Cheikh T. Diagne

Zika Virus Emergence in Mosquitoes in Southeastern Senegal, 2011

Background Zika virus (ZIKV; genus Flavivirus, family Flaviviridae) is maintained in a zoonotic cycle between arboreal Aedes spp. mosquitoes and nonhuman primates in African and Asian forests. Spillover into humans has been documented in both regions and the virus is currently responsible for a large outbreak in French Polynesia. ZIKV amplifications are frequent in southeastern Senegal but little is known about their seasonal and spatial dynamics. The aim of this paper is to describe the spatio-temporal patterns of the 2011 ZIKV amplification in southeastern Senegal. Methodology/Findings Mosquitoes were collected monthly from April to December 2011 except during July. Each evening from 18∶00 to 21∶00 hrs landing collections were performed by teams of 3 persons working simultaneously in forest (canopy and ground), savannah, agriculture, village (indoor and outdoor) and barren land cover sites. Mosquitoes were tested for virus infection by virus isolation and RT-PCR. ZIKV was detected in 31 of the 1,700 mosquito pools (11,247 mosquitoes) tested: Ae. furcifer (5), Ae. luteocephalus (5), Ae. africanus (5), Ae. vittatus (3), Ae. taylori, Ae. dalzieli, Ae. hirsutus and Ae. metallicus (2 each) and Ae. aegypti, Ae. unilinaetus, Ma. uniformis, Cx. perfuscus and An. coustani (1 pool each) collected in June (3), September (10), October (11), November (6) and December (1). ZIKV was detected from mosquitoes collected in all land cover classes except indoor locations within villages. The virus was detected in only one of the ten villages investigated. Conclusions/Significance This ZIKV amplification was widespread in the Kédougou area, involved several mosquito species as probable vectors, and encompassed all investigated land cover classes except indoor locations within villages. Aedes furcifer males and Aedes vittatus were found infected within a village, thus these species are probably involved in the transmission of Zika virus to humans in this environment.

Landscape Ecology of Sylvatic Chikungunya Virus and Mosquito Vectors in Southeastern Senegal

The risk of human infection with sylvatic chikungunya (CHIKV) virus was assessed in a focus of sylvatic arbovirus circulation in Senegal by investigating distribution and abundance of anthropophilic Aedes mosquitoes, as well as the abundance and distribution of CHIKV in these mosquitoes. A 1650 km2 area was classified into five land cover classes: forest, barren, savanna, agriculture and village. A total of 39,799 mosquitoes was sampled from all classes using human landing collections between June 2009 and January 2010. Mosquito diversity was extremely high, and overall vector abundance peaked at the start of the rainy season. CHIKV was detected in 42 mosquito pools. Our data suggest that Aedes furcifer, which occurred abundantly in all land cover classes and landed frequently on humans in villages outside of houses, is probably the major bridge vector responsible for the spillover of sylvatic CHIKV to humans.

Bloodfeeding patterns of sylvatic arbovirus vectors in southeastern Senegal

BACKGROUND Dengue (DENV), yellow fever (YFV) and chikungunya (CHIKV) viruses circulate in sylvatic, enzootic transmission cycles in southeastern Senegal, but understanding of the vector-host interactions involved is limited. METHODS The vertebrate hosts of several potential mosquito vectors of the three viruses were identified by PCR amplification and sequencing portions of the cytochrome b gene from bloodmeals of mosquitoes collected in Kedougou, Senegal, June 2010-January 2011. RESULTS We identified the sources of 65 bloodmeals of 82 engorged mosquitoes. Aedes taylori was the only species that fed on monkeys (Chlorocebus sabaeus and Papio papio). The majority of the avian-derived bloodmeals were from the Western Plantain-eater (Crinifer piscator). CONCLUSION These findings corroborate the importance of Ae. taylori and African monkeys in the sylvatic cycles of YFV, DENV and CHIKV and suggest the possible involvement of other vertebrates.

