Is leprosy transmissible from dogs to humans, humans to dogs, or armadillos to dogs?

Leprosy Transmission Between Humans, Dogs, and Armadillos

Leprosy is not known to be transmissible between dogs and humans in either direction, but there is established evidence of transmission between armadillos and humans, particularly in the Americas. 1

Transmission Pathways of Leprosy

• Leprosy (Hansen's disease) is primarily caused by Mycobacterium leprae and the more recently discovered Mycobacterium lepromatosis 1
• The main route of human-to-human transmission is through respiratory droplets (infectious aerosols created by coughing and sneezing) and possibly direct contact with infected individuals 1
• No evidence exists in the medical literature documenting transmission of leprosy between dogs and humans in either direction 2
• The nine-banded armadillo (Dasypus novemcinctus) has been established as a natural host and reservoir of M. leprae in the Americas 1

Armadillo-Human Transmission Evidence

• Studies have demonstrated that identical M. leprae strains are shared between humans and armadillos, supporting both anthroponotic (human-to-animal) and zoonotic (animal-to-human) transmission 1
• Direct exposure to armadillos roughly doubles the risk of leprosy in humans, with an odds ratio of 2.0 (95% CI: 1.36-2.99) according to case-control studies in Brazil 3
• In southern Texas, 71% of non-Asian patients with Hansen's disease reported either direct or indirect armadillo exposure, suggesting armadillos may act as a reservoir for human disease 4
• High-risk activities include hunting armadillos, cooking armadillo meat, or consuming armadillo meat 5

Other Animal Reservoirs

• Red squirrels (Sciurus vulgaris) in the British Isles have been found with leprosy-like lesions containing M. leprae and M. lepromatosis DNA, representing another potential animal reservoir 1
• Several other animals can be affected by leprosy-like diseases caused by pathogens closely related to M. leprae, which have been proposed to be grouped as a M. leprae-complex 1

Clinical Implications

• Leprosy presents with various clinical forms, from paucibacillary tuberculoid leprosy to multibacillary lepromatous leprosy 6
• The disease has a long incubation period, typically between two and six years 6
• Oral manifestations occur in 20-60% of lepromatous leprosy cases and may include multiple nodules (lepromas) that can progress to necrosis and ulceration 6
• Treatment is challenging as it requires multiple drugs for extended periods 6

Prevention Recommendations

• Avoid direct contact with armadillos, particularly in endemic areas of the Americas 3, 4
• People who hunt armadillos should be educated about the risk of leprosy transmission 5
• Proper hand hygiene after any potential exposure to wild animals is recommended 2
• A One Health transdisciplinary research approach has been proposed to better understand the complex transmission dynamics of leprosy 1

While various zoonotic diseases can be transmitted between humans and animals in public settings, including tuberculosis, Q fever, and various parasitic infections 2, there is no specific evidence in the medical literature documenting leprosy transmission between dogs and humans or armadillos and dogs.