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Viral diversity and blood-feeding patterns of Afrotropical Culicoides biting midges (Diptera: Ceratopogonidae). Front Microbiol 2024; 14:1325473. [PMID: 38249470 PMCID: PMC10797016 DOI: 10.3389/fmicb.2023.1325473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2023] [Accepted: 12/13/2023] [Indexed: 01/23/2024] Open
Abstract
Introduction Culicoides biting midges (Diptera: Ceratopogonidae) are vectors of arboviral pathogens that primarily affect livestock represented by Schmallenberg virus (SBV), epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV). In Kenya, studies examining the bionomic features of Culicoides including species diversity, blood-feeding habits, and association with viruses are limited. Methods Adult Culicoides were surveyed using CDC light traps in two semi-arid ecologies, Baringo and Kajiado counties, in Kenya. Blood-fed specimens were analysed through polymerase chain reaction (PCR) and sequencing of cytochrome oxidase subunit 1 (cox1) barcoding region. Culicoides pools were screened for virus infection by generic RT-PCR and next-generation sequencing (NGS). Results Analysis of blood-fed specimens confirmed that midges had fed on cattle, goats, sheep, zebra, and birds. Cox1 barcoding of the sampled specimens revealed the presence of known vectors of BTV and epizootic hemorrhagic disease virus (EHDV) including species in the Imicola group (Culicoides imicola) and Schultzei group (C. enderleni, C. kingi, and C. chultzei). Culicoides leucostictus and a cryptic species distantly related to the Imicola group were also identified. Screening of generated pools (11,006 individuals assigned to 333 pools) by generic RT-PCR revealed presence of seven phylogenetically distinct viruses grouping in the genera Goukovirus, Pacuvirus and Orthobunyavirus. The viruses showed an overall minimum infection rate (MIR) of 7.0% (66/333, 95% confidence interval (CI) 5.5-8.9). In addition, full coding sequences of two new iflaviruses, tentatively named Oloisinyai_1 and Oloisinyai_2, were generated by next-generation sequencing (NGS) from individual homogenate of Culicoides pool. Conclusion The results indicate a high genetic diversity of viruses in Kenyan biting midges. Further insights into host-vector-virus interactions as well as investigations on the potential clinical significance of the detected viruses are warranted.
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Transmission Dynamics of Crimean-Congo Haemorrhagic Fever Virus (CCHFV): Evidence of Circulation in Humans, Livestock, and Rodents in Diverse Ecologies in Kenya. Viruses 2023; 15:1891. [PMID: 37766297 PMCID: PMC10535211 DOI: 10.3390/v15091891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 08/22/2023] [Accepted: 08/23/2023] [Indexed: 09/29/2023] Open
Abstract
Crimean-Congo haemorrhagic fever virus (CCHFV) is the causative agent of CCHF, a fatal viral haemorrhagic fever disease in humans. The maintenance of CCHFV in the ecosystem remains poorly understood. Certain tick species are considered as vectors and reservoirs of the virus. Diverse animals are suspected as amplifiers, with only scarce knowledge regarding rodents in virus epidemiology. In this study, serum samples from febrile patients, asymptomatic livestock (cattle, donkeys, sheep, and goats), and peridomestic rodents from Baringo (Marigat) and Kajiado (Nguruman) counties within the Kenyan Rift Valley were screened for acute CCHFV infection by RT-PCR and for CCHFV exposure by ELISA. RT-PCR was performed on all livestock samples in pools (5-7/pool by species and site) and in humans and rodents individually. CCHFV seropositivity was significantly higher in livestock (11.9%, 113/951) compared to rodents (6.5%, 6/93) and humans (5.9%, 29/493) (p = 0.001). Among the livestock, seropositivity was the highest in donkeys (31.4%, 16/51), followed by cattle (14.1%, 44/310), sheep (9.8%, 29/295) and goats (8.1%, 24/295). The presence of IgM antibodies against CCHFV was found in febrile patients suggesting acute or recent infection. CCHFV RNA was detected in four pooled sera samples from sheep (1.4%, 4/280) and four rodent tissues (0.83%, 4/480) showing up to 99% pairwise nucleotide identities among each other. Phylogenetic analyses of partial S segment sequences generated from these samples revealed a close relationship of 96-98% nucleotide identity to strains in the CCHFV Africa 3 lineage. The findings of this study suggest active unnoticed circulation of CCHFV in the study area and the involvement of livestock, rodents, and humans in the circulation of CCHFV in Kenya. The detection of CCHF viral RNA and antibodies against CCHFV in rodents suggests that they may participate in the viral transmission cycle.
