Multiple sclerosis (MS) is a disease in which the body's own defence cells attack protective nerve tissue, which can cause pain and problems with vision, movement, memory and thinking.

But scientists in Argentina have published a study claiming that these symptoms of the disease may be lessened in people whose immune system has been affected by a parasite.

"Certain types of immune cells, known as T cells, produce chemicals that trigger the crippling attacks of MS. The scientists found that T cells from the parasite-infected patients were less likely to produce these chemicals. Perhaps the parasites programme the T cells to shut down destructive signals," Nature magazine quoted Jorge

Correale of the Raul Carrea Institute for Neurological Research in Buenos Aires, one of the two scientists who publish today's work, a s saying.

Correale has pointed out that his work supports the so-called 'hygiene hypothesis' - the idea that certain infections may teach the body not to attack itself, preventing problems such as allergies.

"Although doctors don't really know what causes multiple sclerosis, environmental factors can play a key role in the disease," Correale said.

"Indeed, in Latin America, the prevalence of the disease is significantly lower than in Europe, the United States or Canada. One of the environmental factors that 'protects' the patients could be parasite infections," Correale added.

Research in animals has suggested that parasite infections might protect against autoimmune diseases, or those in which the body destroys its own tissues.

If the work holds up, Correale says, the principle may also hold true in other autoimmune conditions such as diabetes and inflammatory bowel disease. Researchers have already tried treating Crohn's disease with so-called 'worm therapy' - dosing patients with a particular gut parasite in order to tweak the immune system2.

Other researchers say that Correale's work is intriguing, but caution that scientists still need to work out which parasites are most likely to help patients before trying worm therapy in other diseases.

Correale has also noted that the doctors who evaluated the patients knew who was infected and who was not - a potential source of bias in the study. And with only 12 patients in each study group, the study is quite small.

Nonetheless, scientists not involved with the work say that the clinical differences between the parasite-infected and non-infected patients looked "dramatic".

"Who knows what's going on in these patients? It's a curious phenomenon." said Ethan Shevach of the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland.