Bacteria found in fleas, ticks and other biting insects could be partly responsible for rheumatoid illnesses among humans, such as arthritis, according to new research.

Bartonella can be transmitted to humans by these parasites or by bites or scratches from infected cats or dogs. One species of the bacteria, B.henselae, can be carried in a cat’s blood for months, even years.

A study carried out at North Carolina State University looked for the link between the bacteria and rheumatoid arthritis by testing blood samples.

A total of 296 patients were tested for evidence of Bartonella infection, most commonly cat scratch disease.

All patients had already been diagnosed with various conditions, such as Lyme disease, arthritis and chronic fatigue

Because those who contract cat scratch disease often suffer from some rheumatic symptoms, the researchers wanted to see if the patients tested positive for B.henselae.

Of the 296 patients 62 percent showed they had been exposed to the bacteria at some point, as their blood contained Bartonella antibodies.

Bacterial DNA was found in nearly half the samples tested.

The researchers say the study can’t prove beyond doubt that rheumatoid illnesses begin with infections, among other factors, but can show that Bartonella is a factor in some cases.

If a link could be confirmed between bacteria and arthritis, treatment could be tailored to fighting the bacteria.

Rheumatoid arthritis is an autoimmune disease in which the body’s immune system attacks healthy tissue, particularly around the joint. The attack causes fluid to build up and causes pain for the sufferer.