Scientists now believe that HIV, the virus which causes AIDS, is a product of rainforest destruction. Far worse may be in store, writes ROBYN MARSHALL.
A virus is a very small infectious particle containing a strand of genetic material, DNA, or sometimes RNA (ribonucleic acid), in which case it is known as a retrovirus. The DNA or RNA is wrapped in a membranous coat of lipid and protein.
A virus is a parasite, having no cell machinery to reproduce itself or make its own proteins. It has to wait until it invades a living cell where it takes over, forcing the cell to making thousands of copies of it. These burst through the cell membrane and are released, killing the cell in the process. Once released, each copy of the virus has to seek the opportunity to invade another cell. The virus's DNA can also insert itself into the host cell's DNA, becoming a permanent resident.
Viruses infect everything that lives, including all animals, plants and even bacteria. A clever virus, such as the retrovirus HIV, kills the host cell very slowly so that it can survive as long as possible. But sometimes accidents happen.
No fossils of viruses have ever been found. Nevertheless, they are thought to be very ancient organisms, possibly primeval. In 1900, the first virus that infects humans was isolated by the US Army; the yellow fever virus was killing many of its personnel while they were invading Latin America.
A virus can mutate rapidly by just one change in the DNA sequence; it may retain its infectivity but the host loses any immunity from previous exposure. This is what happens with the common influenza virus: humans carry more than 100 different flu viruses but continually succumb to new infections.
It is now thought that the HIV virus emerged from the rainforests of central Africa — Zaire or Kenya — perhaps from chimpanzees, its natural host. It mutated and infected humans when men hunting monkeys for research purposes came into contact with monkey blood or bloodied tissue. As more outsiders came into the half-destroyed jungle, the virus entered the general human population.
Some 10 million individuals are infected with HIV, and this will increase to 40 million by the year 2000. The emergence of AIDS appears to be a consequence of the destruction of the tropical biosphere. Unknown viruses are coming out of the equatorial wilderness and discovering human beings. The process has been called the revenge of the rainforest.
Opportunity to mutate
The rainforest, being by far the largest reservoir of plants and animal species, will also be the largest reservoir of viruses. There may be 100 million virus strains. As the stable ecosystem is destroyed, opportunities are created for mutuated viruses to spread in unpredictable ways. Far from the HIV virus being a unique phenomenon, it may be a fairly common event in the future. A rainforest virus might sweep the world and possibly annihilate the human race.
It is now known that an even more virulent virus than HIV did break out in Zaire. The entire incident was kept pretty quiet, but the details have been researched and publicised by Richard Preston, an independent journalist in the USA, who wrote for the New Yorker. A virus called the Ebola Zaire virus broke out in September 1976 near the Ebola River in northern Zaire. It erupted simultaneously in 55 villages, killing 90% of people infected. Victims died within a week.
The first symptom was a headache, then a relentless fever. The virus causes the blood to form large clots, which lodge everywhere in the body, particularly the brain, liver and spleen. As the internal organs become jammed, haemorrhaging begins. The intestines fill up with blood, as do the eyeballs. The eyelids leak blood, and victims vomit a black, bloody fluid. In the last stages, the patient leaks blood containing huge quantities of virus from the nose, mouth, anus, eyes and from broken skin.
People do not develop antibodies against the Ebola Zaire virus, as it seems to crush the immune system totally.
In the township of Nzara in the Sudan, a man who worked at a cotton factory died of haemorrhagic fever in July 1976. The Ebola virus spread through another worker at the cotton factory to infect the entire township and then went east to the town of Maridi, where there is a hospital. There it killed many of the nurses who worked at the hospital, as well as patients. It radiated outwards to the surrounding areas through patients' families.
Initially, its kill rate was 50% but the death rate climbed to 70%, as if the virus was mutating to more virulent forms. For reasons that aren't clear, the Maridi outbreak suddenly subsided.
However, two months later a still more lethal strain of the virus erupted 800 km to the west, in the Yambuku Mission hospital, run by Belgian nuns in the Bumba zone of Zaire, an area of humid rainforest. Spread by the multiple use of needles by the nuns, the virus erupted in 55 villages around the hospital. By the end of September 1976, 67% of the staff were dead and the hospital closed down.
