Patterns of a sylvatic yellow fever virus amplification in southeastern Senegal, 2010

A historical perspective on arboviruses of public health interest in Southern Africa

Arboviruses are an existing and expanding threat globally, with the potential for causing devastating health and socioeconomic impacts. Mitigating this threat necessitates a One Health approach that integrates vector surveillance, rapid disease detection, and innovative prevention and control measures. In Southern Africa, limited data on the epidemiology of arboviruses, their vectors, and their hosts prevent an effective response. We reviewed the current knowledge on arboviruses in Southern Africa and identified opportunities for further research. A literature search was conducted to identify studies published on arboviruses in 10 tropical and temperate countries of the Southern African Development Community (SADC) from 1900 onward. We identified 280 studies, half (51.1%) originating from South Africa, that described 31 arboviral species, their vectors, and their clinical effects on hosts reported in the region. Arboviral research flourished in the SADC in the mid-20th century but then declined, before reemerging in the last two decades. Recent research consists largely of case reports describing outbreaks. Historical vector surveillance and serosurveys from the mid-20th century suggest that arboviruses are plentiful across Southern Africa, but large gaps remain in the current understanding of arboviral distribution, transmission dynamics, and public health impact.

Co-circulation of Chikungunya virus, Zika virus, and serotype 1 of Dengue virus in Western Bahia, Brazil

Chikungunya, mayaro, dengue, zika, and yellow fever are mosquito-borne viral diseases caused, respectively, by Chikungunya virus, Mayaro virus (CHIKV and MAYV, respectively: Togaviridae: Alphavirus), Dengue virus, Zika virus, and Yellow fever virus (DENV, ZIKV, and YFV, respectively: Flaviviridae: Flavivirus). These viruses have an important epidemiological impact worldwide, especially in Brazil. Western Bahia is one of the less studied regions in that country regarding the circulation of these pathogens. In this study, we aimed to apply molecular biology assays to better know the mosquito-borne viruses circulating in Barreiras and Luís Eduardo Magalhães, two main cities of Western Bahia. From March to June 2021, we enrolled 98 patients with the clinical diagnosis of dengue. Personal information (gender and age) were retrieved at the moment of enrollment. Serum samples were obtained from volunteers and used in molecular detection of CHIKV, MAYV, DENV, ZIKV, and YFV by reverse transcription followed by real-time polymerase chain reaction as well as in genome sequencing aiming phylogenetic analysis. As the main result, we found that from the 98 patients 45 were infected by CHIKV, 32 were infected by serotype 1 of DENV (DENV-1) and six were infected by ZIKV, while 15 were negative for all arboviruses tested. In addition, phylogenetic analysis revealed that all CHIKV-positive samples were of the East/Central/South African (ECSA) genotype, while all DENV-1-positive samples were of the V genotype. These results clearly show that epidemiological surveillance cannot be based only on clinical evaluations. Laboratory diagnosis is important in arbovirus infection that are prevalent in a particular area. These findings also demonstrate the co-circulation of many arboviruses in Western Bahia in 2021.

Epidemiology of yellow fever virus in humans, arthropods, and non-human primates in sub-Saharan Africa: A systematic review and meta-analysis

Yellow fever (YF) has re-emerged in the last two decades causing several outbreaks in endemic countries and spreading to new receptive regions. This changing epidemiology of YF creates new challenges for global public health efforts. Yellow fever is caused by the yellow fever virus (YFV) that circulates between humans, the mosquito vector, and non-human primates (NHP). In this systematic review and meta-analysis, we review and analyse data on the case fatality rate (CFR) and prevalence of YFV in humans, and on the prevalence of YFV in arthropods, and NHP in sub-Saharan Africa (SSA). We performed a comprehensive literature search in PubMed, Web of Science, African Journal Online, and African Index Medicus databases. We included studies reporting data on the CFR and/or prevalence of YFV. Extracted data was verified and analysed using the random effect meta-analysis. We conducted subgroup, sensitivity analysis, and publication bias analyses using the random effect meta-analysis while I2 statistic was employed to determine heterogeneity. This review was registered with PROSPERO under the identification CRD42021242444. The final meta-analysis included 55 studies. The overall case fatality rate due to YFV was 31.1% (18.3–45.4) in humans and pooled prevalence of YFV infection was 9.4% (6.9–12.2) in humans. Only five studies in West and East Africa detected the YFV in mosquito species of the genus Aedes and in Anopheles funestus. In NHP, YFV antibodies were found only in members of the Cercopithecidae family. Our analysis provides evidence on the ongoing circulation of the YFV in humans, Aedes mosquitoes and NHP in SSA. These observations highlight the ongoing transmission of the YFV and its potential to cause large outbreaks in SSA. As such, strategies such as those proposed by the WHO’s Eliminate Yellow Fever Epidemics (EYE) initiative are urgently needed to control and prevent yellow fever outbreaks in SSA.