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Analyses of Mosquito Species Composition, Blood-Feeding Habits and Infection with Insect-Specific Flaviviruses in Two Arid, Pastoralist-Dominated Counties in Kenya. Pathogens 2023; 12:967. [PMID: 37513814 PMCID: PMC10386387 DOI: 10.3390/pathogens12070967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 07/17/2023] [Accepted: 07/21/2023] [Indexed: 07/30/2023] Open
Abstract
Insect-specific flaviviruses (ISFs), although not known to be pathogenic to humans and animals, can modulate the transmission of arboviruses by mosquitoes. In this study, we screened 6665 host-seeking, gravid and blood-fed mosquitoes for infection with flaviviruses and assessed the vertebrate hosts of the blood-fed mosquitoes sampled in Baringo and Kajiado counties; both dryland ecosystem counties in the Kenyan Rift Valley. Sequence fragments of two ISFs were detected. Cuacua virus (CuCuV) was found in three blood-fed Mansonia (Ma.) africana. The genome was sequenced by next-generation sequencing (NGS), confirming 95.8% nucleotide sequence identity to CuCuV detected in Mansonia sp. in Mozambique. Sequence fragments of a potential novel ISF showing nucleotide identity of 72% to Aedes flavivirus virus were detected in individual blood-fed Aedes aegypti, Anopheles gambiae s.l., Ma. africana and Culex (Cx.) univittatus, all having fed on human blood. Blood-meal analysis revealed that the collected mosquitoes fed on diverse hosts, primarily humans and livestock, with a minor representation of wild mammals, amphibians and birds. The potential impact of the detected ISFs on arbovirus transmission requires further research.
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Divergent Hantavirus in Somali Shrews ( Crocidura somalica) in the Semi-Arid North Rift, Kenya. Pathogens 2023; 12:pathogens12050685. [PMID: 37242355 DOI: 10.3390/pathogens12050685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 04/21/2023] [Accepted: 05/04/2023] [Indexed: 05/28/2023] Open
Abstract
Hantaviruses are zoonotic rodent-borne viruses that are known to infect humans and cause various symptoms of disease, including hemorrhagic fever with renal and cardiopulmonary syndromes. They have a segmented single-stranded, enveloped, negative-sense RNA genome and are widely distributed. This study aimed to investigate the circulation of rodent-borne hantaviruses in peridomestic rodents and shrews in two semi-arid ecologies within the Kenyan Rift Valley. The small mammals were trapped using baited folding Sherman traps set within and around houses, then they were sedated and euthanatized through cervical dislocation before collecting blood and tissue samples (liver, kidney, spleen, and lungs). Tissue samples were screened with pan-hantavirus PCR primers, targeting the large genome segment (L) encoding the RNA-dependent RNA polymerase (RdRp). Eleven of the small mammals captured were shrews (11/489, 2.5%) and 478 (97.5%) were rodents. A cytochrome b gene-based genetic assay for shrew identification confirmed the eleven shrews sampled to be Crocidura somalica. Hantavirus RNA was detected in three (3/11, 27%) shrews from Baringo County. The sequences showed 93-97% nucleotide and 96-99% amino acid identities among each other, as well as 74-76% nucleotide and 79-83% amino acid identities to other shrew-borne hantaviruses, such as Tanganya virus (TNGV). The detected viruses formed a monophyletic clade with shrew-borne hantaviruses from other parts of Africa. To our knowledge, this constitutes the first report published on the circulation of hantaviruses in shrews in Kenya.
