Marilyn was the only one infected with the simian virus.

What researchers most want to know is why the simian virus doesn't kill the host apes.

He said recent successes in a vaccine against simian virus had also contributed to the optimism.

They studied a recently isolated strain of a simian immunodeficiency virus.

Other tests found evidence of the simian virus.

Blood tests performed repeatedly and frequently since then showed evidence of antibodies to the simian virus, but only for a brief period.

He then began to study how the genome of simian virus 40 (SV40) is duplicated in cells.

And even if a simian virus turned up in the stored samples, it would not prove that it started the epidemic.

If they are infected, they would be the first people reported to be infected with the simian virus.

Thus, the simian foamy viruses may have co-speciated with Old World primates for at least 30 million years.