New Delhi. Aug. 2: A parasitic worm ingested through inadequately cooked crab and crayfish has remained undetected for years in the Northeast and could meddle with tuberculosis-control efforts there, medical researchers have warned.

The parasite that colonises human lungs gives rise to symptoms so similar to TB that doctors, unaware of the parasite, may end up mistakenly treating patients for TB, said scientists at the Regional Medical Research Centre (RMRC) in Dibrugarh.

Doctors had assumed that the parasite belonging to the genus paragonimus was confined to Manipur where it had been detected in the Eighties. But recent surveys by the RMRC have shown that paragonimiasis is also present in Arunachal Pradesh, Assam, Meghalaya, Mizoram and Nagaland.

?It has remained largely unsuspected and undetected by doctors,? said Dr Kanwar Narain, a parasitologist at the RMRC.

A community survey by the RMRC in Changlang district of Arunachal Pradesh three years ago had revealed that nearly 95 per cent of the local residents consume freshwater crab or crayfish, usually roasted but sometimes even raw.

However, not all crabs and crayfish are infected. In one study in Arunachal Pradesh, the RMRC researchers found that 19 out of 32 freshwater crabs collected from a mountain stream were infected with paragonimus.

Narain said preliminary surveys by the RMRC have shown that paragonimiasis is clearly present in the region, but studies under way would help estimate the burden of the infection in different northeastern states.

Once ingested, the parasite invades the human lungs and causes symptoms such as persistent cough, blood-tinged sputum, and fever that are also typical complaints in TB patients. X-rays of lungs harbouring paragonimus worms are similar to the X-rays of patients with lung TB.

While paragonimiasis can cause people to become sick, it is not usually fatal. The infection can be easily treated with an anti-parasitic drug.

?Diagnostic confusion may have a negative impact on TB control,? said Dr Ramesh Mahajan, emeritus professor at the Postgraduate Institute of Medical Education and Research in Chandigarh.

?Patients with paragonimiasis, who do not get well because they are treated with anti-TB drugs, may make people lose faith in TB control,? said Mahajan who has called paragonimus an emerging public health problem in the latest issue of the Indian Journal of Medical Research.

Doctors need to ask patients with suspicious symptoms whether they have eaten poorly-cooked crab or crayfish. Narain and his team at the Dibrugarh centre are trying to develop a rapid screening test that may help doctors distinguish between TB and paragonimiasis.

?Food habits are clearly implicated in this infection,? said Mahajan. Paragonimiasis has long been viewed as a problem in Southeast Asia where dishes often include raw fish. ?When the crab or crayfish is well cooked, there is no danger of infection.?