ResearchPad - mosquitoes https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Selected wetland soil properties correlate to Rift Valley fever livestock mortalities reported in 2009-10 in central South Africa]]> https://www.researchpad.co/article/elastic_article_15754 Outbreaks of Rift Valley fever have devastating impacts on ruminants, humans, as well as on regional and national economies. Although numerous studies on the impact and outbreak of Rift Valley fever exist, relatively little is known about the role of environmental factors, especially soil, on the aestivation of the virus. This study thus selected 22 sites for study in central South Africa, known to be the recurrent epicenter of widespread Rift Valley fever outbreaks in Southern Africa. Soils were described, sampled and analyzed in detail at each site. Of all the soil variables analyzed for, only eight (cation exchange capacity, exchangeable Ca2+, exchangeable K+, exchangeable Mg2+, soluble Ca2+, medium sand, As, and Br) were statistically identified to be potential indicators of sites with reported Rift Valley fever mortalities, as reported for the 2009–2010 Rift Valley fever outbreak. Four soil characteristics (exchangeable K+, exchangeable Mg2+, medium sand, and Br) were subsequently included in a discriminant function that could potentially be used to predict sites that had reported Rift Valley fever-associated mortalities in livestock. This study therefore constitutes an initial attempt to predict sites prone to Rift Valley fever livestock mortality from soil properties and thus serves as a basis for broader research on the interaction between soil, mosquitoes and Rift Valley fever virus. Future research should include other environmental components such as vegetation, climate, and water properties as well as correlating soil properties with floodwater Aedes spp. abundance and Rift Valley fever virus prevalence.

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<![CDATA[Indoor and outdoor residual spraying of a novel formulation of deltamethrin K-Othrine<sup>®</sup> (Polyzone) for the control of simian malaria in Sabah, Malaysia]]> https://www.researchpad.co/article/elastic_article_14704 Since 2000, human malaria cases in Malaysia were rapidly reduced with the use of insecticides in Indoor Residual Spray (IRS) and Long-Lasting Insecticide Net (LLIN). Unfortunately, monkey malaria in humans has shown an increase especially in Sabah and Sarawak. The insecticide currently used in IRS is deltamethrin K-Othrine® WG 250 wettable granule, targeting mosquitoes that rest and feed indoor. In Sabah, the primary vector for knowlesi malaria is An. balabacensis a species known to bite outdoor. This study evaluates an alternative method, the Outdoor Residual Spray (ORS) using a novel formulation of deltamethrin K-Othrine® (PolyZone) to examine it suitability to control knowlesi malaria vector in Sabah, compared to the current method. The study was performed at seven villages in Sabah having similar type of houses (wood, bamboo and concrete). Houses were sprayed with deltamethrin K-Othrine® (PolyZone) at two different dosages, 25 mg/m2 and 30 mg/m2 and deltamethrin K-Othrine® WG 250 wettable granule at 25 mg/m2, sprayed indoor and outdoor. Residual activity on different walls was assessed using standard cone bioassay techniques. For larval surveillances, potential breeding sites were surveyed. Larvae were collected and identified, pre and post spraying. Adult survey was done using Human Landing Catch (HLC) performed outdoor and indoor. Detection of malaria parasite in adults was conducted via microscopy and molecular methods. Deltamethrin K-Othrine® (PolyZone) showed higher efficacy when sprayed outdoor. The efficacy was found varied when sprayed on different types of wall surfaces. Deltamethrin K-Othrine® (PolyZone) at 25 mg/m2 was the most effective with regards to ability to high mortality and effective knock down (KD). The vector population was reduced significantly post-spraying and reduction in breeding sites as well. The number of simian malaria infected vector, human and simian malaria transmission were also greatly reduced.