Spatiotemporal distribution and insecticide resistance status of Aedes aegypti in Ghana

Background

Vector control is the main intervention used to control arboviral diseases transmitted by Aedes mosquitoes because there are no effective vaccines or treatments for most of them. Control of Aedes mosquitoes relies heavily on the use of insecticides, the effectiveness of which may be impacted by resistance. In addition, rational insecticide application requires detailed knowledge of vector distribution, dynamics, resting, and feeding behaviours, which are poorly understood for Aedes mosquitoes in Africa. This study investigated the spatiotemporal distribution and insecticide resistance status of Aedes aegypti across ecological extremes of Ghana.

Methods

Immature mosquitoes were sampled from containers in and around human dwellings at seven study sites in urban, suburban, and rural areas of Ghana. Adult Aedes mosquitoes were sampled indoors and outdoors using Biogents BG-Sentinel 2 mosquito traps, human landing catches, and Prokopack aspiration. Distributions of immature and adult Aedes mosquitoes were determined indoors and outdoors during dry and rainy seasons at all sites. The phenotypic resistance status of Aedes mosquitoes to insecticides was determined using World Health Organization susceptibility bioassays. The host blood meal source was determined by polymerase chain reaction.

Results

A total of 16,711 immature Aedes were sampled, with over 70% found in car tyres. Significantly more breeding containers had Aedes immatures during the rainy season (11,856; 70.95%) compared to the dry season (4855; 29.05%). A total of 1895 adult Aedes mosquitos were collected, including Aedes aegypti (97.8%), Aedes africanus (2.1%) and Aedesluteocephalus (0.1%). Indoor sampling of adult Aedes yielded a total of 381 (20.1%) and outdoor sampling a total of 1514 (79.9%) mosquitoes (z = − 5.427, P = 0.0000) over the entire sampling period. Aedes aegypti populations were resistant to dichlorodiphenyltrichloroethane at all study sites. Vectors showed suspected resistance to bendiocarb (96–97%), permethrin (90–96%) and deltamethrin (91–96%), and were susceptible to the organophosphate for all study sites. Blood meal analysis showed that the Aedes mosquitoes were mostly anthropophilic, with a human blood index of 0.9 (i.e. humans, 90%; human and dog, 5%; dog and cow, 5%).

Conclusions

Aedes mosquitoes were found at high densities in all ecological zones of Ghana. Resistance of Aedes spp. to pyrethroids and carbamates may limit the efficacy of vector control programmes and thus requires careful monitoring.

Graphical abstract

Evidence against Zika virus infection of pets and peri-domestic animals in Latin America and Africa

Decades after its discovery in East Africa, Zika virus (ZIKV) emerged in Brazil in 2013 and infected millions of people during intense urban transmission. Whether vertebrates other than humans are involved in ZIKV transmission cycles remained unclear. Here, we investigate the role of different animals as ZIKV reservoirs by testing 1723 sera of pets, peri-domestic animals and African non-human primates (NHP) sampled during 2013–2018 in Brazil and 2006–2016 in Côte d'Ivoire. Exhaustive neutralization testing substantiated co-circulation of multiple flaviviruses and failed to confirm ZIKV infection in pets or peri-domestic animals in Côte d'Ivoire (n=259) and Brazil (n=1416). In contrast, ZIKV seroprevalence was 22.2% (2/9, 95% CI, 2.8–60.1) in West African chimpanzees (Pan troglodytes verus) and 11.1% (1/9, 95% CI, 0.3–48.3) in king colobus (Colobus polycomos). Our results indicate that while NHP may represent ZIKV reservoirs in Africa, pets or peri-domestic animals likely do not play a role in ZIKV transmission cycles.

