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Futami K, Iwashita H, Higa Y, Lutiali PA, Sonye GO, Mwatele C, Njenga SM, Minakawa N. Geographical Distribution of Aedes aegypti aegypti and Aedes aegypti formosus (Diptera: Culicidae) in Kenya and Environmental Factors Related to Their Relative Abundance. JOURNAL OF MEDICAL ENTOMOLOGY 2020; 57:772-779. [PMID: 31815285 DOI: 10.1093/jme/tjz233] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Indexed: 06/10/2023]
Abstract
The mosquito Aedes aegypti (L.) is the primary vector of various infectious viruses and is typified by a polymorphic color and abundance of white scales on the body. It has been conventionally separated into two subspecies, Ae. aeg. formosus (Walker) (Aaf) and Ae. aeg. aegypti (L.) (Aaa), with Aaf considered a 'sylvan' form and Aaa a 'domestic' form. Because the two subspecies show different susceptibilities to dengue viruses it is important to understand their distribution. In this study, we collected larvae from artificial and natural habitats in southern Kenya and reared them to adults to morphologically identify subspecies. We describe the geographical distribution and relative abundance of Aaa and Aaf in Kenya, and estimate the environmental factors associated with their distributions by GIS using climate and environment data. A total of 5,243 Ae. aegypti adults were collected from 249 sites, with Aaa accounting for 22% of the specimens. The relative abundance of Aaa was higher in coastal areas versus sites in western Kenya. Aaa abundance was also higher in urbanized than forested areas, which is consistent with known ecology. In contrast and inconsistent with previous studies, both Aaa and Aaf were sympatric in artificial and natural habitats. The high relative abundance of Aaa in coastal areas might derive from old populated cities, climate, and/or introduction from abroad.
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Affiliation(s)
- K Futami
- Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
| | - H Iwashita
- Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
- Department of Bacteriology, Graduate School of Medicine, University of the Ryukyus, Nishiharacho, Okinawa, Japan
| | - Y Higa
- Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
- Department of Medical Entomology, National Institute of Infectious Diseases, Shinjuku-ku, Tokyo, Japan
| | - P A Lutiali
- Center for Research in Tropical Medicine and Community Development (CRTMCD), Nairobi, Kenya
| | - G O Sonye
- ASK Community Based Organization located in Mbita, Homabay, Kenya
| | - C Mwatele
- Eastern and Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute, Nairobi, Kenya
| | - S M Njenga
- Eastern and Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute, Nairobi, Kenya
| | - N Minakawa
- Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
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Masika MM, Korhonen EM, Smura T, Uusitalo R, Vapalahti K, Mwaengo D, Jääskeläinen AJ, Anzala O, Vapalahti O, Huhtamo E. Detection of dengue virus type 2 of Indian origin in acute febrile patients in rural Kenya. PLoS Negl Trop Dis 2020; 14:e0008099. [PMID: 32126086 PMCID: PMC7069648 DOI: 10.1371/journal.pntd.0008099] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 03/13/2020] [Accepted: 01/29/2020] [Indexed: 01/25/2023] Open
Abstract
Dengue virus (DENV) has caused recent outbreaks in coastal cities of Kenya, but the epidemiological situation in other areas of Kenya is largely unknown. We investigated the role of DENV infection as a cause of acute febrile disease in non-epidemic settings in rural and urban study areas in Kenya. Altogether, 560 patients were sampled in 2016–2017 in rural Taita–Taveta County (n = 327) and urban slums of Kibera, Nairobi (n = 233). The samples were studied for DENV IgM, IgG, NS1 antigen and flaviviral RNA. IgG seroprevalence was found to be higher in Taita–Taveta (14%) than in Nairobi (3%). Five Taita–Taveta patients were positive for flaviviral RNA, all identified as DENV-2, cosmopolitan genotype. Local transmission in Taita–Taveta was suspected in a patient without travel history. The sequence analysis suggested that DENV-2 strains circulating in coastal and southern Kenya likely arose from a single introduction from India. The molecular clock analyses dated the most recent ancestor to the Kenyan strains a year before the large 2013 outbreak in Mombasa. After this, the virus has been detected in Kilifi in 2014, from our patients in Taita–Taveta in 2016, and in an outbreak in Malindi in 2017. The results highlight that silent transmission occurs between epidemics and also affects rural areas. More information is needed to understand the local epidemiological characteristics and future risks of dengue in Kenya. Dengue virus (DENV) is an emerging mosquito-borne global health threat in the tropics and subtropics. The majority of the world’s population live in areas at risk of dengue that can cause a wide variety of symptoms from febrile illness to haemorrhagic fever. Information of DENV in Africa is limited and fragmented. In Kenya, dengue is a recognized disease in coastal cities that have experienced recent outbreaks. We investigated the role of DENV infection as a cause of acute febrile disease in non-epidemic settings in rural and urban study areas in Kenya. We found DENV-2 in five febrile patients from rural Taita–Taveta, where no dengue has been reported before. Genetic analysis of the virus suggests it to be most likely of Indian origin. This Indian origin DENV-2 was detected in the Mombasa outbreak in 2013, in Kilifi in 2014, in Taita–Taveta in 2016 (our study samples) and again in the Malindi outbreak in 2017. The results suggest that dengue is unrecognized in rural Kenya and more studies are needed for local risk assessment. Our findings of virus transmission between epidemics contribute to better understanding of the epidemiological situation and origins of DENV in Kenya.
