When a single monkey at the California National Primate Research Center
in Davis fell ill with pneumonia, it would have been hard to predict that within just a few weeks 19 monkeys would be dead, and three humans sick. But, that is precisely what happened in May 2009 during the Davis outbreak. Researchers have finally learned where the virus originated, which shows that this is the first ever recorded case of an adenovirus jumping from monkeys to humans.
An adenovirus is a large DNA-based virus, while most other viruses are RNA-based. Adenoviruses are responsible for colds and respiratory infections in humans, in addition to many different illnesses in animals like dogs, horses, pigs, and cattle. But it didn't seem that this type of virus could jump between species. That is, until that single monkey, an adult male titi monkey, started to cough. Within 2 months 23 or the 65 titi monkeys were sick (19 would die) and researchers were left puzzled by what they identified as a completely new adenovirus. Tracking the outbreak brought researchers to a human worker in the lab who had similar symptoms. But had the monkeys infected the human or had the human infected the monkeys, and where had this new virus come from?