally infected with WNV and kept at 18 °C, 21 °C, 24 °C or 27 °C for 14 or 21 days post infection (dpi). Thereafter viable WNV was present in the saliva in all tested taxa, but only at incubation temperatures of 24 °C or 27 °C and predominantly at the extended incubation period of 21 dpi. Highest transmission efficiency rates of 17 % (24 °C) and 24% (27 °C) were found for Cx. torrentium. Culex p. pipiens and Cx. p. molestus showed low transmission efficiencies with a maximum of only 3%. Consequently, temperatures above 21 °C support transmission of WNV, which matches the predominant distribution of human WNV cases around the Mediterranean Sea and in South-East Europe. Culex torrentium has been identified as a potent vector for WNV in Central and Northern Europe, which highlights the need for surveillance of mosquito-borne viruses north of the Alps.

Quantitative Inventory of Mosquito Larvae (Diptera: Culicidae) and Physicochemical Analysis of Aquatic Habitats in the Region of Fez, Morocco.

Mosquitoes occupy a major health problem, as a potential vector for the transmission of many pathogens, the most important of which in Morocco are Plasmodium parasites and West Nile fever virus. Acquiring knowledge about the biotypology of these mosquitoes is an essential step in any control strategy. Thus, the objective of this study is to draw up an inventory of the culicidian fauna in the Fez region (North-central part of Morocco) and to determine the physicochemical parameters influencing the production of mosquito larvae of aquatic habitats in this area. Mosquito larvae of the extant biotopes were sampled every two months between November 2015 and December 2016, by means of the "dipping" method. The physicochemical parameters of the various larval biotopes were collected six times during the year of follow-up. Mosquito species were identified using morphological criteria. The results were analyzed using ecological indices and the generalized linear model (Poisson model) on R software. The identification of the 1,122 mosquito larvae collected from the various studied breeding areas revealed the presence of 11 species belonging to two subfamilies (Culicinae and Anophelinae) and five genera (Anopheles, Culex, Culiseta, Aedes, and Uranotaenia). Anopheles were observed in small numbers in permanent, stagnant, and shallow habitats. The larvae of An. maculipennis s. l. (major vector of malaria in Morocco) were collected. Culex larvae, especially Cx. pipiens (the main vector of WNV in Morocco), were collected in the majority of the larval habitats and on the different types of environments. Two other species of Culex, which plays a significant role in the transmission of WNV, were also collected, particularly, Cx. perexiguus and Cx. theileri. The results found, via this first study of its kind at the regional level, also made it possible to update the list of Culicidae species reported in the Fez region. Four new species have been recorded: Aedes flavescens, Uranotaenia unguiculata, Culiseta longiareolata, and Culex perexiguus. The results of this study will contribute to the provision of information for entomological surveillance and to better plan and guide vector control activities at local and national levels.

Long-term surveillance defines spatial and temporal patterns implicating Culex tarsalis as the primary vector of West Nile virus

West Nile virus (WNV) has become the most epidemiologically important mosquito-borne disease in the United States, causing ~50,000 cases since its introduction in 1999. Transmitted primarily by Culex species, WNV transmission requires the complex interplay between bird reservoirs and mosquito vectors, with human cases the result of epizootic spillover. To better understand the intrinsic factors that drive these interactions, we have compiled infection data from sentinel chickens, mosquito vectors, and human cases in Iowa over a 15 year period (2002–2016) to better understand the spatial and temporal components that drive WNV transmission. Supplementing these findings with mosquito abundance, distribution, and host preferences data, we provide strong support that Culex tarsalis is the most important vector of human WNV infections in the region. Together, our analysis provides new insights into WNV infection patterns in multiple hosts and highlights the importance of long-term surveillance to understand the dynamics of mosquito-borne-disease transmission.

Culex species diversity, susceptibility to insecticides and role as potential vector of Lymphatic filariasis in the city of Yaoundé, Cameroon.

