AIDS: A Clear-Cut Disaster
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In 1933, Aldo Leopold, the “founding father of wildlife ecology,”794 declared, “The real determinants of disease mortality are the environment and the population,” both of which he said were being “doctored daily, for better or for worse, by gun and axe, and by fire and plow.”795 Since Leopold wrote those lines, more than half of the Earth’s tropical forests have been cleared.796 According to the UN Food and Agriculture Organization, expanding livestock production is one of the main drivers of tropical rainforest destruction, particularly in Central and South America.797 This “hamburgerization” of the rainforests sets the stage for disease emergence and transmission in a number of ways.
Many disease-carrying mosquitoes prefer to breed out in the open along partially cleared forest fringes, rather than deep in the forest.798 When livestock are grazed on the cleared land, the animals serve as warm-blooded meals for disease vectors like mosquitoes and biting flies, which may become so numerous they seek out blood meals from humans.799 Clear-cutting can also create a windfall for disease-bearing rodents.
With leading cattle-producing nations at war during WWII, Argentina took advantage of this situation by dramatically expanding its beef industry at the expense of its forests. The ensuing explosion in field mouse populations led to the surfacing of the deadly Junin virus, the cause of Argentine hemorrhagic fever,800 a disease characterized in up to one-third of those infected by extensive bleeding, shock, seizures, and death.801 On cleared cropland, unprotected agriculture workers are on the front line, as harvesting machinery produces clouds of potentially infectious dust and aerosols of blood from animals crushed in the combines.802
This scenario was repeated as humankind intruded into other remote virgin forests. In Bolivia, we discovered the Machupo virus, or, rather, the Machupo virus discovered us. In Brazil, we uncovered the Sabia virus. The Guanarito virus resulted in Venezuelan hemorrhagic fever. “Mostly these days,” wrote one prominent medical microbiologist, “it is man’s intrusion on the natural environment which is the all-important key to emerging viruses.”803
Inroads into Africa’s rainforests exposed other hemorrhagic fever viruses—the Lassa virus, Rift Valley Fever, and Ebola. According to the WHO, all dozen or so804 hemorrhagic fever viruses so far unearthed have been zoonotic, jumping to us from other animals.805 “These zoonotic viruses seem to adhere to the philosophy that says, ‘I won’t bother you if you don’t bother me,’” explained a former Nature editor.806 But then, she said, as people began “pushing back forests, or engaging in agricultural practices that are ecologically congenial to viruses, the viruses could make their way into the human population and multiply and spread.”807
Radical alterations of forest ecosystems can be hazardous in the Amazon Basin or the woods of Connecticut, where Lyme disease was first recognized in 1975. Since then, the disease has spread across all 50 states808 and affected an estimated 100,000 Americans.809 Lyme disease is spread by bacteria-infested ticks that live on deer and mice, animals with whom people have always shared wooded areas. What happened recently was suburbia. Developers chopped America’s woods into subdivisions, scaring away the foxes and bobcats who had previously kept mouse populations in check. Animal ecologists recover some seven times more infected ticks from 1- and 2-acre woodlots than lots of 10 to 15 acres. The pioneer in this area concluded, “You’re more likely to get Lyme disease in Scarsdale than the Catskills.”810
The forests of Africa were not, however, cut down to make golf courses. The inroads into Africa’s rainforests were logging roads, built by transnational timber corporations hacking deep into the most remote regions of the continent. This triggered a mass human migration into the rainforests to set up concessions to support the commercial logging operations. One of the main sources of food for these migrant workers is bushmeat—wild animals killed for food.811 This includes upwards of 26 different species of primates,812 including thousands of endangered great apes—gorillas and chimpanzees—who are shot, butchered, smoked, and sold as food.813 To support the logging industry infrastructure,814 a veritable army of commercial bushmeat hunters are bringing the great apes to the brink of extinction.815 “These logging companies have been promoting the bushmeat trade themselves,” claims one expert. “It is easier to hand out shotgun shells than to truck in beef….”816
The reason french fries can be eaten with abandon without fear of coming down with potato blight is that pathogens adapted to infect plants don’t infect people. The evolutionary span is too wide. Eating animals can certainly give us animal diseases, but near-universal taboos against cannibalism have well served the human race by keeping more closely adapted viruses off our forks.817 Having finally sequenced the genome of the chimpanzee, though, scientists realize we may share more than 95% of our DNA with our fellow great apes.818 “Darwin wasn’t just provocative in saying that we descend from the apes—he didn’t go far enough,” one primatologist said. “We are apes in every way….”819 By cannibalizing our fellow primates, we are exposing ourselves to pathogens particularly fine-tuned to human primate physiology. Recent human outbreaks of Ebola, for example, have been traced to exposure to the dead bodies of infected great apes hunted for food.820 Ebola, one of humanity’s deadliest infections, is not efficiently spread, though, compared to a virus like HIV.
1981 brought us Ronald Reagan taking the oath, MTV’s first broadcast, Pacman-mania, and Raiders of the Lost Ark. In June, the Centers for Disease Control issued a bulletin of nine brief paragraphs. Five gay men in Los Angeles were dying with a strange cluster of symptoms.821 From humble beginnings, AIDS has killed millions.822
The relaxation of sexual mores, blood banking, and injection drug use aided the spread of the AIDS virus, but where did this virus come from? The leading theory is “direct exposure to animal blood and secretions as a result of hunting, butchering, or other activities (such as consumption of uncooked contaminated meat)….”823 Experts believe the most likely scenario is that HIV arose from humans sawing their way into the forests of west equatorial Africa on logging expeditions, butchering chimpanzees for their flesh along the way.824
In Botswana, 39% of the country’s adults are infected with HIV. There are countries in which 15% or more of the nation’s children have been orphaned by AIDS killing both parents. Five people die from AIDS every minute. By 2010, we expect 45 million newly infected people to follow down the same nightmarish path.825 Although there has been progress in the treatment of AIDS, attempts at a vaccine or cure have been undermined by the uncontrollable mutation rate of HIV. Someone butchered a chimp a few decades ago and now 20 million people are dead.826
The bushmeat industry may already be cooking up a new AIDS-like epidemic. Samples of blood were taken from rural villagers in Cameroon, known for their frequent exposure to wild primate body fluids from hunting. Ten were found to be infected with foreign ape viruses.827 “Our study is the first to demonstrate that these retroviruses are actively crossing into people,” the chief investigator said.828 Their article published in Lancet ends, “Our results show simian retroviral zoonosis in people who have direct contact with fresh non-human primate bushmeat, and suggest that such zoonoses are more frequent, widespread, and contemporary than previously appreciated.”829 In the accompanying Lancet editorial, we are reminded that zoonotic cross-species infections are “among the most important public health threats facing humanity.”830
While zoonotic diseases like rabies kill about 50,000 people globally a year,831 humans generally end up as the dead-end host for the virus. In terms of global public health implications, the greatest fear surrounds viruses that can not only jump from animals to humans, but then spread person to person. Only a few people eat chimpanzees, but many people in the world have sex.