Giant pouched rats sniff out tuberculosis in Africa

At a time when tuberculosis-related death rates worldwide surpass those from AIDS, two African countries are trying a TB test that is faster, cheaper and unorthodox: giant pouched rats.

TB, caused by bacteria, is a top infectious disease killer worldwide, according to the World Health Organization. It infects about nine million people around the world each year and about 1.5 million don't survive. Nearly 10 per cent of these deaths are children.

Doctors say poor diagnostics, such as a lack of chest X-rays and weak health systems, contribute to the scope of the problem in developing countries.

• Tuberculosis rivals AIDS as leading cause of death: WHO

The United Nations aims to end the TB epidemic by 2030. Towards that end, researchers in Mozambique and Tanzania seeking a better diagnostic tool have used giant pouched rats to sniff out the disease. The rats, which are about the size of a cat, identified 10,000 TB patients who were missed by conventional lab screens.

The intelligent and sensitive sniffers were originally trained to detect land mines.

"It is a little bit unorthodox," acknowledged Montrealer Dr. Stewart Reid, the Zambia-based medical adviser for the HeroRAT program by the non-profit group called Apopo.

TB bacteria release several compounds in human saliva and the rats are able to detect the bouquet consistently and with a considerable degree of accuracy, Reid said in an interview from Lusaka, Zambia.

The rats are exposed to the sputum in a cup. They're rewarded for their efforts with mashed banana.

In standard TB screens in developing countries, a technician analyzes a saliva smear under a microscope.

"A technician working at a microscope can identify or screen approximately 20 patients a day, whereas a rat can actually screen 100 patients in 20 minutes," Reid said.

Dr. Kamran Khan, of St. Michael's Hospital in Toronto, studies ways to detect and control diseases such as tuberculosis.  He regularly treats people for TB using advanced diagnostic tools that aren't available in developing countries.

About a third of the world's population is currently infected with TB at a dormant stage, which makes it a challenge to eliminate the infection, Khan said.

The pouched rats could supplement diagnostic capabilities while bypassing the need for the high-tech solutions, such as X-rays or molecular tests that are out of reach in low-income countries, he said.

"I think it's an intriguing development," Khan said. "It's really an interesting sign of innovation and people being creative in these resource-limited settings."

The devil is in the details, including how many false negatives and positives are identified by the rats, Khan cautioned.

"A false negative is an important consequence because that basically means to say that a person doesn't have TB when they do. So they could go back to their home or to work, to other places in the community and spread the infection."

Alternatively, a false diagnosis of TB could result in a regime of multiple medications, many with potentially serious side-effects, Khan said. 

While WHO doesn't consider the rats to be sophisticated enough to use for standard TB screening, Ethiopia plans to use the animals for secondary tests to detect the disease. TB is treatable if caught in time.