Which scenario best illustrates spillover from bats to humans?

• A. Transmission from bats to humans via intermediate hosts.
• B. Transmission from humans to dogs.
• C. Transmission from plants to humans.
• D. Transmission only within the same species.

Answer: (A)

Spillover happens when a pathogen that is maintained in a reservoir species crosses into a new host species. Bats are a well-known reservoir for several viruses, so a scenario where the virus moves from bats to humans via an intermediate host demonstrates this cross-species jump and the bridging role an intermediate host can play. The intermediate host can amplify the pathogen and bring it into closer contact with humans, making transmission to people more likely, as seen in real events like Nipah virus outbreaks where bats transmit to pigs and then to humans (the pigs serve as the bridge).

The other options don’t fit this pattern: transmission from humans to dogs is a reverse zoonosis and starts in humans rather than from the bat reservoir; transmission from plants to humans isn’t a wildlife-to-human spillover; and transmission only within the same species involves no cross-species jump.