African giant pouched rats, which are already widely used to sniff out landmines, are being trained to conduct mass screening for tuberculosis (TB) in crowded prisons in Mozambique and Tanzania.

The rats are large, nocturnal creatures that can grow up to 3 feet in length. Although they have poor eyesight, this is compensated by their highly developed sense of smell and hearing.

Trained rats are taught to distinguish positive from negative sputum samples, the mucus coughed by patients from their lower airways, using their highly sensitive sense of smell to detect TB.

The rats are presented with a row of 10 sputum samples and then hovers over the TB-positive sample for 3 seconds.

Compared with a laboratory technician who may require four days to detect TB, a trained rat is capable of screening 100 samples in as little as 20 minutes. WHO likewise recommends that a lab technician should not test more than 20 patients in a day. Exceeding this number may boost chances of misdiagnosis.

The accuracy of the creatures at detecting TB is nearly 100 percent albeit they cannot differentiate between the normal and drug resistant strains.

Experts hope that the animals will boost the accuracy and speed of testing for TB which could lead to fewer undiagnosed cases. Early detection of TB cases could mean early treatment as well as reduce transmission of the disease. Trained rats also offers cost-effective option. Rat screening is cheap costing as little as 20 U.S. cents.

"This programme is very important as the rats will enable Active TB case detection which means early detection of TB in risk populations such as prisoners and prison staff," said Apopo Tanzania tuberculosis programme manager Georgies Mgode.

"The early detection of TB cases enhances an early treatment initiation which also reduces transmission or dissemination of TB to others from an untreated patient."

Apopo, a non-governmental organization that has been training rats to carry out the mass screenings said that prisons are considered as incubators of TB because of the high number of inmates and confined conditions.

Studies from Malawi, Tanzania and Ivory Coast reveal that TB rates are 10 times higher in prisons compared with the general population.

TB, an infectious disease, is the second leading cause of death worldwide. Figures from the World Health Organization (WHO) show there are about 9 million new cases of TB, 2 million of which ends in death.

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