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<![CDATA[Fine-scale population genetic structure of dengue mosquito vector, <i>Aedes aegypti</i>, in Metropolitan Manila, Philippines]]> https://www.researchpad.co/article/elastic_article_14656 Aedes aegypti is an efficient vector of dengue due to its highly adaptive nature to the urban environment. Although it is observed to have a short dispersal (active) capability, it has been shown to be capable of traveling long distances (passive) via human-mediated transportation. This duality may expand the distribution of the mosquito vector in urbanized areas. In this study, we examined the population genetic structure of Ae. aegypti in a highly urbanized and dengue-endemic region of the Philippines, Metropolitan Manila. Our findings indicated the dual dispersal nature of Ae. aegypti. The use of microsatellites as genetic markers also allowed us to describe the potential long-distance dispersal patterns, possibly through human-aided land transportation via the existing road networks of Metropolitan Manila.

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<![CDATA[Identification and detection of a novel point mutation in the Chitin Synthase gene of <i>Culex pipiens</i> associated with diflubenzuron resistance]]> https://www.researchpad.co/article/elastic_article_14502 Diflubenzuron is one of the main larvicides used for the control of the West Nile Virus vector Culex pipiens in the Mediterranean. However, the efficiency of control is now under threat due to the selection of insecticide resistance. Two point mutations were previously identified at the Chitin synthase and shown to confer low and high levels of resistance and a diagnostic was developed to monitor the trait. This study reports the identification of a third mutation associated with high levels of diflubenzuron resistance in Italy. This mutation was also detected in France, whereas no resistance mutations were found in Cx. pipiens mosquitoes sampled from Greece, Portugal and Israel. The findings are of major concern for mosquito control programs in S. Europe, which rely on the use of a limited number of larvicides.

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<![CDATA[Assessing entomological risk factors for arboviral disease transmission in the French Territory of the Wallis and Futuna Islands]]> https://www.researchpad.co/article/elastic_article_13872 The French overseas Territory of the Wallis and Futuna Islands, located in the South Pacific, has been affected by several dengue epidemics, but did not face Zika or chikungunya outbreaks, unlike other neighboring islands. The near-exclusive presence of the Aedes polynesiensis mosquito in the islands of Wallis and Futuna confirmed the role played by this mosquito as a vector of dengue fever. A local Ae. polynesiensis population was recently shown to be able to transmit the Zika virus under experimental conditions, but its susceptibility to the chikungunya virus was still unknown, and recent data on the presence of other potential arbovirus vectors were missing. Therefore, we investigated the entomological risk factors for the transmission of arboviral diseases in the Wallis and Futuna Islands. We reported the occurrence and distribution of different Aedes species, especially the abundant presence of Ae. polynesiensis across the territory and the spread of Ae. aegypti in the island of Wallis. Our results demonstrated the ability of local Ae. polynesiensis populations to transmit the chikungunya virus. These findings highlight the risk of arbovirus transmission in the Wallis and Futuna Islands and provide relevant data to guide prevention and vector control strategies in the territory.

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<![CDATA[A systematic review of alternative surveillance approaches for lymphatic filariasis in low prevalence settings: Implications for post-validation settings]]> https://www.researchpad.co/article/elastic_article_13802 Lymphatic filariasis (LF) is a mosquito-borne disease, which can result in complications including swelling affecting the limbs (lymphoedema) or scrotum (hydrocele). LF can be eliminated by mass drug administration (MDA) which involves whole communities taking drug treatment at regular intervals. After MDA programmes, country programmes conduct the Transmission Assessment Survey (TAS), which tests school children for LF. It is important to continue testing for LF after elimination because there can be a 10-year period between becoming infected and developing symptoms, but it is thought that the use of TAS in such settings is likely to be too expensive and also not sensitive enough to detect low-level infections. Our study assesses the results from 44 studies in areas of low LF prevalence that have investigated methods of surveillance for LF which differ from the standardised TAS approach. These include both human and mosquito studies. Results show that there is currently no standardised approach to testing, but that surveillance can be made more sensitive through the use of new diagnostic tests, such as antibody testing, and also by targeting higher risk populations. However, further research is needed to understand whether these approaches work in a range of settings and whether they are affordable on the ground.

