In a related study presented here Friday, researchers from the Centers for Disease Control and Prevention estimated that 56 percent of people eligible for antiretroviral treatment on clinical grounds were getting it in 2003.
Of those who were not getting treatment, 42 percent were unaware they were infected. The rest knew they were HIV-positive, but were either not under medical care or were in care but did not want, or could not get, antiretroviral therapy.
In other research news from the conference, scientists from the CDC and Johns Hopkins University reported the discovery of two new viruses in Central African men with heavy exposure to the blood and tissue of monkeys and apes.
The finding suggests that the sort of cross-species infection that first put the AIDS virus into human beings continues today and probably is not rare.
The two new microbes are retroviruses like the AIDS virus, and specifically fall into the group known as human T-cell lymphotrophic viruses. That family's two previously known members, HTLV-1 and HTLV-2, infect about 22 million people worldwide and can be passed person-to-person through sex, birth and body fluids.
About 5 percent of HTLV-infected people eventually develop illness, usually decades after infection. Whether that is true for the new microbes -- which together double the size of the HTLV family -- is unknown.
"It is possible they may cause disease," said Walid Heneine, the chief of CDC's retrovirus surveillance laboratory. "We need to follow these people. We need to reach the contacts of the hunters and look for human-to-human transmission."
One of the new microbes, named HTLV-3, resembles a simian, or monkey-derived, virus called STLV-3. The other, HTLV-4, does not have a known primate equivalent, although one presumably exists.
The viruses were found in a survey of 930 people living in 12 villages in the central African nation of Cameroon.
All reported contact with primate "bush meat," usually as hunters or butchers. The species included chimpanzees, mandrills and several types of monkeys. The two new viruses were carried by one person each, and the other 11 people all had HTLV-1 strains.
HTLV-1 can cause leukemia and a spinal-cord disease known as "tropical spastic paraparesis." For reasons that are unclear, it is most common in southern Japan, the Caribbean and South America. HTLV-2 causes illness much less frequently.
