Migration shapes patterns of disease transmission

Long-distance animal migrations can trigger relapse of dormant infections, influencing when and where infection risk peaks, according to a new paper in Proceedings of the Royal Society B. The findings demonstrate that relapse can increase or decrease infection levels in migratory species, depending how deadly the disease is, and where in the migratory range it can be transmitted. As migratory animals often carry diseases that can jump from animals to humans, understanding how migratory relapse can shape infection risk has implications for public health.

Animal migration has the potential to influence the transmission of infectious diseases through several mechanisms. Migration can expose hosts to a greater number of infectious diseases because they cover a larger area and visit more habitats than residents. However, as long-distance movement is energetically taxing, migration can have a culling effect on infected hosts, thus reducing infection risk.

To better understand this phenomenon, known as migratory relapse, Hall and colleagues Daniel Becker and Ellen Ketterson of Indiana University developed a mathematical model to explore patterns of relapsing infections in migratory animals, and the implications for where and when infectious disease risk is highest.

Their model describes the annual cycle of a migratory animal, including a breeding season, a migration season and an overwintering season. It shows that for more benign pathogens that typically don’t kill their hosts, relapse can amplify infection throughout the year, and may play a key role in maintaining those pathogens in migratory populations. However, for deadlier and more easily transmitted pathogens, migratory relapse can have the opposite effect, reducing infection across the annual cycle by culling infected hosts during travel.

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