BackgroundCulex species are widespread across Cameroon and responsible for high burden of nuisance in most urban settings. However, despite their high nuisance, they remain less studied compared to anophelines. The present study aimed to assess Culex species distribution, susceptibility to insecticide, bionomics and role in Lymphatic Filariasis (LF) transmission in the city of Yaoundé.MethodsMosquito collections were conducted from March to December 2017 using Centre for Disease Control light traps (CDC-LT), human landing catches (HLC) and larval collections. Mosquitoes were identified using morphological identification keys. Mosquitoes from the Culex pipiens complex were further identified using Polymerase Chain Reaction (PCR) to assess the presence of sibling species. Bioassays were conducted with 2–5 day-old unfed females to assess mosquito susceptibility to DDT, permethrin, deltamethrin and bendiocarb following WHO guidelines. Dead, control and surviving mosquitoes from bioassays were screened by PCR to detect the presence of knockdown resistance (kdr) alleles. Pools of mosquitoes were examined by PCR to detect the presence of Wuchereria bancrofti.ResultsA total of 197,956 mosquitoes belonging to thirteen species were collected. The density of mosquito collected varied according to the collection methods, districts and seasons. Culex quinquefasciatus emerged as the most abundant and the only species of the Culex pipiens complex in Yaoundé. Culex species were found breeding in different types of breeding sites including polluted and unpolluted sites. All Culex species including Cx antennatus, Cx duttoni, Cx perfuscus and Cx tigripes were found to be highly resistant to permethrin, deltamethrin and DDT. Culex quinquefasciatus was also found to be resistant to bendiocarb. A high frequency of the West Africa kdr allele was recorded in resistant Cx. quinquefasciatus. Out of the 247 pooled samples of 25 Culex spp. examined for the presence of Wuchereria bancrofti, none was found infected.ConclusionThe study confirms the high adaptation of Culex species particularly Culex quinquefasciatus to the urban environment and no implication of this species in the transmission of LF in Yaoundé Cameroon. Culex species predominance in urban settings highlight potential transmission risk of West Nile and rift valley fever in Yaoundé.

Prevalence of Wuchereria bancrofti Infection in Mosquitoes from Pangani District, Northeastern Tanzania

Background: Wuchereria bancrofti is the most widely distributed of the 3 nematodes known to cause lymphatic filariasis, the other 2 being Brugia malayi and Brugia timori. Anopheles gambiae and Anopheles funestus are the main vectors. However, the relative contributions of mosquito vectors to disease burden and infectivity are becoming increasingly important in coastal East Africa, and this is particularly true in the urban and semiurban areas of Pangani District, Tanzania. Methods: Mosquitoes were sampled from 5 randomly selected villages of Pangani District, namely, Bweni, Madanga, Meka, Msaraza, and Pangani West. Sampling of mosquitoes was done using standard Centers for Disease Control light traps with incandescent light bulbs. The presence of W. bancrofti in mosquitoes was determined via polymerase chain reaction (PCR) assays using NV1 and NV2 primers, and PoolScreen 2 software was used to determine the estimated rate of W. bancrofti infection in mosquitoes. Results: A total of 951 mosquitoes were collected, of which 99.36% were Culex quinquefasciatus, 0.32% were Anopheles gambiae, and 0.32% other Culex species. The estimated rate of W. bancrofti infection among these mosquitoes was 3.3%. Conclusion: This was the first study employing the use of PoolScreen PCR to detect W. bancrofti circulating in mosquito vectors in Pangani District, northeastern Tanzania. The presence of W. bancrofti infection suggests the possibility of infected humans in the area. The high abundance of Cx. quinquefasciatus calls for integrated mosquito control interventions to minimise the risk of W. bancrofti transmission to humans. Further research is required to gain an in-depth understanding of the W. bancrofti larval stages in mosquitoes, their drug sensitivity and susceptibility profiles, and their fecundity.

Prevalence of Wuchereria bancrofti Infection in Mosquitoes from Pangani District, Northeastern Tanzania

Background: Wuchereria bancrofti is the most widely distributed of the 3 nematodes known to cause lymphatic filariasis, the other 2 being Brugia malayi and Brugia timori. Anopheles gambiae and Anopheles funestus are the main vectors. However, the relative contributions of mosquito vectors to disease burden and infectivity are becoming increasingly important in coastal East Africa, and this is particularly true in the urban and semiurban areas of Pangani District, Tanzania. Methods: Mosquitoes were sampled from 5 randomly selected villages of Pangani District, namely, Bweni, Madanga, Meka, Msaraza, and Pangani West. Sampling of mosquitoes was done using standard Centers for Disease Control light traps with incandescent light bulbs. The presence of W. bancrofti in mosquitoes was determined via polymerase chain reaction (PCR) assays using NV1 and NV2 primers, and PoolScreen 2 software was used to determine the estimated rate of W. bancrofti infection in mosquitoes. Results: A total of 951 mosquitoes were collected, of which 99.36% were Culex quinquefasciatus, 0.32% were Anopheles gambiae, and 0.32% other Culex species. The estimated rate of W. bancrofti infection among these mosquitoes was 3.3%. Conclusion: This was the first study employing the use of PoolScreen PCR to detect W. bancrofti circulating in mosquito vectors in Pangani District, northeastern Tanzania. The presence of W. bancrofti infection suggests the possibility of infected humans in the area. The high abundance of Cx. quinquefasciatus calls for integrated mosquito control interventions to minimise the risk of W. bancrofti transmission to humans. Further research is required to gain an in-depth understanding of the W. bancrofti larval stages in mosquitoes, their drug sensitivity and susceptibility profiles, and their fecundity.

