Beasts of the Earth: Animals, Humans, and Disease

Chapter Ten: The Coming Plagues: Lessons from AIDS, West Nile Virus, and Lyme Disease

1 2 4 = 10= C H A P T E R The Coming Plagues Lessons from AIDS, West Nile Virus, and Lyme Disease It is therefore as an animal that we must first consider man in his struggles with the environment. For man evolved as an animal, even while he was dreaming of God and the stars. Rene Dubos, Mirage of Health, 1959 In 1969, the bar of human hubris was raised significantly when William H. Stewart, surgeon general of the United States, announced: “The war against infectious diseases has been won.”1 Considering that bacteria, viruses, and protozoa had a more than two-billion-year head start in this war, a victory by recently arrived Homo sapiens would be remarkable. In fact, the war against infectious diseases has just begun and is guaranteed to continue for as long as humans inhabit the planet. Previews of possible future skirmishes against animal microbes occur every day in hundreds of places around the world. We remain unaware of most of these, but a few come to our attention. For example, animal disease outbreaks that occurred in a random two-month period, May and June 2003, and that were reported by ProMED-mail, an Internet service that monitors emerging infectious diseases, included the following: • A “mystery venereal disease” was affecting baboons in Tanzania, destroying their reproductive organs and causing them to die “in excruciating pain.” • Akabane virus, spread by flying insects, was affecting pregnant cows in Australia, producing “horribly deformed calves which rarely survive.” R3186.indb 124 R3186.indb 124 11/3/04 6:44:45 AM 11/3/04 6:44:45 AM T h e C o m i n g P l a g u e s = 1 2 5 • Large numbers of monkeys were dying from Kyasanur Forest Disease virus in India, with the outbreak labeled “the most serious in years.” • A case of malignant catarrhal fever, caused by a herpesvirus, was reported among cows, sheep, and pigs in Finland, with an “extremely high mortality” rate. • The cause of a “mysterious trout disease” in India, identified as an iridovirus, was said to be killing “thousands of trout fish” by causing them to bleed to death. • An outbreak of gastroenteritis caused by a coronavirus was reported among young pigs in Cuba, with a 43 percent mortality rate. • An outbreak of bluetongue virus disease was reported among sheep and goats in Brazil. • A previously unknown disease, probably viral in origin, was spreading among caged parakeets in England and was said to have “a very high death rate.” • African swine fever was reported from the Congo Democratic Republic with “a high mortality rate” among the infected pigs. • A “highly pathogenic” avian influenza (bird flu) epidemic was being brought under control in the Netherlands, Belgium, and Germany by killing 1.5 million chickens, ducks, and other birds in the affected areas.2 Fortunately, most animal disease outbreaks, like those just cited, are caused by microbes that are species specific and therefore do not affect humans . Occasionally, however, when conditions are propitious, animal microbes do cross from one animal species to another. When the new species happens to be humans, the result can be disastrous. The conditions under which animal microbes are most likely to cross to the human species include changes in human behavior, changes in technology , and changes in ecology. Human Behavior and AIDS The microbes that cause human AIDS are primate retroviruses that have existed in African monkeys for millions of years, causing little or no illness in most of them. HIV-2, which causes the milder form of AIDS, is a slight modi- fication of a simian immunodeficiency virus (SIV) carried by sooty mangabey monkeys in West Africa. HIV-1, the more severe form, is a combination of SIV strains carried by two species of monkeys in central Africa. The two strains simultaneously infected a chimpanzee species, Pan troglodytes troglodytes and combined into a new strain of SIV, which was then transmitted to humans.3 R3186.indb 125 R3186.indb 125 11/3/04 6:44:46 AM 11/3/04 6:44:46 AM 1 2 6 = B e a s t s o f t h e E a r t h Evidence that supports primates as the source of human HIV is strong. At a molecular level, HIV-1 and HIV-2 are very similar to the viruses carried by...