Biology subjects

Oundo, J. W.

Publications and source records attributed to Oundo, J. W..

5 recordsLinked to original sources

bioRxiv2024

Biological tick control: modeling the potential impact of entomopathogenic fungi on the transmission of East Coast fever in cattle

Biological control of ticks using entomopathogenic fungi (EPF) is a highly desired alternative to chemical acaricides for the control of tick-borne pathogens. For Metarhizium anisopliae isolate ICIPE 7, one of these EPFs, efficacy against multiple tick species has been demonstrated in laboratory and field settings. However, we currently have little quantitative understanding of how EPFs can impact transmission. We developed a deterministic model of tick-host-pathogen interactions to explore how the effects of EPF on Rhipicephalus appendiculatus ticks may impact the transmission dynamics of East Coast fever (ECF) in cattle populations. We parameterized the multi-faceted effects of EPFs on tick dynamics using experimental data on Tickoff(R) biopesticide (a novel formulation of M. anisopliae ICIPE 7) and related EPFs. The epidemiological impact of EPF was evaluated across a range of product profiles and implementation strategies. Model results indicate that, for the explored product profiles, EPF derives most of its epidemiological impact through the delayed mortality effect. This EPF-induced mortality could not only reduce the onward Theileria parva transmission to cattle (both treated and untreated) but could also cause a reduction in the tick-to-host ratio and thus cattle exposure to ticks. The effects of EPF on reproduction fitness and engorgement of ticks elicit negligible impact. High levels of population coverage and treatment frequency are needed to reduce the tick population size and reach meaningful epidemiological impact in cattle populations. Additionally, increasing the persistence time of fungal conidia on cattle skin - through technological improvements to the EPF formulation - can substantially reduce acute infections when combined with appreciable population coverage levels, treatment frequency, and efficient spraying techniques. Our model analysis provides insights into the potential impact of EPF when deployed at a population level, and lends support to further research and development of this biological tick control tool.

microbiology↗

bioRxiv2020

Tsetse blood-meal sources, endosymbionts, and trypanosome infections provide insight into African trypanosomiasis transmission in the Maasai Mara National Reserve, a wildlife-human-livestock interface

BackgroundAfrican trypanosomiasis (AT) is a neglected disease of both humans and animals caused by Trypanosoma parasites, which are transmitted by obligate hematophagous tsetse flies (Glossina spp.). Understanding of AT transmission is hampered by limited knowledge on interactions of tsetse flies with their vertebrate hosts and the influence of endosymbionts on vector competence, especially in wildlife-human-livestock interfaces. We identified the tsetse species, their blood-meal sources, and the correlation between endosymbiont and trypanosome infection status in the trypanosome-endemic Maasai Mara National Reserve (MMNR) of Kenya. Methodology/Principal FindingsAmong 1167 tsetse flies (1136 Glossina pallidipes, 31 Glossina swynnertoni) collected from 10 sampling sites, 28 (2.4%) were positive by PCR for trypanosomes, majority (17/28) being Trypanosoma vivax. Blood-meal analyses based on high-resolution melting analysis of mitochondrial cytochrome c oxidase 1 and cytochrome b gene PCR products (n = 345) identified humans as the most common vertebrate host (37%), followed by hippopotamus (29.1%), African buffalo (26.3%), elephant (3.39%), and giraffe (0.84%). Trypanosome-infected flies had fed on hippopotamus and buffalo. Additionally, PCR analysis revealed that tsetse flies were more likely to be infected with trypanosomes if they were infected with the Sodalis glossinidius endosymbiont (P = 0.0022 Fishers exact test). Conclusions/SignificanceDiverse species of wildlife hosts may contribute to the maintenance of tsetse populations and/or persistent circulation of African trypanosomes in the MMNR. Although the African buffalo is known to be a key reservoir of AT, the higher proportion of hippopotamus blood-meals in trypanosomes-infected flies identified here indicates that other wildlife species may also be important to transmission cycles. No trypanosomes associated with human disease were identified, but the high proportion of human blood-meals identified are indicative of human African trypanosomiasis transmission risk. Furthermore, this work provides data showing that Sodalis endosymbionts can is associated with increased trypanosome infection rates in endemic ecologies. Author summaryHuman and animal African trypanosomiasis are neglected tropical diseases with potential to spread to new areas. Wild animals are important reservoirs for African trypanosomes and crucial in the emergence and re-emergence of AT. Vertebrate host-vector-parasite interactions are integral to trypanosome transmission. We investigated the vertebrate blood-meals and trypanosomes-endosymbionts co-infections in tsetse flies, which have been associated with reservoirs and vector competence, respectively, on AT transmission in Kenyas Maasai Mara National Reserve. We identified tsetse fly diversity, trypanosome and endosymbiont infection status, and vertebrate blood-meal hosts to infer potential transmission dynamics. We found that Glossina pallidipes was the major tsetse fly vector and that Trypanosoma vivax was the main trypanosome species circulating in the region. Humans, hippopotamus, and buffalo were the most frequented for blood-meals. Buffalo and hippopotamus blood-meals were identified in trypanosome infected flies. Feeding of the flies on both humans and wildlife may potentiate the risk of the human trypanosomiasis in this ecology. Additionally, we found that the endosymbiont Sodalis glossinidius is associated with higher trypanosome infection rates in wild tsetse flies. These findings emphasize the importance of understanding the interaction of tsetse flies with vertebrate blood-meal sources and their endosymbionts in the transmission and control of AT.