Prevalence of Wuchereria bancrofti Infection in Mosquitoes from Pangani District, Northeastern Tanzania

Background: Wuchereria bancrofti is the most widely distributed of the 3 nematodes known to cause lymphatic filariasis, the other 2 being Brugia malayi and Brugia timori. Anopheles gambiae and Anopheles funestus are the main vectors. However, the relative contributions of mosquito vectors to disease burden and infectivity are becoming increasingly important in coastal East Africa, and this is particularly true in the urban and semiurban areas of Pangani District, Tanzania. Methods: Mosquitoes were sampled from 5 randomly selected villages of Pangani District, namely, Bweni, Madanga, Meka, Msaraza, and Pangani West. Sampling of mosquitoes was done using standard Centers for Disease Control light traps with incandescent light bulbs. The presence of W. bancrofti in mosquitoes was determined via polymerase chain reaction (PCR) assays using NV1 and NV2 primers, and PoolScreen 2 software was used to determine the estimated rate of W. bancrofti infection in mosquitoes. Results: A total of 951 mosquitoes were collected, of which 99.36% were Culex quinquefasciatus, 0.32% were Anopheles gambiae, and 0.32% other Culex species. The estimated rate of W. bancrofti infection among these mosquitoes was 3.3%. Conclusion: This was the first study employing the use of PoolScreen PCR to detect W. bancrofti circulating in mosquito vectors in Pangani District, northeastern Tanzania. The presence of W. bancrofti infection suggests the possibility of infected humans in the area. The high abundance of Cx. quinquefasciatus calls for integrated mosquito control interventions to minimise the risk of W. bancrofti transmission to humans. Further research is required to gain an in-depth understanding of the W. bancrofti larval stages in mosquitoes, their drug sensitivity and susceptibility profiles, and their fecundity.

Prevalence of Wuchereria bancrofti Infection in Mosquitoes from Pangani District, Northeastern Tanzania

Background: Wuchereria bancrofti is the most widely distributed of the 3 nematodes known to cause lymphatic filariasis, the other 2 being Brugia malayi and Brugia timori. Anopheles gambiae and Anopheles funestus are the main vectors. However, the relative contributions of mosquito vectors to disease burden and infectivity are becoming increasingly important in coastal East Africa, and this is particularly true in the urban and semiurban areas of Pangani District, Tanzania. Methods: Mosquitoes were sampled from 5 randomly selected villages of Pangani District, namely, Bweni, Madanga, Meka, Msaraza, and Pangani West. Sampling of mosquitoes was done using standard Centers for Disease Control light traps with incandescent light bulbs. The presence of W. bancrofti in mosquitoes was determined via polymerase chain reaction (PCR) assays using NV1 and NV2 primers, and PoolScreen 2 software was used to determine the estimated rate of W. bancrofti infection in mosquitoes. Results: A total of 951 mosquitoes were collected, of which 99.36% were Culex quinquefasciatus, 0.32% were Anopheles gambiae, and 0.32% other Culex species. The estimated rate of W. bancrofti infection among these mosquitoes was 3.3%. Conclusion: This was the first study employing the use of PoolScreen PCR to detect W. bancrofti circulating in mosquito vectors in Pangani District, northeastern Tanzania. The presence of W. bancrofti infection suggests the possibility of infected humans in the area. The high abundance of Cx. quinquefasciatus calls for integrated mosquito control interventions to minimise the risk of W. bancrofti transmission to humans. Further research is required to gain an in-depth understanding of the W. bancrofti larval stages in mosquitoes, their drug sensitivity and susceptibility profiles, and their fecundity.

