A comparative assessment of adult mosquito trapping methods to estimate spatial patterns of abundance and community composition in southern Africa

Background Assessing adult mosquito populations is an important component of disease surveillance programs and ecosystem health assessments. Inference from adult trapping datasets involves comparing populations across space and time, but comparisons based on different trapping methods may be biased if traps have different efficiencies or sample different subsets of the mosquito community. Methods We compared four widely-used trapping methods for adult mosquito data collection in Kruger National Park (KNP), South Africa: Centers for Disease Control miniature light trap (CDC), Biogents Sentinel trap (BG), Biogents gravid Aedes trap (GAT) and a net trap. We quantified how trap choice and sampling effort influence inferences on the regional distribution of mosquito abundance, richness and community composition. Results The CDC and net traps together collected 96% (47% and 49% individually) of the 955 female mosquitoes sampled and 100% (85% and 78% individually) of the 40 species or species complexes identified. The CDC and net trap also identified similar regional patterns of community composition. However, inference on the regional patterns of abundance differed between these traps because mosquito abundance in the net trap was influenced by variation in weather conditions. The BG and GAT traps collected significantly fewer mosquitoes, limiting regional comparisons of abundance and community composition. Conclusions This study represents the first systematic assessment of trapping methods in natural savanna ecosystems in southern Africa. We recommend the CDC trap or the net trap for future monitoring and surveillance programs

Aedes species (Diptera: Culicidae) ecological and host feeding patterns in the north-eastern parts of South Africa, 2014–2018

BACKGROUND: There is a paucity of recent data and knowledge on mosquito diversity and potential vectors of arboviruses in South Africa, with most of the available data dating back to the 1950s–1970s. Aedes and Culex species are the major vectors of some of the principal arboviruses which have emerged and re-emerged in the past few decades. METHODS: In this study we used entomological surveillance in selected areas in the north-eastern parts of South Africa from 2014 to 2018 to assess mosquito diversity, with special emphasis on the Aedes species. The impact of trap types and environmental conditions was also investigated. Identifcation of the blood meal sources of engorged females collected during the study period was carried out, and DNA barcodes were generated for selected species. RESULTS: Overall, 18.5% of the total Culicidae mosquitoes collected belonged to the genus Aedes, with 14 species recognised or suspected vectors of arboviruses. Species belonging to the Neomelaniconion subgenus were commonly collected in the Bushveld savanna at conservation areas, especially Aedes mcintoshi and Aedes circumluteolus. Aedes aegypti was present in all sites, albeit in low numbers. Temperature was a limiting factor for the Aedes population, and they were almost exclusively collected at temperatures between 18 °C and 27 °C. The cytochrome oxidase subunit I (COI) barcode fragment was amplifed for 21 Aedes species, and for nine of these species it was the frst sequence information uploaded on GenBank. CONCLUSION: This study provides a better understanding of the diversity and relative abundance of Aedes species in the north-east of South Africa. The information provided here will contribute to future arboviral research and implementation of efcient vector control and prevention strategies.The Centers for Disease Control and Preventionhttp://www.parasitesandvectors.compm2022Medical VirologyUP Centre for Sustainable Malaria Control (UP CSMC

Detection of insect-specific flaviviruses in mosquitoes (diptera: culicidae) in Northeastern regions of South Africa

Mosquitoes in the Aedes and Culex genera are considered the main vectors of pathogenic flaviviruses worldwide. Entomological surveillance using universal flavivirus sets of primers in mosquitoes can detect not only pathogenic viruses but also insect-specific ones. It is hypothesized that insect-specific flaviviruses, which naturally infect these mosquitoes, may influence their vector competence for zoonotic arboviruses. Here, entomological surveillance was performed between January 2014 and May 2018 in five different provinces in the northeastern parts of South Africa, with the aim of identifying circulating flaviviruses. Mosquitoes were sampled using different carbon dioxide trap types. Overall, 64,603 adult mosquitoes were collected, which were screened by RT-PCR and sequencing. In total, 17 pools were found positive for insect-specific Flaviviruses in the mosquito genera Aedes (12/17, 70.59) and Anopheles (5/17, 29.41). No insect-specific viruses were detected in Culex species. Cell-fusing agent viruses were detected in Aedes aegypti and Aedes caballus. A range of anopheline mosquitoes, including Anopheles coustani, An. squamosus and An. maculipalpis, were positive for Culex flavivirus-like and Anopheles flaviviruses. These results confirm the presence of insect-specific flaviviruses in mosquito populations in South Africa, expands their geographical range and indicates potential mosquito species as vector species

Detection of insect-specific flaviviruses in mosquitoes (Diptera: Culicidae) in northeastern regions of South Africa