Vector Competence of Aedes aegypti and Aedes vittatus (Diptera: Culicidae) from Senegal and Cape Verde Archipelago for West African Lineages of Chikungunya Virus

To assess the risk of emergence of chikungunya virus (CHIKV) in West Africa, vector competence of wild-type, urban, and non-urban Aedes aegypti and Ae. vittatus from Senegal and Cape Verde for CHIKV was investigated. Mosquitoes were fed orally with CHIKV isolates from mosquitoes (ArD30237), bats (CS13-288), and humans (HD180738). After 5, 10, and 15 days of incubation following an infectious blood meal, presence of CHIKV RNA was determined in bodies, legs/wings, and saliva using real-time reverse transcription-polymerase chain reaction. Aedes vittatus showed high susceptibility (50-100%) and early dissemination and transmission of all CHIKV strains tested. Aedes aegypti exhibited infection rates ranging from 0% to 50%. Aedes aegypti from Cape Verde and Kedougou, but not those from Dakar, showed the potential to transmit CHIKV in saliva. Analysis of biology and competence showed relatively high infective survival rates for Ae. vittatus and Ae. aegypti from Cape Verde, suggesting their efficient vector capacity in West Africa.

Insecticide susceptibility of Aedes aegypti populations from Senegal and Cape Verde Archipelago

BackgroundTwo concomitant dengue 3 (DEN-3) epidemics occurred in Cape Verde Archipelago and Senegal between September and October 2009. Aedes aegypti was identified as the vector of these epidemics as several DEN-3 virus strains were isolated from this species in both countries. The susceptibility to pyrethroids, organochlorine, organophosphates and carbamate was investigated in two field strains of Aedes aegypti from both countries using WHO diagnostic bioassay kits in order to monitor their the current status of insecticide susceptibility.FindingsThe two tested strains were highly resistant to DDT. The Cape Verde strain was found to be susceptible to all others tested insecticides except for propoxur 0.1%, which needs further investigation. The Dakar strain was susceptible to fenitrothion 1% and permethrin 0.75%, but displayed reduced susceptibility to deltamethrin, lambda-cyhalothrin and propoxur.ConclusionsAs base-line results, our observations stress a careful management of insecticide use for the control of Ae. aegypti. Indeed, they indicate that DDT is no longer efficient for the control of Ae. aegypti populations in Cape Verde and Dakar and further suggest a thorough follow-up of propoxur susceptibility status in both sites and that of deltamethrin and lambda-cyhalothrin in Ae. aegypti populations in Dakar. Thus, regular monitoring of susceptibility is greatly needed as well as the knowing if this observed resistance/susceptibility is focal or not and for observed resistance, the use of biochemical methods is needed with detailed comparison of resistance levels over a large geographic area.KeywordsAedes aegypti, Insecticides, Susceptibility, Cape Verde, Senegal

Larval ecology of mosquitoes in sylvatic arbovirus foci in southeastern Senegal.

BackgroundAlthough adult mosquito vectors of sylvatic arbovirus [yellow fever (YFV), dengue-2 (DENV-2) and chikungunya (CHIKV)] have been studied for the past 40 years in southeastern Senegal, data are still lacking on the ecology of larval mosquitoes in this area. In this study, we investigated the larval habitats of mosquitoes and characterized their seasonal and spatial dynamics in arbovirus foci.MethodsWe searched for wet microhabitats, classified in 9 categories, in five land cover classes (agriculture, forest, savannah, barren and village) from June, 2010 to January, 2011. Mosquito immatures were sampled monthly in up to 30 microhabitats of each category per land cover and bred until adult stage for determination.ResultsNo wet microhabitats were found in the agricultural sites; in the remaining land covers immature stages of 35 mosquito species in 7 genera were sampled from 9 microhabitats (tree holes, fresh fruit husks, decaying fruit husks, puddles, bamboo holes, discarded containers, tires, rock holes and storage containers). The most abundant species was Aedes aegypti formosus, representing 30.2% of the collections, followed by 12 species, representing each more than 1% of the total, among them the arbovirus vectors Ae. vittatus (7.9%), Ae. luteocephalus (5.7%), Ae. taylori (5.0%), and Ae. furcifer (1.3%). Aedes aegypti, Cx. nebulosus, Cx. perfuscus, Cx. tritaeniorhynchus, Er. chrysogster and Ae. vittatus were the only common species collected from all land covers. Aedes furcifer and Ae. taylori were collected in fresh fruit husks and tree holes. Species richness and dominance varied significantly in land covers and microhabitats. Positive associations were found mainly between Ae. furcifer, Ae. taylori and Ae. luteocephalus. A high proportion of potential enzootic vectors that are not anthropophilic were found in the larval mosquito fauna.ConclusionsIn southeastern Senegal, Ae. furcifer and Ae. taylori larvae showed a more limited distribution among both land cover and microhabitat types than the other common species. Uniquely among vector species, Ae. aegypti formosus larvae occurred at the highest frequency in villages. Finally, a high proportion of the potential non-anthropophilic vectors were represented in the larval mosquito fauna, suggesting the existence of unidentified sylvatic arbovirus cycles in southeastern Senegal.