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<![CDATA[Evidence for both sequential mutations and recombination in the evolution of kdr alleles in Aedes aegypti]]> https://www.researchpad.co/article/N8479e8f6-b6ad-4aa7-91b1-bf6bde90184a

Background

Aedes aegypti is a globally distributed vector of human diseases including dengue, yellow fever, chikungunya, and Zika. Pyrethroid insecticides are the primary means of controlling adult A. aegypti populations to suppress arbovirus outbreaks, but resistance to pyrethroid insecticides has become a global problem. Mutations in the voltage-sensitive sodium channel (Vssc) gene are a major mechanism of pyrethroid resistance in A. aegypti. Vssc resistance alleles in A. aegypti commonly have more than one mutation. However, our understanding of the evolutionary dynamics of how alleles with multiple mutations arose is poorly understood.

Methodology/Principal findings

We examined the geographic distribution and association between the common Vssc mutations (V410L, S989P, V1016G/I and F1534C) in A. aegypti by analyzing the relevant Vssc fragments in 25 collections, mainly from Asia and the Americas. Our results showed all 11 Asian populations had two types of resistance alleles: 1534C and 989P+1016G. The 1534C allele was more common with frequencies ranging from 0.31 to 0.88, while the 989P+1016G frequency ranged from 0.13 to 0.50. Four distinct alleles (410L, 1534C, 410L+1534C and 410L+1016I+1534C) were detected in populations from the Americas. The most common was 410L+1016I+1534C with frequencies ranging from 0.50 to 1.00, followed by 1534C with frequencies ranging from 0.13 to 0.50. Our phylogenetic analysis of Vssc supported multiple independent origins of the F1534C mutation. Our results indicated the 410L+1534C allele may have arisen by addition of the V410L mutation to the 1534C allele, or by a crossover event. The 410L+1016I+1534C allele was the result of one or two mutational steps from a 1534C background.

Conclusions/Significance

Our data corroborated previous geographic distributions of resistance mutations and provided evidence for both recombination and sequential accumulation of mutations contributing to the molecular evolution of resistance alleles in A. aegypti.

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<![CDATA[A mathematical model for assessing the effectiveness of controlling relapse in Plasmodium vivax malaria endemic in the Republic of Korea]]> https://www.researchpad.co/article/Nf3d8dda1-10e2-4286-9776-07d534017a03

Malaria has persisted as an endemic near the Demilitarized Zone in the Republic of Korea since the re-emergence of Plasmodium vivax malaria in 1993. The number of patients affected by malaria has increased recently despite many controls tools, one of the reasons behind which is the relapse of malaria via liver hypnozoites. Tafenoquine, a new drug approved by the United States Food and Drug Administration in 2018, is expected to reduce the rate of relapse of malaria hypnozoites and thereby decrease the prevalence of malaria among the population. In this work, we have developed a new transmission model for Plasmodium vivax that takes into account a more realistic intrinsic distribution from existing literature to quantify the current values of relapse parameters and to evaluate the effectiveness of the anti-relapse therapy. The model is especially suitable for estimating parameters near the Demilitarized Zone in Korea, in which the disease follows a distinguishable seasonality. Results were shown that radical cure could significantly reduce the prevalence level of malaria. However, eradication would still take a long time (over 10 years) even if the high-level treatment were to persist. In addition, considering that the vector’s behavior is manipulated by the malaria parasite, relapse repression through vector control at the current level may result in a negative effect in containing the disease. We conclude that the use of effective drugs should be considered together with the increased level of the vector control to reduce malaria prevalence.

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<![CDATA[Prediction model for dengue fever based on interactive effects between multiple meteorological factors in Guangdong, China (2008–2016)]]> https://www.researchpad.co/article/Nfe4e2064-ca0a-4d6d-a8b7-4f75eb296e9a

Introduction

In order to improve the prediction accuracy of dengue fever incidence, we constructed a prediction model with interactive effects between meteorological factors, based on weekly dengue fever cases in Guangdong, China from 2008 to 2016.