Mosquitoes in the Aedes and Culex genera are considered the main vectors of pathogenic flaviviruses worldwide. Entomological surveillance using universal flavivirus sets of primers in mosquitoes can detect not only pathogenic viruses but also insect-specific ones. It is hypothesized that insect-specific flaviviruses, which naturally infect these mosquitoes, may influence their vector competence for zoonotic arboviruses. Here, entomological surveillance was performed between January 2014 and May 2018 in five different provinces in the northeastern parts of South Africa, with the aim of identifying circulating flaviviruses. Mosquitoes were sampled using different carbon dioxide trap types. Overall, 64,603 adult mosquitoes were collected, which were screened by RT-PCR and sequencing. In total, 17 pools were found positive for insect-specific Flaviviruses in the mosquito genera Aedes (12/17, 70.59%) and Anopheles (5/17, 29.41%). No insect-specific viruses were detected in Culex species. Cell-fusing agent viruses were detected in Aedes aegypti and Aedes caballus. A range of anopheline mosquitoes, including Anopheles coustani, An. squamosus and An. maculipalpis, were positive for Culex flavivirus-like and Anopheles flaviviruses. These results confirm the presence of insect-specific flaviviruses in mosquito populations in South Africa, expands their geographical range and indicates potential mosquito species as vector species.Gratama Fund; Uyttenboogaart-Eliasen foundation; RCN-IDEAS travel grant; National Research Foundation; The World Academy of Sciences; Global Health and Tropical Medicine; Professor Programme by the University of Pretoria, SA and Centres for Disease Control and Prevention.http://www.mdpi.com/journal/virusespm2022UP Centre for Sustainable Malaria Control (UP CSMC

Human practices promote presence and abundance of disease-transmitting mosquito species

Humans alter the environment at unprecedented rates through habitat destruction, nutrient pollution and the application of agrochemicals. This has recently been proposed to act as a potentially significant driver of pathogen-carrying mosquito species (disease vectors) that pose a health risk to humans and livestock. Here, we use a unique set of locations along a large geographical gradient to show that landscapes disturbed by a variety of anthropogenic stressors are consistently associated with vector-dominated mosquito communities for a wide range of human and livestock infections. This strongly suggests that human alterations to the environment promote the presence and abundance of disease vectors across large spatial extents. As such, it warrants further studies aimed at unravelling mechanisms underlying vector prevalence in mosquito communities, and opens up new opportunities for preventative action and predictive modelling of vector borne disease risks in relation to degradation of natural ecosystems

Vector competence of populations of Aedes aegypti from three distinct cities in Kenya for chikungunya virus

BACKGROUND : In April, 2004, chikungunya virus (CHIKV) re-emerged in Kenya and eventually spread to the islands in the Indian Ocean basin, South-East Asia, and the Americas. The virus, which is often associated with high levels of viremia in humans, is mostly transmitted by the urban vector, Aedes aegypti. The expansion of CHIKV presents a public health challenge both locally and internationally. In this study, we investigated the ability of Ae. aegypti mosquitoes from three distinct cities in Kenya; Mombasa (outbreak prone), Kisumu, and Nairobi (no documented outbreak) to transmit CHIKV. METHODOLOGY/PRINCIPAL FINDINGS : Aedes aegypti mosquito populations were exposed to different doses of CHIKV (105.6±7.5 plaque-forming units[PFU]/ml) in an infectious blood meal. Transmission was ascertained by collecting and testing saliva samples from individual mosquitoes at 5, 7, 9, and 14 days post exposure. Infection and dissemination were estimated by testing body and legs, respectively, for individual mosquitoes at selected days post exposure. Tissue culture assays were used to determine the presence of infectious viral particles in the body, leg, and saliva samples. The number of days post exposure had no effect on infection, dissemination, or transmission rates, but these rates increased with an increase in exposure dose in all three populations. Although the rates were highest in Ae. aegypti from Mombasa at titers 106.9 PFU/ml, the differences observed were not statistically significant (χ2 1.04, DF = 1, P 0.31). Overall, about 71% of the infected mosquitoes developed a disseminated infection, of which 21% successfully transmitted the virus into a capillary tube, giving an estimated transmission rate of about 10% for mosquitoes that ingested 106.9 PFU/ml of CHIKV. All three populations of Ae. aegypti were infectious as early as 5±7 days post exposure. On average, viral dissemination only occurred when body titers were 104 PFU/ ml in all populations. CONCLUSIONS/SIGNIFICANCE : Populations of Ae. aegypti from Mombasa, Nairobi, and Kisumu were all competent laboratory vectors of CHIKV. Viremia of the infectious blood meal was an important factor in Ae. aegypti susceptibility and transmission of CHIKV. In addition to viremia levels, temperature and feeding behavior of Ae. aegypti may also contribute to the observed disease patterns.The National Institutes of Health (NIH), Grant No. 1R01AI099736-01A1 to RS, UK's Department for International Development (DFID), Swedish International Development Cooperation Agency (Sida), the Swiss Agency for Development and Cooperation (SDC) and the Kenyan Government.http://www.plosntds.orgam2017Medical Virolog

