This antigenic shift could cause the formation of a highly virulent virus.

If human to human transmission became commonplace among any virulent avian virus, the results could be disastrous.

He knew that a virulent virus, like this one, would probably have found its way through the entire population already.

But in the laboratory, the virulent viruses died, leaving only the helper viruses, which do not themselves cause disease.

A virus following a lytic cycle is called a virulent virus.

A common and very virulent polymorphic virus is the file infecter Virut.

Computers in at least 150 city public schools have been affected by a number of "particularly virulent" viruses, Department of Education officials said yesterday.

Twenty-five of our comrades died before we were able to bring the most virulent viruses and bacteria under control.

It is a virulent, blood-borne virus that sends its hosts into a state of extreme rage.

This highly virulent virus was later discovered to be a chimaera of two distinct begomovirus species.