Yellow Fever Outbreak in Eastern Senegal, 2020-2021

Yellow fever virus remains a major threat in low resource countries in South America and Africa despite the existence of an effective vaccine. In Senegal and particularly in the eastern part of the country, periodic sylvatic circulation has been demonstrated with varying degrees of impact on populations in perpetual renewal. We report an outbreak that occurred from October 2020 to February 2021 in eastern Senegal, notified and managed through the synergistic effort yellow fever national surveillance implemented by the Senegalese Ministry of Health in collaboration with the World Health Organization, the countrywide 4S network set up by the Ministry of Health, the Institut Pasteur de Dakar, and the surveillance of arboviruses and hemorrhagic fever viruses in human and vector populations implemented since mid 2020 in eastern Senegal. Virological analyses highlighted the implication of sylvatic mosquito species in virus transmission. Genomic analysis showed a close relationship between the circulating strain in eastern Senegal, 2020, and another one from the West African lineage previously detected and sequenced two years ago from an unvaccinated Dutch traveler who visited the Gambia and Senegal before developing signs after returning to Europe. Moreover, genome analysis identified a 6-nucleotide deletion in the variable domain of the 3′UTR with potential impact on the biology of the viral strain that merits further investigations. Integrated surveillance of yellow fever virus but also of other arboviruses of public health interest is crucial in an ecosystem such as eastern Senegal.

Zika virus exposure affects neuron-glia communication in the hippocampal slices of adult rats

Zika virus (ZIKV) infection during pregnancy was associated with microcephaly in neonates, but clinical and experimental evidence indicate that ZIKV also causes neurological complications in adults. However, the changes in neuron-glial communication, which is essential for brain homeostasis, are still unknown. Here, we report that hippocampal slices from adult rats exposed acutely to ZIKV showed significant cellular alterations regarding to redox homeostasis, inflammatory process, neurotrophic functions and molecular signalling pathways associated with neurons and glial cells. Our findings support the hypothesis that ZIKV is highly neurotropic and its infection readily induces an inflammatory response, characterized by an increased expression and/or release of pro-inflammatory cytokines. We also observed changes in neural parameters, such as adenosine receptor A2a expression, as well as in the release of brain-derived neurotrophic factor and neuron-specific enolase, indicating plasticity synaptic impairment/neuronal damage. In addition, ZIKV induced a glial commitment, with alterations in specific and functional parameters such as aquaporin 4 expression, S100B secretion and glutathione synthesis. ZIKV also induced p21 senescence-associated gene expression, indicating that ZIKV may induce early senescence. Taken together, our results indicate that ZIKV-induced neuroinflammation, involving nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor κB (NFκB) pathways, affects important aspects of neuron-glia communication. Therefore, although ZIKV infection is transient, long-term consequences might be associated with neurological and/or neurodegenerative diseases.

Morphology and taxonomic status of Aedes aegypti populations across Senegal

Aedes aegypti is the primary vector of dengue, Zika, yellow fever and chikungunya viruses to humans. In Africa, two subspecies, Ae. aegypti aegypti (Aaa) and Ae. aegypti formosus (Aaf) have been described. Until very recently, it was considered that the two forms were sympatric in East Africa and that only Aaf was present in Central and West Africa. However, recent data suggests that Aaa was also common in Senegal without any clear evidence of genetic differences with Aaf. This study was carried out in different Ae. aegypti populations from Senegal to better clarify their taxonomic status. The larvae, pupae and eggs were collected between July and September 2018 and reared individually to adult stage. For each population, F1 progeny from eggs laid by a single female F0 were reared as sibling samples. The number of pale scales on the first abdominal tergite (T1) and the basal part of the second tergite (T2) were counted. Individuals with no pale scale on T1 were classified as Aaf while those with at least one pale scale on this tergite were classified as Aaa. The morphological variations within families of Aaf were studied across 4 generations. In total, 2400 individuals constituting 240 families were identified, of which 42.5% were heterogeneous (families with both forms). Multivariate statistical analysis of variance including T1 and T2 data together showed that populations were significantly different from each other. Statistical analysis of T1 alone showed a similarity between populations from the southeast while variations were observed within northwest population. The analysis of family composition across generations showed the presence of Aaa and Aaf forms in each generation. The classification of Ae. aegypti into two subspecies is invalid in Senegal. Populations exhibit morphological polymorphism at the intra-family level that could have biological and epidemiological impacts.

