Rats Twice as Accurate as Traditional Tests in Detecting TB

Researchers from Tanzania recently made a bold claim: Rats can be trained to successfully detect tuberculosis (TB). Even more, they noted, rats are better than the traditional sputum smear microscopy test in detecting cases of TB in children. Much better.

Could these rodents be the missing link to more accurately detecting a disease that killed 1.3 million people worldwide in 2016, 130,000 of whom were children?

Deficiencies With Current TB Detection Methods

For this study, doctors from Sokoine University of Agriculture in Morogoro, Tanzania and experts from APOPO—a nonprofit group that trains and deploys rats to detect abandoned land mines and TB—took a closer look at how using rats might increase TB-detection rates in children under the age of 5. Their findings were recently published in Pediatric Research.

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Previous research has concluded that TB case detection rates increased by over 40% in the general population when trained rats were used as an enhanced case-finding tool. Interestingly, a 2014 Scientific American article also claimed that a single rat could evaluate more samples in 10 minutes than a lab technician could complete in an entire day.

The authors homed in on the pediatric group because current TB tests have poor success rates in this age group, largely because children cannot produce adequate sputum to yield accurate results on smear tests.

Results of a 2010 study showed that pediatric TB in northern Tanzania contributed to 13% of the total TB burden in the country and that 75% of those affected had pulmonary TB, of which only 5.8% of cases were bacteriologically confirmed. Because pediatric TB has proven difficult to diagnose, an estimated 94% of children are treated empirically.

Detection Success Rates With Rats

From January 2011 to June 2015, a total of 55,148 presumptive TB patients were tested. Over 90% of the participants were from Dar es Salaam, and the additional patients were from Morogoro. Children under the age of 5 comprised 1.8% of the sample (n = 982), with an equal ratio of male and female participants.

For the study, African giant pouched rats—which can grow to 3 feet in length and weigh 3 pounds—were used as the secondary detection tool. The primary method was the sputum smear microscopy test conducted at a local Tanzanian clinic. Prior to being presented to the rats, the sputum samples were heat inactivated for 30 minutes to kill microorganisms and render them safe for subsequent handling and evaluations. The samples were then randomly arranged in containment bars and presented to the trained rats. Animals were rewarded upon correct identification of known TB-positive control samples.

Within the sample group of children under age 5 years, 34 cases were confirmed bacteriologically, and trained rats detected an additional 23 cases—an increase of 67%.

The trained rats were also able to correctly identify TB in older children, adolescents, and adults, albeit in decreased rates:

• In children aged 6 to 10, rats increased case detection by 37%.
• In adolescents aged 11 to 18, rats increased case detection by 22%.
• In participants over 18 years old, rats increased case detection by 33%.

The proportion of smear-positive TB patients missed by microscopy who were detected by rats was statistically significantly higher in children aged 1 to 14 years than in adults, indicating that trained rats can help address the difficulties of detecting pediatric TB, the authors concluded. They also added that further determination of the accuracy of rats involving other sample types is still needed.