Exotic Pets Can Carry Exotic Diseases

The Centers for Disease Control and Prevention estimate that 60 percent of the currently known human pathogens and 75 percent of emerging infectious pathogens are zoonotic; they include rabies, plague, leptospirosis, tularemia, West Nile virus, Ebola, Marburg, SARS, and Nipah (CDC 2007). Even domestic cats and dogs can serve as a source of human disease, but the risks posed by Fluffy and Fido are well known and understood. These species have been the companions of humans for thousands of years, and, at least in the developed world, most of the risks from them can be controlled: vaccinating prevents the spread of rabies, deworming kills the intestinal parasites that cause ocular or visceral larval migrans, and applying insecticides repels ticks that spread the agent of Lyme disease.

Cats and dogs are no longer the only pets found in US homes, however. The Captive Wild Animal Protection Coalition estimates that 10,000 to 20,000 large exotic felids, 17.3 million birds, 8.8 million reptiles, and 3000 great apes are being kept as pets in this country. In 2005 alone, 210 million animals were legally imported into the United States to satisfy the growing demand for exotic species. An unknowable number of pets, animal parts, and meat were smuggled in during the same time period, making up a large part—a portion ranked second only to the illegal drug trade—of the estimated $10 billion per year international black market (Ebrahim 2006).

Introducing so many animals into a new and unnatural environment—our homes—after removing them from the ecosystems in which they evolved represents a disruption of substantial magnitude. This displacement brings these animals into close proximity with species they have not previously encountered, and the public health consequences may be startling.

The most famous, or perhaps infamous, example is the outbreak in the United States of monkeypox in humans, a result of humans's close contact with prairie dogs sold as pets. Human monkeypox, which in its original environment affects primarily children, has a clinical course similar to that of smallpox, although its fatality rate is lower. This disease, which had not previously been seen outside of Africa (where exposure is thought to take place through contact with wild rodents), was diagnosed in 81 patients in the American Midwest during the summer of 2003. It turned out that Gambian giant rats, imported into the United States for the pet trade, had been housed next to prairie dogs. Asymptomatically infected rats transmitted the virus to the prairie dogs, which then passed it along to the humans who brought them home. Curiously, no suspected, probable, or confirmed cases of monkeypox occurred in humans who had contact only with the Gambian rats, or with any other African rodents (CDC 2003).

Clearly, the surprising thing is not that monkeypox infected US residents, but that such cases have not arisen more often. With our penchant for sharing our living spaces with creatures from foreign lands, outbreaks of other diseases will surely occur. What isn'st clear is how to best protect ourselves.

One approach, the one used most often to augment the generic requirement for a health certificate, is to regulate and legislate for known risks—it is now illegal to import African rodents into the United States, for example. Unfortunately, this approach is reactive rather than proactive, because it relies on the transmission of disease to humans—exactly what we are trying to prevent.

A more proactive alternative would be to regulate the unknown risks—in other words, prevent the importation of species (and thus the pathogens they harbor) that are not well understood. The precautionary principle supports this approach: it puts the onus on the importers and the eventual owners either to prove that a particular species does not have the potential to cause harm, or to provide ways to mitigate any risk. A third approach, a complete ban on importing exotic species for pets, has also been proposed, but is strongly opposed by both potential owners and members of the pet-trade industry. No matter which approach is eventually taken, however, it would be prudent to remember the already vast scale of the illegal market.
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People living in Florida are no strangers to exotic pets being released and then reproducing wildly with no natural predators to keep them in check. As this National Geographic article points out, we are undergoing immense ecological damage from exotic animals imported for the pet market that owners tire of and release, or the animals become too dangerous for the owners and the owners set them free without thinking of, or caring about, the consequences.

I would be delighted if the exotic animal trade were shut down tomorrow.