Dormant infections can relapse under the influence of long distance animal migrations, according to a new study.
The study in Proceedings of the Royal Society B said that a clear understanding of how migratory relapse shapes infection risk is good as migratory animals are known to carry diseases that can be transmitted to humans as well.
The researchers say that relapse can increase or decrease infection levels in migratory species. It depends on how deadly the disease is and where in the migratory range it can be transmitted.
The study notes that animal migration can influence transmission of infectious diseases through several mechanisms. One such is that migration can expose hosts to a greater number of infectious diseases as they cover a larger area and visit more habitats.
However, the researchers also say that infected animals are less likely to survive migratory journeys. This is just like a person having some flu running a marathon who will find it difficult to complete the race, the researchers said.
The study said that some migratory animals and birds may not fully clear the infection and may be dormant until it is reactivated by events like migration.
The researchers developed a mathematical model to explore patterns of relapsing infections in migratory animals. The model looked into the annual cycle of a migratory animal that included a breeding season, migration season and overwintering season. It showed that relapse can amplify infection throughout the year in benign pathogens that don’t kill their hosts. These pathogens are maintained in migratory populations. However, migratory relapse can also have the opposite effect for deadlier and more easily transmitted pathogens as the hosts die during travel.
The researchers developed the model using data from dark-eyed junco, a North American migratory songbird.