Adding to the evidence was a tantalizing snippet of another AIDS-like virus found in a tube of blood from a baby chimpanzee that had died.

Proof would require finding an AIDS-like virus in the polio vaccine samples.

An AIDS-like virus could still lurk in the polio vaccine, even if the scientists do not detect it.

Investigators also found a fourth captive chimpanzee that was infected with a genetically distinct AIDS-like virus.

And so, she said, she and her colleagues set out to find a way to detect AIDS-like viruses in wild chimpanzees.

And researchers have found that other animals have their own AIDS-like viruses and are widely infected with them but do not become ill.

At least 20 species of African primates are infected with, but seemingly unaffected by, AIDS-like viruses.

But chimpanzees are not widely infected with an AIDS-like virus.

Then, in June, a report about oral transmission of an AIDS-like virus in six rhesus monkeys implied that the common wisdom was false.

The concept of transient infection has had support from observations of an AIDS-like virus in animals.