Publications by authors named "Hellen Koka"

Ticks are ecto-parasites of domestic animals, rodents, and wildlife living for periods at a time on one or more vertebrate hosts. They are important vectors of viral, bacterial, or parasitic diseases in livestock and humans. Crimean-Congo haemorrhagic fever virus and the spotted fever rickettsiae are some of the tick-borne diseases of public health importance reported in Kenya.

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Introduction: Emerging tick-borne viruses of medical and veterinary importance are increasingly being reported globally. This resurgence emphasizes the need for sustained surveillance to provide insights into tick-borne viral diversity and associated potential public health risks. We report on a virus tentatively designated Kinna virus (KIV) in the family Phenuiviridae and genus Bandavirus.

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Article Synopsis
  • The West Nile virus (WNV) Koutango lineage (WN-KOUTV) has been isolated from phlebotomine sandflies in Kenya, expanding understanding of this virus found primarily in mosquitoes.
  • This study involved sampling sandflies, identifying species, isolating the virus, and analyzing its genetic sequences to understand its evolutionary relationships and variations.
  • Results indicated WN-KOUTV shows unique genetic traits and replicated effectively in both mammalian and mosquito cell lines, which could imply the sandflies might play a role as potential vectors for the virus.
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Phleboviruses are an emerging threat to public health. Recent surveillance efforts in Kenya have unveiled novel phleboviruses. Despite these efforts, there remain knowledge gaps.

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The emergence and rapid spread of SARS-CoV-2 variants of concern (VOC) have been linked to new waves of COVID-19 epidemics occurring in different regions of the world. The VOC have acquired adaptive mutations that have enhanced virus transmissibility, increased virulence, and reduced response to neutralizing antibodies. Kenya has experienced six waves of COVID-19 epidemics.

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Background: Arbovirus surveillance and recurrence of outbreaks in Kenya continues to reveal the re-emergence of viruses of public health importance. This calls for sustained efforts in early detection and characterization of these agents to avert future potential outbreaks.

Methods: A larval survey was carried out in three different sites in Kwale County, Vanga, Jego and Lunga Lunga.

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Background: Chikungunya virus is an alphavirus, primarily transmitted by Aedes aegypti and Ae. albopictus. In late 2017-2018, an outbreak of chikungunya occurred in Mombasa county, Kenya, and investigations were conducted to establish associated entomological risk factors.

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Between late 2017 and mid-2018, a chikungunya fever outbreak occurred in Mombasa, Kenya that followed an earlier outbreak in mid-2016 in Mandera County on the border with Somalia. Using targeted Next Generation Sequencing, we obtained genomes from clinical samples collected during the 2017/2018 Mombasa outbreak. We compared data from the 2016 Mandera outbreak with the 2017/2018 Mombasa outbreak, and found that both had the Aedes aegypti adapting mutations, E1:K211E and E2:V264A.

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Chikungunya is a reemerging vector borne pathogen associated with severe morbidity in affected populations. Lamu, along the Kenyan coast was affected by a major chikungunya outbreak in 2004. Twelve years later, we report on entomologic investigations and laboratory confirmed chikungunya cases in northeastern Kenya.

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Ticks are important disease vectors in Kenya with documented evidence of carriage of zoonotic pathogens. is an important tick-borne pathogen that is underreported in Kenya and yet this infection likely contributes to undiagnosed febrile disease in pastoral communities. Archived human blood (278) and tick pool samples (380) collected from five pastoral communities in Kenya were screened for by PCR using primers targeting the transposon-like IS1111 region.

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In this study, ticks from pastoral communities in Kenya were tested for Rickettsia spp. infections in geographical regions where the presence of tick-borne arboviruses had previously been reported. Rickettsial and arbovirus infections have similar clinical features which makes differential diagnosis challenging when both diseases occur.

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Background: Dengue fever, a mosquito-borne disease, is associated with illness of varying severity in countries in the tropics and sub tropics. Dengue cases continue to be detected more frequently and its geographic range continues to expand. We report the largest documented laboratory confirmed circulation of dengue virus in parts of Kenya since 1982.

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Dengue outbreaks were first reported in East Africa in the late 1970s to early 1980s including the 1982 outbreak on the Kenyan coast. In 2011, dengue outbreaks occurred in Mandera in northern Kenya and subsequently in Mombasa city along the Kenyan coast in 2013-2014. Following laboratory confirmation of dengue fever cases, an entomologic investigation was conducted to establish the mosquito species, and densities, causing the outbreak.

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Biodiversity and relative abundance of ticks and associated arboviruses in Garissa (northeastern) and Isiolo (eastern) provinces of Kenya were evaluated. Ticks were collected from livestock, identified to species, pooled, and processed for virus isolation. In Garissa, Rhipicephalus pulchellus Gerstacker (57.

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Background: Increased frequency of arbovirus outbreaks in East Africa necessitated the determination of distribution of risk by entomologic arbovirus surveillance. A systematic vector surveillance programme spanning 5 years and covering 11 sites representing seven of the eight provinces in Kenya and located in diverse ecological zones was carried out.

Methods: Mosquitoes were sampled bi-annually during the wet seasons and screened for arboviruses.

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West Nile virus (WNV) is currently active in Kenya as evidenced by the detection of antibodies in birds bled as part of an avian influenza surveillance program in 2009. Although WNV has been isolated from several mosquito species in Kenya, no studies have ever been conducted to determine which of these species are competent vectors of this virus. Therefore, we allowed Kenyan mosquitoes to feed on 2- or 3-d-old chickens that had been infected with a Lineage one strain of WNV 24-48 h earlier.

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As part of ongoing arbovirus surveillance, we screened ticks obtained from livestock in northeastern Kenya in 2008 to assess the risk for human exposure to tick-borne viruses. Of 1,144 pools of 8,600 Hyalomma spp. ticks screened for Congo-Crimean hemorrhagic fever virus by reverse transcription PCR, 23 pools were infected, demonstrating a potential for human exposure.

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In December 2006, Rift Valley fever (RVF) was diagnosed in humans in Garissa Hospital, Kenya and an outbreak reported affecting 11 districts. Entomologic surveillance was performed in four districts to determine the epidemic/epizootic vectors of RVF virus (RVFV). Approximately 297,000 mosquitoes were collected, 164,626 identified to species, 72,058 sorted into 3,003 pools and tested for RVFV by reverse transcription-polymerase chain reaction.

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