Community-based sero-prevalence of chikungunya and yellow fever in the South Omo Valley of Southern Ethiopia

Background

Chikungunya (CHIK) and yellow fever (YF) are becoming major public health threats in East African countries including Ethiopia. In Ethiopia, there is no reliable information about the epidemiology of CHIK. This study aimed to assess a community-based sero-prevalence of CHIK and YF in the South Omo Valley, an endemic area for YF.

Methods

Between February and June 2018, blood samples were collected from study participants and screened for IgG antibody against CHIK virus (CHIKV) and YF virus (YFV) infections using ELISA. Data were computerized using Epi Data Software v.3.1 and analyzed using SPSS.

Results

A total of 360 participants (51.7% males, age range from 6 to 80, mean age ± SD = 31.95 ± 14.05 years) participated in this study. The overall sero-prevalence of IgG antibody was 43.6% (157/360) against CHIKV, while it was 49.5% (155/313) against YFV. Out of 155 samples which were positive for IgG antibody to YFV, 93 (60.0%) were positive for IgG antibody to CHIKV. Out of 158 samples which were negative for IgG antibody to YFV, 64(40.5%) were positive for IgG antibody to CHIKV. There was a significant positive correlation between IgG antibodies to CHIKV and YFV (sr = 0.82; P<0.01). Residency in the Debub Ari district (AOR = 8.47; 95% CI: 1.50, 47.74) and travel history to sylvatic areas (AOR = 2.21; 95% CI: 1.02, 4.81) were significantly and positively associated with high sero-prevalence of IgG antibody to CHIKV and YFV, respectively.

Conclusion

High sero-prevalence of IgG antibody to CHIKV shows the circulation of the virus in the present study area. A low sero-prevalence of IgG antibody to YFV in YF vaccine received individuals is highly concerning from a public health point of view as waning of immune response to YFV infection could result in a periodic outbreaks of YF in endemic areas.Nevertheless, the present study has not investigated for possible cross-reactivity of antibody to CHIKV with other alphaviruses like O’nyong-nyong virus and antibody to YFV with other flaviviruses like Dengue fever virus and this warrants further studies in the present study area.

Mosquito-borne viral diseases including yellow fever and chikungunya are becoming major public health problem in Africa. Community-based sero-epidemiological studies of mosquito-borne viral infections are important to known the occurrence of these diseases and to design appropriate prevention and control strategies. In this study, we assessed the sero-prevalence of IgG antibody against Chikungunya virus and Yellow fever virus in 360 study participants and associated risk factors among the community members of South Omo, Southern Ethiopia. Our study showed a sero-prevalence of IgG antibody; 43.6%, (157 out of 360) to Chikungunya virus, and 49.5% (155 out of 313) against Yellow fever virus in the study participants.Further studies on active case detection of chikungunya and raising awareness, advocating policies to mitigate the risk of arboviral infections have paramount importance in the present study area.

Concurrent amplification of Zika, chikungunya, and yellow fever virus in a sylvatic focus of arboviruses in Southeastern Senegal, 2015

Background

Chikungunya (CHIKV), yellow fever (YFV) and Zika (ZIKV) viruses circulate in sylvatic transmission cycles in southeastern Senegal, where they share common hosts and vectors. All three viruses undergo periodic amplifications, during which they are detected in mosquitoes and sometimes in hosts. However, little is known about their spatio-temporal patterns in years in which they undergo concurrent amplification. The aim of this study was to describe the co-amplification of ZIKV, CHIKV, and YFV, and the daily dynamics of these arboviruses and theirs vectors within villages in southeastern Senegal.

