Entomological assessment of tsetse-borne trypanosome risk in the Shimba Hills human-wildlife-livestock interface, Kenya

Abstract

Shimba Hills is a wildlife area in Kenya and a major focus of tsetse-borne trypanosomes in East Africa. In Shimba Hills, tsetse-borne trypanosomes constrain animal health and smallholder livelihoods. However, epidemiological data to guide hotspot-targeted control of infections are limited. This study assessed the dynamics of tsetse-borne trypanosome risk in Shimba Hills with the objective to describe infection hotspots for targeted control. Tsetse flies (n = 696) collected in field surveys between November 2018 and September 2019 in Shimba Hills were characterized for chronological age and phenotypic sizes and screened for trypanosome and cattle DNA. Entomological inoculation rates for trypanosome risk assessment were derived from the product of fly abundance and molecular rates of vector infection and confirmed cattle bloodmeals in tsetse flies. In addition, cattle health indicators including anemia scores were assessed in contemporaneous parasitological surveys that screened livestock blood samples (n = 1,417) for trypanosome using the buffy-coat technique. Compared with Glossina brevipalpis and G. austeni, G. pallidipes was the most abundant tsetse fly species in Shimba Hills and had a wider spatial distribution and greater likelihood for infectious bites on cattle. The risk of cattle infection was similar along the Shimba Hills human-wildlife-livestock interface and high within one thousand meters of the wildlife reserve boundary. Trypanosomes in tsetse flies were highly diverse and included parasites of wild-suids probably acquired from warthogs in Shimba Hills. Age and phenotypic sizes were similar between tsetse fly populations and did not affect the probability of infection or cattle bloodmeals in the vectors. Anemia was more likely in trypanosome-positive cattle whilst parasitological infection rates in cattle samples maintained a weak relationship with entomological inoculation rates probably because of the limited time scale of sample collection. Trypanosome risk in Shimba Hills is high in locations close to the wildlife reserve and driven by G. pallidipes infectious bites on cattle. Therefore, trypanosome vector control programmes in the area should be designed to reduce G. pallidipes abundance and tailored to target sites close to the wildlife reserve.

Evidence-based advice on timing and location of tsetse control measures in Shimba Hills National reserve, Kenya

“…In Kenya, there is a positive correlation between the occurrence of tsetse flies and the locations of protected areas (Kenya Tsetse and Trypanosomiasis Eradication Council). Although protected areas serve as breeding hotspots for tsetse flies, these flies are found to be distributed extensively beyond the boundaries of these protected areas [ 27 , 28 ]. The Kenya Wildlife Service (KWS) manages these protected areas and prohibits the control of tsetse flies within them, as part of its duty to protect all animals, thereby preventing the deployment of odour-baited targets at any density within the national reserve.…”

Insights into Trypanosomiasis Transmission: Age, Infection Rates, and Bloodmeal Analysis ofGlossina fuscipes fuscipesin N.W. Uganda

“…Recognition of the limitations of dissection-based methods has led to greater use of PCR as a diagnostic tool [18–20]. However, studies using PCR-based methods alone are unable to distinguish tsetse with mature infections from immature ones, and it is only the former that are infectious.…”

“…This, coupled with the fact that traps tend to be biased towards the capture of old flies [17] means that the infection rate among trap-caught flies will tend to be greater than in the population as a whole. Recognition of the limitations of dissection-based methods has led to greater use of PCR as a diagnostic tool [18][19][20]. However, studies using PCR-based methods alone are unable to distinguish tsetse with mature infections from immature ones, and it is only the former that are infectious.…”

Modelling the spatial and temporal distribution of tsetse flies for targeted control

“…Despite these opposing forces, trypanosomiasis remains a problematic disease; for communities residing along the tsetse-wildlife interface (Figure 1.2), the impact of trypanosomiasis on both livestock and humans is devastating (Meyer et al, 2016;Lord et al, 2020;Ebhodaghe et al, 2022).…”

“…In Kenya, there is a positive correlation between the occurrence of tsetse flies and the locations of protected areas (Kenya Tsetse and Trypanosomiasis Eradication Council). Although protected areas serve as breeding hotspots for tsetse flies, these flies are found to be distributed extensively beyond the boundaries of these protected areas (Saini et al, 2017;Ebhodaghe et al, 2022). The Kenya Wildlife Service (KWS) manages these protected areas and prohibits the control of tsetse flies within them, as part of its duty to protect all animals, thereby preventing the deployment of odour-baited targets at any density within the national reserve.…”