The risk of animals passing diseases to humans could increase in some cases, but decrease in others, as people encroach on and disrupt wildlife migration paths, according to a review in Science (21 January). Climate change is also affecting migration patterns, and the review says there is an urgent need for research on how changes in habitat and climate will affect disease in migratory animals, to predict risks for both people and wildlife.

Although there is a general assumption that long-distance movements of migrating animals can increase the spread of pathogens, including zoonotic pathogens that jump from animals to humans, such as Ebola virus in bats and avian flu viruses in birds, the evidence for this is scarce, the review says.

"There are examples that suggest that most wild birds aren't likely to spread the most pathogenic strains of avian flu over long distances, as was previously suspected," Sonia Altizer, at the Odum School of Ecology, University of Georgia, United States, told SciDev.Net.

There might even be a decrease in transmission risk for some diseases, according to the review, but more research is needed to make accurate predictions.

"One of the biggest surprises is that there aren't a lot of clear, published cases of migratory species carrying infectious diseases. This could be partly because of the challenges of studying species across international borders," Altizer said.

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