Scientists discovered that certain bacteria, found in a third of British cattle, can lead to the agonising condition.
The US team found a direct link between a germ known as MAP and rheumatoid arthritis during trials with 100 patients.
The bacterium is commonly found in cows, but researchers warned it can be spread to humans through infected milk, beef and produce fertilised by cow manure.
It is hoped the discovery could see more effective treatments for the condition which is currently incurable.
The University of Central Florida team had previously discovered a connection between MAP and Crohn’s disease, and used this link to establish the germ as a trigger for arthritis.
Study leader Saleh Naser said: “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.
“Do they have a common trigger? That was the question we raised.
“We believe individuals born with this genetic mutation and later exposed to MAP through consuming contaminated milk or meat from infected cattle are at a higher risk of developing rheumatoid arthritis.”
Researchers recruited 100 patients who volunteered clinical samples for testing.
Some 78 per cent of the patients with rheumatoid arthritis were found to have the same genetic mutation found in Crohn’s patients. And 40 per cent of that number also tested positive for MAP.
Dr Nasser added: “Understanding the role of MAP in rheumatoid arthritis means the disease could be treated more effectively.”
Natalie Carter, of Arthritis Research UK, said: “This research is a first step into exploring whether MAP bacteria is an additional trigger for people at risk of rheumatoid arthritis.
“More than 400,000 people live with rheumatoid arthritis, which makes it extremely difficult for people to do things most of us take for granted – like getting dressed, or going to work.
“People living with these challenges will naturally follow the latest research with interest and hope.”
In the UK, 10 million people have arthritis, with about 400,000 suffering from rheumatoid arthritis, an autoimmune disease in which the body’s own immune system attacks the joints.
The crippling condition affects people’s knees, elbows, wrists and other major joints.
It is typically diagnosed in people aged 40 to 70 and affects three times as many women as men.
The study’s findings are published this week in the journal Frontiers In Cellular And Infection Microbiology.