However a critically ill nun was flown to Kinshasa, the capital of Zaire. She was nursed by another nun, and both died of the deadly virus in Ngaliema Hospital. Then another nurse at the hospital developed the same fever and bleeding. The nurse had had face-to-face contact with many people in the city before she died. The virus was about to begin an explosive chain in the crowded city of 2 million poor people.
Kinshasa has direct air links with the capitals of Europe. The potential epidemic started a panic among European governments, which were considering blocking all air flights from Zaire. The Zairean army blocked off all roads in the Bumba zone, and all radio contact with the province was lost.
The World Health Organisation hastily sent a medical team to Kinshasa, with full-face respirators, gowns and overshoes. They set up a containment pavilion at the Ngaliema Hospital, where they shut in 37 people who had had contact with the dying nurse. The room where the nuns and nurse had died was a horrible scene of devastation, stained with blood, which covered the floors, the furniture and the walls. Everything was washed with bleach and smoked with formaldehyde vapour. No-one else in the containment pavilion or the city fell ill with the virus. But it was a close shave.
The Ebola virus was only partly contagious through the formation of aerosols. If it had had any major respiratory method of infection, the world would be a different place today. When the WHO team arrived at Bumba, the epidemic was also on the wane; village elders had isolated each victim in a hut and pushed food and water through the door. If the victim didn't emerge, the hut was burned down. It's not known how many victims of the Ebola virus died in Zaire.
Leaps the oceans
The virus next appeared in Reston, Virginia, near Washington, in November 1989. A month before, a company called Hazelton Research Products had received a shipment of 100 wild macaque monkeys from the Philippines.
Within four weeks, 27 monkeys in quarantine at the Reston animal house had died of a virus that had some of the features of simian haemorrhagic fever. This is lethal to monkeys but does not affect humans. The company veterinarian sent some blood and tissue samples to a colleague in the US Army Medical Research Institute.
The virus was not treated with top-level safety precautions. It was tentatively identified as a the simian haemorrhagic virus. However, a technician noticed that the cells in which the virus was growing were dead and full of holes, nothing like the effects of the simian virus.
Finally a PhD student at the institute looked in an electron microscope at cells taken from a monkey's liver. He found the liver cells wall to wall with virus particles. All day was spent testing to identify the virus. It was Ebola, the killer virus that had broken out in Zaire 13 years earlier.
There were panic meetings all over Washington, phone calls to Army headquarters at Fort Derrick to organise army units to deal with a virus outbreak among the population. A power struggle developed between the Army and the Centre for Disease Control as to who was to control the situation. The US Army won out. The technicians, the student and his superior, and the animal caretaker at the quarantine company at Reston were all expected to die within a week, and they spent an anxious time waiting for the fierce headache to begin.
The immediate problem was the animal house in Reston, where the virus was rampant. An Army unit was dispatched to destroy every monkey and disinfect every single drop of blood and tissue as well as the air inside the building. The biohazard group all drove out in civilian cars so as not to draw attention to themselves and suited up behind the monkey house, out of sight of the road. It was a dangerous procedure, for they had to inject the monkeys but not get bitten in the process. It took three days to kill all the monkeys.
As it turned out, no-one developed Ebola virus infection. The Ebola Reston virus was a mutated form that did not harm humans. The caretaker and four others had developed antibodies to the virus, so it had multiplied inside their tissue but they had not developed any signs of the illness.
The virus was almost certainly transmitted by an airborne route. The Ebola Reston virus is extremely similar to the Ebola Zaire virus. They look alike in the electron microscope; the genetic sequence is also very similar. Again, it was a close shave, for the virus had infected humans before it was identified.
Bacteria too
The US Institute of Medicine recently released a report, two years in preparation, which said that not only emerging viruses but also mutant bacteria, strains that cause drug-resistant TB and protozoa such as mutant strains of malaria, have become major and growing threats to the population. "We can be confident that new diseases will emerge, although it is impossible to predict their individual emergence in time and place."
The report finds a general breakdown in the public health system in the US at the very time when a monster could appear. The Reston event frightened a lot of epidemiologists.
There has been some debate recently among scientists about whether the HIV virus could mutate into an airborne disease like flu. The AIDS-flu would circle the globe in a flash. There is no reason in principle why HIV couldn't spread by a respiratory route; the question is whether the virus in mutating to a flu-like form would remain fatal. But if one in three people on Earth died, as happened in Europe with the Black Death in the 15th century, social organisation would break down.