Feline Leprosy: Mycobacterial Skin Signs and Treatment

Feline leprosy is a mycobacterial skin disease causing painless nodules and non-healing wounds on the face, limbs, and trunk of outdoor cats. While alarming in appearance, it is not transmissible to humans and typically responds to several months of combination antibiotic therapy.

Last reviewed: June 2026

What Is Feline Leprosy?

Feline leprosy is a cutaneous mycobacterial infection — not the same disease as human leprosy, but sharing the name because of its similar appearance: chronic, granulomatous skin nodules with a tendency to recur. The most common cause worldwide is Mycobacterium lepraemurium, a slow-growing organism associated with rodents. A second form caused by novel Mycobacterium species produces a different clinical syndrome in some geographic regions, particularly in Australia and New Zealand.

Affected cats are most often young to middle-aged (typically 1–3 years), predominantly male, and have outdoor access with likely rodent contact. ABCD (Advisory Board on Cat Diseases) guidelines classify feline mycobacterial disease by organism type, as the treatment and prognosis differ between the lepromatous (M. lepraemurium) and tuberculoid forms (Gunn-Moore et al., 2024, PMC — ABCD Mycobacterioses Guidelines).

Signs of Feline Leprosy

Signs are confined to the skin in the vast majority of cases; cats are generally systemically well.

Skin signs:

• Soft, painless, freely moveable subcutaneous nodules — the hallmark lesion
• Non-healing wounds or draining tracts at nodule sites
• Ulceration of the overlying skin
• Preferred locations: face (especially around the muzzle and ears), distal limbs, tail base, perineum, and ventral abdomen
• Nodules may grow slowly over weeks to months before the owner notices
• Lymph node enlargement near affected skin areas

Systemic signs (rare, indicates dissemination):

• Weight loss
• Lethargy
• Reduced appetite
• If the novel Mycobacterium species is involved, dissemination to lymph nodes and internal organs is more likely

Diagnosis and Treatment

Diagnosis:

• Fine needle aspirate (FNA) of a nodule and cytological examination — Romanowsky staining reveals macrophages packed with negatively staining rod-shaped organisms (acid-fast bacilli visible with special Ziehl-Neelsen stain)
• PCR on aspirate or biopsy material definitively identifies the species — essential for distinguishing M. lepraemurium from tuberculosis-complex species, which carry different public health implications
• Histopathology of excised nodule shows characteristic granulomatous inflammation

As described in Greene's Infectious Diseases of the Dog and Cat, cytological identification of acid-fast bacilli in cat skin lesions is rapid, inexpensive, and diagnostically useful, but species-level PCR confirmation is necessary before initiating long-term antibiotic therapy.

Treatment:

• Combination antibiotic therapy — the standard regimen uses two or three drugs from: clarithromycin, rifampicin, and clofazimine; a typical course is 3–6 months minimum, often longer
• Surgical excision — indicated for solitary or small clusters of nodules; surgery combined with antibiotics reduces recurrence compared with either alone
• Monitoring — nodules should be re-examined at 4–6 weeks; lesion reduction confirms treatment response; PCR repeat may be used after course completion
• Prednisone is not used — immunosuppression worsens mycobacterial disease

The AAFP-AAHA Feline Life Stage Guidelines, 2021 underscore annual wellness examinations that include thorough skin and lymph node assessment — the most reliable way to catch slow-growing nodular skin disease before it spreads.

When to See a Vet

Call your vet today if:

• Your cat has a new skin nodule, lump, or non-healing wound, especially on the face or limbs
• A skin lesion on your outdoor cat has been present for more than two weeks without improving
• You notice multiple painless lumps that are slowly growing

Go to the ER immediately if:

• Your cat develops systemic signs — significant weight loss, marked lethargy, or complete anorexia — alongside skin lesions
• Lesions are growing rapidly (days rather than weeks) or there are signs of severe local infection (hot, swollen, intensely painful)

Frequently Asked Questions

Is feline leprosy contagious to humans? Mycobacterium lepraemurium, the most common cause, has not been documented to cause disease in humans. The tuberculosis-complex mycobacteria (rarely responsible for feline skin disease) can potentially infect humans, which is why PCR species identification is recommended before extensive handling of discharge from lesions. Standard hygiene — washing hands after handling affected areas — is sensible precaution.

How long does treatment take for feline leprosy? Most veterinary protocols call for at least 3–6 months of combination antibiotic therapy (clarithromycin + rifampicin ± clofazimine). Lesions may begin to regress within 4–8 weeks of starting treatment, but stopping early risks relapse. Cats with extensive or recurrent disease may need longer courses.

How much does treating feline leprosy cost? An initial vet exam with FNA cytology typically runs $100–250. PCR species testing adds $150–300. Surgery for nodule excision runs $400–1,200 depending on number and location. Combination antibiotic therapy (clarithromycin + rifampicin) costs approximately $50–150 per month depending on dosing and cat weight. Multi-drug courses lasting several months mean total costs of $500–2,000 are common.

Will the skin nodules go away on their own? In most cats, nodules caused by M. lepraemurium do not resolve without treatment and gradually enlarge or multiply. Unlike abscess or lipoma, mycobacterial granulomas actively expand as the infection persists in macrophages. Treatment is necessary for resolution.

Can indoor cats get feline leprosy? It is very uncommon. M. lepraemurium is associated with rodent contact — the most plausible route of transmission is a bite or scratch from an infected rodent. Strictly indoor cats without rodent exposure have very low risk. Outdoor hunting cats in areas with rat and mouse populations carry the highest risk.

Still Not Sure if Your Cat Needs a Vet?

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