AIDS SI virus is considered a precursor to HIV

AIDS: SI virus is considered a precursor to HIV and is already several tens of thousands of years old. The SIV is a prototype of HIV.

(17.09.2010) The predecessor of the HIV virus (AIDS) seems to be tens of thousands of years old. In the scientific community, the virus is called "simian immunodeficiency virus (SIV)" and was apparently transported for thousands of years in the organism of monkeys.

The SI virus is according to recent scientific investigations a forerunner of the today's AIDS-exciter (HIV). Scientists have now found that the virus is much older than previously thought. So far, DNA studies have argued that the virus is only a few hundred years old. Even today, the virus is very widespread among African monkeys.

Scientists led by biologist Michael Worobey of the University of Arizona and virologist Preston Marx of the Tulane National Primate Research Center in Louisiana have discovered numerous variants of the so-called SI virus in samples of monkey meat from the African island of Biko. Based on in-depth analysis, it was found that the virus must be between 32 and 75 thousand years old. But how did the researchers arrive at this assumption??

On the assumption that the virus must be older than previously thought, the scientists came up with the method of the argumentative double step. The island of Biko was separated from the African continent about 10,000 years ago, as the sea level rose. The monkeys lived since then separated from the mainland and were isolated. However, since the animals were previously infected with the SI virus, the virus must be older than the separation of the island from the mainland.

Another interpretation is that the primates of the genus Bioko-Drills living on the island as well as the viruses have genetically related species on the mainland of Africa. A laboratory comparison of the DNA of the viruses showed that they mutate many more slowly than previously thought. Due to the 10,000-year-old separation of primates from the mainland, the DNA of the viruses had very few changes. The so-called molecular clock thus ran slower than it otherwise is the case when viral strains do not mutate in isolation. To substantiate the findings, researchers used empirical data to determine the course and number of genetic mutations to determine the age of their most recent common ancestor. From the values, the age of SI viruses could now be estimated to be at least 32,000 years.

Monkeys infected with the SI virus, in fact, extremely rarely develop AIDS-related immune deficiency disease. Because the SIV is considered rather harmless compared to HIV. "The Simiane immunodeficiency virus, unlike HIV, does not trigger AIDS in most afflicted primates," explains Preston Marx.

According to scientists, the low virulence of the virus, that is, the low ability of a pathogen to actually cause disease, could have developed over the last few millennia. The SI virus coexists with the monkeys without inducing disease. The HI virus, however, is much younger and therefore more aggressive towards the host. Due to the low age of the AIDS pathogen, the researchers are that a timely virulence is excluded. According to this, it is "not to be expected so soon" that the HIV virus will soon develop in a similar way. After all, the SI virus has only become harmless for millennia.

The research results now provide further questions in AIDS research. Why did not the spread of the HIV virus start until the 20th century, when people have been in contact with SI-infected viruses for many thousands of years? There are no answers yet. The study results were published in the scientific journal "Science".

More than 33 million people are infected with the deadly HI virus (HIV). About 2 million people die each year as a result of the immunodeficiency disease AIDS (acquired immune deficiency syndrome) In Germany, 3000 HIV new diagnoses are made each year. Although modern drugs alleviate the course of the disease, effective drugs have not been developed. (Sb)

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Picture credits: pixelio / Rolf van Melis