Methods

Dengue fever data were derived from statistical data from the China National Notifiable Infectious Disease Reporting Information System. Daily meteorological data were obtained from the China Integrated Meteorological Information Sharing System. The minimum temperature for transmission was identified using data fitting and the Ross-Macdonald model. Correlations and interactive effects were examined using Spearman’s rank correlation and multivariate analysis of variance. A probit regression model to describe the incidence of dengue fever from 2008 to 2016 and forecast the 2017 incidence was constructed, based on key meteorological factors, interactive effects, mosquito-vector factors, and other important factors.

Results

We found the minimum temperature suitable for dengue transmission was ≥18°C, and as 97.91% of cases occurred when the minimum temperature was above 18 °C, the data were used for model training and construction. Epidemics of dengue are related to mean temperature, maximum/minimum and mean atmospheric pressure, and mean relative humidity. Moreover, interactions occur between mean temperature, minimum atmospheric pressure, and mean relative humidity. Our weekly probit regression prediction model is 0.72. Prediction of dengue cases for the first 41 weeks of 2017 exhibited goodness of fit of 0.60.

Conclusion

Our model was accurate and timely, with consideration of interactive effects between meteorological factors.

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<![CDATA[Individual-based network model for Rift Valley fever in Kabale District, Uganda]]> https://www.researchpad.co/article/5c8823c9d5eed0c484638ffb

Rift Valley fever (RVF) is a zoonotic disease, that causes significant morbidity and mortality among ungulate livestock and humans in endemic regions. In East Africa, the causative agent of the disease is Rift Valley fever virus (RVFV) which is primarily transmitted by multiple mosquito species in Aedes and Mansonia genera during both epizootic and enzootic periods in a complex transmission cycle largely driven by environmental and climatic factors. However, recent RVFV activity in Uganda demonstrated the capability of the virus to spread into new regions through livestock movements, and underscored the need to develop effective mitigation strategies to reduce transmission and prevent spread among cattle populations. We simulated RVFV transmission among cows in 22 different locations of the Kabale District in Uganda using real world livestock data in a network-based model. This model considered livestock as a spatially explicit factor in different locations subjected to specific vector and environmental factors, and was configured to investigate and quantitatively evaluate the relative impacts of mosquito control, livestock movement, and diversity in cattle populations on the spread of the RVF epizootic. We concluded that cattle movement should be restricted for periods of high mosquito abundance to control epizootic spreading among locations during an RVF outbreak. Importantly, simulation results also showed that cattle populations with heterogeneous genetic diversity as crossbreeds were less susceptible to infection compared to homogenous cattle populations.

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<![CDATA[Behavior and abundance of Anopheles darlingi in communities living in the Colombian Amazon riverside]]> https://www.researchpad.co/article/5c8acc3ed5eed0c48498f2cc

In the past few years, relative frequencies of malaria parasite species in communities living in the Colombian Amazon riverside have changed, being Plasmodium vivax (61.4%) and Plasmodium malariae (43.8%) the most frequent. Given this epidemiological scenario, it is important to determine the species of anophelines involved in these parasites’ transmission. This study was carried out in June 2016 in two indigenous communities living close to the tributaries of the Amazon River using protected human bait. The results of this study showed a total abundance of 1,085 mosquitos, of which 99.2% corresponded to Anopheles darlingi. Additionally, only two anopheline species were found, showing low diversity in the study areas. Molecular confirmation of some individuals was then followed by evolutionary analysis by using the COI gene. Nested PCR was used for identifying the three Plasmodium species circulating in the study areas. Of the two species collected in this study, 21.0% of the An. darlingi mosquitoes were infected with P. malariae, 21.9% with P. vivax and 10.3% with Plasmodium falciparum. It exhibited exophilic and exophagic behavior in both study areas, having marked differences regarding its abundance in each community (Tipisca first sampling 49.4%, Tipisca second sampling 39.6% and Doce de Octubre 10.9%). Interestingly, An. mattogrossensis infected by P. vivax was found for the first time in Colombia (in 50% of the four females collected). Analysis of An. darlingi COI gene diversity indicated a single population maintaining a high gene flow between the study areas. The An. darlingi behavior pattern found in both communities represents a risk factor for the region’s inhabitants living/working near these sites. This highlights the need for vector control efforts such as the use of personal repellents and insecticides for use on cattle, which must be made available in order to reduce this Anopheline’s abundance.

