Detection of pathogenic bacteria in ticks from Isiolo and Kwale counties of Kenya using metagenomics

Ticks are arachnid ectoparasites that rank second only to mosquitoes in the transmission of human diseases including bacteria responsible for anaplasmosis, ehrlichiosis, spotted fevers, and Lyme disease among other febrile illnesses. Due to the paucity of data on bacteria transmitted by ticks in Kenya, this study undertook a bacterial metagenomic-based characterization of ticks collected from Isiolo, a semi-arid pastoralist County in Eastern Kenya, and Kwale, a coastal County with a monsoon climate in the southern Kenyan border with Tanzania. A total of 2,918 ticks belonging to 3 genera and 10 species were pooled and screened in this study. Tick identification was confirmed through the sequencing of the Cytochrome C Oxidase Subunit 1 (COI) gene. Bacterial 16S rRNA gene PCR amplicons obtained from the above samples were sequenced using the MinION (Oxford Nanopore Technologies) platform. The resulting reads were demultiplexed in Porechop, followed by trimming and filtering in Trimmomatic before clustering using Qiime2-VSearch. A SILVA database pretrained naïve Bayes classifier was used to classify the Operational Taxonomic Units (OTUs) taxonomically. The bacteria of clinical interest detected in pooled tick assays were as follows: Rickettsia spp. 59.43% of pools, Coxiella burnetii 37.88%, Proteus mirabilis 5.08%, Cutibacterium acnes 6.08%, and Corynebacterium ulcerans 2.43%. These bacteria are responsible for spotted fevers, query fever (Q-fever), urinary tract infections, skin and soft tissue infections, eye infections, and diphtheria-like infections in humans, respectively. P. mirabilis, C. acnes, and C. ulcerans were detected only in Isiolo. Additionally, COI sequences allowed for the identification of Rickettsia and Coxiella species to strain levels in some of the pools. Diversity analysis revealed that the tick genera had high levels of Alpha diversity but the differences between the microbiomes of the three tick genera studied were not significant. The detection of C. acnes, commonly associated with human skin flora suggests that the ticks may have contact with humans potentially exposing them to bacterial infections. The findings in this study highlight the need for further investigation into the viability of these bacteria and the competency of ticks to transmit them. Clinicians in these high-risk areas also need to be appraised for them to include Rickettsial diseases and Q-fever as part of their differential diagnosis.

Genome sequences of Phasi Charoen-like phasivirus and Fako virus from Aedes aegypti mosquitoes collected in coastal Kenya

We report the sequencing of two viruses, Phasi Charoen-like phasivirus (PCLV) and Fako virus (FAKV), which were detected in a pool of Aedes aegypti from Kenya. Analysis showed a high similarity of PCLV to publicly available PCLV genomes from Kenya. FAKV showed a high genetic divergence from publicly available FAKV genomes.

Malaria Transmission Dynamics in a High-Transmission Setting of Western Kenya and the Inadequate Treatment Response to Artemether-Lumefantrine in an Asymptomatic Population

BACKGROUND

Assessing the infectious reservoir is critical in malaria control and elimination strategies. We conducted a longitudinal epidemiological study in a high-malaria-burden region in Kenya to characterize transmission in an asymptomatic population.

METHODS

488 study participants encompassing all ages in 120 households within 30 clusters were followed for 1 year with monthly sampling. Malaria was diagnosed by microscopy and molecular methods. Transmission potential in gametocytemic participants was assessed using direct skin and/or membrane mosquito feeding assays, then treated with artemether-lumefantrine. Study variables were assessed using mixed-effects generalized linear models.

RESULTS

Asexual and sexual parasite data were collected from 3792 participant visits, with 903 linked with feeding assays. Univariate analysis revealed that the 6-11-year-old age group was at higher risk of harboring asexual and sexual infections than those <6 years old (odds ratio [OR] 1.68, P < .001; and OR 1.81, P < .001), respectively. Participants with submicroscopic parasitemia were at a lower risk of gametocytemia compared with microscopic parasitemia (OR 0.04, P < .001), but they transmitted at a significantly higher rate (OR 2.00, P = .002). A large proportion of the study population who were infected at least once remained infected (despite treatment) with asexual (71.7%, 291/406) or sexual (37.4%, 152/406) parasites. 88.6% (365/412) of feeding assays conducted in individuals who failed treatment the previous month resulted in transmissions.

CONCLUSIONS

Individuals with asymptomatic infection sustain the transmission cycle, with the 6-11-year age group serving as an important reservoir. The high rates of artemether-lumefantrine treatment failures suggest surveillance programs using molecular methods need to be expanded for accurate monitoring and evaluation of treatment outcomes.