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Phlebovirus diversity in ticks from livestock in arid ecologies in Kenya. Ticks Tick Borne Dis 2023; 14:102087. [PMID: 36459866 DOI: 10.1016/j.ttbdis.2022.102087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2022] [Revised: 10/11/2022] [Accepted: 11/09/2022] [Indexed: 11/21/2022]
Abstract
Phleboviruses are emerging pathogens of public health importance. However, their association with ticks is poorly described, particularly in Africa. Here, adult ticks infesting cattle, goats and sheep were collected in two dryland pastoralist ecosystems of Kenya (Baringo and Kajiado counties) and were screened for infection with phleboviruses. Ticks mainly belonged to the species Rhipicephalus appendiculatus, Hyalomma impeltatum, and Hyalomma rufipes. A fragment of the RNA-dependent RNA polymerase (RdRp) gene was identified in thirty of 671 tick pools, of which twenty-nine were from livestock sampled in Baringo county. Phylogenetic analyses revealed that twenty-five sequences were falling in three clades within the group of tick-associated phleboviruses. The sequences of the three clades showed nucleotide distances 8%, 19% and 22%, respectively, to previously known viruses suggesting that these sequence fragments may belong to three distinct viruses. Viruses of the group of tick-associated phleboviruses have been found in several countries and continents but so far have not been associated with disease in humans or animals. In addition, five sequences were found to group with the sandfly-associated phleboviruses Bogoria virus, Perkerra virus and Ntepes virus recently detected in the same region. Further studies are needed to investigate the transmission and maintenance cycles of these viruses, as well as to assess their potential to infect vertebrates.
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Abstract
Jingmen tick virus (JMTV) is an arbovirus with a multisegmented genome related to those of unsegmented flaviviruses. The virus first described in Rhipicephalus microplus ticks collected in Jingmen city (Hubei Province, China) in 2010 is associated with febrile illness in humans. Since then, the geographic range has expanded to include Trinidad and Tobago, Brazil, and Uganda. However, the ecology of JMTV remains poorly described in Africa. We screened adult ticks (n = 4550, 718 pools) for JMTV infection by reverse transcription polymerase chain reaction (RT-PCR). Ticks were collected from cattle (n = 859, 18.88%), goats (n = 2070, 45.49%), sheep (n = 1574, 34.59%), and free-ranging tortoises (Leopard tortoise, Stigmochelys pardalis) (n = 47, 1.03%) in two Kenyan pastoralist-dominated areas (Baringo and Kajiado counties) with a history of undiagnosed febrile human illness. Surprisingly, ticks collected from goats (0.3%, 95% confidence interval (CI) 0.1-0.5), sheep (1.8%, 95% CI 1.2-2.5), and tortoise (74.5%, 95% CI 60.9-85.4, were found infected with JMTV, but ticks collected from cattle were all negative. JMTV ribonucleic acid (RNA) was also detected in blood from tortoises (66.7%, 95% CI 16.1-97.7). Intragenetic distance of JMTV sequences originating from tortoise-associated ticks was greater than that of sheep-associated ticks. Phylogenetic analyses of seven complete-coding genome sequences generated from tortoise-associated ticks formed a monophyletic clade within JMTV strains from other countries. In summary, our findings confirm the circulation of JMTV in ticks in Kenya. Further epidemiological surveys are needed to assess the potential public health impact of JMTV in Kenya.
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Outdoor malaria vector species profile in dryland ecosystems of Kenya. Sci Rep 2022; 12:7131. [PMID: 35505087 PMCID: PMC9065082 DOI: 10.1038/s41598-022-11333-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Accepted: 04/11/2022] [Indexed: 11/09/2022] Open
Abstract
Outdoor biting by anopheline mosquitoes is one of the contributors to residual malaria transmission, but the profile of vectors driving this phenomenon is not well understood. Here, we studied the bionomics and genetically characterized populations of An. gambiae and An. funestus complexes trapped outdoors in three selected dryland areas including Kerio Valley, Nguruman and Rabai in Kenya. We observed a higher abundance of Anopheles funestus group members (n = 639, 90.6%) compared to those of the An. gambiae complex (n = 66, 9.4%) with An. longipalpis C as the dominant vector species with a Plasmodium falciparum sporozoite rate (Pfsp) of 5.2% (19/362). The known malaria vectors including An. funestus s.s. (8.7%, 2/23), An. gambiae (14.3%, 2/14), An. rivulorum (14.1%, 9/64), An. arabiensis (1.9%, 1/52) occurred in low densities and displayed high Pfsp rates, which varied with the site. Additionally, six cryptic species found associated with the An. funestus group harbored Pf sporozoites (cumulative Pfsp rate = 7.2%, 13/181). We detected low frequency of resistant 119F-GSTe2 alleles in An. funestus s.s. (15.6%) and An. longipalpis C (3.1%) in Kerio Valley only. Evidence of outdoor activity, emergence of novel and divergent vectors and detection of mutations conferring metabolic resistance to pyrethroid/DDT could contribute to residual malaria transmission posing a threat to effective malaria control.
