Leprosy, also known as Hansen’s disease, is an ancient infectious condition caused by the slow-growing bacteria Mycobacterium leprae or Mycobacterium lepromatosis. This disease primarily affects humans, targeting the skin, nerves, upper respiratory tract, eyes, and testes. While human-to-human transmission through prolonged close contact is the most common route, certain animal species have been identified as carriers of these bacteria, leading to occasional transmission to people.
Armadillos: A Primary Reservoir
The nine-banded armadillo (Dasypus novemcinctus) is the animal most widely recognized as a natural carrier of Mycobacterium leprae. These unique mammals are susceptible to the bacteria due to their relatively low body temperature, typically around 90 degrees Fahrenheit (32-35 degrees Celsius), which provides an ideal environment for the bacteria to multiply.
Armadillos are found throughout the Americas, with a significant presence in the southeastern United States, Central America, and South America. The geographic distribution of armadillos carrying M. leprae directly correlates with some human leprosy cases linked to animal exposure, particularly in states like Florida. Up to 20% of some wild armadillo populations are thought to be infected. While the armadillo is a natural host, these animals may have initially acquired the bacteria from humans centuries ago, possibly from early European explorers.
Other Animals Found with Leprosy
Beyond armadillos, other animal species carry Mycobacterium leprae, though their role in human transmission is less significant. Red squirrels (Sciurus vulgaris) in the British Isles are natural reservoirs for both M. leprae and M. lepromatosis. Genetic analysis suggests medieval English red squirrel strains were closely related to human strains, indicating historical transmission. However, there have been no definite cases of leprosy acquired in the UK since the late 1700s, suggesting modern red squirrels pose a very low risk to humans.
Natural leprosy infections have also been observed in non-human primates, including chimpanzees and sooty mangabeys in Africa. Naturally acquired cases in wild chimpanzees were recently reported in 2021 in Guinea-Bissau and Ivory Coast. Studies suggest that M. leprae can be transmitted from humans to non-human primates and between primate species. The prevalence of leprosy in wild non-human primates is low, and their direct contribution to human cases is not as established as that of armadillos.
Understanding Transmission and Prevention
Transmission of Mycobacterium leprae from animals to humans, particularly from armadillos, can occur through direct contact. This includes handling infected animals, especially sick or dead ones, or through cuts and abrasions on the skin. Another potential route of exposure is the consumption of undercooked armadillo meat. While the exact mechanism of transmission is not fully understood, the bacteria can enter the human body through the respiratory tract or skin.
Despite the presence of M. leprae in certain animal populations, the overall risk of contracting leprosy from animals is low for most people. For individuals in areas where armadillos are prevalent or those who frequently interact with these animals, precautions are advisable. Avoiding unnecessary contact with wild armadillos is a primary recommendation. If handling an armadillo is necessary, wearing gloves can reduce the risk of exposure. Thoroughly cooking any game meat, including armadillo, is also a recommended practice to eliminate potential bacteria.