RESUMEN
For grazing herbivores, dung density in feeding areas is an important determinant of exposure risk to fecal-orally transmitted parasites. When host species share the same parasite species, a nonrandom distribution of their cumulative dung density and/or nonrandom ranging and feeding behavior may skew exposure risk and the relative selection pressure parasites impose on each host. The arid-adapted Grevy's zebra (Equus grevyi) can range more widely than the water-dependent plains zebra (Equus quagga), with which it shares the same species of gastrointestinal nematodes. We studied how the spatial distribution of zebra dung relates to ranging and feeding behavior to assess parasite exposure risk in Grevy's and plains zebras at a site inhabited by both zebra species. We found that zebra dung density declined with distance from water, Grevy's zebra home ranges (excluding those of territorial males) were farther from water than those of plains zebras, and plains zebra grazing areas had higher dung density than random points while Grevy's zebra grazing areas did not, suggesting a greater exposure risk in plains zebras associated with their water dependence. Fecal egg counts increased with home range proximity to water for both species, but the response was stronger in plains zebras, indicating that this host species may be particularly vulnerable to the elevated exposure risk close to water. We further ran experiments on microclimatic effects on dung infectivity and showed that fewer nematode eggs embryonated in dung in the sun than in the shade. However, only 5% of the zebra dung on the landscape was in shade, indicating that the microclimatic effects of shade on the density of infective larvae is not a major influence on exposure risk dynamics. Ranging constraints based on water requirements appear to be key mediators of nematode parasite exposure in free-ranging equids.
RESUMEN
[This corrects the article DOI: 10.3389/fvets.2021.637580.].
RESUMEN
More than 50 million cattle are likely exposed to bovine tuberculosis (bTB) worldwide, highlighting an urgent need for bTB control strategies in low- and middle-income countries (LMICs) and other regions where the disease remains endemic and test-and-slaughter approaches are unfeasible. While Bacillus Calmette-Guérin (BCG) was first developed as a vaccine for use in cattle even before its widespread use in humans, its efficacy against bTB remains poorly understood. To address this important knowledge gap, we conducted a systematic review and meta-analysis to determine the direct efficacy of BCG against bTB challenge in cattle, and performed scenario analyses with transmission dynamic models incorporating direct and indirect vaccinal effects ("herd-immunity") to assess potential impact on herd level disease control. The analysis shows a relative risk of infection of 0.75 (95% CI: 0.68, 0.82) in 1,902 vaccinates as compared with 1,667 controls, corresponding to a direct vaccine efficacy of 25% (95% CI: 18, 32). Importantly, scenario analyses considering both direct and indirect effects suggest that disease prevalence could be driven down close to Officially TB-Free (OTF) status (<0.1%), if BCG were introduced in the next 10-year time period in low to moderate (<15%) prevalence settings, and that 50-95% of cumulative cases may be averted over the next 50 years even in high (20-40%) disease burden settings with immediate implementation of BCG vaccination. Taken together, the analyses suggest that BCG vaccination may help accelerate control of bTB in endemic settings, particularly with early implementation in the face of dairy intensification in regions that currently lack effective bTB control programs.