Serological evidence of chikungunya virus infection among suspected measles cases in selected regions of Kenya : 2008-2014

Chikungunya virus (family Togavirdae and genus Alphavirus) is an emerging and reemerging virus of public health importance both regionally and globally. In Kenya, about 50-60% of the suspected measles cases remain undiagnosed once measles and rubella is ruled out by immunoglobulin M (IgM) ELISA thus prompted the need to do differential diagnosis on the measles/rubella negative samples. Nothing is known about the role played by chikungunya infection among these suspected measles cases. Febrile rash illness is a common clinical presentation of arboviruses, including chikungunya. In this study, we conducted a serosurvey to explore the possible role of chikungunya infections among suspected measles cases in Kenya that had tested negative for measles and rubella. Sera were tested by commercially available ELISA for the presence of IgG and IgM antibodies against the chikungunya virus. All positive samples for chikungunya by ELISA were confirmed by plaque reduction neutralization test (PRNT), and to rule out cross-reactivity with other alphaviruses a panel of viruses was used, namely o' nyong' nyong, Semliki Forest, and Sindbis viruses. Of the 392 serum samples screened, 0.3% (n = 1) tested positive for IgM antibodies, while 4.6% (n = 18) tested positive for IgG antibodies against the chikungunya virus. PRNT results indicated 2 (11%) chikungunya positives and 7 (38.9%) o' nyong' nyong positives. We recommend awareness among health care providers and improved surveillance for these arboviruses by both serology and molecular testing. Testing for other pathogens should also be done to improve disease detection and diagnosis.http://online.liebertpub.com/VBZ2021-12-01hj2020Medical Virolog

Seroprevalence of Crimean Congo hemorrhagic fever virus in Ijara District, Kenya

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne viral disease mainly affecting pastoralists who come in contact with animals infested with Hyalomma ticks, which are the key vectors of CCHF virus (CCHFV). CCHFV has been detected among these ticks in parts of North Eastern Kenya. This study aimed to identify acute cases of CCHF, and to determine the extent of previous exposure to CCHFV in an outpatient population attending Sangailu and Ijara health centers, Ijara District, North Eastern Kenya, presenting with acute febrile illnesses. A total of 517 human serum samples were collected from these patients. The samples were screened for the presence of IgM and IgG antibodies to CCHF using CCCHF-IgG and IgM ELISA test kits. A multivariable logistic regression model was used to investigate the risk factors associated with evidence of exposure to CCHFV. A single patient tested positive for anti-CCHF IgM, while 96 were positive for anti-CCHF IgG. The seroprevalence of CCHFV was 23% in Sangailu and 14% in Ijara. Most exposed persons were aged 40–49 years. The likelihood of exposure was highest among farmers (29%). Age, location, and contact with donkeys were significantly associated with exposure to CCHFV. Acute CCHFV infections could be occurring without being detected in this population. This study confirms human exposure to CCHF virus in Ijara District, Kenya, and identifies several significant risk factors associated with exposure to CCHFV.Google.org, the philanthropic arm of Google.http://www.liebertpub.com/publication.aspx?pub_id=6

Serological evidence of Flavivirus circulation in human populations in Northern Kenya : an assessment of disease risk 2016-2017