Preliminary Report on the Reduction of Adult Mosquitoes in Housing Compounds in Western Kenya Using the ProVector Flower and Entobac Bait Pads Containing Bacillus thuringiensis israelensis With Honey Bait

Reducing mosquito populations indoors and outdoors can have a significant impact on malaria and other mosquito-borne diseases. A new formulation and delivery system for Bacillus thuringiensis israelensis (Bti) was tested against adult mosquitoes. One Entobac bait with 7% Bti in a honey solution was placed within each ProVector Flower applicator. The applicators were placed in nine housing compounds, one on the outside of each home in Ahero and Nyalenda, Kenya, in June 2009. Seven housing compounds with no applicators were included as controls in the study area. After 1 mo, there was a significant reduction of mosquitoes in all nine compounds with the ProVector Flower compared to two of the seven control compounds. The overall mosquito population was reduced by 69% in housing compounds with the ProVector Flower whereas the mosquito population grew by nearly 15% in the control compounds. There was a significant reduction of the median number of mosquitoes in the test compounds than in the control compounds. The proportion of mosquitoes collected was significantly reduced in the test compounds within 1 mo for several species of Aedes, Anopheles, Coquillettidia, Culex, and Mansonia. This study provides evidence that Bti-laced bait may be used as an alternative adulticide and be delivered in an applicator to reduce mosquito populations of several species. This method may significantly reduce the cost of pesticide application through target specificity and by reducing the amount of pesticide placed into the environment.

Abundance, diversity, and distribution of mosquito vectors in selected ecological regions of Kenya: public health implications

The diversity of mosquito arbovirus vectors was investigated to define regional risk of arbovirus transmission in Kenya. Mosquitoes were sampled between April, 2007 and December, 2010 at thirteen sites across seven administrative provinces and ecological zones. CDC light traps were used to collect mosquitoes while human-landing collection was conducted in five of the sites to target day-feeding Aedes (Stegomyia) species. Over 524,000 mosquitoes were collected and identified into 101 species, 30 of them known vectors of arboviruses endemic to Kenya. Ae. (Neomelaniconion) mcintoshi and Ae. (Aedimorphus) ochraceus were most abundant in Garissa in the arid northeastern province, and Mansonia uniformis and Mn. africana in semi-arid Baringo in the Rift Valley Province. Ae. ochraceus, Mn. africana and Mn. uniformis were also significant in Nyanza Province, while Ae. (Neomelaniconion) circumluteolus predominated in Budalangi, Western Province. Aedes (Stegomyia) aegypti was predominant in Rabai in the Coast Province but insignificant in the western and Nyanza sites. Culex pipiens was abundant in Rift Valley and Nyanza Provinces around the lake shores. This study highlights the potential for emergence and re-emergence of arboviral diseases among vulnerable populations. This calls for comprehensive mapping of vector distribution and abundance for planning focused vector control measures.

Mosquito-borne arbovirus surveillance at selected sites in diverse ecological zones of Kenya; 2007 - 2012

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. Mosquitoes were identified to species, pooled by species, collection date and site and screened for arboviruses by isolation in cell culture and/or RT-PCR screening and sequencing.

RESULTS

Over 450,000 mosquitoes in 15,890 pools were screened with 83 viruses being detected/isolated that include members of the alphavirus, flavivirus and orthobunyavirus genera many of which are known to be of significant public health importance in the East African region. These include West Nile, Ndumu, Sindbis, Bunyamwera, Pongola and Usutu viruses detected from diverse sites. Ngari virus, which was associated with hemorrhagic fever in northern Kenya in 1997/98 was isolated from a pool of Anopheles funestus sampled from Tana-delta and from Aedes mcintoshi from Garissa. Insect only flaviviruses previously undescribed in Kenya were also isolated in the coastal site of Rabai. A flavivirus most closely related to the Chaoyang virus, a new virus recently identified in China and two isolates closely related to Quang Binh virus previously unreported in Kenya were also detected.

CONCLUSION

Active transmission of arboviruses of public health significance continues in various parts of the country with possible undetermined human impact. Arbovirus activity was highest in the pastoralist dominated semi-arid to arid zones sites of the country where 49% of the viruses were isolated suggesting a role of animals as amplifiers and indicating the need for improved arbovirus disease diagnosis among pastoral communities.

Crimean-Congo hemorrhagic fever virus in Hyalommid ticks, northeastern Kenya

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.

Ability of selected Kenyan mosquito (Diptera: Culicidae) species to transmit West Nile virus under laboratory conditions

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. These mosquitoes were tested approximately 2 wk later to determine infection, dissemination, and transmission rates. All five species [Culex quinquefasciatus Say, Culex univittatus Theobald, Culex vansomereni Edwards, Mansonia africana (Theobald), and Mansonia uniformis (Theobald)] were susceptible to infection, but disseminated infections were detected only in the three Culex, and not the two Mansonia species. Culex mosquitoes with a disseminated infection readily transmitted virus by bite, but even when inoculated with WNV, the two Mansonia failed to transmit virus, indicating a salivary gland barrier. These studies indicate that the three Culex species may play a role in the transmission of WNV in Kenya.