AIDSWEEKLY Plus; Monday, September 28, 1998
Daniel J. DeNoon, Senior Editor
The virus and its three subsequently discovered relatives belong neither to the main group (group M) or to the outlyer group (Group O) of HIV-1. Discoverers Francois Simon and colleagues propose naming the new group "Group N" for new or, alternatively, non-M/non-O.
The virus appears to have infected only a small number of people in the west African nation of Cameroon. But as it is infectious and capable of causing AIDS, Simon et al. warn that it could spread.
"The recent history of the HIV pandemic shows that the currently low prevalence of these strains in no way obviates a future considerable impact on public health," they wrote in the journal Nature Medicine ("Identification of a New Human Immunodeficiency Virus Type 1 Distinct from Group M and Group O," Nature Med, 1998;4(9):1032- 7).
In an accompanying editorial (("More Ado about HIV's Origins," Nature Med, 1998;4(9):1001-2), Pasteur Institute researcher Simon Wain-Hobson cited the principle of Murphy's Law in predicting that the new viruses "will spread just enough to make life difficult for viral diagnostics."
In an interview with Science magazine writer Michael Balter, Wain- Hobson darkly noted that it appears likely for ever-new HIV-1 variants to appear ("New HIV Strain Could Pose Health Threat," Science, 1998;281:1425-6).
"A continuous search for new variants is necessary to assure the safety of blood donation," Balter quoted Wain-Hobson as saying. "These viruses are on standby, waiting for favorable conditions."
The similarities between Group O viruses and simian immunodeficiency virus (SIV) from sooty mangabey monkeys (SIVsm) lead most observers to believe that Group O HIV-1 strains crossed the species barrier from sooty mangabeys. Group M HIV-1 resembles SIV from chimpanzees (SIVcpz), but so few SIVcpz strains have been isolated that the connection remains unproven.
The new Group N viruses fall about halfway between Group M HIV-1 and SIVcpz in the phylogenetic tree. They lend credence to the theory that SIVcpz jumped species from chimpanzees at least twice.
"Cross-species transmission probably occurs far more frequently than we care to know," Wain-Hobson commented.
Simon et al. obtained their first Group N isolate, designated YBF30, in 1995 from a 40-year-old female AIDS patient in Cameroon. The patient later died in Yaounde Hospital of AIDS-associated diagnoses.
Serological typing showed that the isolate was negative with both Group M and Group O peptides, reacting only with a V3-loop peptide from SIVcpz. The researchers obtained another isolate, YBF31, from stored sera taken from the same patient.
Simon et al. developed an enzyme immunoassay from the YBF30 V3 loop and used it to screen 700 HIV positive serum samples obtained in Cameroon. Three of these sera reacted strongly with the YBF30 peptides; one could be confirmed related to YBF30 via analysis of a pol gene fragment.
"The public health implications of such variants must now be established," Simon et al. wrote. "YBF30 is a highly replicative virus; ... the patient's death from AIDS confirmed the pathogenicity of the strain. The patient's serum was negative for anti-HIV-1 antibodies in a specific HIV-1 Group M competitive EIA [enzyme-linked immunoassay]. ... This raises the possibility that such a variant could escape detection by current HIV screening tests, as do HIV-1 Group O strains."
The researchers concluded that their data show HIV-1 to be actively emerging in humans.
"Cameroon has a broad human genetic diversity, with more than 200 ethnic groups," they noted. "A high rate of infectious diseases in these regions, such as holoendemic malaria, maintains these populations under stimulation by a wide range of antigens. This genetic polymorphism and host immune responses could provide ample opportunities for human retrovirus diversification."
The corresponding author for this study is Francois Simon, Laboratoire de Virologie, Hopital Bichat, Paris, France. Email: <francois.simon@bch.ap-hop-paris.fr>.
Correspondence regarding the accompanying editorial may be addressed to Simon Wain-Hobson, Unite de Retrovirologie Moleculair, Institut Pasteur, 75724 Paris Cedex 15, France. Email: <simon@pasteur.fr>.
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