to the zoonosis hall of fame.
Zoonotic diseases are far from new. In fact, they have been around as long as there have been people, animals and microbes. We can't offer an exhaustive history of animal-borne diseases here -- you wouldn't want us to -- but here are a few of history's greatest zoonotic hits.
Plague is still endemic to parts of Asia, Africa, and the Americas. It appears periodically, and since its host animals -- rodents -- are likely to be around for a long time, so is the disease. It's worst in places where people live closely together and poverty rages. A 1994 outbreak in Surat, India, left 500 people dead. Considered by some to be a reemerging disease, the plague's geographic range has expanded steadily in the last century. The World Health Organization reports that an average of 547 cases -- and 181 deaths -- occur each year. Thankfully, antibiotics -- when available -- can usually treat the disease successfully.
42 million people worldwide -- 38.6 million adults and 3.2 million children -- are HIV positive. About 70 percent of these people live in Sub-Saharan Africa.
The WHO reported that five million new HIV infections occurred worldwide in 2002. That's an average of 14,000 new infections each day. More than 95 percent occurred in developing countries.
More than three million people died from AIDS in 2002.
According to the CDC, 40,000 new HIV infections occur each year in the United States. Of these newly infected people, half are 25 years old or younger.
Beatrice Hahn was a member of the team who first described AIDS as a zoonosis in 2000. The team wrote that HIV-1, the virus responsible for the global AIDS pandemic, first spread to humans from contact with chimpanzees in Africa. And HIV-2, a form of the virus that remains confined to Africa, originated in another African primate species, the sooty mangabey. The jump probably occurred when hunters in the forests of the Congo basin came into contact with monkey blood infected with simian immunodeficiency virus (SIV), a relative of HIV.
This June, however, the team reported an interesting new twist: The SIV variant that led to HIV-1 appeared even earlier in a species of monkey eaten by the chimps.
"We had always lumped chimps together with all the other primate species that naturally harbor SIV," Hahn says. "This finding showed us that chimps acquired it by predation, which is very similar to how humans acquired it."
The hunting of wild primates for food is still a widespread practice in Africa, Hahn warns. Last year, her team documented the presence of multiple SIV strains in African primates. Hahn worries that new varieties of HIV might emerge where hunters -- and consumers -- of wild primates are exposed to different strains of SIV.
Sometimes, the flu virus evolves into a more dangerous, or more communicable, disease. That's what happened in 1918, when the insidious "Spanish Flu" killed 40 million people worldwide. More recently, two pandemics involving strains of the virus related to the Spanish Flu arose in 1957 ("Asian influenza") and 1968 ("Hong Kong influenza").
As a matter of probability, scientists say the likelihood of a harsh, fast-spreading flu grows with Asia's burgeoning cities. The CDC has warned that a such an outbreak could strike within ten years, quite possibly on the scale of the 1918 epidemic.
And there may be more to come.
©2003, University of Wisconsin, Board of Regents.