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Giant rats used to sniff out TB in Africa

Microphoto of TB bacteria (seen in red) found in sample of sputum.
Microphoto of TB bacteria (seen in red) found in sample of sputum.
CDC public domain

Using giant rats to sniff out landmines in Africa is nothing new. However, the idea of using them to detect whether someone is infected with tuberculosis new concept being ecplored by the Belgian non-profit group APOPO, which actually began using them to detect TB at 21 medical centers in Dar es Salaam Tanzania in 2008. The project was then expanded last year by using the rodents to “double-check 75% of potential TB samples from similar vacilities in Maputo, Mozambique.
"We know that we need a new approach in the diagnosis of TB, so this could be one of the approaches," said Gaël Claquin, a TB/HIV specialist and former national program officer for TB at the World Health Organization in Mozambique, who is not directly involved in the APOPO program.
Up until now the country has relied on trained lab technicians using microscopes to look at mucus, or saliva samples to see if tuberculosis bacteria is present. Unfortunately, “more than half the cases are missed, stated Claquin. The rats, however maybe able to help fill in the gap. According to APOPO, the rats were used to evaluate samples from approximately 12,500 during the first 16 months of the Maputo project. While lab techs found 1,700 of the samples to have been positive, the rats detected an additional 764 people infected with the disease, bringing the number up another 44% (or so). In addition, “each rodent can evaluate far more samples in 10 minutes than lab personnel can evaluate in an entire day.”

"Rats are very fast," said trainer, Catia Souto, adding that “one rat takes only eight minutes to get through five trays containing a total of 50 samples.”

To do this, Souto places a removeable tray with 10 samples of mucus from human subjects beneath the cage floor, and lets the rat walk across it. When the animal decides it has found something “positive” it then scratches the floor triggering a buzzer and is rewarded with a treat. It should be noted, however, that the rat does not have the last say, especially since they seem unable to tell the difference between tuberculosis and a drug-resistant strain of the disease, added Claquin. As a result, each suspected sample is then triple checked in the lab to be sure.

Another advantage of the rat test is that it only costs around $6,700 to $8,000 to train each rodent, yet relatively little to maintain the animals which can live 6-8years. However, a new quick diagnostic test developed by GeneXpert runs around $17,000 per device and between almost $10 and $17 per test.

According to estimates by the World Health Organization, approximately 1/3 of the world's population is thought to have been infected with M. tuberculosis, with one of the largest concentrations in Africa. The disease reportedly was responsible for nearly a half million deaths on the continent in 2012, with 58,000 of those in Mozambique

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