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Viruses in search of 'compatible' diseases.

Viruses in search of "compatible' diseases

Despite massive efforts by medical science to match diseases with specific causes, new agents of disease can appear without warning and disrupt any scientific self-confidence. The viral cause of AIDS, for example, existed for many years, yet researchers only recently identified the human immunodeficiency virus (HIV) and its devastating results. Scientists meeting last week emphasized that there are other "new' viruses whose complete medical consequences are undiscovered. These viruses include those that may be responsible for fetal death, the controversial chronic fatigue syndrome and lymph node cancers, according to participants of the Interscience Conference on Antimicrobial Agents and Chemotherapy held in New York City.

One such agent, human parvovirus B19, was "a virus looking for a disease' until 1981--when it was first associated with aplastic crisis, a shutdown of the bone marrow's production of blood cells, says Larry Anderson of the Centers for Disease Control (CDC) in Atlanta. Researchers later tied the virus to severe skin rashes and arthritis.

This year, says Anderson, reports to the CDC indicate that the virus also may be responsible for some fetal deaths, as well as for bone marrow failure among patients with defective immune systems. Scientists now think the threat of parvovirus B19 may be most severe for AIDS patients, who cannot defend themselves against additional infections. Studies are underway at CDC, says Anderson, to determine the prevalence of B19 infection in the general population and to confirm the link between the virus and specific diseases.

The human B-lymphotropic herpesvirus (HBLV), first described in 1986, is another example of a virus with an incomplete medical history. The virus is unusual in that it is released from infected cells in membrane-bound packets, rather than through disruption of the cell. But this lack of cell "lysis' during HBLV infection does not mean the virus is harmless. Preliminary studies by Zaki Salahuddin of the National Cancer Institute and others have found HBLV in patients with various lymph node cancers, although no direct association between the virus and malignancy has been established.

The new virus also may be a factor in the course of AIDS, suggests Salahuddin. A random screening of subjects without detectable disease found about 16 percent had low levels of antibodies against the virus, while a survey of AIDS patients found that up to 70 percent had high HBLV-antibody levels.

Salahuddin says the antibody profile produced in response to HBLV is "very confusing and interesting.' Antibodies from humans infected with the virus unexpectedly cross-react with the chicken herpesvirus, but not with herpesviruses from other animal sources. This cross-reactivity--which usually signals some similarity between two viruses --coupled with the fact that there is no satisfactory way to detect the virus, leaves many unanswered questions about HBLV.

"We're really nowhere near drawing a conclusion regarding [HBLV's] pathological role,' says Salahuddin.

Scientists at CDC are developing an assay for a herpesvirus they recently isolated, which appears to be identical to the HBLV found by Salahuddin's group, says CDC's Carlos Lopez. "We do not know what disease it causes, but I think we can fairly assume that this virus can cause human disease,' he says. Using the test, the scientists are tracking the virus, which they call human herpesvirus VI (HHV-VI).

On the basis of these studies, Lopez says that "first and foremost, this is a disease of children.' Antibody production against HHV-VI apparently peaks sometime early in life, then "dwindles' as a person ages, says Lopez. Despite its apparent affinity for children, the virus is being considered by CDC, along with Epstein-Barr virus, as a possible cause of the adult condition called chronic fatigue syndrome, which scientists say may or may not be a distinct medical disorder. Officials at CDC currently are writing a description of the disease to be used for diagnosis, says Lopez.

Other early data suggest that HHV-VI can be sexually transmitted, and that in the general population, women are more likely than men to be infected. Lopez suggests that this higher incidence among women may be due to mothers' handling of infected children, or to the fact that the virus can be passed sexually from men to women more easily than from women to men.

Another curious aspect of the new herpesvirus is that it apparently inhibits HIV replication in cell cultures by 50 percent. But Lopez says the significance of this observation is still unclear.
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Author:Edwards, Diane D.
Publication:Science News
Date:Oct 17, 1987
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