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Leprosy lurks in armadillos in Brazil’s Amazon

The South American country has the world’s second-highest number of cases of the disease

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2:00pm, June 28, 2018
nine-banded armadillo

ARMADILLO INFECTION  Nine-banded armadillos (one shown) may help spread leprosy to people in Brazil.

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Brazilians who hunt or eat armadillos are at a higher risk of catching leprosy than people who don’t interact with the animals, a new study finds.

More than 60 percent of armadillos tested in Brazil’s Amazonian state of Pará carry the leprosy bacterium Mycobacterium leprae. And about 63 percent of people tested in two villages in the region have antibodies against the bacterium, suggesting that they had been infected. People who ate armadillos more often had more of these antibodies in their blood, researchers report June 28 in PLOS Neglected Tropical Diseases.  

The findings may settle a debate about whether armadillos are implicated in the spread of leprosy, also known as Hansen’s disease, in Brazil. Knowing whether armadillos are involved in leprosy’s spread could potentially help public health officials limit the spread of the debilitating disease, which can cause nerve damage and disfigurement.

Brazil has the second highest number of leprosy cases in the world. In 2016, 25,218 new cases of leprosy were diagnosed. Only India had more, with 135,485 new cases, according to the World Health Organization.

Case counts

Brazil is among the countries with the biggest leprosy problem in the world. In 2016, 214,783 people worldwide developed leprosy. Here are the five countries with the most new cases recorded in 2016.

graph showing number of new cases of leprosy in 2016

Source: World Health Organization 2017

Many cases of leprosy, which can be cured with antibiotics, are probably spread from person-to-person, says study coauthor and immunologist John Spencer of Colorado State University in Fort Collins. The leprosy bacterium can live in people’s noses and may be shed in droplets when a person sneezes, coughs or breathes.

About 95 percent of the global population is immune to leprosy. But among those who are susceptible, it’s not entirely clear how some get infected. Many people newly diagnosed with the disease say they never met anyone else who had leprosy, says Richard Truman, a leprosy researcher at Louisiana State University in Baton Rouge. Although the infection may take years to produce symptoms, people might remember encountering someone with the disease because transmission of leprosy seems to require close, long-term contact with an infected person, such as living with a family member. The source of those people’s leprosy is a mystery.

Truman and colleagues reported in 2011 that nine-banded armadillos in the southeastern United States carry the same strain of leprosy as people do (SN: 5/21/11, p. 9), suggesting that people were being infected after contact with the burrowing animals. Red squirrels in Great Britain and some amoebae are the only other creatures known to harbor M. leprae. After the armadillo link was discovered in the United States, researchers wondered whether the animals were also contributing to the problem in Brazil. Several studies came up with mixed results.

The new research examined 16 armadillos that residents of São Jorge and Corpus Christi had hunted in the forests surrounding the villages. Spencer and colleagues found M. leprae DNA in the spleens of 10 of the armadillos, and bacteria in some of the animals’ tissues. As for people, of 146 villagers, 96 had handled or cooked armadillo meat. And 91 people reported eating armadillo within the last year, with 27 of those people saying that they ate armadillo more than once a month. Those frequent armadillo eaters were at slightly higher risk of contracting the disease than people who didn’t dine on armadillo, the team found.

Armadillo hunters were particularly threatened. Their risk of getting leprosy was nearly seven times greater than normal, the researchers say.

The evidence suggests that, people who come into frequent contact with armadillos may catch leprosy from the animals, Truman says. But to really establish the connection, researchers would need to show that the M. leprae bacteria in the armadillos are the same strains as those infecting people.

Getting a diagnosis of leprosy provokes anxiety in many patients, Truman says. “Many fear they are cursed and fear how their families will survive the stigma of the disease.” But understanding that the disease can come from something common like armadillos may help allay those fears and erase stigma. “This gives them a plausible biological explanation for their disease,” he says.

Spencer isn’t sure that his findings will stop people from hunting and eating armadillos. When he and his team told villagers they could get leprosy from armadillos, “they said, ‘we don’t care. We love to eat them.’ It wasn’t going to change their behavior,” Spencer recalls. That’s not so different from anyone else, he says. After all, plenty of people eat sushi knowing that consuming raw fish puts people at risk of some parasite infections.

Citations

M.B. de Silva et al. Evidence of zoonotic leprosy in Pará, Brazilian Amazon, and risks associated with human contact or consumption of armadillos. PLOS Neglected Tropical Diseases. Vol. 12, June 28, 2018. doi:10.1371/journal.pntd.0006532.

Further Reading

L. Hamers. British red squirrels serve as leprosy reservoir. Science News. Vol. 190, December 10, 2016, p. 9.

N. Seppa. Armadillos may spread leprosy. Science News. Vol. 179, May 21, 2011, p. 9.

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