Effects of wildlife and cattle on tick abundance in central Kenya

Abstract

In African savannas, large mammals, both wild and domestic, support an abundant and diverse population of tick ectoparasites. Because of the density of ticks and the many pathogens that they vector, cattle in East Africa are often treated with acaricides. While acaricides are known to be effective at reducing tick burdens on cattle, their effects on the overall abundance and community composition of ticks in savanna ecosystems are less well understood. It is also not known how well tick populations can be maintained in the absence of large mammals. We evaluated the effects of wildlife and of acaricide-treated cattle on host-seeking tick populations in a long-term, exclusion experiment in central Kenya. Over seven years, we sampled larval, nymphal, and adult ticks monthly on replicated treatment plots that controlled for the presence of cattle and for the presence of two guilds of large wild mammals: megaherbivores (giraffes and elephants) and all other large wild herbivores (> 15 kg). Two species of ticks were found in this habitat; across all surveys, 93% were Rhipicephalus pulchellus and 7% were R. praetextatus. The presence of acaricide-treated cattle dramatically reduced the abundance of host-seeking nymphal and adult ticks but did not affect the abundance of host-seeking larval ticks. The abundance of larval ticks was determined by the presence of large wild mammals, which appear to import gravid female ticks into the experimental plots. On plots with no large mammals, either wild or domestic, larval and nymphal ticks were rare. Adult R. pulchellus were most abundant in plots that allowed wildlife but excluded cattle. Adult R. praetextatus were relatively abundant in plots without any large mammals. These differences suggest that these ticks utilize different members of the host community. The reduction in ticks that results from the presence of acaricide-treated cattle has potential health benefits for humans and wildlife, but these benefits must be weighed against potential costs, including reduced availability of food for birds such as oxpeckers that feed on ticks.

Serosurvey of Coxiella burnetii (Q fever) in Dromedary Camels (Camelus dromedarius) in Laikipia County, Kenya

“…Camel bomas or enclosures are typically relocated every few months to allow for new foraging areas to be accessed, which further increases tick exposure for camels while browsing in new environments. Acaricide use on cattle has been found to reduce the population of adult and nymphal host seeking ticks that feed on cattle and wildlife; therefore, continued acaricide use in camels could reduce Q fever transmission to wildlife in the area (Keesing et al., ). The presence of C. burnetii seropositive camels in Laikipia County, Kenya, suggests that camels may play a role in the C. burnetii livestock reservoir, tick vector, wildlife cycle in the area.…”

Declines in large wildlife increase landscape-level prevalence of rodent-borne disease in Africa

“…From a human risk perspective, the wild ungulates and large carnivores excluded in this study are also unlikely to interact closely with humans, making transmission less likely than rodent-human transmission. However, we expect that diseases transmitted by ectoparasites more common on ungulates than on rodents (e.g., predominantly tick-borne pathogens) will show very different, even inverted, responses (60,61).…”

Conservation lessons from large‐mammal manipulations in East African savannas: the KLEE, UHURU, and GLADE experiments

“…Notably, the strengths of these herbivore‐initiated indirect effects are variable in space, in ways that seem to be explained at least in part by underlying differences in primary productivity. Exclusion of wild LMH systematically increases population size structure and abundance of a common understory shrub, Hibiscus meyeri , as rainfall increases . Exclusion of (acaricide‐treated) cattle increased abundances of nymphal and adult ticks, an effect borne out across entire landscapes .…”