Animal movements have played a critical role in the spread of MRSA in Danish pigs

Pig movements have facilitated the spread of a few MRSA lineages highly adapted to the selection pressures exerted by antimicrobial use in pigs

In a study published in mBio, Danish and U.S. researchers have shown that the rapid spread of livestock-associated methicillin-resistant Staphylococcus aureus clonal complex 398 (LA-MRSA CC398) is due to the expansion of 3 successful lineages, which are particularly resistant to antibiotics that are used to treat pigs. The study also revealed that pig movements have facilitated the spread of these lineages.

Marc Stegger, who co-led the study, said, “Our study shows that there were many different MRSA lineages present in the Danish pig population 10 years ago, but none of them were very successful. At some point, 3 of these lineages began to spread quite fast, and it is those lineages that are responsible for the high rate of positive pig farms that we see today.”

The other co-leader of the study, Jesper Larsen, continues, “The 3 lineages are particularly well adapted to a life in a pig farm. Besides being methicillin-resistant, they are also resistant to those antibiotics that are used most frequently in Danish pig production.”

The results also show that the same lineages are responsible for the increasing number of infections, particularly in pig farmers but also in people with no contact with pigs.

“This spread to people without pig contact is worrisome, because it might affect elderly and immune-compromised individuals who have a higher risk of developing serious and even life-threatening infections,” says Jesper Larsen.

Raphael Sieber, first author of the article in mBio, analysed whether animal movements could explain the rapid spread of MRSA in the Danish pig population. “The results show that movement of animals has played an important role in the dissemination of MRSA between pig farms in Denmark. But it’s important to stress that our findings don’t rule out other ways of transmission, for example via people or through the environment,” says Sieber.

Article: Drivers and Dynamics of Methicillin-Resistant Livestock-Associated Staphylococcus aureus CC398 in Pigs and Humans in Denmark by Raphael N. Sieber, Robert L. Skov, Jens Nielsen, Jana Schulz, Lance B. Price, Frank M. Aarestrup, Anders R. Larsen, Marc Stegger and Jesper Larsen, published in mBio (2018) 9:e02142-18, doi: 10.1128/mBio.02142-18.

[SOURCE: American Society for Microbiology]