Patterns of a Sylvatic Yellow Fever Virus Amplification in Southeastern Senegal, 2010

During the wet season of 2010, yellow fever virus (YFV) was detected in field-collected mosquitoes in the Kédougou region in southeastern Senegal. During this outbreak, we studied the association of the abundance of YFV-infected mosquitoes and land cover features to try and understand the dynamics of YFV transmission within the region. In total, 41,234 mosquito females were collected and tested for virus infection in 5,152 pools. YFV was detected in 67 pools; species including Aedes furcifer (52.2% of the infected pools), Ae. luteocephalus (31.3% of the infected pools), Ae. taylori (6.0% of the infected pools) and six other species (10.4% of the infected pools) captured in September (13.4%), October (70.1%), and November (16.4%). Spatially, YFV was detected from mosquitoes collected in all land cover classes but mainly, forest canopies (49.2%). Human infection is likely mediated by Ae. furcifer, the only species found infected with YFV within villages. Villages containing YFV-infected mosquitoes were significantly closer to large forests (> 2 ha) than villages in which no infected mosquitoes were detected.

Oral susceptibility of Aedes aegypti (Diptera: Culicidae) from Senegal for dengue serotypes 1 and 3 viruses

To investigate the potential for domestic and wild populations of Aedes aegypti from Dakar and Kedougou to develop a disseminated infection after exposure to DENV‐3 and DENV‐1.

Internally Controlled, Multiplex Real-Time Reverse Transcription PCR for Dengue Virus and Yellow Fever Virus Detection

The differential diagnosis of dengue virus (DENV) and yellow fever virus (YFV) infections in endemic areas is complicated by nonspecific early clinical manifestations. In this study, we describe an internally controlled, multiplex real-time reverse transcription polymerase chain reaction (rRT-PCR) for the detection of DENV and YFV. The DENV-YFV assay demonstrated specific detection and had a dynamic range of 2.0-8.0 log10 copies/μL of eluate for each DENV serotype and YFV. Clinical performance was similar to a published pan-DENV assay: 48/48 acute-phase samples from dengue cases were detected in both assays. For YFV detection, mock samples were prepared with nine geographically diverse YFV isolates over a range of concentrations. The DENV-YFV assay detected 62/65 replicates, whereas 54/65 were detected using a reference YFV rRT-PCR. Given the reemergence of DENV and YFV in areas around the world, the DENV-YFV assay should be a useful tool to narrow the differential diagnosis and provide early case detection.

Chikungunya Outbreak in Kedougou, Southeastern Senegal in 2009–2010

Abstract Background In Senegal, Chikungunya virus (CHIKV), which is an emerging mosquito-borne alphavirus, circulates in a sylvatic and urban/domestic cycle and has caused sporadic human cases and epidemics since 1960s. However, the real impact of the CHIKV sylvatic cycle in humans and mechanisms underlying its emergence still remains unknown. Methodology One thousand four hundred nine suspect cases of CHIKV infection, recruited from 5 health facilities located in Kedougou region, south-eastern Senegal, between May 2009 to March 2010, together with 866 serum samples collected from schoolchildren from 4 elementary schools in May and November 2009 from Kedougou were screened for anti-CHIKV immunoglobulin (Ig)M antibodies and, when appropriate, for viral nucleic acid by real-time polymerase chain reaction (rPCR) and virus isolation. In addition, mosquitoes collected in the same area from May 2009 to January 2010 were tested for CHIKV by rPCR and by virus isolation, and 116 monkeys sera collected from March 2010 to May 2010 were tested for anti-CHIKV IgM and neutralizing antibodies. Results The main clinical manifestations of the CHIKV suspect cases were headache, myalgia, and arthralgia. Evidence for CHIKV infection was observed in 1.4% (20 of 1409) of patients among suspect cases. No significant difference was observed among age or sex groups. In addition, 25 (2.9%) students had evidence of CHIKV infection in November 2009. Chikungunya virus was detected in 42 pools of mosquitoes, mainly from Aedes furcifer, and 83% of monkeys sampled were seropositive. Conclusions Our findings further documented that CHIKV is maintained in a sylvatic transmission cycle among monkeys and Aedes mosquitoes in Kedougou, and humans become infected by exposure to the virus in the forest.