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Indian researchers have developed a simple, accurate leprosy test for use in the field.

There are around 200,000 cases of leprosy per year in 115 countries, including India, according to the World Health Organization. The disease is caused by Mycobacterium leprae bacteria which attack the skin and nerves.

The new test was developed by researchers at the Central Drug Research Institute in Lucknow and the National JALMA Institute for Leprosy and other Mycobacterial Diseases in Agra, both in northern India.

The current method for diagnosing leprosy is the detection of M. leprae by smear microscopy of skin samples. This test has a low sensitivity and cannot detect all cases of paucibacillary leprosy ― where a person has less than five lesions on their skin.

The team worked on detecting M. leprae proteins in skin scrapings, rather than the bacteria themselves, to give the test a higher sensitivity.

They tested 30 patients with paucibacillary leprosy, eight with multibacillary leprosy (more than five lesions), and five healthy subjects.

The team used a rapid and simplified version of ELISA ― a technique used for detecting the presence of proteins ― called Dot-ELISA.

In this test, the skin samples were suspended in sterile saline and then dotted onto a membrane. Antibodies against M. leprae were then applied to the samples. If proteins of M. leprae were present, the reaction caused by the antibody binding created a colour change on the membrane.

They found that the test was sensitive, detecting proteins of M. leprae in all the multibacillary cases, 76 per cent of the paucibacillary patients with more than one lesion, and 62 per cent of the paucibacillary patients with only one lesion. None of the healthy volunteers tested positive.

Bikram Saha, an assistant professor at Midnapore Medical College and Hospital in West Bengal, said, "The test can be better than smear microscopy because it can be easily and effectively performed in the field, its sensitivity is impressive and it can accurately exclude healthy individuals."

"Smear microscopy lacks effectiveness in paucibacillary leprosy, while other diagnostic tests such as polymerase chain reactions are not as promising, particularly under field conditions," he adds.

The study was published online in the Transactions of the Royal Society of Tropical Medicine and Hygiene journal on 18 April.

Reference: Transactions of the Royal Society of Tropical Medicine and Hygiene doi 10.1016/j.trstmh.2007.02.026 (2007)

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