Results

Mosquitoes were collected monthly from July to December 2015. Each evening, from 6 to 9 PM, landing collections were performed by teams of 3 persons working simultaneously in 70 sites situated in forest (canopy and ground), savannah, agriculture, barren, and village (indoor and outdoor) land covers. Collections within villages were continued until 6 AM. Mosquitoes were tested for virus infection by virus isolation and RT-PCR. Seventy-five mosquito pools comprising 10 mosquito species contained at least one virus. Ae. furcifer and Ae. luteocephalus were infected by all three viruses, Ae. taylori by YFV and ZIKV, and remaining seven species by only, only YFV or only ZIKV. No single mosquito pool contained more than one virus. CHIKV was the only virus detected in all land cover classes and was found in the greatest number of sampling sites (32.9%, n = 70). The proportion of sites in which more than one virus was detected was less than 6%. Ae. aegypti formosus, Ae. furcifer, Ae. luteocephalus, Ae. minutus, Ae. vittatus, and An. gambiae were found within villages. These vectors were mainly active around dusk but Ae. furcifer was collected until dawn. All viruses save ZIKV were detected indoors and outdoors, mainly around dusk. Virus positive pools were detected over 2, 3 and 4 months for YFV, CHIKV and ZIKV, respectively.

Conclusion

Our data indicate that the distribution of different vector species and different arboviruses vary substantially between sites, suggesting that CHIKV, YFV, and ZIKV may have different transmission cycles in Southeastern Senegal.

Dianke virus: A new mesonivirus species isolated from mosquitoes in Eastern Senegal

An increasing number of insect-specific viruses are found around the world. Very recently, a new group of insect-specific viruses, the Mesoniviridae family, was discovered in Africa, Asia, North America and Australia. Here we report the first detection and isolation of a new virus belonging to Mesonivirus genus in Senegal, West Africa. The so-called Dianke virus was detected in 21 species of arthropods trapped in the eastern part of the country. Male individuals were also infected, supporting vertical transmission assertion of insect specific viruses. As described for other mesoniviruses, no viral replication was observed after inoculation of mammalian cells. Viral replication in mosquito cells was blocked at a temperature of 37 °C, highlighting the importance of thermal conditions in Mesonivirus host restriction. Similar to our study, where a diverse range of arthropod vectors were found infected by the new virus, several studies have detected mesonivirus infection in mosquitoes with concerns for human health. It has been shown that dual infections in mosquito can alter viral infectivity. Due to their extensive geographic distribution and host range, as well as their use as potential disease control agents in vector populations, more studies should be done for a better knowledge of arthropod-restricted viruses prevalence and diversity.

Origin of the São Paulo Yellow Fever epidemic of 2017-2018 revealed through molecular epidemiological analysis of fatal cases

The largest outbreak of yellow fever of the 21^st century in the Americas began in 2016, with intense circulation in the southeastern states of Brazil, particularly in sylvatic environments near densely populated areas including the metropolitan region of São Paulo city (MRSP) during 2017–2018. Herein, we describe the origin and molecular epidemiology of yellow fever virus (YFV) during this outbreak inferred from 36 full genome sequences taken from individuals who died following infection with zoonotic YFV. Our analysis revealed that these deaths were due to three genetic variants of sylvatic YFV that belong the South American I genotype and that were related to viruses previously isolated in 2017 from other locations in Brazil (Minas Gerais, Espírito Santo, Bahia and Rio de Janeiro states). Each variant represented an independent virus introduction into the MRSP. Phylogeographic and geopositioning analyses suggested that the virus moved around the peri-urban area without detectable human-to-human transmission, and towards the Atlantic rain forest causing human spill-over in nearby cities, yet in the absence of sustained viral transmission in the urban environment.

Ultrasound-guided minimally invasive autopsy as a tool for rapid post-mortem diagnosis in the 2018 Sao Paulo yellow fever epidemic: Correlation with conventional autopsy

Background

New strategies for collecting post-mortem tissue are necessary, particularly in areas with emerging infections. Minimally invasive autopsy (MIA) has been proposed as an alternative to conventional autopsy (CA), with promising results. Previous studies using MIA addressed the cause of death in adults and children in developing countries. However, none of these studies was conducted in areas with an undergoing infectious disease epidemic. We have recently experienced an epidemic of yellow fever (YF) in Brazil. Aiming to provide new information on low-cost post-mortem techniques that could be applied in regions at risk for infectious outbreaks, we tested the efficacy of ultrasound-guided MIA (MIA-US) in the diagnosis of patients who died during the epidemic.

