The vast majority of TB-related deaths — that is, over 95 percent of them — tend to occur in low- and middle-income countries.
Such countries include India, Indonesia, China, the Philippines, Pakistan, Nigeria, and South Africa.
But in the United States, too, as the Centers for Disease Control and Prevention (CDC) explain, "too many people" are affected by the disease, with 9,272 cases being diagnosed in 2016.
In that same year, the WHO estimate that 1 million children contracted TB worldwide, and a quarter of them died from the disease.
Detecting TB in children is particularly tricky because standard diagnosis tests require a fair amount of sputum to be tested, which is something that cannot be collected from very young children.
Why we need better TB detection tools
This is why a team — led by Georgies Mgode, of the Sokoine University of Agriculture in Morogoro, Tanzania — set out to investigate alternative ways of detecting the disease.
In the new study — which has been published in the journal Pediatric Research — Mgode explains that anecdotal evidence of people who have TB emitting a specific smell was what motivated the team to explore the possibility of devising a "sniff test" using rats.
The researchers were also prompted by the lack of appropriate detection tests, particularly in low-income countries in Sub-Saharan Africa and South East Asia, where TB is most widespread.
"[M]any children with TB are not bacteriologically confirmed or even diagnosed, which then has major implications for their possible successful treatment," says Mgode.
"There is a need for new diagnostic tests to better detect TB in children, especially in low- and middle-income countries," he adds.
Rats detect 68 percent more cases of TB
The researchers used a species of rat called Cricetomys ansorgei, or the African giant pouched rat. Previous research had shown that these rodents can detect the odor emitted by Mycobacterium tuberculosis molecules.
As the scientists explain, the technique used to train the rats is similar to that used to enable them to detect landmines.
Mgode and colleagues analyzed sputum samples from 982 children under 5 years old, all of whom had been screened for TB using standard microscopy tests in Tanzanian clinics.
The standard tests detected TB in 34 children, but when the researchers used rats, a further 57 cases were found and confirmed. This amounts to almost 68 percent more cases.
The scientists conclude, "Trained rats increase pediatric TB detection significantly and could help address the pediatric TB diagnosis challenges."
Mgode comments on the clinical significance of the findings.
"This intervention involving [...] trained rats and community-based patient tracking of new TB patients missed by hospitals enables treatment initiation of up to 70 percent."
"This is a significant proportion," he adds, "given that these additional patients were considered TB negative in hospitals, hence were initially left untreated."
However, "Further determination of accuracy of rats involving other sample types is still needed," admit the researchers.