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<![CDATA[A survey on Mycobacterium ulcerans in Mosquitoes and March flies captured from endemic areas of Northern Queensland, Australia]]> https://www.researchpad.co/article/5c784fb8d5eed0c4840073ed

Mycobacterium ulcerans is the causative agent of Buruli ulcer (BU). This nontuberculous mycobacterial infection has been reported in 34 countries worldwide. In Australia, the majority of cases of BU have been recorded in coastal Victoria and the Mossman-Daintree areas of north Queensland. Mosquitoes have been postulated as a vector of M. ulcerans in Victoria, however the specific mode of transmission of this disease is still far from being well understood. In the current study, we trapped and analysed 16,900 (allocated to 845 pools) mosquitoes and 296 March flies from the endemic areas of north Queensland to examine for the presence of M. ulcerans DNA by polymerase chain reaction. Seven of 845 pools of mosquitoes were positive on screening using the IS2404 PCR target (maximum likelihood estimate 0.4/1,000). M. ulcerans DNA was detected from one pool of mosquitoes from which all three PCR targets: IS2404, IS2606 and the ketoreductase B domain of mycolactone polyketide synthase gene were detected. None of the March fly samples were positive for the presence of M. ulcerans DNA.

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<![CDATA[Epidemiological and clinical characteristics of Dengue virus outbreaks in two regions of China, 2014 – 2015]]> https://www.researchpad.co/article/5c8823dcd5eed0c4846391a6

Dengue virus (DENV), a single-stranded RNA virus and Flaviviridae family member, is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. DENV causes dengue fever, which may progress to severe dengue. Hospital-based surveillance was performed in two Chinese regions, Guangzhou and Xishuangbanna, during the dengue epidemics in 2014 and 2015, respectively. Acute-phase serum was obtained from 133 patients with suspected dengue infections during the peak season for dengue cases. Viremia levels, virus sero-positivity, serotype distribution, infection type, clinical manifestations and virus phylogenetics were investigated. Of the 112 DENV-confirmed cases, 92(82.14%) were IgM antibody-positive for DENV, and 69(51.88%) were positive for DENV RNA. From these cases, 47(41.96%) were classified as primary infections, 39(34.82%) as secondary infections and 26 (23.21%) as undetermined infections. The viremia levels were negatively correlated with IgM presence, but had no relationship with the infection type. DENV-1 genotype V dominated in Guangzhou, whereas the DENV-2 Cosmopolitan genotype dominated in Xishuangbanna, where fewer DENV-1 genotype I cases occurred. DENV-2 is associated with severe dengue illness with more serious clinical issues. The strains isolated during 2014–2015 are closely related to the isolates obtained from other Chinese regions and to those isolated recently in Southeast Asian countries. Our results indicate that DENV is no longer an imported virus and is now endemic in China. An extensive seroepidemiological study of DENV and the implementation of vector control measures against it are now warranted in China.

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<![CDATA[Urban and semi-urban mosquitoes of Mexico City: A risk for endemic mosquito-borne disease transmission]]> https://www.researchpad.co/article/5c897788d5eed0c4847d2f3b

