New research shows that many armadillos in the Brazilian Amazon carry the bacteria that causes leprosy.

The findings, published in the journal PLOS Neglected Tropical Diseases, suggest the disease is likely being transmitted to local humans who use armadillos as a dietary source of protein.

Leprosy, which is caused by the bacterium Mycobacterium leprae, is a slowly developing chronic disease that if left untreated causes skin lesions as well as nerve damage, leading to muscle atrophy, paralysis and blindness. Recent evidence shows that it infects immune cells in the vicinity of nerve endings. The cells then destroy the protective myelin layer on the nerves and damages the nerve fibres. It is considered an infectious neurodegenerative disease.

Most people are able to swiftly fight off an M. leprae infection before leprosy can develop, but not everyone is so lucky. Over 200,000 new cases are recorded each year worldwide.

While this represents a significant decline in prevalence over the past few decades, for the endemic pockets where these cases are concentrated, the disease remains a major health concern. In 2016, 80% of all cases were found in India, Indonesia and Brazil. Currently, Brazil is the only country in the world with more than one case per 10,000 population, and many of these cases occur in the Brazilian Amazon.

Although the most common transmission route for leprosy is through contact with infected humans, people are not the only hosts.

It turns out armadillos are a natural reservoir for the bacterium. They can even develop leprosy themselves. It seems their immune response is quite similar to that of humans, with the disease taking a similar course of progressive nerve damage. Moreover, research suggests infected animals can transmit it to humans.

Given the relatively high rate of leprosy in people living in the Brazilian Amazon, coupled with the fact that wild armadillos comprise part of their diet, John Spencer at Colorado State University in the US and Claudio Salgado at Universidade Federal do Pará in Brazil wanted to find out whether armadillos in the region were infected and, if so, whether it was possible they were passing on the infection to humans.

Spencer, Salgado and colleagues focussed their investigation on Belterra in the state of Pará, which sits in the heart of the Amazon. They collaborated with the residents of two villages in the area, for whom armadillos from the surrounding rainforest formed part of their diet. Tissue samples from 16 captured animals revealed 62% carried M. leprae.

Meanwhile, the researchers also surveyed 146 residents and found that the majority (65%) had regular contact with armadillos through hunting, preparing meat, or eating.

Of those surveyed, seven were diagnosed with leprosy, while 92 had the antibody to M. leprae in their blood, suggesting they had been exposed to the bacteria at some point. Villagers who ate armadillo meat most frequently — more than once a month — had the highest levels of antibodies, indicating the highest level of exposure.

The findings support the hypothesis that armadillos are a reservoir for leprosy in the Brazilian Amazon and that locals who hunt, process and consume their meat are at significant risk of infection.