Many of the deadly diseases that afflict humans were originally acquired through contact with animals. However new research shows that pathogens can also jump the species barrier to move in the other direction: from humans to animals.
The study, published in the journal Applied and Environmental Microbiology, shows that green monkeys in The Gambia acquired Staphylococcus aureus, also known as MRSA, from humans.
Researchers isolated strains of S. aureus from the noses of healthy monkeys and compared the monkey strains with strains isolated from humans in similar locations.
“We used a technique known as high-throughput sequencing to gain an exquisitely detailed view of the relationships between the various strains. The results showed that monkeys had acquired S. aureus strains from humans on multiple occasions,” says Mark Pallen, professor of microbial genomics at the University of Warwick.
Most of the S. aureus found in monkeys were part of a clade, a group with common ancestors, which appeared to have resulted from a human-to-monkey transmission event that occurred 2,700 years ago.
Two of the most recent human-to-monkey transmission events appear to have taken place around three decades ago, and roughly seven years ago, respectively. These events appear to be the result of human encroachment into the monkeys’ natural habitat, and probably resulted from transfer of human bacteria from hands to food that was then fed to monkeys, researchers say.
“Although wild, these monkeys are accustomed to humans, who often feed them peanuts,” says coauthor Martin Antonio, principal investigator and a unit molecular biologist who led the work.
There was no evidence of transmission of S. aureus from monkeys to humans. Interestingly, strains that jump from humans to monkeys lose genes that are known to confer adaptation to the human host.
Humans acquired many of the diseases that have been among the deadliest, historically, from the livestock domesticated in the early years of civilization. In the last few generations, the combination of increasing human encroachment on wild ecosystems, and increasing human travel has led to acquisition and spread of diseases ranging from HIV to Lyme disease, Pallen says.
“As humans encroach ever more steadily into natural ecosystems, the risk increases that pathogens will be transmitted from humans to animals, or vice versa.”
Source: University of Warwick