Methodology/principal findings

In this observational study, we performed MIA-US in 20 patients with suspected or confirmed YF and compared the results with those obtained in subsequent CAs. Ultrasound-guided biopsies were used for tissue sampling of liver, kidneys, lungs, spleen, and heart. Liver samples from MIA-US and CA were submitted for RT-PCR and immunohistochemistry for detection of YF virus antigen. Of the 20 patients, 17 had YF diagnosis confirmed after autopsy by histopathological and molecular analysis. There was 100% agreement between MIA-US and CA in determining the cause of death (panlobular hepatitis with hepatic failure) and main disease (yellow fever). Further, MIA-US obtained samples with good quality for molecular studies and for the assessment of the systemic involvement of the disease. Main extrahepatic findings were pulmonary hemorrhage, pneumonia, acute tubular necrosis, and glomerulonephritis. One patient was a 24-year-old, 27-week pregnant woman; MIA-US assessed the placenta and provided adequate placental tissue for analysis.

Conclusions

MIA-US is a reliable tool for rapid post-mortem diagnosis of yellow fever and can be used as an alternative to conventional autopsy in regions at risk for hemorrhagic fever outbreaks with limited resources to perform complete diagnostic autopsy.

Reliable mortality information is of paramount importance to establish sound public health policies. Autopsy is an important tool not only for determining the cause of death, but also for the detection of novel diseases. In the last decades, we have been globally identifying an unprecedented number of emerging infections. Therefore, there is great interest in the development of less invasive and low-cost tools for the accurate post-mortem diagnosis in fatal cases. Minimally invasive autopsy (MIA), conceived as targeting diagnostic biopsies of key organs by needle puncture, has been proposed as an alternative to conventional autopsy (CA) for the determination of cause of death in developing countries. In this research, we tested the efficacy of MIA in the post-mortem diagnosis of 20 patients with suspected or confirmed yellow fever who died during the recent epidemic of yellow fever that occurred in Brazil. There was a perfect agreement between MIA and CA in determining the cause of death (hepatic failure) and main disease (yellow fever) in all patients with confirmed yellow fever. This finding indicates that MIA can be used as an alternative to CA in regions at risk for infectious disease outbreaks with limited resources to perform conventional autopsies.

Biodiversity Pattern of Mosquitoes in Southeastern Senegal, Epidemiological Implication in Arbovirus and Malaria Transmission

The composition, density, diversity, and temporal distribution of mosquito species and the influence of temperature, relative humidity, and rainfall on these data were investigated in 50 sites across five land cover classes (forest, savannah, barren, village, and agriculture) in southeastern Senegal. Mosquitoes were collected monthly in each site between June 2009 and March 2011, with three people collecting mosquitoes landing on their legs for one to four consecutive days. In total, 81,219 specimens, belonging to 60 species and 7 genera, were collected. The most abundant species were Aedes furcifer (Edwards) (Diptera: Culicidae) (20.7%), Ae. vittatus (Bigot) (19.5%), Ae. dalzieli (Theobald) (14.7%), and Ae. luteocephalus (Newstead) (13.7%). Ae. dalzieli, Ae. furcifer, Ae. vittatus, Ae. luteocephalus, Ae. taylori Edwards, Ae. africanus (Theobald), Ae. minutus (Theobald), Anopheles coustani Laveran, Culex quinquefasciatus Say, and Mansonia uniformis (Theobald) comprised ≥10% of the total collection, in at least one land cover. The lowest species richness and Brillouin diversity index (HB = 1.55) were observed in the forest-canopy. The urban-indoor fauna showed the highest dissimilarity with other land covers and was most similar to the urban-outdoor fauna following Jaccard and Morisita index. Mosquito abundance peaked in June and October 2009 and July and October 2010. The highest species density was recorded in October. The maximum temperature was correlated positively with mean temperature and negatively with rainfall and relative humidity. Rainfall showed a positive correlation with mosquito abundance and species density. These data will be useful for understanding the transmission of arboviruses and human malaria in the region.

