Organ transplant recipients who get West Nile virus are more likely than those in the general population to get the most severe systems, according to a new Canadian study.

Transplant patients take drugs to suppress their immune system to prevent rejection, but the drugs also put them at higher risk of infection.

"If a transplant patient gets West Nile, their immune system is not able to control the virus in the same way that you or I would if we got infected and because of that they get more serious infection," said Dr. Atul Humar of the organ transplant program at the University Health Network in Toronto.

Dr. Atul Humar

In Humar's study of 855 transplant patients, six tested positive for the virus in 2002. Of those, four were severely ill and one of them died.

The results mean the rate of severe illness such as meningitis and encephalitis among infected transplanted patients was 66 per cent in the study, compared to 0.7 per cent of those infected in the general population.

Toronto's transplant program is warning its patients about the increased risk, saying they need to take more precautions than the average person, said Humar.

The precautions themselves are the same as for anybody, such as wearing long-sleeved clothing and repellent outdoors.

It's also possible people with HIV/AIDS or cancer may be at increased risk. In Humar's opinion, anyone with a compromised immune system who lives in an area prone to West Nile virus should be cautious around mosquitoes.