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Vol. 7 No. 4 - October 2001

Origin of AIDS Virus Linked to Rainforest Destruction

J. K. Maheshwari

The destruction of tropical rainforests is the serious ecological catastrophe of our time. The felling of trees for wood, called logging, accounts for 70 percent of forest losses, both directly and indirectly, by encouraging settlement, development and slash-and-burn farming along logging tracks and new highways. The environment in which the humans evolved and developed their basic defenses against diseases was one that remained largely and basically stable for thousands of years. In the past hundred years, it has changed radically- in forest cover, air and water quality, diet, and most recently in patterns of climate and weather. These changes have boosted the spread of microbes (bacteria, viruses and fungi), thereby leading to the emergence or re-emergence of a number of different diseases and increasing human vulnerability to infection. Among the extraordinary biodiversity of rainforests are a multitude of viruses and other diseases that have not yet come in contact with humans. Viruses, which previously remained hidden in remote rainforests suddenly have access to large human populations. The appearance of such "rainforest diseases" as HIV/AIDS, Ebola and Marburg suggests that these could result from tropical deforestation. The rainforests hold such viruses in check, but without the forests to 'lock' them in, they would be free to infect humans and other species. There are several ways in which ecological changes can activate the transmission and virulence of infectious diseases. The movement of people, plants, animals and goods - known as biological mixing - can increase exposure to diseases. The phrase "viral traffic" was coined recently to describe the transfer of viruses to new species or new areas, often through human acts.

Deforestation for the development of agriculture at new forest-farmland margins exposes humans and domesticated animals to new vectors, pathogens and arthropods (mosquitoes, flies, lice, fleas, bedbugs, ticks, etc.). Modern means of travel, too, can spread new diseases around the world with great speed, enlarging the pool of infected people and making the control of the disease more difficult. In such circumstances, the risk of transfer of viruses from the wild to humans is greatly increased. Many of the human diseases that have emerged and re-emerged at the close of the 20`h century are caused by pathogens originating from an animal or from products of animal origin. HIV-1 and HIV-2 causing AIDS are new human viruses of animal origin. A wide variety of animal species, both domesticated and wild, act as reservoirs for these pathogens, which may be viruses, bacteria or parasites. The pathogens that cause these diseases may reach us through our physical contact with living animals and their waste products, or through our consumption of certain food products of animal origin. During the past two decades, at least 30 new diseases have appeared on our planet. Of these, the Human Immunodeficiency Virus (HIV) which causes AIDS has had by far the most profound global impact. An unknown disease before 1981, AIDS originated in Central Africa and has caused an estimated 22 million deaths worldwide. More than 5 million people were infected with HIV in the year 2000 alone. Whereas sub-Saharan Africa is the worst affected region, HIV infection is spreading quickly in Asia, especially South and South-East Asia where 7.2 million people were affected at the end of 1998. About 4.5 million people are estimated to be infected with HIV in India. The virus infects almost 16,000 new persons each day. UNAIDS estimated that by the year 2010, AIDS may increase infant mortality by as much as 75 per cent and under-five child mortality by more than 100 percent in the countries hardest hit by the epidemic. These are alarming statistics, which underline the need for dealing with AIDS on a war footing.

AIDS is an acronym for Acquired Immune Deficiency Syndrome - a set of diseases, disorders and malignancies, which result from the destruction of body's defense systems by the Human Immunodeficiency Virus - HIV. There has been much speculation in both the scientific literature and in the popular press on the origin of HIV, the virus that causes AIDS. Genetic sequencing data suggests that HIV first entered the human population around 1930. In the 1970s, the paving of the Kinshasa Highway across Central Africa gave a fateful boost to the outbreak of AIDS in humans. Recent research suggests that the central African bushmeat trade may have sparked the AIDS epidemic. It is likely that the original host of the HIV virus was a subspecies of chimpanzees (Pan troglodytes) found in the old-growth rainforests of Cameroon and Gabon in Africa. The chimpanzees living in that area are commonly hunted for their meat. It is possible that the virus made its disastrous from monkeys to humans as a result of monkey bite or a hunter being contaminated through preparing or eating monkey flesh. Dr. Beatrice Hahn and her team of scientists working at the University of Alabama in Birmingham believe that the virus may have been transmitted to humans through exposure to the blood of chimpanzees either during hunting or during the handling of chimpanzee meat. Perhaps the most important aspect of the discovery is that the chimpanzees - who are ninety-eight per cent genetically identical to humans - are apparently able to live with the virus without becoming sick. This gives researchers a strong reason to believe that further study of the biological differences between chimpanzees and humans as well as further study of the ecology of the chimpanzees' rainforest habitat, will result in the development of ways to prevent or treat the AIDS virus. One aim of the research will be to determine whether the different outcomes of infection in humans and chimpanzees result from tiny changes in the genetic makeup of the virus or the host. Another aim would be to determine why the chimpanzees' immune system appears to resist the damaging effects of the AIDS virus while the human's is susceptible. Unfortunately, the wild population of chimpanzees needed for study is being pushed to the brink of extinction by a dramatic increase in the commercial bushmeat trade and rainforest destruction. The logging industry has played a large part in the proliferation of bushmeat trade. By building up an extensive network of roads into the heart of old-growth rainforests, the logging companies are allowing hunters easy access to previously impenetrable forest areas. The roads and the trucks that travel them become conduits for a vast commercial trade in wild meat. It is also a matter of great concern that the bushmeat trade may be putting the people at risk of continuing cross-species transmission of known, and unknown viruses.

Late Dr. J.K. Maheshwari was a Fellow of the National Institute of Ecology and Retd. Scientist, National Botanical Research Institute, Lucknow, India.


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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