Since past century, vector-borne diseases have been a major public health concern in several states of Mexico. However, Mexico City continues to be free of endemic mosquito-borne viral diseases. The city is the most important politic and economic state of Mexico and one of the most important city of Latin America. Its subtropical highland climate and high elevation (2240 masl) had historically made the occurrence of Aedes species unlikely. However, the presence of other potential disease vectors (Culex spp, Culiseta spp), and the current intermittent introductions of Aedes aegypti, have revealed that control programs must adopt routine vector surveillance in the city. In this study, we provide an updated species list from a five-years of vector surveillance performed in Mexico City. A total of 18,553 mosquito larvae were collected. Twenty-two species from genus Culex, Aedes, Culiseta, Anopheles, Lutzia and Uranotaenia were observed. Nine new mosquito records for the city were found. Ae. albopictus was recorded for the first time in Mexico City. Interestingly, a new record, Ae. epactius was the most frequent species reported. Cx. pipiens quinquefasciatus exhibited the highest number of individuals collected. We detected six areas which harbor the highest mosquito species records in the city. Cemeteries included 68.9% of our collection sites. Temporarily ponds showed the highest species diversity. We detected an increasing presence of Ae. aegypti, which was detected for three consecutive years (2015–2017), predominantly in the warmer microclimates of the city. We found a possible correlation between increasing temperature and Ae. aegypti and Ae. albopictus expanding range. This study provides a starting point for developing strategies related to environmental management for mosquito control. The promotion of mosquito control practices through community participation, mass media and education programmes in schools should be introduced in the city.

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<![CDATA[Comparative fitness of West Nile virus isolated during California epidemics]]> https://www.researchpad.co/article/5c61e907d5eed0c48496f68c

West Nile virus (WNV) has been circulating in California since its first detection in 2003, causing repeated outbreaks affecting public, wildlife and veterinary health. Epidemics of WNV are difficult to predict due to the multitude of factors influencing transmission dynamics among avian and mosquito hosts. Typically, high levels of WNV amplification are required for outbreaks to occur, and therefore associated viral strains may exhibit enhanced virulence and mortality in competent bird species resulting in increased mosquito infection prevalence. In our previous study, most WNV isolates made from California during 2007–08 showed increased fitness when competed in House Finches (HOFI, Haemorhous mexicanus) and Culex tarsalis Coquillett mosquitoes against COAV997-5nt, a genetically marked recombinant virus derived from a 2003 California strain. Herein, we evaluated the competitive fitness of WNV strains isolated during California epidemics in 2004, 2005, 2007, 2011 and 2012 against COAV997-5nt. These outbreak isolates did not produce elevated mortality in HOFIs, but replicated more efficiently than did COAV997-5nt based on quantification of WNV RNA copies in sera, thereby demonstrating increased competitive fitness. Oral co-infections in Cx. tarsalis resulted in similar virus-specific infection and transmission rates, indicating that outbreak isolates did not have a fitness advantage over COAV997-5nt. Collectively, WNV isolates from outbreaks demonstrated relatively greater avian, but not vector, replicative fitness compared to COAV997-5nt, similar to previously characterized non-outbreak isolates of WNV. Our results indicated that ecological rather than viral factors may facilitate WNV amplification to outbreak levels, but monitoring viral phenotypes through competitive fitness studies may provide insight into altered replication and transmission potential among emerging WNV strains.

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<![CDATA[Water-induced strong protection against acute exposure to low subzero temperature of adult Aedes albopictus]]> https://www.researchpad.co/article/5c61e909d5eed0c48496f6ed

As an important vector of dengue and Zika, Aedes albopictus has been the fastest spreading invasive mosquitoes in the world over the last 3–4 decades. Cold tolerance is important for survival and expansion of insects. Ae. albopictus adults are generally considered to be cold-intolerant that cannot survive at subzero temperature. However, we found that Ae. albopictus could survive for several hours’ exposure to -9 to -19 oC so long as it was exposed with water. Median lethal time (LT50) of Ae. albopictus exposed to -15 and -19 oC with water increased by more than 100 times compared to those exposed to the same subzero temperature without water. This phenomenon also existed in adult Aedes aegypti and Culex quinquefasciatus. Ae. albopictus female adults which exposed to low subzero temperature at -9 oC with water had similar longevity and reproductive capacity to those of females without cold exposure. Cold exposure after a blood meal also have no detrimental impact on survival capacity of female adult Ae. albopictus compared with those cold exposed without a blood meal. Moreover, our results showed that rapid cold hardening (RCH) was induced in Ae. albopictus during exposing to low subzero temperature with water. Both the RCH and the relative high subzero temperature of water immediate after cold exposure might provide this strong protection against low subzero temperature. The molecular basis of water-induced protection for Ae. albopictus might refer to the increased glycerol during cold exposure, as well as the increased glucose and hsp70 during recovery from cold exposure. Our results suggested that the water-induced strong protection against acute decrease of air temperature for adult mosquitoes might be important for the survival and rapid expansion of Ae. albopictus.

