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Strain of deadly superbug found in pigs can spread to humans



A closeup shot of big pigs on the mug in the farmland
(Photo by Oakland Images via Shutterstock)

By Jim Leffman via SWNS

A highly antibiotic-resistant strain of the deadly superbug MRSA found in pigs can jump to humans, Cambridge scientists have revealed.

And they believe it could be the result of decades of widespread antibiotic use in pig farming.

In 2019, MRSA, methicillin-resistant Staphylococcus aureus, killed around 100,000 people worldwide and The World Health Organisation now considers it one of the world’s greatest threats to human health.

The strain found in pigs, CC398, has become the dominant type in European livestock in the last 50 years and is a growing cause of human MRSA infections.

The study, published in the journal eLife, revealed that CC398 has been found in people with no link to livestock.

More worryingly it seems to be just as antibiotic-resistant in human as it is in pigs, though it doesn’t cause disease in them.

MRSA was first identified in human patients in 1960 but due to its resistance to antibiotics, it is much harder to treat than other bacterial infections.

Dr. Gemma Murray, a lead author of the study, previously in the University of Cambridge’s Department of Veterinary Medicine and now at the Wellcome Sanger Institute said: "Historically high levels of antibiotic use may have led to the evolution of this highly antibiotic-resistant strain of MRSA on pig farms.

"We found that the antibiotic resistance in this livestock-associated MRSA is extremely stable.

"It has persisted over several decades, and also as the bacteria has spread across different livestock species.”

A close up shot of a pig peacefully sleeping in the dirt.
(Photo by Juice Verve via Shutterstock)

Although the use of antibiotics on farms has been reduced it is unlikely to affect this strain because it is so stable.

CC398 is found across livestock but is associated mostly with pigs, especially in Danish pig farms where it has jumped from 5% to 90% in the ten years from 2008-2018.

Senior author Dr. Lucy Weinert in the University of Cambridge’s Department of Veterinary Medicine, added: “Understanding the emergence and success of CC398 in European livestock and its capacity to infect humans is vitally important in managing the risk it poses to public health."

The team found that the bacteria can jump to humans due to mobile genetic elements in its genome.

These are chunks of genetic material that give the MRSA certain characteristics, including its resistance to antibiotics and its ability to evade the human immune system.

Two particular mobile genetic elements that give it antibiotic resistance persist when CC398 jumps to humans whilst a third appears and disappears in both pigs and us, showing it can rapidly adapt to humans.

Dr. Weinart added: “Cases of livestock-associated MRSA in humans are still only a small fraction of all MRSA cases in human populations but the fact that they’re increasing is a worrying sign."

Intensification of farming, combined with high levels of antibiotic use in livestock, has led to particular concerns about livestock as reservoirs of antibiotic-resistant human infections.

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