Identification and phylogenetic analysis of Aedes species (Diptera: Culicidae) and arboviruses associated with them across tropical and temperate regions of South Africa (2015-2018)

Emerging and re-emerging diseases have increased worldwide in incidence in the past decades. Of these emerging diseases 60.3% are caused by zoonotic pathogens of which 22.8% are arboviruses or arthropod borne viruses. Arboviruses are transmitted by hematophagous insects, especially moquitoes. Multiple factors such as human population growth, climate change and adaptations of certain Aedes mosquito vector species to urban environments and anthropophilic have been attributed to causing this rise in arboviral infections. In Southern Africa, zoonotic arboviruses belonging to the families Flaviviridae (genus Flavivirus), Togaviridae (genus Alphavirus), and those in the order Bunyavirales, family Phenuiviridae: (genus Phlebovirus) and Peribunyaviridae (genus Orthobunyaviruses), have proven, in the past, to be of both medical and veterinary importance. Recent detection of neurological cases in South Africa, most likely, due to flaviviruses, alphaviruses and orthobunyaviruses in the Simbu serogroup, has rekindled interest in these zoonotic diseases. This interest is also warranted because of lack of recent information on arboviral prevalence in mosquito species, distributions, abundance, and ecology, especially of Aedes species, the likely primary vectors of these arboviruses in Southern Africa. To update this lack of information, this study t reports on zoonotic arboviruses circulating in selected areas in the north-eastern provinces of South Africa in mosquitoes with a focus on Aedes. Many Aedes species are morphologically quite difficult to identify especially when they are old, and scales rubbed off in the process of trapping. To aid in the identification of Aedes in this study we provide molecular barcodes for Aedes species occurring in in South Africa and define their phylogenetic relationship with other mainly Afrotropical Aedes mosquitoes based on the cytochrome oxidase I gene sequences. The first Chapter provides a comprehensive review of the literature and describes the importance of arboviruses worldwide and in South Africa, highlighting the role of Aedes mosquitoes as vectors. In Chapter 2, what is known about the broad patterns of Aedes mosquito species diversity, abundance, and distribution in different habitats across selected sites in five different provinces in South Africa is described. The sites selected were chosen because of evidence of neurological cases in humans and animals in recent years likely due to arboviral infections. In total, 61,737 adult mosquitoes were collected from January 2014 to May 2018, using three kinds of carbon dioxide baited trap types About 16% (11,440) were Aedes species, of which, 14 species were recognised or suspected vectors of mosquito-borne diseases because of positive infections, including Aedes mcintoshi which was the most abundant Aedes species captured. The effect of the climatic conditions on the mosquito population dynamics were also investigated. Aedes species were present in the sites following the peak of the rainfall and were mostly captured in temperatures between 18°C and 27°C. Chapter 3 focuses on determining the blood meal source present in engorged Aedes mosquitoes sampled to give an assessment of blood feeding tendencies that would serve useful to determine their vector status. Aedes species were identified feeding on a broad range of livestock, and wildlife, only two specimens were identified as feeding on avian species.Chapter 4 focuses on interpretations of cytochrome oxidase subunit 1 (COI) gene sequences to identify Aedes species in South Africa and to analyse the relationship among the species. A total of 52 COI sequences were aligned representing 21 Aedes species. In several cases these were the first African aedine species uploaded in NCBI GenBank. Neomelaniconion species clustered together, except for Ae. aurovenatus. Finally, the data also suggested that Ae. cumminsii present in South Africa belongs to the subspecies ssp. mediopunctatus. In Chapter 5 results of arboviral infections in Culicidae mosquitoes captured from the selected sites, particularly Aedes species is provided. Arboviral infection or prevalence screening was performed using multiple genus specific polymerase chain reactions (PCR). Alphavirus and Orthobunyavirus were detected in different Culicidae genera, including Aedes, Culex, Anopheles and Mansonia. There were no isolations of pathogenic flaviviruses in mosquitoes. The only alphaviruses detected in mosquitoes were Middelburg, Sindbis and Ndumu viruses during the period of the study. Shuni virus was the only member of Orthobunyavirus genus, detected. Even though, the main aim was to identify pathogenic viruses, several insect-specific viruses belonging to Alphavirus and Flavivirus genera were also detected and these are described in Chapter 6. The numerous arboviruses detected in Culicine mosquitoes, including Aedes species, demonstrate that some species are likely maintaining natural cycling of these arboviruses. Noteworthy, is that mosquito species positive for arboviruses are often the most abundant in the selected sampling locations and that these species blood feed mostly on the larger vertebrates present in the area. Outbreaks possibly occur when the prevalence of certainmosquito species are high due to favourable climatic conditions. Highest arbovirus detections occurred in peri-urban, rural, and conservation areas, indicating that livestock and wildlife likely play an important role in the amplification of these arboviruses. This study highlights the importance of a continues mosquito-based surveillance for arboviruses in South Africa, and the role that Aedes species might be playing in the circulation of these arboviruses. Surveillance for the species that tested positive for pathogenic arboviruses during the arbovirus season may act as an early warning system and can also help to avoid spill over in animals and humans in the area surveyed.Thesis (PhD)--University of Pretoria, 2020.Centres for Disease Control and Prevention National Research FoundationMedical VirologyPhDUnrestricte

