Rainfall as a driver of seasonality in parasitism

International Journal for Parasitology: Parasites and Wildlife

Summary by Kailah Massey

Corresponding authors: Vanessa Ezenwa, vezenwa@uga.edu

Seasonal changes in rainfall, temperature, and the amount of food available, are known to affect parasitism in host populations. Rainfall in particular has been shown to have a strong effect on helminths, parasitic worms that can cause weakness or disease in their hosts. . In the short-term, rainfall influences helminth survival and animal movement, thus influencing the chances of parasite exposure. Rainfall can also affect parasitism in the long-term by influencing the quality and quantity of food available for host species. This can in turn affect host body condition and immune function, making them more or less susceptible to parasitism. A better understanding of how rainfall affects parasite exposure and host susceptibility is needed to understand the relationship between seasonality and parasite infection.

To test the relative importance of the immediate and delayed effects of rainfall on parasitism,  Professor Vanessa Ezenwa (a CEID member), and student Caroline Shearer examined the impacts of seasonal changes in rainfall on helminth infection in Grant’s gazelle.Using data from an earlier study on parasitism in Grant’s gazelles, Ezenwa and Shearer compared parasite fecal egg and larval counts to rainfall at the time of sampling, and 1 and 2 months prior to sampling. Using parasitological and statistical analyses, they assessed the associations between parasite burden and amount of rainfall.

They found that the delayed effects of rainfall were better predictors of parasitism rates, than the immediate effects – thus the effects of rainfall on host susceptibility may be more important than the effects on parasite exposure.  Overall, the study supports rainfall as an important driver of seasonal variation in parasitism, with the effects of low rainfall on host susceptibility to be of particular importance. They note that further research is needed to better understand how various pathways linking rainfall and parasitism interact.

Shearer, C. L., & Ezenwa, V. O. (2020). Rainfall as a driver of seasonality in parasitism. International Journal for Parasitology: Parasites and Wildlife.

Photo credit:

“Grant’s Gazelle (Nanger granti) (7667412914)” by Bernard DUPONT is licensed under CC By-SA 2.0