Rheumatoid arthritis is an autoimmune disease that affects 1.3 million adults in the nation

The bacteria, MAP, is found in nearly half the cows in the US

Hamburgers and milkshakes could increase the risk of developing rheumatoid arthritis, a new study warns.

Researchers discovered that a strain of bacteria found in milk and beef could be a trigger for developing the agonizing condition in those genetically at risk.

Mycobacterium avium subspecies paratuberculosis, dubbed MAP, is found in about half the cows in the US and can be spread to humans through consumption of infected milk, beef and produce fertilized by cattle manure.

The study, published in Frontiers in Cellular and Infection Microbiology, is the first to link cow products to the joint disease and could lead to better arthritis treatments that target the bacteria.

Researchers revealed that bacteria commonly found in milk and beef is linked to rheumatoid arthritis

Rheumatoid arthritis, which affects nearly 1.3 million adults in the US, is an autoimmune and inflammatory disease that can cause long-lasting or chronic pain and deformity.

The condition causes the immune system to attack healthy cells in the body by mistake, resulting in painful swelling in the affected parts of the body.

'We don't know the cause of rheumatoid arthritis so we're excited we have found this association,' said researcher Dr. Shazia Bég, rheumatologist at the University of Central Florida.

For the study, researchers analyzed blood samples of 100 people.

They found that 78 percent of those with rheumatoid arthritis were found to have a variant of the gene PTPN2/22, and 40 percent 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,' said Dr Saleh Naser, researcher and infectious disease specialist.

Although milk is considered good for bones, joints can be another matter for some people.

The same team previously linked the disease to Crohn's disease — a chronic inflammatory disorder of the gastrointestinal tract.

'Here you have two inflammatory diseases — one affects the intestine and the other affects the joints and both share the same genetic defect and are treated with the same drugs,' Dr Naser said.

Rheumatoid arthritis, which affects nearly 1.3 million adults in the US, is an autoimmune and inflammatory disease that can cause permanent joint changes likes knobby finger joints.

The condition causes the immune system to attack healthy cells in the body by mistake, causing painful swelling in the affected parts of the body.

The disease commonly affects joints in the hands, wrists, and knees.

Women are up to three times more likely to develop the condition than men. Those with family history of rheumatoid arthritis are also more vulnerable.