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<![CDATA[Potential for sylvatic and urban Aedes mosquitoes from Senegal to transmit the new emerging dengue serotypes 1, 3 and 4 in West Africa]]> https://www.researchpad.co/article/5c6dc998d5eed0c484529ea3

Dengue fever (DEN) is the most common arboviral disease in the world and dengue virus (DENV) causes 390 million annual infections around the world, of which 240 million are inapparent and 96 million are symptomatic. During the past decade a changing epidemiological pattern has been observed in Africa, with DEN outbreaks reported in all regions. In Senegal, all DENV serotypes have been reported. These important changes in the epidemiological profile of DEN are occurring in a context where there is no qualified vaccine against DEN. Further there is significant gap of knowledge on the vector bionomics and transmission dynamics in the African region to effectively prevent and control epidemics. Except for DENV-2, few studies have been performed with serotypes 1, 3, and 4, so this study was undertaken to fill out this gap. We assessed the vector competence of Aedes (Diceromyia) furcifer, Ae. (Diceromyia) taylori, Ae. (Stegomyia) luteocephalus, sylvatic and urban Ae. (Stegomyia) aegypti populations from Senegal for DENV-1, DENV-3 and DENV-4 using experimental oral infection. Whole bodies and wings/legs were tested for DENV presence by cell culture assays and saliva samples were tested by real time RT-PCR to estimate infection, disseminated infection and transmission rates. Our results revealed a low capacity of sylvatic and urban Aedes mosquitoes from Senegal to transmit DENV-1, DENV-3 and DENV-4 and an impact of infection on their mortality. The highest potential transmission rate was 20% despite the high susceptibility and disseminated infection rates up to 93.7% for the 3 Ae. aegypti populations tested, and 84.6% for the sylvatic vectors Ae. furcifer, Ae. taylori and Ae. luteocephalus.

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<![CDATA[Spatial and temporal development of deltamethrin resistance in malaria vectors of the Anopheles gambiae complex from North Cameroon]]> https://www.researchpad.co/article/5c75ac7cd5eed0c484d088a5

The effectiveness of insecticide-based malaria vector control interventions in Africa is threatened by the spread and intensification of pyrethroid resistance in targeted mosquito populations. The present study aimed at investigating the temporal and spatial dynamics of deltamethrin resistance in An. gambiae s.l. populations from North Cameroon. Mosquito larvae were collected from 24 settings of the Garoua, Pitoa and Mayo Oulo Health Districts (HDs) from 2011 to 2015. Two to five days old female An. gambiae s.l. emerging from larval collections were tested for deltamethrin resistance using the World Health Organization’s (WHO) standard protocol. Sub samples of test mosquitoes were identified to species using PCR-RFLP and genotyped for knockdown resistance alleles (Kdr 1014F and 1014S) using Hot Ligation Oligonucleotide Assay (HOLA). All the tested mosquitoes were identified as belonging to the An. gambiae complex, including 3 sibling species mostly represented by Anopheles arabiensis (67.6%), followed by Anopheles coluzzii (25.4%) and Anopheles gambiae (7%). Deltamethrin resistance frequencies increased significantly between 2011 and 2015, with mosquito mortality rates declining from 70–85% to 49–73% in the three HDs (Jonckheere-Terstra test statistic (JT) = 5638, P< 0.001), although a temporary increase of mortality rates (91–97%) was seen in the Pitoa and Mayo Oulo HDs in 2012. Overall, confirmed resistance emerged in 10 An. gambiae s.l. populations over the 24 field populations monitored during the study period, from 2011 to 2015. Phenotypic resistance was mostly found in urban settings compared with semi-urban and rural settings (JT = 5282, P< 0.0001), with a spatial autocorrelation between neighboring localities. The Kdr 1014F allelic frequencies in study HDs increased from 0–30% in 2011 to 18–61% in 2014–2015 (JT = 620, P <0.001), especially in An. coluzzii samples. The overall frequency of the Kdr 1014S allele was 0.1%. This study revealed a rapid increase and widespread deltamethrin resistance frequency as well as Kdr 1014F allelic frequencies in An. gambiae s.l. populations over time, emphasizing the urgent need for vector surveillance and insecticide resistance management strategies in Cameroon.

