Fight fire with fire

One disease protects against another. Hepatitis G may have a dramatic benefit in the survival of HIV-infected patients

By Owen Dyer

Can two viruses be better than one? Groundbreaking research in the March 4 issue of the New England Journal of Medicine appears to suggest that sometimes they can. Which can only be good news when one of the viruses is HIV.

American researchers have found that long-term infection with the apparently harmless hepatitis G virus, also known as GBV-C, brings a dramatic benefit in long-term survival of HIV-infected patients.

Several leading research institutions in the US collaborated in this study, which followed 271 men from the Multicenter Acquired Immunodeficiency Syndrome Cohort Study.

Subjects were tested for GBV-C viremia, or the E2 antibody to the infection, 12 to 18 months after testing positive for HIV. A subgroup of 138 was again tested five to six years after discovering they were HIV positive. It was that second visit that seems to have settled the issue once and for all.

This question has been raised before, notably by two studies published in the NEJM in 2001 that also found a survival benefit from GBV-C. But while six studies showed evidence of an association, three others didn't. The authors of this latest research say those studies were compromised by a methodological flaw � using E2 antibodies as markers of GBV-C, rather than looking at those patients who were actively infected.

The authors say it's long-term infection with GBV-C that confers protection. A short-term infection or an immune memory of a cleared infection isn't enough. A positive test for GBV-C antibodies wasn't significantly associated with survival, nor was viremia 12 to 18 months after HIV seroconversion. But five to six years following seroconversion, those who tested negative for GBV-C viremia were 2.78 times as likely to have died as GBV-C viremia-positive men.

The hepatitis G or GBV-C virus was only discovered in 1995 and it's still not fully understood. But there's good evidence to suggest that it doesn't cause serious liver inflammation. People have carried the virus for years without displaying symptoms.

One study carried out in the US found that 1.8% of otherwise healthy blood donors were infected with GVB-C. A similar study carried out in South Africa found a much higher rate, with 11% of volunteer blood donors infected. It's believed the virus may be sexually transmitted, and is more prevalent in people with other STDs. Between 15% and 40% of HIV-positive patients are estimated to have it.

The authors of this study don't know the mechanism by which GBV-C confers protection. The most obvious explanation is that antibodies to GBV-C are also recognizing sites on the AIDS retrovirus. In other words, like cowpox it may be a naturally-occurring vaccine against a more serious disease.