New strain of HIV appears in Cameroon

Cameroon, which has been a crucible for rare strains of HIV in the past, has earned that dubious distinction again.

 French researchers report finding a novel strain of HIV, the virus that causes AIDS, in blood collected 3 years ago from a woman in this central African country. The new strain apparently evolved from either a more common HIV or its simian counterpart, SIV. The report, in the September Nature Medicine, raises concerns that this subtype of HIV may be spreading gradually in Africa but not showing up on currently used diagnostic tests.

"It very likely will not have public health consequences," says Anthony S. Fauci of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. Although the rare viral strain may not be picked up by initial screening, the national blood supply will continue to be protected by the many layers of controls currently in place, he says.

 HIV-1 and HIV-2, the two known types of the AIDS virus, arose in East and West Africa, respectively. HIV-1, which more frequently causes a lethal disease, includes two broad strains, dubbed group M (for major) and group O (for outlier). Group M encompasses several subtypes, which together account for most HIV infections worldwide. Group O contains only a few uncommon but deadly viruses, appearing mainly in Cameroonians.

 The newfound strain requires a new group. "This group is genetically distinct from group M and group O," says Francine E. McCutchan, a molecular biologist at the Henry M. Jackson Foundation in Rockville, Md. Scientists have named the puzzling strain HIV-1 group N, although it shows some genetic characteristics of SIV.

 Researchers discovered the new virus in a frozen sample of the woman's blood taken in 1995. After characterizing the strain's DNA, they checked for its presence in 700 frozen blood samples taken from HIV-1-positive Cameroonians between 1988 and 1997. Most were infected with group M viral strains, and 65 showed group O. Among 16 samples that matched neither group, 3 had viruses strongly resembling the group N strain.

 The new strain is as different from SIV as it is from known HIV-1 strains. "[It] can thus be considered as the prototype strain of a new human immunodeficiency virus group," say study coauthor Francois Simon of the Bichat Hospital in Paris and his colleagues.

 Although the virus isn't widespread, it can be lethal. The woman who gave the original blood sample in 1995 died of AIDS later that year at the age of 40.

 While it remains unclear whether the new strain evolved from HIV or SIV, scientists have clues as to why it arose in Cameroon. In the rain forest, people encounter many primate species, facilitating the spread of primate viruses into the human population, McCutchan suggests. In the same issue of Nature Medicine, Simon Wain-Hobson of the Pasteur Institute in Paris suggests that the new strain, though rare, may "spread just enough to make life difficult for viral diagnostics." Tests may eventually have to screen for this new HIV strain, McCutchan says.