Leprosy is an ancient disease, the oldest disease known to be associated with humans, with evidence of bone corrosion and characteristic deformities found in cemeteries in India since 2000 BC
Therefore, it is natural for many to think that the disease is a relic of the past. My studies in 2018 in a Brazilian state where the disease is prevalent show that leprosy is closer to us than we might think, however. The disease is growing in armadillos. And although these animals aren’t exactly the cuddly type that attracts humans, contact between armadillos and humans is spreading. And when species interact, armadillos are returning leprosy.
An ugly animal, a worse disease
Leprosy, also called leprosy, is caused by infection by the bacteria Mycobacterium leprae, causing skin lesions, nerve damage, disfigurement and disability, leading to the social stigmatization common to people with this disease. It is transmitted mainly by aerosol infection, or coughing and sneezing, from person to person.
Usually, the infection requires close contact with an untreated infected individual. Symptoms develop slowly, up to three to seven years after infection. It is rare in the United States, with an average of less than 200 cases diagnosed each year for the past 10 years, especially in individuals who have immigrated from foreign countries where the disease is prevalent. It is found mainly in tropical countries like Brazil, India, Indonesia and other countries in Africa, Southeast Asia and the Pacific Islands. There were 214,783 new cases worldwide in 2016.
Although drugs to treat and cure leprosy are inexpensive and available for free to anyone diagnosed with the disease, the high incidence pockets in dozens of countries have prevented the numbers from declining sharply in recent years. The root causes of high prevalence rates continue to be poverty, poor sanitation and nutrition and a lack of medical care to treat people diagnosed before nerve damage and disability occur.
Enter the armadillos
Dasypus novemcinctus, commonly known as nine-banded armadillo in the United States or chicken armadillo in Brazil, is the only species whose distribution includes North, Central and South America. These armadillos first extended their reach from Mexico to Texas around 1850 and then they went north and east to the southern Gulf states of the United States. In the late 1940s, another group of armadillos escaped captivity in central Florida and spread throughout Florida, eventually merging with the Texan armadillos in the early 1970s in the Florida Panhandle.
Around that time, Dr. Eleanor Storrs discovered that armadillos infected with M. leprae experimentally, he ended up showing symptoms of leprosy, even with the same skin lesions and nerve damage found in human cases. Shortly thereafter, she and her team discovered that armadillos that lived in the wild in Texas and Louisiana were naturally infected with M. leprae. Analysis of serum samples filed for antibodies specific to the bacterium indicated that animals in that area had probably been infected since 1960. It is not clear exactly how armadillos were infected by humans, but one theory is that they caught it on the ground contaminated by digging. Survey of armadillos in the Gulf states revealed that up to 20 percent were infected with M. leprae.
At first, the susceptibility of armadillos to leprosy was a boost for science and medicine. Because they are the only animal other than man in which the bacteria could be isolated, armadillos allowed scientists to study leprosy and possible treatments.
There are now millions of armadillos in the southern United States and people interact with them in a variety of ways. The animals’ leather shells were transformed into bags and boots; some were kept as pets at home or brought to entertain people at zoos, nursery schools and armadillo races at county fairs. In certain areas, people hunted them for barbecues.
This whole exposure ended up having consequences. In 2011, Dr. Richard Truman of the National Hansen’s Disease Program in Baton Rouge, Louisiana, published a study showing that the strain that infects most armadillos and leprosy patients native to Texas and Louisiana was identical, indicating that the disease was a zoonotic infection being transmitted to humans.
In 2015, another study by the same group found that a different type of strain that existed only in central Florida was causing a second group of cases in armadillos and humans. Both reports caused a great deal of media coverage, with people getting somewhat surprised and alarmed that this clumsy and not too fluffy animal was transmitting the oldest and one of the most feared diseases to humans. Still, once the excitement has subsided, most people have likely resumed their behavior with these animals, ignoring the possible risks involved.
What goes, comes back: The same goes for Brazil
Two things stand out in Brazil. Armadillos are native to South America; and leprosy, first brought to Brazil over 500 years ago by European explorers and through the West African slave trade, has been spreading there for hundreds of years. Knowing this, our research team wanted to know how much human contact there was with armadillos in Brazil and whether this could lead to the transmission of leprosy in these animals, as had been shown in the southern United States.
Our study focused on people living in a rural area in the west of the state of Pará, in the Brazilian Amazon, in the city of Belterra. People who live there often ate armadillos as a source of protein. And there was a lot of interaction between the people of this city and the armadillos: 19% hunted the animals in the woods and 65% cleaned the meat to cook or ate armadillos at least once a year. The percentage of people with a positive antibody response to the bacterium (63% were positive, normal for this region) indicated that most people had been infected with M. leprae.
A surprising 62% of armadillos killed by hunters showed signs of infection with M. leprae, a rate three times higher than in Texas and Louisiana. Most importantly, a group of 27 individuals who ate armadillo meat more often had antibody levels 50% higher than other groups, indicating that increased consumption almost doubled the risk of disease. The study concluded that, similar to the southern states of the United States, leprosy is being transmitted from armadillos to people in Brazil.
The broader message about this work is that wild animals harbor all kinds of diseases that can be transmitted to man, especially when there may be contact with blood or when eating meat. Although leprosy remains a disease that few people in the United States worry about, people should be careful about how they interact with armadillos.
This article was republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts.
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John Stewart Spencer receives funding from The Heiser Program of the New York Community Trust for Research in Hanseny and a J. William Fulbright Scholar to Brazil Award 2015-2016.