Describe the ecological concept of spillover and provide a One Health example.

• A. Spillover is pathogen transmission from a reservoir host to a new species; example: coronaviruses crossing from bats/potential intermediate hosts to humans.
• B. Spillover is transmission from humans to plants.
• C. Spillover is disease transmission only within domestic animals.
• D. Spillover is antibody movement between species.

Answer: (A)

Spillover is when a pathogen that is circulating in one species or population jumps to a different host species, starting infection there and potentially causing disease. This cross-species transmission is a central concern in One Health because it links ecological change, wildlife, livestock, and human health through shared pathogens and interfaces where contact occurs.

A One Health example is coronaviruses that circulate in bat populations and occasionally infect other species, including humans. Often an intermediate host facilitates the jump, such as civets in the SARS outbreak or camels in MERS, with SARS-CoV-2 broadly associated with a bat reservoir and possible intermediate species before human infection. These spillover events are influenced by factors like habitat disruption, wildlife trade, livestock farming practices, and climate change, all of which bring humans and wildlife into closer contact and create opportunities for pathogens to cross species barriers.

The other ideas don’t fit spillover: transmission to plants isn’t the cross-species pathogen jump under discussion, transmission confined to domestic animals doesn’t involve a new host species, and antibody movement between species is about immune components, not the pathogen spreading across species boundaries.