Hostswitching

Hostswitching refers to the process by which a parasite, pathogen, or symbiont moves from its original host species to a new one, establishing at least transient or sustained infection. A host switch may involve direct transmission between species or expansion via vectors, and it does not always result in a stable or transmissible infection in the new host.

It is a central concept in disease ecology, parasitology, and evolutionary biology because cross-species transmission can give rise to emerging infectious diseases and alter ecosystem dynamics. Successful host switches require compatibility between the pathogen’s life cycle and the biology of the new host, and often involve genetic changes that enhance receptor binding, immune evasion, or replication in the new host.

Drivers include ecological overlap between species, habitat disturbance, climate change, and increased movement of people, animals, and goods that bring distinct host populations into contact. Vectors such as mosquitoes or ticks can also facilitate host-switching by delivering pathogens to new hosts.

Examples include influenza A viruses that jump between birds, swine, and humans; HIV-1 arising from simian immunodeficiency viruses crossing into humans; and various parasites that have shifted from wildlife reservoirs to domestic animals or humans. In some cases, the new host supports only limited transmission, while in others the pathogen becomes endemic and causes sustained outbreaks.

Understanding host-switching is essential for surveillance, risk assessment, and control strategies. Monitoring genetic changes, host range, and ecological interfaces helps predict and prevent spillover events.