Mosquito community composition and abundance at contrasting sites in northern South Africa, 2014–2017

Most data on species associations and vector potential of mosquitoes in relation to arboviral infections in South Africa date back from the 1940s to late 1990s. Contextual information crucial for disease risk management and control, such as the sampling effort, diversity, abundance, and distribution of mosquitoes in large parts of South Africa still remains limited. Adult mosquitoes were collected routinely from two horse farms in Gauteng Province; two wildlife reserves in Limpopo Province, at Orpen Gate in Kruger National Park (KNP) and Mnisi Area in Mpumalanga Province between 2014–2017, using carbon dioxide‐baited light and tent traps. Mosquito diversity and richness are greater in untransformed natural and mixed rural settings. In untransformed wilderness areas, the most dominant species were Culex poicilipes , Anopheles coustani, and Aedes mcintoshi, while in mixed rural settings such as the Mnisi area, the two most abundant species were Cx. poicilipes and Mansonia uniformis . However, in peri‐urban areas, Cx. theileri , Cx. univittatus, and Cx. pipiens sensu lato were the most dominant. Aedes aegypti, Ae. mcintoshi , Ae. metallicus , Ae. vittatus , Cx. pipiens s.l., Cx. theileri, and Cx. univittatus had the widest geographical distribution in northern South Africa. Also collected were Anopheles arabiensis and An. vaneedeni , both known malaria vectors in South Africa. Arbovirus surveillance and vector control programs should be augmented in mixed rural and peri‐urban areas where the risk for mosquito‐borne disease transmission to humans and domestic stock is greater.Centers for Disease Control and Prevention (CDC). Grant Number: 5 NU2GGH001874-02-00https://onlinelibrary.wiley.com/journal/194871342021-06-01hj2020Medical VirologyUP Centre for Sustainable Malaria Control (UP CSMC

Human practices promote presence and abundance of disease-transmitting mosquito species

Humans alter the environment at unprecedented rates through habitat destruction, nutrient pollution and the application of agrochemicals. This has recently been proposed to act as a potentially significant driver of pathogen-carrying mosquito species (disease vectors) that pose a health risk to humans and livestock. Here, we use a unique set of locations along a large geographical gradient to show that landscapes disturbed by a variety of anthropogenic stressors are consistently associated with vector-dominated mosquito communities for a wide range of human and livestock infections. This strongly suggests that human alterations to the environment promote the presence and abundance of disease vectors across large spatial extents. As such, it warrants further studies aimed at unravelling mechanisms underlying vector prevalence in mosquito communities, and opens up new opportunities for preventative action and predictive modelling of vector borne disease risks in relation to degradation of natural ecosystems

Alphaviruses detected in mosquitoes in the North-Eastern regions of South Africa, 2014 to 2018

The prevalence and distribution of African alphaviruses such as chikungunya have increased in recent years. Therefore, a better understanding of the local distribution of alphaviruses in vectors across the African continent is important. Here, entomological surveillance was performed from 2014 to 2018 at selected sites in north-eastern parts of South Africa where alphaviruses have been identified during outbreaks in humans and animals in the past. Mosquitoes were collected using a net, CDC-light, and BG-traps. An alphavirus genus-specific nested RT-PCR was used for screening, and positive pools were confirmed by sequencing and phylogenetic analysis. We collected 64,603 mosquitoes from 11 genera, of which 39,035 females were tested. Overall, 1462 mosquito pools were tested, of which 21 were positive for alphaviruses. Sindbis (61.9%, N = 13) and Middelburg (28.6%, N = 6) viruses were the most prevalent. Ndumu virus was detected in two pools (9.5%, N = 2). No chikungunya positive pools were identified. Arboviral activity was concentrated in peri-urban, rural, and conservation areas. A range of Culicidae species, including Culex univittatus, Cx. pipiens s.l., Aedes durbanensis, and the Ae. dentatus group, were identified as potential vectors. These findings confirm the active circulation and distribution of alphaviruses in regions where human or animal infections were identified in South Africa