A strain of bacteria commonly found in milk and beef may be a trigger for developing rheumatoid arthritis in people who are genetically at risk, according to a study.
Researchers at the University of Central Florida (UCF) in the US have discovered a link between rheumatoid arthritis and Mycobacterium avium subspecies paratuberculosis, known as MAP, a bacteria found in about half the cows in the US.
The bacteria can be spread to humans through the consumption of infected milk, beef and produce fertilised by cow manure.
The researchers are the first to report this connection between MAP and rheumatoid arthritis in a study published in the journal Frontiers in Cellular and Infection Microbiology.
They had previously discovered a connection between MAP and Crohn's disease.
Crohn's and rheumatoid arthritis (RA) share the same genetic predispositions and both are often treated using the same types of immunosuppressive drugs.
"Here you have two inflammatory diseases, one affects the intestine and the other affects the joints, and both share the same genetic defect and treated with the same drugs," said Saleh Naser, UCF infectious disease specialist.
For the study, Shazia Beg, rheumatologist at UCF recruited 100 of her patients who volunteered clinical samples for testing.
Seventy-eight per cent of the patients with rheumatoid arthritis were found to have a mutation in the PTPN2/22 gene, the same genetic mutation found in Crohn's patients, and 40 per cent of that number tested positive for MAP.
"We believe that individuals born with this genetic mutation and who are later exposed to MAP through consuming contaminated milk or meat from infected cattle are at a higher risk of developing rheumatoid arthritis," Naser said.
Rheumatoid arthritis is an autoimmune and inflammatory disease that causes the immune system to attack a person's joints, muscles, bones and organs.
Patients suffer from pain and deformities mostly in the hands and feet. It can occur at any age but the most common onset is between 40 and 60 years old and is three times more prevalent in women.
"We do not know the cause of rheumatoid arthritis, so we are excited that we have found this association," Beg said.
"But there is still a long way to go. We need to find out why MAP is more predominant in these patients - whether it is present because they have RA, or whether it caused RA in these patients. If we find that out, then we can target treatment towards the MAP bacteria," she said.