Ecological niche modeling of Aedes mosquito vectors of chikungunya virus in southeastern Senegal

Background

Chikungunya virus (CHIKV) originated in a sylvatic cycle of transmission between non-human animal hosts and vector mosquitoes in the forests of Africa. Subsequently the virus jumped out of this ancestral cycle into a human-endemic transmission cycle vectored by anthropophilic mosquitoes. Sylvatic CHIKV cycles persist in Africa and continue to spill over into humans, creating the potential for new CHIKV strains to enter human-endemic transmission. To mitigate such spillover, it is first necessary to delineate the distributions of the sylvatic mosquito vectors of CHIKV, to identify the environmental factors that shape these distributions, and to determine the association of mosquito presence with key drivers of virus spillover, including mosquito and CHIKV abundance. We therefore modeled the distribution of seven CHIKV mosquito vectors over two sequential rainy seasons in Kédougou, Senegal using Maxent.

Methods

Mosquito data were collected in fifty sites distributed in five land cover classes across the study area. Environmental data representing land cover, topographic, and climatic factors were included in the models. Models were compared and evaluated using area under the receiver operating characteristic curve (AUROC) statistics. The correlation of model outputs with abundance of individual mosquito species as well as CHIKV-positive mosquito pools was tested.

Results

Fourteen models were produced and evaluated; the environmental variables most strongly associated with mosquito distributions were distance to large patches of forest, landscape patch size, rainfall, and the normalized difference vegetation index (NDVI). Seven models were positively correlated with mosquito abundance and one (Aedes taylori) was consistently, positively correlated with CHIKV-positive mosquito pools. Eight models predicted high relative occurrence rates of mosquitoes near the villages of Tenkoto and Ngary, the areas with the highest frequency of CHIKV-positive mosquito pools.

Conclusions

Of the environmental factors considered here, landscape fragmentation and configuration had the strongest influence on mosquito distributions. Of the mosquito species modeled, the distribution of Ae. taylori correlated most strongly with abundance of CHIKV, suggesting that presence of this species will be a useful predictor of sylvatic CHIKV presence.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2832-6) contains supplementary material, which is available to authorized users.

Role of monkeys in the sylvatic cycle of chikungunya virus in Senegal

Arboviruses spillover into humans either as a one-step jump from a reservoir host species into humans or as a two-step jump from the reservoir to an amplification host species and thence to humans. Little is known about arbovirus transmission dynamics in reservoir and amplification hosts. Here we elucidate the role of monkeys in the sylvatic, enzootic cycle of chikungunya virus (CHIKV) in the region around Kédougou, Senegal. Over 3 years, 737 monkeys were captured, aged using anthropometry and dentition, and tested for exposure to CHIKV by detection of neutralizing antibodies. Infant monkeys were positive for CHIKV even when the virus was not detected in a concurrent survey of mosquitoes and when population immunity was too high for monkeys alone to support continuous transmission. We conclude that monkeys in this region serve as amplification hosts of CHIKV. Additional efforts are needed to identify other hosts capable of supporting continuous circulation.

Evidence for multiple sylvatic transmission cycles during the 2016-2017 yellow fever virus outbreak, Brazil

OBJECTIVES

Since December 2016, Brazil has experienced an unusually large outbreak of yellow fever (YF). Whether urban transmission may contribute to the extent of the outbreak is unclear. The objective of this study was to characterize YF virus (YFV) genomes and to identify spatial patterns to determine the distribution and origin of YF cases in Minas Gerais, Espírito Santo and Rio de Janeiro, the most affected Brazilian states during the current YFV outbreak.

METHODS

We characterized near-complete YFV genomes from 14 human cases and two nonhuman primates (NHP), sampled from February to April 2017, retrieved epidemiologic data of cases and used a geographic information system to investigate the geospatial spread of YFV.

RESULTS

All YFV strains were closely related. On the basis of signature mutations, we identified two cocirculating YFV clusters. One was restricted to the hinterland of Espírito Santo state, and another formed a coastal cluster encompassing several hundred kilometers. Both clusters comprised strains from humans living in rural areas and NHP. Another NHP lineage clustered in a basal relationship. No signs of adaptation of YFV strains to human hosts were detected.

CONCLUSIONS

Our data suggest sylvatic transmission during the current outbreak. Additionally, cocirculation of two distinct YFV clades occurring in humans and NHP suggests the existence of multiple sylvatic transmission cycles. Increased detection of YFV might be facilitated by raised awareness for arbovirus-mediated disease after Zika and chikungunya virus outbreaks. Further surveillance is required, as reemergence of YFV from NHPs might continue and facilitate the appearance of urban transmission cycles.

