So far, many have been found only to be carriers and cannot transmit disease.
Their ability to transmit the disease to others might diminish as well.
And all groups worry about the potential for transmitting disease from one species to another.
Finally, insects have also been shown to transmit the disease.
Women and men with the affected gene can transmit the disease.
"They are food for carnivores, and so would not be around to transmit the disease to people."
The addicts then transmit the disease to their sexual partners and children.
There is no evidence that dogs can transmit the disease directly to humans.
There is no evidence that they transmit diseases to humans or other animals.