Feline Leprosy (Mycobacterial Skin Disease)

Feline leprosy is a descriptive name for a group of slow-growing skin infections caused by mycobacteria. Despite the alarming label, it has nothing to do with human leprosy, is not a fever-and-wasting illness, and usually affects otherwise healthy cats. What it produces instead are firm nodules in and under the skin — single or multiple — that may break down into ulcers that stubbornly refuse to heal.

The bacteria responsible are environmental and rodent-associated mycobacteria that are thought to enter through bite wounds or contaminated scratches. This helps explain the typical patient: an outdoor cat that hunts or fights, with lesions cropping up on the head, limbs or trunk where such wounds occur. The infection tends to stay in the skin and local tissues rather than making the cat systemically ill.

Because the lumps look like many other things — from cysts and abscesses to tumours and other granulomatous diseases — diagnosis depends on a biopsy. Special stains can reveal the characteristic bacteria within the tissue, and culture or PCR testing identifies the exact organism, which matters because it guides the choice of antibiotics.

Treatment is a marathon, not a sprint. Localised nodules are often removed surgically, and this is combined with a long course of specific antibiotics — frequently a combination, given for weeks to months, because mycobacteria grow so slowly. Stopping early invites relapse. With an accurate diagnosis and a full, patient course of treatment, the outlook for most cats is good, and any lump or sore that will not heal is well worth investigating early.