Yellow Fever Virus RNA in Urine and Semen of Convalescent Patient, Brazil

Yellow fever virus RNA is usually detected in blood of infected humans. We detected virus RNA in urine and semen samples from a convalescent patient. A complete virus genome was sequenced for an isolate from a urine sample. This virus had a South American I genotype and unique synapomorphic changes.

Mosquito-borne and sexual transmission of Zika virus: Recent developments and future directions

Zika virus (ZIKV; Genus Flavivirus, Family Flaviviridae) has recently emerged in Asia and the Americas to cause large outbreaks of human disease. The outbreak has been characterized by high attack rates, birth defects in infants and severe neurological complications in adults. ZIKV is transmitted to humans by Aedes mosquitoes, but recent evidence implicates sexual transmission as playing an important role as well. This review highlights the transmission of ZIKV in humans, with a focus on both mosquito and sexually-transmitted routes and their outcomes. We also discuss critical directions for future research.

Emergence of Wesselsbron virus among black rat and humans in Eastern Senegal in 2013

Wesselsbron disease is a neglected mosquito transmitted Flavivirus infection that causes abortions and has teratogenic effects on sheep and cattle in Africa. Human can also be infected. The detection of human or animal cases is complicated by the non-specific symptoms close to Rift Valley Fever (RVF) in domestic livestock species or Dengue like syndrome in humans. Then, these detections are usually made during RVF investigations in sheep. These domestic animals should take a role in the life cycle of the virus but some evidences of Wesselsbron virus (WSLV) presence in wild animals suggest that the latter may be involved in the virus maintenance in nature. However, the reservoir status of wild vertebrate in general and rodents particularly for WSLV is only based on an isolation from a Cape short-eared gerbil in southern Africa. Most of WSLV isolations are from southern parts of Africa even if it has been found in western and central Africa or Madagascar. In Senegal, there are serological evidences of WSLV circulation in human since the 1970s and some isolations, the last one of which dates back in 1992. Despite the detection of the virus on mosquitoes until the 2000s in different parts of the country, no new human case has been noted. In this paper, we report the WSLV re-emergence in eastern Senegal in 2013 with 2 human cases and its first isolation from a black rat Rattus rattus. Sequencing analyses show the circulation of the same strain between these humans and the commensal rodent. The putative impact on WSLV transmission to human populations could be more important if the reservoir status of the black rat is confirmed. Focused survey in human populations, specific entomological and mammalogical investigations would permit a better understanding of the life cycle of the virus and its impact on public health.

Potential of selected Senegalese Aedes spp. mosquitoes (Diptera: Culicidae) to transmit Zika virus

BACKGROUND

Zika virus (ZIKV; genus Flavivirus, family Flaviviridae) is an emerging virus of medical importance maintained in a zoonotic cycle between arboreal Aedes spp. mosquitoes and nonhuman primates in African and Asian forests. Serological evidence and virus isolations have demonstrated widespread distribution of the virus in Senegal. Several mosquito species have been found naturally infected by ZIKV but little is known about their vector competence.

METHODS

We assessed the vector competence of Ae. aegypti from Kedougou and Dakar, Ae. unilineatus, Ae. vittatus and Ae. luteocephalus from Kedougou in Senegal for 6 ZIKV strains using experimental oral infection. Fully engorged female mosquitoes were maintained in an environmental chamber set at 27 ± 1 °C and 80 ± 5% Relative humidity. At day 5, 10 and 15 days post infection (dpi), individual mosquito saliva, legs/wings and bodies were tested for the presence of ZIKV genome using real time RT-PCR to estimate the infection, dissemination, and transmission rates.

RESULTS

All the species tested were infected by all viral strains but only Ae. vittatus and Ae. luteocephalus were potentially capable of transmitting ZIKV after 15 dpi with 20 and 50% of mosquitoes, respectively, delivering epidemic (HD 78788) and prototype (MR 766) ZIKV strains in saliva.

CONCLUSION

All the species tested here were susceptible to oral infection of ZIKV but only a low proportion of Ae. vittatus and Ae. luteocephalus had the viral genome in their saliva and thus the potential to transmit the virus. Further investigations are needed on the vector competence of other species associated with ZIKV for better understanding of the ecology and epidemiology of this virus in Senegal.

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.