BACKGROUND: Yellow fever, Dengue, West Nile and Zika viruses are re-emerging mosquito-borne Flaviviruses of public health concern. However, the extent of human exposure to these viruses and associated disease burden in Kenya and Africa at large remains unknown. We assessed the seroprevalence of Yellow fever and other Flaviviruses in human populations in West Pokot and Turkana Counties of Kenya. These areas border Uganda, South Sudan and Ethiopia where recent outbreaks of Yellow fever and Dengue have been reported, with possibility of spillover to Kenya. METHODOLOGY: Human serum samples collected through a cross-sectional survey in West Pokot and Turkana Counties were screened for neutralizing antibodies to Yellow fever, Dengue-2, West Nile and Zika virus using the Plaque Reduction Neutralization Test (PRNT). Seroprevalence was compared by county, site and important human demographic characteristics. Adjusted odds ratios (aOR) were estimated using Firth logistic regression model. RESULTS: Of 877 samples tested, 127 neutralized with at least one of the four flaviviruses (14.5, 95% CI 12.3–17.0%), with a higher proportion in Turkana (21.1%, n = 87/413) than in West Pokot (8.6%, n = 40/464). Zika virus seroprevalence was significantly higher in West Pokot (7.11%) than in Turkana County (0.24%; χ 2 P < 0.0001). A significantly higher Yellow fever virus seroprevalence was also observed in Turkana (10.7%) compared to West Pokot (1.29%; χ 2 P < 0.0001). A high prevalence of West Nile virus was detected in Turkana County only (10.2%) while Dengue was only detected in one sample, from West Pokot. The odds of infection with West Nile virus was significantly higher in males than in females (aOR = 2.55, 95% CI 1.22–5.34). Similarly, the risk of Zika virus infection in West Pokot was twice higher in males than females (aOR = 2.01, 95% CI 0.91–4.41). CONCLUSION: Evidence of neutralizing antibodies to West Nile and Zika viruses indicates that they have been circulating undetected in human populations in these areas. While the observed Yellow Fever prevalence in Turkana and West Pokot Counties may imply virus activity, we speculate that this could also be as a result of vaccination following the Yellow Fever outbreak in the Omo river valley, South Sudan and Uganda across the borderNational Institutes of Health (NIH), UK Aid from the UK Government, Swedish International Development Cooperation Agency (Sida), Swiss Agency for Development and Cooperation (SDC) and the Kenyan Government.http://www.virologyj.compm2020Medical Virolog

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

Assessing the risk of Transmission of Yellow Fever and Dengue viruses by Aedes (Stegomyia) mosquito populations in Northern Kenya

East Africa has been experiencing an increase in the occurrence of emerging infectious diseases such as yellow fever (YF) and dengue (DEN). Increasing frequency of YF activity in East Africa constitutes a re-emergence that was not detected for over 40 years. Additionally, DEN outbreaks have also increased in frequency and continue to be detected in Kenya and in neighboring countries like Tanzania, Somalia, Djibouti, Eritrea and South Sudan. The renewed vigor of YF and dengue fever (DF) re-emergence in East Africa presents a new challenge to public health in spite of the availability of a safe and effective vaccine for YF. However, there is need to understand the potential for YF and DEN transmission along the border areas of Kenya, because Kenya is classified among countries with medium to high risk for YF transmission. This classification was mainly based on historical data, proximity to countries reporting recent YF outbreaks, the presence of non-human primates known reservoirs for these viruses, unrestricted human movement and presence of potential vector mosquito species. Both YF and DEN share a similar niche in the ecosystem and are associated with Aedes mosquito species of the subgenus Stegomyia. While the factors leading to the re-emergence of these diseases are poorly understood, a better epidemiologic understanding relating to disease ecology including presence of potential vectors, their host blood feeding preferences, the vector competence in transmission of these viruses and evidence of virus circulation in human population, will guide assessment of disease risk in the target areas and help to prevent or mitigate severe outbreaks in this region.Thesis (PhD)--University of Pretoria,2020National Institute of Health Sciences L'oreal- UNESCO for women in scienceMedical VirologyPhD in Medical VirologyRestricte

A previously unreported potential malaria vector in a dry ecology of Kenya

Abstract Background In Kenya, malaria remains a major public health menace equally affecting the semi-arid to arid ecologies. However, entomologic knowledge of malaria vectors in such areas remains poor. Methods Morphologically-identified wild-caught Anopheles funestus (s.l.) specimens trapped outdoors from the semi-arid to arid area of Kacheliba, West Pokot County, Kenya, were analysed by PCR and sequencing for species identification, malaria parasite infection and host blood-meal sources. Results Three hundred and thirty specimens were analysed to identify sibling species of the An. funestus group, none of which amplified using the available primers; two were infected with Plasmodium falciparum and Plasmodium ovale, separately, while 84% (n = 25) of the blood-fed specimens had fed on humans. Mitochondrial cytochrome c oxidase subunit 1 (cox1) and nuclear ribosomal internal transcribed spacer 2 (ITS2) sequences of 55 specimens (Plasmodium-positive, blood-fed and Plasmodium-negative) did not match reference sequences, possibly suggesting a previously unreported species, resolving as two clades. Conclusions Our findings indicate the existence of yet-to-be identified and described anopheline species with a potential as malaria vectors in Kenya

The occurrence, diversity and blood feeding patterns of potential vectors of dengue and yellow fever in Kacheliba, West Pokot County, Kenya

