Leprosy is a disease caused by Mycobacterium leprae. While long recognized in humans, infections in various species of animals are less well known and understood. The U.S. National Hansen’s Disease Program states “Armadillos are the only other known natural hosts of leprosy bacteria.” (1) That may not be true.
There are several studies that demonstrate that the nine-banded armadillo (Dasypus novemcintus) can contract leprosy. (2) (3) Truman, et al., found evidence that the infection can be transmitted from armadillos to humans.
Studies have shown that M. leprae can infect protozoans, free-living amoebae, and remain viable. (4) (5) It has not been determined if ingestion of infected amoebae can result in infection by M. leprae. Wheat, et al., found that the bacillus can remain viable for as long as eight months in some cases.
There is no proof that leprosy can be transmitted through an insect bite. The mosquito species Aedes aegypti and Culex fatigans (quinquefasciatus) have been shown to be competent to transmit the illness. (6) Cimex hempterus (bedbugs) has also been found to harbor the bacillus. (7) There is no clear evidence that any biting insect is acting as a vector for leprosy, however.
Squirrels and Other Rodent
In the British Isles, red squirrels (Sciurus vulgaris) have been documented as having leprosy. (8) (9) Laboratory mice are routinely used to investigate the disease. (10)
Naturally acquired leprosy has been reported in wild nine-banded armadillos (Dasypus novemcinctus) and in three species of non-human primates (chimpanzees [Pan troglodytes], sooty mangabey monkeys [Cercocebus atys] and cynomolgus macaques [Macaca fascicularis]) (11)
In addition, researchers have successfully infected rhesus monkeys [Macaca mulatta] and African green monkeys [Chlorocebus sabaeus]. (12) A chimpanzee in captivity developed leprosy some 26 years after capture. (13) While monkey to human transmission has not been documented, leprosy could be considered a zoonosis. (14)
Any disease or infection that is naturally transmissible from vertebrate animals to humans and vice-versa is classified as a zoonosis (15)
Mycobacterium leprae can be detected in both urine and feces. (16) (17) This suggests the potential for transmission to humans through exposure to animal wastes. In addition, armadillos and monkeys are food for many in regions where those animals and leprosy both exist.
As we learn more about the various ways that Mycobacterium leprae has adapted to survive in various hosts, we learn more about how the bacillus can infect humans. Too much of “what we know” is based upon consensus and not research.
- Truman, Richard W., et al. “Probable zoonotic leprosy in the southern United States.” New England Journal of Medicine 364.17 (2011): 1626-1633.
- Balamayooran, Gayathriy, et al. “The armadillo as an animal model and reservoir host for Mycobacterium leprae.” Clinics in dermatology 33.1 (2015): 108-115.
- Cardona Castro, N., J. C. Beltrán, and A. Ortiz Bernal. “Detection of Mycobacterium leprae DNA in nine-banded armadillos (Dasypus novemcinctus) from the Andean region of Colombia.” (2009).
- Lahiri, Ramanuj, and James L. Krahenbuhl. “The role of free-living pathogenic amoeba in the transmission of leprosy: a proof of principle.” Leprosy review 79.4 (2008): 401.
- Wheat, William H. et al. “Long-Term Survival and Virulence of Mycobacterium Leprae in Amoebal Cysts.” Ed. Joseph M. Vinetz. PLoS Neglected Tropical Diseases 8.12 (2014): e3405. PMC. Web. 30 May 2016.
- Blake, Leslie A., et al. “Environmental nonhuman sources of leprosy.” Review of Infectious Diseases 9.3 (1987): 562-577.
- Narayanan, E., Manja, K. S., Kirchheimer, W. F., & Balasubrahmanyan, M. (1972). Occurrence of Mycobacterium leprae in arthropods. Leprosy review, 43(4), 194-8.
- Meredith, Anna, et al. “Leprosy in red squirrels in Scotland.” Veterinary Record 175.11 (2014): 285-286.
- Simpson, Vic, et al. “Leprosy in red squirrels on the Isle of Wight and Brownsea Island.” Veterinary Record 177.8 (2015): 206-207.
- Job, C. K., S. K. Chehl, and R. C. Hastings. “New findings on the mode of entry of Mycobacterium leprae in nude mice.” International Journal of Leprosy 58.4 (1990): 726-729.
- Meyers, Wayne M., et al. “Naturally acquired and experimental leprosy in nonhuman primates.” The American journal of tropical medicine and hygiene 44.4 Pt 2 (1991): 24-27.
- Hagstad, H. V. “Leprosy in sub-human primates: potential risk for transfer of M. leprae to humans.” International journal of zoonoses 10.2 (1983): 127-131.
- Hubbard, G. B., et al. “Spontaneous Leprosy in a Chimpanzee.” Am J Pathol 51 (1967): 225-242.
- Walsh, Gerald P., et al. “Leprosy-a zoonosis.” Lepr Rev 52.Suppl 1 (1981): 77-83.
- World Health Organization. Zoonoses and the Human-Animal-Ecosystems Interface. http://www.who.int/zoonoses/en/
- KALDANY, RASHAD?RUDOLF J., et al. “Methods for the detection of a specific Mycobacterium leprae antigen in the urine of leprosy patients.” Scandinavian journal of immunology 25.1 (1987): 37-43.
- Koshy, A., and A. B. A. Karat. “A study of acid-fast bacilli in the urine, gastric juice and faeces of patients with lepromatous leprosy.” Leprosy in India 43.1/4 (1971): 3-7.