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<![CDATA[Optimization of irradiation dose to Aedes aegypti and Ae. albopictus in a sterile insect technique program]]> https://www.researchpad.co/article/5c75ac86d5eed0c484d0898f

The sterile insect technique (SIT) may offer a means to control the transmission of mosquito borne diseases. SIT involves the release of male insects that have been sterilized by exposure to ionizing radiation. We determined the effects of different doses of radiation on the survival and reproductive capacity of local strains of Aedes aegypti and Ae. albopictus in southern Mexico. The survival of irradiated pupae was invariably greater than 90% and did not differ significantly in either sex for either species. Irradiation had no significant adverse effects on the flight ability (capacity to fly out of a test device) of male mosquitoes, which consistently exceeded 91% in Ae. aegypti and 96% in Ae. albopictus. The average number of eggs laid per female was significantly reduced in Ae. aegypti at doses of 15 and 30 Gy and no eggs were laid by females that had been exposed to 50 Gy. Similarly, in Ae. albopictus, egg production was reduced at doses of 15 and 25 Gy and was eliminated at 35 Gy. In Ae. aegypti, fertility in males was eliminated at 70 Gy and was eliminated at 30 Gy in females, whereas in Ae. albopictus, the fertility of males that mated with untreated females was almost zero (0.1%) in the 50 Gy treatment and female fertility was eliminated at 35 Gy. Irradiation treatments resulted in reduced ovary length and fewer follicles in both species. The adult median survival time of both species was reduced by irradiation in a dose-dependent manner. However, sterilizing doses of 35 Gy and 50 Gy resulted in little reduction in survival times of males of Ae. albopictus and Ae. aegypti, respectively, indicating that these doses should be suitable for future evaluations of SIT-based control of these species. The results of the present study will be applied to studies of male sexual competitiveness and to stepwise evaluations of the sterile insect technique for population suppression of these vectors in Mexico.

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<![CDATA[Vector competence of biting midges and mosquitoes for Shuni virus]]> https://www.researchpad.co/article/5c6c75dfd5eed0c4843d037a

Background

Shuni virus (SHUV) is an orthobunyavirus that belongs to the Simbu serogroup. SHUV was isolated from diverse species of domesticated animals and wildlife, and is associated with neurological disease, abortions, and congenital malformations. Recently, SHUV caused outbreaks among ruminants in Israel, representing the first incursions outside the African continent. The isolation of SHUV from a febrile child in Nigeria and seroprevalence among veterinarians in South Africa suggests that the virus may have zoonotic potential as well. The high pathogenicity, extremely broad tropism, potential transmission via both biting midges and mosquitoes, and zoonotic features of SHUV require further investigation. This is important to accurately determine the risk for animal and human health, and to facilitate preparations for potential epidemics. To gain first insight into the potential involvement of biting midges and mosquitoes in SHUV transmission we have investigated the ability of SHUV to infect two species of laboratory-colonised biting midges and two species of mosquitoes.

Methodology/Principal findings

Culicoides nubeculosus, C. sonorensis, Culex pipiens pipiens, and Aedes aegypti were orally exposed to SHUV by providing an infectious blood meal. Biting midges showed high infection rates of approximately 40%-60%, whereas infection rates of mosquitoes were only 0–2%. Moreover, successful dissemination in both species of biting midges and no evidence for transmission by orally exposed mosquitoes was found.

Conclusions/Significance

The results of this study suggest that different species of Culicoides midges are efficient in SHUV transmission, while the involvement of mosquitoes has not been supported.

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