Severe flu doubles the risk of Parkinson's disease, new study says. However people who had red measles when they were kids have 35 percent lower chance of developing Parkinson's disease.

Parkinson's disease occurs when the part of the brain that controls movement doesn't function properly because the neurons that produce a chemical dopamine- that regulates body movements- die. The symptoms of the disease include trembling hands or legs, stiffness, poor balance, co-ordination between hands and legs, slow movements. PD usually affects men more than women. Although the disease starts usually after 60 years of age, it can occur earlier as well.

What causes Parkinson's disease is not known. Previous research has shown that some environmental and occupational causes can lead to the disease.

For the new study, researchers interviewed more than 800 people; 403 with Parkinson's disease and 405 without the disease (controls). The researchers found that exposure to certain animals, particularly cats and cattle, increases risk for Parkinson's.

"There are no cures or prevention programs for Parkinson's, in part because we still don't understand what triggers it in some people and not others. This kind of painstaking epidemiological detective work is crucial in identifying the mechanisms that might be at work, allowing the development of effective prevention strategies," said Anne Harris, who conducted the research at University of British Columbia, in a press release.
Occupational Causes for Parkinson's disease

Researchers say that occupational exposure to vibrations- like operating machinery at construction sites- can decrease a person's chances of developing the disease by up to 33 percent. But, driving snowmobiles or high speed boats increase the risk of Parkinson's disease.

Other studies have shown that exposure to metals like copper of manganese increase risk of Parkinson's disease in urban areas.

According to estimates, about 50,000 people in the U.S. are diagnosed with Parkinson's disease each year.

The study is published in the journal Movement Disorders.