The transmission of the filovirus Ebola from bats to humans illustrates the complexity of the spread of these diseases and its relation to climate change and land disturbance. Simple bat-human contact isn’t sufficient for the filovirus Ebola to erupt.
“It’s a cascade of events” that bring bats, apes, and humans together in unusual ways, aggravated in part by “unique climatic conditions,” says World Health Organization zoonoses expert Pierre Formenty. According to a NASA analysis of meteorologic satellite data, Ebola outbreaks correlate with heavy rains at the end of a period of intense aridity. Extremely dry conditions force some fruit trees to defer fruiting. When the rains come and the stricken trees put out fruit, all manner of fruit-starved species, including Pteropus bats and apes, gather to feast. Large numbers of creatures concentrated under newly fruit-heavy trees provide microbes such as Ebola a prime opportunity to jump from one species to another. And once Ebola starts circulating heavily in a new species such as apes or bats, it can readily be transmitted through infected blood and other fluids to humans.
Whether the warming planet will aggravate the unusual rainfall patterns that set the scene for Ebola outbreaks remains unclear. While experts in conservation medicine have made great strides delineating the links between climate and disease, projections about how disease patterns will shift as the climate changes are still nascent. Worryingly, however, a trend toward aridity has already been noted across African rainforests.