Droughts Can Alter Disease Dynamics in Aquatic Ecosystems, Study Finds

A recent study co-authored by researchers from the Cary Institute of Ecosystem Studies, published in Trends in Ecology and Evolution, explores how droughts can influence the dynamics of water-related diseases. The study provides a framework to understand how certain parasites may thrive or decline during drought conditions.

The research highlights that while droughts can sometimes reduce aquatic diseases, they can also lead to an increase in diseases that depend on water. For instance, during droughts, animals may gather around remaining water sources, creating hotspots for parasite transmission. This was observed in East Africa, where watering holes became centers for gastrointestinal nematode transmission among herbivores.

The study identifies three key mechanisms that determine the fate of parasites during droughts: changes in host distribution, impacts on host and parasite health, and the favoring of drought-tolerant species. Droughts can alter water quality, affecting parasite survival and host susceptibility. For example, increased salinity can boost perkinsosis infections in oysters but reduce copepod infections in fish.

Moreover, droughts can favor species that thrive in reduced water conditions, such as mosquitoes, which breed in shallow waters. This can lead to an increase in vector-borne diseases. The study emphasizes the importance of understanding these mechanisms to predict emerging disease threats in a world facing more frequent droughts.

The study was inspired by observations of amphibians and their parasites in California ponds during droughts between 2012 and 2025. These observations revealed that droughts significantly alter ecological interactions, affecting how diseases spread.