Posted by Potentially, anyway. One of the challenges facing infectious disease medicine in the developing world is the cost of diagnosis: diagnostic tests are often invented in wealthy countries with access to expensive equipment and supplies (and, in those countries, these don’t seem very expensive at all). Tuberculosis (TB) is difficult to diagnose in wealthy countries, and the inability to afford expensive diagnostics in the developing world–where most TB cases occur–only further compounds the problem.
So this report of a potentially cheap and more effective way to figure out if someone has TB provides some hope:
Researchers have found a new way of testing for tuberculosis that is fast, cheap and widely available: large rats that can smell the bacteria in a sputum sample.
There are expensive and complicated laboratory tests for tuberculosis, and the World Health Organization recently endorsed a new machine that can give accurate results in under two hours. But the device costs $17,000, and each test requires a $17 cartridge.
Whatever else can be said about them, rats are cheaper.
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 colors only Mycobacterium tuberculosis, the germ that causes TB, and examining the sample under a microscope.
The technique can be used in places where facilities are minimal, but it is not very sensitive — unless there is a high concentration of them, the bacilli are easy to miss, and that results in as many as 60 to 80 percent of positive cases going undiagnosed….
Writing in the December issue of The American Journal of Tropical Medicine and Hygiene, Dr. Poling and his colleagues report a test of the rats using samples that were confirmed by laboratory culture as either positive or negative.
The animals’ sensitivity — that is, their ability to detect the presence of tuberculosis — ranged as high as 86.6 percent, and their specificity, or ability to detect the absence of the germ, was over 93 percent.
In another test that compared the rats’ success to microscopy, the rats picked up 44 percent more positive cases.
Meet your diagnostic:
Sala Lewis/Reuters
Of course, you have to train the rats:
When the rats are about 8 weeks old, the trainers put 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 bananas. Eventually, the rats learn that a longer sniff at a positive sample gets a reward, and that negative samples are unproductive and should be skipped over quickly.
It remains to be seen how effective and reproducible this will be, but, if it works, these furballs could save lives.
January 7, 2011
January 7, 2011
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