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Aedes vector-host olfactory interactions in sylvatic and domestic dengue transmission environments. Proc Biol Sci 2019; 286:20192136. [PMID: 31690238 DOI: 10.1098/rspb.2019.2136] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Interactions between Aedes (Stegomyia) species and non-human primate (NHP) and human hosts govern the transmission of the pathogens, dengue, zika, yellow fever and chikungunya viruses. Little is known about Aedes mosquito olfactory interactions with these hosts in the domestic and sylvatic cycles where these viruses circulate. Here, we explore how the different host-derived skin odours influence Aedes mosquito responses in these two environments. In field assays, we show that the cyclic ketone cyclohexanone is a signature cue for Aedes mosquitoes to detect the NHP baboon, sykes and vervet, whereas for humans, it is the unsaturated aliphatic keto-analogue 6-methyl-5-hepten-2-one (sulcatone). We find that in the sylvatic environment, CO2-baited traps combined with either cyclohexanone or sulcatone increased trap catches of Aedes mosquitoes compared to traps either baited with CO2 alone or CO2 combined with NHP- or human-derived crude skin odours. In the domestic environment, each of these odourants and crude human skin odours increased Aedes aegypti catches in CO2-baited traps. These results expand our knowledge on the role of host odours in the ecologies of Aedes mosquitoes, and the likelihood of associated spread of pathogens between primates and humans. Both cyclohexanone and sulcatone have potential practical applications as lures for monitoring Aedes disease vectors.
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A previously unreported potential malaria vector in a dry ecology of Kenya. Parasit Vectors 2019; 12:80. [PMID: 30744665 PMCID: PMC6369554 DOI: 10.1186/s13071-019-3332-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 01/31/2019] [Indexed: 12/23/2022] Open
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.
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Population genetics of Anopheles funestus, the African malaria vector, Kenya. Parasit Vectors 2019; 12:15. [PMID: 30621756 PMCID: PMC6323828 DOI: 10.1186/s13071-018-3252-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 12/03/2018] [Indexed: 11/10/2022] Open
Abstract
Background Anopheles funestus is among the major malaria vectors in Kenya and sub-Saharan Africa and has been recently implicated in persistent malaria transmission. However, its ecology and genetic diversity remain poorly understood in Kenya. Methods Using 16 microsatellite loci, we examined the genetic structure of An. funestus sampled from 11 locations (n = 426 individuals) across a wide geographical range in Kenya spanning coastal, western and Rift Valley areas. Results Kenyan An. funestus resolved as three genetically distinct clusters. The largest cluster (FUN1) broadly included samples from western and Rift Valley areas of Kenya with two clusters identified from coastal Kenya (FUN2 and FUN3), not previously reported. Geographical distance had no effect on population differentiation of An. funestus. We found a significant variation in the mean Plasmodium infectivity between the clusters (χ2 = 12.1, df = 2, P = 0.002) and proportional to the malaria prevalence in the different risk zones of Kenya. Notably, there was variation in estimated effective population sizes between the clusters, suggesting possible differential impact of anti-vector interventions in represented areas. Conclusions Heterogeneity among Kenyan populations of An. funestus will impact malaria vector control with practical implications for the development of gene-drive technologies. The difference in Plasmodium infectivity and effective population size between the clusters could suggest potential variation in phenotypic characteristics relating to competence or insecticide resistance. This is worth examining in future studies. Electronic supplementary material The online version of this article (10.1186/s13071-018-3252-3) contains supplementary material, which is available to authorized users.
