If the international experts gathered at the Novartis Institute for Tropical Diseases (NITD) Symposium on Tuberculosis in Tanzania last month thought they could smell a rat, they weren’t far off the mark. Perched at the back of the conference centre was a gargantuan beast munching contentedly on a bit of blackened banana. The rat wasn’t there in its usual designation of pesky critter, however, but rather — as the members of the Belgium humanitarian research group Apopo hoped to demonstrate — as helpful sniffer.
The research group has already had measurable success using the African giant pouched rat’s highly developed olfactory ability to sniff out land mines in Mozambique. They were present at the symposium partly in the hope of securing funding to further explore the potential of putting the rodents to work as an alternative diagnostic tool for the early detection of tuberculosis (TB) in humans.
The idea is to train the rats to differentiate the “target” smell of the mycrobacterium tuberculosis in human sputum or even breath samples from a variety of background scents. A rat is released down a structure that contains a multitude of “sniffer holes” under which the sputum samples are placed. When a rat comes across a “positive” sample it will sniff and bite at the hole or remain stationary with its nose in the hole, indicating to its trainer that the TB scent is present. The rat is given a food reward to ensure that incentive remains high.
Apopo has already set up a training and evaluation laboratory at the Sokoine University of Agriculture in Tanzania which has the capacity to process 200 sputum samples per hour.
The researchers maintain that one rat can potentially analyse about 100 samples in 20 minutes, which makes for pretty impressive numbers if compared with the average maximum of 40 samples that can be analysed by a lab technician per day using microscopy.
Added to this, the researchers hope to prove that this sniffer “technology” could considerably reduce public health costs because of the shorter time it takes to train technical staff and also the fact that no expensive equipment is required.
Bart Weetjens, director of Apopo, says it is hard to calculate the exact amount it takes to train an individual rat because there are still a lot of research costs involved. However, “roughly one could say that it is a magnitude less than it costs to train a detection dog. A dog takes about $40 000 [to train], while rats would cost less than $5 000 when fully trained.”
The amount is also considerably less than it takes to educate a human in microscopy and rats aren’t picky about where they want to practise their skills, so the problem of retaining laboratory staff in rural areas is, at least in part, somewhat reduced.
The potential beauty of this really comes into play in sub-Saharan Africa where the estimated incidence of TB per capita is nearly twice that of South-East Asia, at 350 cases per 100 000 population. The pouched rats are endemic in the region and resistant to most tropical diseases, and to TB.
They are also small and therefore easily transported and housed. They are easy to breed and train and, because they respond to food rewards, they can be handled by a variety of trainers. The animals also have the ability to concentrate for long periods of time and one handler can work with many rodents consecutively.
Apopo’s intermediary results were met with enthusiasm from the delegates at the symposium, among whom were representatives from big pharma, the World Health Organisation, the National Institute of Health and other major public health organisations.
“We got a big applause, lots of questions and we were approached for potential funding after the lecture,” says Weetjens. “If this will effectively result in a grant is still open to question, but consciousness of our rats is certainly growing. The potential benefits for use in an African context is just too overwhelming not to further investigate it.”