Much like HIV made the leap from non-human primates to us, a strain of the antibacterial-resistant pathogen MRSA seems to have originated with cattle:
A strain of bacteria that causes skin and soft tissue infections in humans originally came from cattle, according to a study to be published in mBio®, the online open-access journal of the American Society for Microbiology. The researchers who conducted the genetic analysis of strains of Staphylococcus aureus known as CC97 say these strains developed resistance to methicillin after they crossed over into humans around forty years ago. Today, methicillin-resistant S. aureus (MRSA) strain CC97 is an emerging human pathogen in Europe, North and South America, Africa, and Asia. The findings highlight the potential for cows to serve as a reservoir for bacteria with the capacity for pandemic spread in humans.
The researchers sequenced the genomes of 43 different CC97 isolates from humans, cattle, and other animals, and plotted their genetic relationships in a phylogenetic tree. Corresponding author Ross Fitzgerald of the Roslin Institute and the University of Edinburgh in Scotland says strains of CC97 found in cows appear to be the ancestors of CC97 strains from humans.
“Bovine strains seemed to occupy deeper parts of the phylogenetic tree – they were closer to the root than the human strains. This led us to conclude that the strains infecting humans originated in cows and that they had evolved from bovine to human host jumps,” says Fitzgerald.