That disease is caused by a mutation.

She talked about her worries to her friend.

She is prone to worrying, so she is always thinking about something.

He is an expert in virology.

My computer got infected with a computer virus.

The Ebola virus is a very infectious virus.

The poliovirus is a virus that primarily enters the body through the mouth and destroys the nervous system.

Norovirus can be prevented by hand washing and disinfection.

Please use the emergency stairs in case of a fire.

Due to the earthquake, the city declared a state of emergency.