This is the cheapest way for detecting tuberculosis and may become the first line of test provided it is accepted by the medical community.
Presently smear microscopy
is the most commonly used method in developing countries. This technique is 100 years old and involves staining the sputum with a dye that colors only Mycobacterium Tuberculosis bacteria, which can then be examined under a microscope. This technique can be used in places with minimum diagnostic facilities, but is not very sensitive unless the bacilli concentration in sputum is high. Almost 60-80% of tuberculosis cases can go undiagnosed with this method. Recently the World Health Organization
(WHO) has endorsed a new machine that gives accurate results within 2 hours. However this device costs $17,000 and each test requires $17 cartridge.
Studies conducted at the Western Michigan University suggest that the Gambian pouched rat
can do better. This species of rat can smell the difference between tuberculosis bacilli and the other germs
that may be present in human phlegm. The samples used during the study were later confirmed by laboratory culture. It was found that the rat's sensitivity to correctly detect the presence of bacilli was as high as 86.6%, while their specificity to detect the absence of the bacilli was over 93%.
Similarly when the rat's success was compared to smear microscopy, it was found that the rats were 44% more accurate in picking up the positive cases. The rats have to be trained for doing the same when they are about 8weeks old. Positive and negative sputum samples are put under the sniffing hole and when the rats spend more than 5 seconds on a positive sample they are rewarded.
By 26 weeks the rats are trained to spend more time sniffing the positive samples and spend lesser time at the negative samples.
The lead author of the study and a professor of Psychology, Dr. Alan Poling said that the medical fraternity is still skeptical about the acceptance of animals as a reasonable diagnostic tool. He said that research on the rats was still in the preliminary stage
but eventually they could be used in the first-line screening for tuberculosis.