Controlling infection without clearing it
An immune system does not have to make every virus disappear to keep an animal functioning. In some bats, defenses can restrain viral activity while avoiding an intense, damaging inflammatory response—the body’s alarm reaction to infection. That balance can help limit illness even when some virus remains in the body.
This is different from sterilizing immunity, which stops an infection from taking hold or clears it so completely that no virus remains. If a virus persists, it may still multiply and leave the bat in bodily fluids or waste. The animal can therefore look healthy while remaining a possible source of exposure.
Why the distinction matters
Visible sickness is an unreliable guide to whether a virus is present. A sick animal may be easy to notice, but a healthy-looking carrier can shed virus without signaling danger. Risk to people depends on the particular virus and on how exposure occurs; simply being near a bat does not mean infection will follow.
The key point is that less disease in the host does not necessarily mean less virus available to spread. A bat’s ability to tolerate infection can protect the animal, while leaving open a route for a virus to reach another host.