INTRODUCTION : Yellow fever (YF) and dengue (DEN) viruses are important re-emerging mosquito-borne viruses sharing similar vectors and reservoirs. The last documented YF outbreak in Kenya occurred in 1992–95. However, YF virus is re-emerging in bordering countries including Uganda, Ethiopia and South Sudan with the potential for spread to the neighboring regions in Kenya. Dengue is endemic in Kenya with outbreaks being detected in various towns in the north and the coast. This study reports on the Aedes (Stegomyia) mosquito species occurrence, diversity, and blood feeding patterns, as means of measuring the risk of transmission of YF and DEN in Kacheliba sub-county, West Pokot County, which borders previous YF outbreak areas in eastern Uganda. METHODOLOGY : Adult mosquitoes were collected using CO2-baited BG Sentinel traps at three time points during the rainy season. Mosquitoes were identified to the species level. Species abundance during the three sampling periods were compared, with emphasis on Aedes aegypti and other Stegomyia species, using generalized linear models that included mosquito diversity. Individually blood-fed mosquitoes were analyzed by DNA amplification of the 12S rRNA gene followed by sequencing to determine the source of blood meal. RESULTS : Overall, 8605 mosquitoes comprising 22 species in 5 genera were collected. Sampled Stegomyia species included Ae. aegypti (77.3%), Ae. vittatus (11.4%), Ae. metallicus (10.2%) and Ae. unilineatus (1.1%). Ae. aegypti dominated the blood-fed specimens (77%, n = 68) and were found to have fed mostly on rock hyraxes (79%), followed by goats (9%), humans and cattle (each 4%), with a minor proportion on hippopotamus and rock monitor lizards (each comprising 1%). CONCLUSION : Our findings reveal the presence of important Stegomyia species, which are known potential vectors of YF and DEN viruses. In addition, evidence of more host feeding on wild and domestic animals (hyrax and goat) than humans was observed. How the low feeding on humans translates to risk of transmission of these viruses, remains unclear, but calls for further research including vector competence studies of the mosquito populations for these viruses. This forms part of a comprehensive risk assessment package to guide decisions on implementation of affordable and sustainable vaccination (YF) and vector control plans in West Pokot County, Kenya.http://www.elsevier.com/locate/actatropica2019-10-01hj2018Medical Virolog

Vector competence of Aedes bromeliae and Aedes vitattus mosquito populations from Kenya for chikungunya virus.

BACKGROUND:Kenya has experienced outbreaks of chikungunya in the past years with the most recent outbreak occurring in Mandera in the northern region in May 2016 and in Mombasa in the coastal region from November 2017 to February 2018. Despite the outbreaks in Kenya, studies on vector competence have only been conducted on Aedes aegypti. However, the role played by other mosquito species in transmission and maintenance of the virus in endemic areas remains unclear. This study sought to determine the possible role of rural Aedes bromeliae and Aedes vittatus in the transmission of chikungunya virus, focusing on Kilifi and West Pokot regions of Kenya. METHODS:Four day old female mosquitoes were orally fed on chikungunya virus-infected blood at a dilution of 1:1 of the viral isolate and blood (10(6.4) plaque-forming units [PFU]/ml) using artificial membrane feeder (Hemotek system) for 45 minutes. The engorged mosquitoes were picked and incubated at 29-30°C ambient temperature and 70-80% humidity in the insectary. At days 5, 7 and 10 post-infection, the mosquitoes were carefully dissected to separate the legs and wings from the body and their proboscis individually inserted in the capillary tube containing minimum essential media (MEM) to collect salivary expectorate. The resultant homogenates and the salivary expectorates were tested by plaque assay to determine virus infection, dissemination and transmission potential of the mosquitoes. RESULTS:A total of 515 female mosquitoes (311 Ae. bromeliae and 204 Ae. vittatus) were exposed to the East/Central/South Africa (ECSA) lineage of chikungunya virus. Aedes vittatus showed high susceptibility to the virus ranging between 75-90% and moderate dissemination and transmission rates ranging from 35-50%. Aedes bromeliae had moderate susceptibility ranging between 26-40% with moderate dissemination and transmission rates ranging from 27-55%. CONCLUSION:This study demonstrates that both Ae. vittatus and Ae. bromeliae populations from West Pokot and Kilifi counties in Kenya are competent vectors of chikungunya virus. Based on these results, the two areas are at risk of virus transmission in the event of an outbreak. This study underscores the need to institute vector competence studies for populations of potential vector species as a means of evaluating risk of transmission of the emerging and re-emerging arboviruses in diverse regions of Kenya