Increased Biting Rate of Insecticide-Resistant Culex Mosquitoes and Community Adherence to IRS for Malaria Control in Urban Malabo, Bioko Island, Equatorial Guinea.

Sustaining high levels of indoor residual spraying (IRS) coverage (≥85%) for community protection against malaria remains a challenge for IRS campaigns. We examined biting rates and insecticide resistance in Culex species and Anopheles gambiae s.l., and their potential effect on community adherence to IRS. The average IRS coverage in urban Malabo between 2015 and 2017 remained at 80%. Culex biting rate increased 6.0-fold (P < 0.001) between 2014 and 2017, reaching 8.08 bites per person per night, whereas that of An. gambiae s.l. remained steady at around 0.68. Although An. gambiae s.l. was susceptible to carbamates and organophosphates insecticides, Culex spp. were phenotypically resistant to all four main classes of WHO-recommended IRS insecticides. Similarly, the residual activity of the organophosphate insecticide used since 2017, ACTELLIC 300CS, was 8 mo for An. gambiae s.l., but was almost absent against Culex for 2 mo post-spray. A survey conducted in 2018 within urban Malabo indicated that 77.0% of respondents related IRS as means of protection against mosquito bites, but only 3.2% knew that only Anopheles mosquitoes transmit malaria. Therefore, the increasing biting rates of culicines in urban Malabo, and their resistance to all IRS insecticides, is raising concern that a growing number of people may refuse to participate in IRS as result of its perceived failure in controlling mosquitoes. Although this is not yet the case on Bioko Island, communication strategies need refining to sensitize communities about the effectiveness of IRS in controlling malaria vectors in the midst of insecticide resistance in nonmalaria vector mosquitoes.

Rift Valley fever: An open-source transmission dynamics simulation model.

Rift Valley fever (RVF) is one of the major viral zoonoses in Africa, affecting humans and several domestic animal species. The epidemics in eastern Africa occur in a 5-15 year cycle coinciding with abnormally high rainfall generally associated to the warm phase of the El Niño event. However, recently, evidence has been gathered of inter-epidemic transmission. An open-source, easily applicable, accessible and modifiable model was built to simulate the transmission dynamics of RVF. The model was calibrated using data collected in the Kilombero Valley in Tanzania with people and cattle as host species and Ædes mcintoshi, Æ. ægypti and two Culex species as vectors. Simulations were run over a period of 27 years using standard parameter values derived from two previous studies in this region. Our model predicts low-level transmission of RVF, which is in line with epidemiological studies in this area. Emphasis in our simulation was put on both the dynamics and composition of vector populations in three ecological zones, in order to elucidate the respective roles played by different vector species: the model output did indicate the necessity of Culex involvement and also indicated that vertical transmission in Ædes mcintoshi may be underestimated. This model, being built with open-source software and with an easy-to-use interface, can be adapted by researchers and control program managers to their specific needs by plugging in new parameters relevant to their situation and locality.

Effectiveness of landmark- and semi-landmark-based geometric morphometric to identify four species of Culex mosquitoes in Thailand.

Objective:This research aims to study the effectiveness of landmark- and semi-landmark-based geometric morphometric (LMSL) in the identification of four Culex vectors, namely, C. quinquefasciatus, C. visnui, C. sitiens, and C. whitmorei in Thailand and also compared the potential between LMSL and the landmark-based geometric morphometric method (LM).Materials and Methods:The overall size of the wing sample was estimated by the centroid size. Shape variables were computed as principal components of the “partial warp” calculated after generalized procrustes analysis of raw coordinates. Discriminant analysis of the canonical variables performed to explore the shape dissimilarity between Culex species has been shown as a factor map and to calculate the Mahalanobis distance. Size and shape differences based on pairwise Mahalanobis distances were tested using non-parametric methods (1,000 cycles) with Bonferroni correction at a p-value of <0.05.Results:A total of 120 individuals were used that were divided into 30 individuals per Culex species. The mean CS of C. sitiens had the largest wings followed by C. visnui, C. quinquefasciatus, and C. whitmorei in LM and LMSM. The patterns of statistical difference in CS of both methods were similar and wing shapes among Culex species were different based on a comparison of pairwise Mahalanobis distances (p < 0.05) in both methods. For the cross-validated reclassification test, LM provided Culex species separation ranging from 54% to 84% and 51% to 93% for LMSM.Conclusion:Thus, LMSM is another option to use for the identification in mosquito vectors that have a curved line on the wing specific to the species.