When new infectious diseases are discovered, one of the first questions is “where did this come from?” More often than not, the answer is one of our animal friends—a kind of disease called a zoonosis.
Studies have shown that about 75 percent of emerging infectious diseases (diseases that are newly discovered, are increasing in frequency, or have moved into a new geographic area) are of animal origin, as are 60 percent of all known pathogens. Even diseases that have spread freely in the human population, such as tuberculosis, HIV, measles, and smallpox, have their roots in infections carried by animals.
Which animals are the most likely to harbor zoonotic pathogens?
For reasons that are not currently understood, bats are able to be infected with a huge variety of viruses. They pass these viruses to other animal species via bites or guano. The classic bat-origin virus is rabies, but bats have also been implicated as possible reservoir species for the Ebola and Marburg viruses, Nipah, Hendra, and others. Even influenza has recently been found in bats.
Bats also appear to be the reservoir for the SARS coronavirus, which surfaced in 2002 in Asia. SARS eventually infected more than 8,000 individuals around the world and killed almost 800 of them between November 2002 and July 2003, spreading to at least 37 countries. A new SARS-related virus has recently surfaced in Saudi Arabia, and speculation is that it’s also from bats.