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Affiliation(s)
- Moses Muia Masika
- Department of Medical Microbiology, University of Nairobi, Nairobi, Kenya
- KAVI Institute of Clinical Research, University of Nairobi, Nairobi, Kenya
| | - Essi M. Korhonen
- Department of Virology, Medicum, University of Helsinki, Helsinki, Finland
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
- * E-mail:
| | - Teemu Smura
- Department of Virology, Medicum, University of Helsinki, Helsinki, Finland
| | - Ruut Uusitalo
- Department of Virology, Medicum, University of Helsinki, Helsinki, Finland
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
- Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
| | - Katariina Vapalahti
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
| | - Dufton Mwaengo
- Department of Medical Microbiology, University of Nairobi, Nairobi, Kenya
- Institute of Tropical and Infectious Diseases, University of Nairobi, Nairobi, Kenya
| | - Anne J. Jääskeläinen
- Department of Virology, Medicum, University of Helsinki, Helsinki, Finland
- Department of Virology and Immunology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Omu Anzala
- Department of Medical Microbiology, University of Nairobi, Nairobi, Kenya
- KAVI Institute of Clinical Research, University of Nairobi, Nairobi, Kenya
| | - Olli Vapalahti
- Department of Virology, Medicum, University of Helsinki, Helsinki, Finland
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
- Department of Virology and Immunology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Eili Huhtamo
- Department of Virology, Medicum, University of Helsinki, Helsinki, Finland
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
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Evans MV, Dallas TA, Han BA, Murdock CC, Drake JM. Data-driven identification of potential Zika virus vectors. eLife 2017; 6:e22053. [PMID: 28244371 PMCID: PMC5342824 DOI: 10.7554/elife.22053] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Accepted: 02/13/2017] [Indexed: 11/13/2022] Open
Abstract
Zika is an emerging virus whose rapid spread is of great public health concern. Knowledge about transmission remains incomplete, especially concerning potential transmission in geographic areas in which it has not yet been introduced. To identify unknown vectors of Zika, we developed a data-driven model linking vector species and the Zika virus via vector-virus trait combinations that confer a propensity toward associations in an ecological network connecting flaviviruses and their mosquito vectors. Our model predicts that thirty-five species may be able to transmit the virus, seven of which are found in the continental United States, including Culex quinquefasciatus and Cx. pipiens. We suggest that empirical studies prioritize these species to confirm predictions of vector competence, enabling the correct identification of populations at risk for transmission within the United States.
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Affiliation(s)
- Michelle V Evans
- Odum School of Ecology, University of Georgia, Athens, United States
- Center for the Ecology of Infectious Diseases, University of Georgia, Athens, United States
| | - Tad A Dallas
- Odum School of Ecology, University of Georgia, Athens, United States
- Department of Environmental Science and Policy, University of California-Davis, Davis, United States
| | - Barbara A Han
- Cary Institute of Ecosystem Studies, Millbrook, United States
| | - Courtney C Murdock
- Odum School of Ecology, University of Georgia, Athens, United States
- Center for the Ecology of Infectious Diseases, University of Georgia, Athens, United States
- Department of Infectious Disease, University of Georgia, Athens, United States
- Center for Tropical Emerging Global Diseases, University of Georgia, Athens, United States
- Center for Vaccines and Immunology, University of Georgia, Athens, United States
- River Basin Center, University of Georgia, Athens, United States
| | - John M Drake
- Odum School of Ecology, University of Georgia, Athens, United States
- Center for the Ecology of Infectious Diseases, University of Georgia, Athens, United States
- River Basin Center, University of Georgia, Athens, United States
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Evolutionary and ecological factors underlying the tempo and distribution of yellow fever virus activity. INFECTION GENETICS AND EVOLUTION 2012; 13:198-210. [PMID: 22981999 DOI: 10.1016/j.meegid.2012.08.015] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 08/15/2012] [Accepted: 08/16/2012] [Indexed: 02/08/2023]
Abstract
Yellow fever virus (YFV) is historically one of the most important viruses to affect human populations. Despite the existence of highly effective vaccines for over 70 years, yellow fever remains a significant and re-emerging cause of morbidity and mortality in endemic and high-risk regions of South America and Africa. The virus may be maintained in sylvatic enzootic/epizootic, transitional and urban epidemic transmission cycles with geographic variation in terms of levels of genetic diversity, the nature of transmission cycles and patterns of outbreak activity. In this review we consider evolutionary and ecological factors underlying YFV emergence, maintenance and spread, geographic distribution and patterns of epizootic/epidemic activity.
