July 2003, spreading to at least 37 countries. A new SARS-related virus has recently surfaced in Saudi Arabia, and speculation is that its also from bats.Other Wild AnimalsWhile bats appear to be responsible for a disproportionate amount of novel pathogens, every animal species carries its own unique microbiotathe collection of microbes that live on and in an animals body. Some of those can also spread to humans. As mentioned above, birds can spread many different types of influenza viruses. In fact, wild waterfowl serve as the ultimate reservoir for all known types of influenza viruses. Birds also can transmit a number of encephalitis viruses, such as West Nile. Because many migrate long distances, birds may be particularly efficient at introducing pathogens into new areas.Primates also harbor a number of pathogens that have crossed over into human populations, often an easy jump since we are so closely related. HIV is the result of multiple species jumps from nonhuman primates into human populations, likely due to butchering of infected animals. Research carried out by Nathan Wolfe and others has shown that bushmeat hunters in Africa are still being infected with viruses from our primate relatives.Rats and mice, of course, have long been associated with disease. Plague-infected fleas on rats spread Yersinia pestis, the bacterium responsible for the Black Death. We know today that other species can also transmit this pathogenincluding much cuter prairie dogs in the southwestern United States. Mice have recently been implicated in an outbreak of hantavirus pulmonary syndrome in Yosemite National Park that has killed three and sickened at least 10 campers. Mice carry this virus without showing symptoms and spread it to humans via urine and feces.Livestock and PetsThe domestication of livestock and the taming of animals for pets certainly marked a turning point in human history. Having these animals on hand to provide food and milk, as well as companionship and assistance with hunting, gave humans a more ready food supply and meant less time had to be spent gathering food. However, it also put us in regular contact with germs that these animals carried. Human measles virus infections may have evolved from a similar cattle virus, rinderpest. Cattle can also be a source of tuberculosis in humans, even today. Industrial livestock production means that its not just a farm family that may be sickened by pathogens from a pig or cow, but potentially hundreds or thousands who consume meat or other products from those animals. Foodborne illnesses are estimated to sicken 76 million people yearly in the United Statesand kill approximately 5,000. Economic costs from these food-borne illnesses alone are estimated at approximately $77 billion per yearFinally, our smaller domesticated friends can expose us to their own pathogens, including the parasite Toxoplasma gondii in cats (which is particularly dangerous to pregnant women), and they can also bring along unintended visitors and their pathogens into the home in the form of fleas and ticks. Even pocket pets such as hamsters and guinea pigs can bring along potentially deadly viruses and infect their owners.So, Why Arent We All Dead?With so