Abstract
BackgroundWest Nile fever virus is a zoonotic arboviral infection maintained in a sylvatic cycle involving mosquito vectors and birds. It is one the arboviruses whose geographical range is expanding because of climate and land use changes that enhance the densities of mosquitoes and promote mosquito-bird-human interactions. We carried out a survey to determine the reservoirs of WNV among wild birds in Tana River and Garissa counties, Kenya.MethodsBlood samples were obtained from 361 randomly trapped wild birds. Using real-time polymerase chain reaction (PCR), all samples were screened for WNV using gene specific primer sets amplifying a portion of the E region of the genome encoding the envelope protein.ResultsSixty five (65) out of 361 birds screened tested positive for WNV on real-time PCR assay. Sequencing of the selected positive samples reveals that the isolated WNV were most closely related to strains isolated from China (2011). A regression analysis indicated that sampling location influenced the occurrence of WNV while species, age, weight and sex of the birds did not have any effect.ConclusionsThis study provides baseline information on the existing circulation of WNV in this region among wild bird reservoirs that could spill over to the human population and points to the need for implementation of surveillance programs to map the distribution of the virus among reservoirs. Awareness creation about West Nile fever in this region is important to improve its detection and management.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-016-2019-8) contains supplementary material, which is available to authorized users.
Highlights
West Nile fever virus is a zoonotic arboviral infection maintained in a sylvatic cycle involving mosquito vectors and birds
West Nile virus (WNV) is a small single-stranded Ribonucleic Acid (RNA) virus classified under the genus flavivirus and grouped in the Japanese encephalitis virus sero-complex [1, 2]
Reverse transcription Complementary DNA was synthesized from the extracted RNA with SuperScriptTM II (SS II) first strand synthesis system for RT-polymerase chain reaction (PCR) (Invitrogen) following manufacturer’s instructions
Summary
Description of the study area The study area traversed two neighboring counties – Tana River and Garissa – in the eastern part of Kenya (Fig. 1). Reverse transcription Complementary DNA was synthesized from the extracted RNA with SuperScriptTM II (SS II) first strand synthesis system for RT-PCR (Invitrogen) following manufacturer’s instructions. Samples with specific targeted 445 bp fragments were purified using a mini-elute purification kit (Qiagen) according to the manufacturer’ instructions and if the concentration was good quality with a concentration above 20 ng/μl submitted for Sanger sequencing using Big Dye Terminator Cycle chemistry and 3730 DNA Analyzer (Applied Biosystems, Foster, CA). Data analysis In order to establish the relationship between the occurrences of WNV, the site of sampling and bird characteristics (age, sex and species), a regression analysis in a generalized linear model with a logit link implemented in R software was used. The dendrogram was constructed using the neighbor-joining method supported with a bootstrap test of 1000 replicates in MEGA 6 software [22]
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