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Insights into malaria transmission among Anopheles funestus mosquitoes, Kenya. Parasit Vectors 2018; 11:577. [PMID: 30400976 PMCID: PMC6219006 DOI: 10.1186/s13071-018-3171-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 10/25/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Most malaria vectors belong to species complexes. Sibling species often exhibit divergent behaviors dictating the measures that can be deployed effectively in their control. Despite the importance of the Anopheles funestus complex in malaria transmission in sub-Saharan Africa, sibling species have rarely been identified in the past and their vectoring potential remains understudied. METHODS We analyzed 1149 wild-caught An. funestus (senso lato) specimens from 21 sites in Kenya, covering the major malaria endemic areas including western, central and coastal areas. Indoor and outdoor collection tools were used targeting host-seeking and resting mosquitoes. The identity of sibling species, infection with malaria Plasmodium parasites, and the host blood meal sources of engorged specimens were analyzed using PCR-based and sequencing methods. RESULTS The most abundant sibling species collected in all study sites were Anopheles funestus (59.8%) and Anopheles rivulorum (32.4%) among the 1062 successfully amplified specimens of the An. funestus complex. Proportionally, An. funestus dominated in indoor collections whilst An. rivulorum dominated in outdoor collections. Other species identified were Anopheles leesoni (4.6%), Anopheles parensis (2.4%), Anopheles vaneedeni (0.1%) and for the first time in Kenya, Anopheles longipalpis C (0.7%). Anopheles funestus had an overall Plasmodium infection rate of 9.7% (62/636), predominantly Plasmodium falciparum (59), with two infected with Plasmodium ovale and one with Plasmodium malariae. There was no difference in the infection rate between indoor and outdoor collections. Out of 344 An. rivulorum, only one carried P. falciparum. We also detected P. falciparum infection in two non-blood-fed An. longipalpis C (2/7) which is the first record for this species in Kenya. The mean human blood indices for An. funestus and An. rivulorum were 68% (93/136) and 64% (45/70), respectively, with feeding tendencies on a broad host range including humans and domestic animals such as cow, goat, sheep, chicken and pig. CONCLUSIONS Our findings underscore the importance of active surveillance through application of molecular approaches to unravel novel parasite-vector associations possibly contributed by cryptic species with important implications for effective malaria control and elimination.
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Abstract
BACKGROUND Coronary artery disease (CAD) is a growing epidemic on the African continent. It remains uncertain whether the risk factors identified as contributing to CAD in white populations contribute to a similar extent to CAD incidence in black populations. No data of the local population exists that is based on the coronary angiogram (CA). OBJECTIVES To analyse the relationship of conventional cardiovascular risk factors with presence of CAD in black Africans. DESIGN This was a dual-armed study, consisting of retrospective and prospective comparative arms. SUBJECTS Black Africans who underwent coronary angiography. SETTING Nairobi Hospital, Cathereterization laboratory. MAIN OUTCOME MEASURES The conventional risk factors: age, male gender, hypertension, obesity, smoking, diabetes mellitus, dyslipidaemia, alcohol use and interventricular septum (IVS) hypertrophy, as a marker of LVH. RESULTS One hundred and sixty nine patients fulfilled the inclusion criteria; 144 in the retrospective arm and 25 in the prospective. The larger retrospective arm showed that the group with CAD, compared to the normal group, was significantly older, with a higher mean age of 54.4 years compared to 49.8 years (P=0.005); had significantly more males, with a male to female ratio of 5.5:1 compared to 2.3:1 (P=0.045); had a very significantly larger proportion of diabetics (38.5% compared to 12%, P=0.0002), and also had a significantly larger proportion of patients with dyslipidaemia (67.3% compared to 35.9%, P=0.0003). The percentage of hypertensives was high in both groups, with (65.4%) in the CAD group and 62% in the Normal group being hypertensive (P=0.68). The percentage of smokers was small in both groups, being 15.4% and 13% respectively. Smoking, increased BMI, alcohol use, and increased IVS were each found to be distributed equally in both groups. In addition, the Waist hip ratio (WHR) and waist circumference (WC) did not differ significantly between the two groups studied. CONCLUSIONS The risk factors found to be most strongly associated with presence of angiographically-detected CAD in the population studied were diabetes mellitus, dyslipidaemia, age and male gender. There was a high prevalence of hypertension, with equal distribution in both groups under study; hence this risk factor was not discriminatory for CAD. There was a low prevalence of cigarette smoking in this particular study; it was not predictive of presence of CAD.
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