Scientists discover rats species that can detect TB bacteria in sputum

By MAORE ITHULA

Scientists have established that a special species of rats can detect Tuberculosis Bacilli (TB) bacteria just by smelling sputum of a patient.

In the latest report published by The American Journal of Tropical Medicine and Hygiene in December lasts year, researchers found that the Gambian pouched rat (Cricetomys gambianus), which is prevalent all over Sub-Saharan Africa, can smell the difference between TB bacteria and other germs found in human phlegm (the thick mucus secreted by the walls of the respiratory passages, especially during a cold).

Smear technique

The research that was conducted in Tanzania established that the unique rodents could identify the bacterium with 86 per cent accuracy and picked up 44 per cent more positive cases than sorting out the disease causing pathogens through a microscope.

The method has been in use for several years in the East African country but this is the first time the technique has been given a clean bill of health by a comprehensive study by experts from the Columbia University and Western Michigan University, both of the United States.

Prof Alan Poling, a scholar of psychology at Western Michigan University who is the lead author of the study on the rats observed that while the little animals had been accepted as a reasonable diagnostic tool in Tanzania, "the medical community is still skeptical."

Writing in the journal, Poling and his colleagues report a test of the rats using samples that were confirmed by laboratory culture as either positive or negative.

"The small animals’ ability to detect the presence of tuberculosis bacterae ranged as high as 86.6 per cent and their prowess to detect the absence of the germ, was over 93 pe cent accurate," the researchers report.

This rare method, the report observes, is cheaper and user friendly. Existing methods of testing TB are costly and complicated.

The World Health Organisation recently approved a device that provides accurate results in less than two hours.

The kit costs US$17,000 (Sh1.4 million) while each test consumes a cartridge worth US$17 (Sh1,400).

Statistics by the Ministry of Health show that in the absence of HIV, the number of new TB infections in Kenya is between 40,000 to 60,000 new TB cases each year. And the disease kills about 4.5 million people around the world every year.

Today, the most commonly used detection method in developing countries is smear microscopy. This 100-year-old technique involves collecting sputum, dyeing it with a substance that colours only Mycobacterium tuberculosis, the germ that causes TB, and examining the sample under a microscope.

Now, the rat technique can be used in places where facilities are minimal, but it is not very sensitive unless there is a high concentration of the TB germs (the bacilli), which are easy to miss.

"In the event that the bacilli are not highly concentrated in the sputum, as many as 60 to 80 percent of positive cases can go undiagnosed," the report observes.

The Gambian pouched rat is an omnivorous rodent with puffy cheeks, weighs 10 to 15 pounds and thrives in colonies of up to 20 all over Sub-Saharan Africa.

The unique rodent has also been trained to sniff out land mines and it is also too light to set them off.

An eight-week rodent is old enough to start doing its the job-testing TB.

Trainers put two sets of sputum samples-positive and negative for tuberculosis, under "sniffing holes" in a specially designed cage.

When a rat spends at least five seconds at a positive sample, it is rewarded with peanuts and/or bananas. Eventually, the rats learn that a longer sniff at a positive sample gets a reward, and that negative samples are not worthy the effort and should be skipped over quickly.

Work ahead

By the time they are 26 weeks old, the foolish ones will not have learnt how to test these germs while their cleverer colleagues get picked and employed as experts.

"These rats can do something amazing," observed Dr Neil W. Schluger, a professor of medicine at Columbia University a specialist in lung diseases.

He continued: "But even if you accept that it worked within their lab, are they still good at it a year later? Do they all have to be trained by the same person? How do they have to be cared for? If you change their cage or their bedding, does it still work? There is still a lot of work ahead of us regarding this issue."

Dr Poling conceded that research on the rats was still preliminary. But he said, "We think that eventually there will be a place for them in first-line screening."