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Ellis BR, Sang RC, Horne KM, Higgs S, Wesson DM. Yellow fever virus susceptibility of two mosquito vectors from Kenya, East Africa. Trans R Soc Trop Med Hyg 2012; 106:387-9. [PMID: 22521217 DOI: 10.1016/j.trstmh.2012.02.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 01/25/2012] [Accepted: 02/29/2012] [Indexed: 11/19/2022] Open
Abstract
Yellow fever is an unpredictable disease of increasing epidemic threat in East Africa. Aedes (Stegomyia) aegypti has never been implicated as a vector in this region and recent outbreaks have involved a newly emerging virus genotype (East African). To better understand the increasing epidemic risk of yellow fever in East Africa, this study is the first to investigate the vector competence for an emerging East African virus genotype in Kenyan A. aegypti sensu latu (s.l) and A. (Stegomyia) simpsoni s.l. mosquito species. Using first filial generation mosquitoes and a low passage yellow fever virus, this study demonstrated that although A. aegypti s.l. is a competent vector, A. simpsoni s.l. is likely a more efficient vector.
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Affiliation(s)
- Brett R Ellis
- Department of Tropical Medicine, Tulane University, 1440 Canal Street Suite 2210-SL17, New Orleans, Louisiana 70112, USA.
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Blaylock JM, Maranich A, Bauer K, Nyakoe N, Waitumbi J, Martinez LJ, Lynch J. The seroprevalence and seroincidence of dengue virus infection in western Kenya. Travel Med Infect Dis 2011; 9:246-8. [PMID: 21778117 DOI: 10.1016/j.tmaid.2011.06.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 06/24/2011] [Accepted: 06/29/2011] [Indexed: 11/30/2022]
Abstract
Epidemics of dengue fever have been documented throughout the African continent over the past several decades, however little is known about the prevalence or incidence of dengue virus infection in the absence of an outbreak. No studies have analyzed the prevalence of dengue infection in western Kenya to date. This study describes the seroincidence and seroprevalence of dengue infection in western Kenya. Banked sera obtained from 354 healthy, afebrile children ages 12-47 months from Kisumu District, Kenya, were analyzed for antibodies to dengue virus using an IgG indirect ELISA. We found a seroprevalence of 1.1% (4 of 354 samples) and incidence of 8.5 seroconversions per 1000 persons per year in this study population. This appears to be similar to that previously reported in coastal regions of the country outside of known epidemic periods. Since there has never been a reported dengue epidemic in western Kenya, continued investigation and evaluation in a patient population presenting with fever is necessary to further confirm this finding.
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Affiliation(s)
- Jason M Blaylock
- Department of Infectious Diseases, Walter Reed Army Medical Center, 6900 Georgia Ave., NW, Washington, DC 20307-5001, USA.
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Abstract
Despite a safe and effective vaccine, there are approximately 200,000 cases, including 30,000 deaths, due to yellow fever virus (YFV) each year, of which 90% are in Africa. The natural history of YFV has been well described, especially in West Africa, but in East Africa yellow fever (YF) remains characterised by unpredictable focal periodicity and a precarious potential for large epidemics. Recent outbreaks of YF in Kenya (1992-1993) and Sudan (2003 and 2005) are important because each of these outbreaks have involved the re-emergence of a YFV genotype (East Africa) that remained undetected for nearly 40 years and was previously unconfirmed in a clinically apparent outbreak. In addition, unlike West Africa and South America, YF has yet to emerge in urban areas of East Africa and be vectored by Aedes (Stegomyia) aegypti. This is a significant public health concern in a region where the majority of the population remains unvaccinated. This review describes historical findings, highlights a number of disease indicators, and provides clarification regarding the natural history, recent emergence and future risk of YF in East Africa.
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Affiliation(s)
- Brett R Ellis
- Department of Tropical Medicine, Tulane University, New Orleans, LA, USA.
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