Though environmental fluctuations are related to anthrax temporal dynamics, the causal relationships mostly involve animal behavioral change in response to environment. Herbivores are known to switch their foraging strategies, resulting in different exposure to pathogens since foraging at carcass sites is known to be the most important transmission pathway. My second study aims to investigate the change in exposure due to the shift in herbivore spatiotemporal foraging patterns. I fitted zebras and wildebeests with satellite GPS collars. Using telemetry data from the two species, I categorize 30-min readings into different behavioral states relying on the movement parameters by hidden Markov models and simulate relative population exposure to anthrax by season. 

Herbivores use different habitat when the resource availability varies. My last study aims to use resource selection function from telemetry data and spatial anthrax mortality distribution to understand the habitat use of herbivores in different rainfall years and how the resource availability ends up changing herbivore anthrax risk because of spatial variability of anthrax exposure.

The causes underlying dynamics in infectious diseases are frequently perplexing. Many different mechanisms may cause pathogens or vectors to vary in their reproduction and survivability in environments. On the other hand, host-dependent causes also include a variety of factors. In response to changes of weather, predation pressure, or food availability, organisms adjust behaviorally and physiologically. Behavioral change in turn alters disease transmissibility  mostly owing to change in the contact frequency between hosts and pathogens. Shifts in host immune function due to factors such as weather, nutrition, or breeding can cause variation in host susceptibility. In addition, reproduction also results in a change of transmission due to a pulse in recruitment of new immunologically naïve host individuals. My PhD research is investigating the contribution to anthrax dynamics in herbivorous wildlife by changes in weather, vegetation, and host movement and behavior in Etosha National Park, Namibia and Kruger National Park, South Africa. The study starts with temporal dynamics in the both parks and reveals the spatially anthrax dynamics in Etosha as well.

The first study is an analysis of long-term datasets on weather, NDVI, and anthrax mortalities. It has been documented that environmental variation, specifically precipitation, temperature and vegetation, are related to disease dynamics. Revealing how environmental changes relate to outbreaks, and at what scales, will help resolve the issue of how weather correlates with outbreaks. Thus, this study aims to reveal certain weather or vegetation signals associated with anthrax outbreaks intra-annually and inter-annually.

Ph.D. Student in Wildlife Ecology
University of Wisconsin-Madison

Yen-Hua Huang, D.V.M