molecular biology↗

bioRxiv2020

Pathogens, endosymbionts, and blood-meal sources of host-seeking ticks in the fast-changing Maasai Mara wildlife ecosystem

BackgroundThe role of questing ticks in the epidemiology of tick-borne diseases in Kenyas Maasai Mara National Reserve (MMNR), an ecosystem with intensified human-wildlife-livestock interactions, remains poorly understood. Therefore, we carried out a survey of the diversity of questing ticks, their blood-meal hosts, and tick-borne pathogens to understand potential effects to human and livestock health. MethodsQuesting ticks were collected by flagging and hand picks from vegetation in 25 localities and identified based on morphologic and molecular criteria. We used PCR with high-resolution melting (HRM) analysis, and sequencing to identify Anaplasma, Babesia, Coxiella, Ehrlichia, Rickettsia, and Theileria pathogen diversities and blood meals in 231 tick pools. ResultsA total of 1,465 host-seeking ticks were collected, including Rhipicephalus appendiculatus (n = 1,125), Rhipicephalus pulchellus (n = 6), Rhipicephalus evertsi (n = 5), Amblyomma cf. gemma (n = 178), Amblyomma gemma (n = 145), Amblyomma variegatum (n = 4), Amblyomma sp. (n = 1), and Haemaphysalis leachi (n = 1). Remnant blood-meals from humans, wildebeest, and African buffalo were detected in Rh. appendiculatus, goat in Rh. evertsi, sheep in Am. gemma, and cattle in Am. variegatum. Rickettsia africae was detected in Am. gemma (1/25 pools) that had blood-meal remnant from sheep and Am. variegatum (4/25 pools) that had fed on cattle. Rickettsia spp. were found in Am. gemma (4/25 pools) and Rh. evertsi (1/4 pools). Anaplasma ovis was detected in Rh. appendiculatus (1/172 pools) and Rh. evertsi (1/4 pools), while Anaplasma bovis was detected in Rh. appendiculatus (1/172 pools). Theileria parva was detected in Rh. appendiculatus (27/172 pools). Babesia, Ehrlichia and Coxiella pathogens were not found in any ticks. Unexpectedly, diverse Coxiella sp. endosymbionts were detected in all tick genera (174/231 pools). ConclusionsThe data shows that ticks from the rapidly-changing MMNR are infected with zoonotic R.africae and unclassified Rickettsia spp, demonstrating the persistent risk of African tick-bite fever and other and Spotted Fever Group rickettsioses to local dwellers and visitors to the Maasai Mara ecosystem. Protozoan pathogens that may pose risk to livestock production were also identified. We also highlight possible existence of morphotypic variants of Amblyomma species, based on the observation of Ambyomma cf. gemma, which may be potential human parasites or emergent disease vectors. Our findings also demonstrate that questing ticks in this ecosystem have dynamic vertebrate blood sources including humans, wildlife and domestic animals, which may amplify transmission of tickborne zoonoses and livestock diseases. Further studies are needed to determine the role of Coxiella endosymbionts in tick physiology and vector competence.

molecular biology↗

bioRxiv2019

A Microsporidian blocks Plasmodium falciparum transmission in Anopheles arabiensis mosquitoes

Malaria imposes an enormous burden on sub-Saharan Africa, and evidence that incidence could be starting to increase again1 suggests the limits of currently applied control strategies have now been reached. A possible novel control approach involves the dissemination in mosquitoes of inherited symbiotic microbes to block transmission. This strategy is exemplified by the use of transmission-blocking Wolbachia in Aedes aegypti against dengue virus2-7. However, in the Anopheles gambiae complex, the primary African vectors of malaria, there limited reports of inherited symbionts with transmission-blocking capacity8-10. Here we show that a newly discovered vertically transmitted species of Microsporidia symbiont in the An. gambiae complex blocks Plasmodium transmission. Microsporidia MB is present at moderate prevalence in geographically dispersed populations of An. arabienesis in Kenya, localized to the mosquito midgut and ovaries, and is not associated with significant reductions in adult host fecundity or survival. Field collected Microsporidia MB-infected An. arabiensis were never found to harbor P. falciparum gametocytes and on experimental infection with P. falciparum no sporozoites could be detected in Microsporidia MB-infected mosquitos. As a Plasmodium transmission-blocking microbe that is non-virulent and vertically transmitted, Microsporidia MB could be exploited as a novel malaria control tool.

microbiology↗

bioRxiv2019

Three-gene PCR and high-resolution melting analysis for differentiating vertebrate species mitochondrial DNA for forensic and biodiversity research pipelines

Reliable molecular identification of vertebrate species from morphologically unidentifiable tissue is critical for the prosecution of illegally-traded wildlife products, conservation-based biodiversity research, and identification of blood-meal hosts of hematophagous invertebrates. However, forensic identification of vertebrate tissue relies on the sequencing of mitochondrial cytochrome oxidase I (COI) barcode genes, which remains costly for purposes of screening large numbers of unknown samples during routine surveillance. Here, we adopted a rapid, low-cost approach to differentiate 10 domestic and 24 wildlife species that are common in the East African illegal wildlife products trade based on their unique high-resolution melting profiles from COI, cytochrome b, and 16S ribosomal RNA gene PCR products. Using the approach, we identified (i) giraffe among covertly sampled meat from Kenyan butcheries, and (ii) forest elephant mitochondrial sequences among savannah elephant reference samples. This approach is being adopted for high-throughput pre-screening of potential bushmeat samples in East African forensic science pipelines.

molecular biology↗