Two Variant AIDS Viruses--a Windfall for Researchers
The recent discovery of two variant AIDS viruses in West Africa has given scientists a major and unexpected opportunity to study the deadly acquired immune deficiency syndrome, according to the French and American researchers who separately isolated the variants.
But the researchers cannot agree whether the new viruses pose significant health threats, although their ongoing studies will likely answer this question within the next year.
In the next few months, the complete genetic maps of both variant viruses should be known, allowing scientists to directly compare the genes of the two new viruses to the genes of the original AIDS virus and to each other.
Such comparisons, according to the French and American scientists, may hold the key to more accurate blood tests to detect the virus and lead to progress in the development of treatments for AIDS and perhaps a protective vaccine.
“The faster we find all the parts of the puzzle, the faster we can find a solution,” said Dr. Jay Levy, an AIDS researcher at the UC Medical Center, San Francisco.
By studying the variant viruses, for example, scientists hope to learn if infection with one can protect people against infection with other AIDS viruses. If such cross-protection exists, it could make it easier to develop an AIDS vaccine; if it does not, researchers face the daunting prospect of combining many different strains of the AIDS virus into one vaccine.
In a recent interview, Dr. Myron Essex of the Harvard School of Public Health, who led the research team that discovered one of the variant AIDS viruses, said he has “very strong suggestions” that even more AIDS-related viruses will be isolated in the months ahead. The significance of finding additional variants remains to be seen.
Already, researchers at the federal Centers for Disease Control and the New England Primate Center are using the variants of the AIDS virus to develop new animal models for AIDS.
The only animal that can be successfully infected by the original AIDS virus is the chimpanzee, which is a rare and expensive laboratory animal. If macaques and other monkeys, which are less expensive and more plentiful, can be infected with variant AIDS viruses, it will be easier for researchers to test AIDS vaccines and drugs.
The AIDS virus cripples the body’s immune system, leaving it vulnerable to a variety of infections and tumors. It was separately isolated in 1984 by Dr. Luc Montagnier of the Pasteur Institute in Paris, who called it LAV-I, and by Dr. Robert Gallo of the National Cancer Institute, who called it HTLV-III.
At the center of the scientific debate about variant AIDS viruses are Montagnier and Harvard’s Essex. They announced in March that their research teams had separately discovered such viruses during 1985 in West Africa, where AIDS is much less common than in Central and East Africa.
They said the variant viruses appear to be more similar to each other than to the original AIDS virus. Neither has been found in the United States.
Montagnier’s new virus, called LAV-II, was isolated from patients with AIDS-like illnesses in Guinea-Bissau and the Cape Verde Islands. It has been shown to cause AIDS and related illnesses in 21 people, seven of whom have died, according to the researcher.
In addition, LAV-II has been detected through blood tests in 43 West Africans out of 1,000 tested; these people are not ill, he said.
Described as Deadly
Earlier this month, Montagnier warned at a medical meeting in San Francisco that LAV-II appears to be just as deadly as the original AIDS virus. He said it is a major cause of AIDS in West Africa and has spread to several Western European countries. He predicted that it might eventually spread throughout the world.
But Essex, at a medical meeting in Anaheim last week, expressed “surprise” about Montagnier’s statements because his research team has found “very little evidence” to support the French researcher’s findings.
Instead, Essex believes LAV-II is a slight but uncommon variant of his new virus, called HTLV-IV. HTLV-IV was first isolated from several healthy female prostitutes in Senegal. It has not been associated with human disease or with laboratory evidence of immune system abnormalities.
This year, HTLV-IV has been detected in the blood of about 375 people out of 4,000 tested in eight West African countries, including Senegal and the Ivory Coast, according to Essex.
Medical Disagreement
Montagnier believes it is just a matter of time before some patients infected with HTLV-IV become ill and develop AIDS or related disorders. But Essex disagrees.
“There is a virus in West Africa that is quite prevalent but is not causing AIDS,” Essex said. “We can’t rule out (that it causes) rare disease later in life. But it would be unfortunate if there is panic in relationship to this virus because of the expectation that it will cause a lot of AIDS.”
LAV-II and HTLV-IV are often not detected by the standard blood tests for the original AIDS virus. Compared to the original AIDS virus, they have significant differences--perhaps up to 50%--in their genetic material and protein coats.
Isolates of the original AIDS virus also show a great deal of variation--up to 25%--in their genes and proteins. This variation makes it more difficult to determine if in fact Montagnier and Essex have isolated new viruses or only extreme forms of the same virus.
Variations are not unique to the AIDS virus. The structure of other viruses, such as the flu virus, also changes frequently, although many isolates of the flu virus in a given year are virtually identical. By comparison, every single isolate of the AIDS virus seems to be different.
Common Characteristics
All of the AIDS family of viruses, however, have many things in common. They are closely related to similar viruses found in monkeys. They appear to be transmitted in the same ways--through sexual contact, contaminated blood or needles and from infected mother to child. The viruses also infect the same type of white blood cell, called the T-4 cell.
“There is ample opportunity for these viruses to recombine (in white blood cells) by taking parts of one and parts of another,” Essex said. “It is a conducive environment to generate new viruses rapidly.”
Both Montagnier and Essex believe that future tests to safeguard transfused blood and to diagnose AIDS infection will have to be modified to account for the variant viruses. “Eventually a lot more blood-screening tests are going to have to be used,” Essex said. “People don’t want to be transfused with these things (whether or not they cause disease).”
