Merck Manual

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Pet Owner Version

Tuberculosis in Cats


Charles O. Thoen

, DVM, PhD, Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University

Reviewed/Revised Aug 2018 | Modified Oct 2022

Tuberculosis is an infectious disease caused by bacteria of the genus Mycobacterium. The disease affects practically all species of vertebrates, and, before control measures were adopted, was a major disease of humans and domestic animals. Signs and lesions are generally similar in the various species. Tuberculosis is uncommon in cats in North America.

There are several species of bacteria that cause tuberculosis. Each type is mainly found in one host species but may produce infection in other host species. Three of the main types of tubercle bacilli recognized are human (Mycobacterium tuberculosis), bovine (Mycobacterium bovis), and avian (Mycobacterium avium). Cats are quite resistant to the human form.

Ingestion, particularly via contaminated food or milk, is the most common source of infection in cats and affects the digestive tract and associated lymph nodes. The bacteria may also spread rapidly through the bloodstream and lymphatic channels and cause death. Alternatively, a prolonged course of disease may ensue. The organism can also be inhaled or enter through the skin. The signs reflect the extent and location of infection plus the underlying condition caused by the spread through the bloodstream. Generalized signs include lethargy, weakness, loss of appetite and weight, and fever. The pneumonia of the respiratory form of the disease causes a chronic, intermittent, moist cough with later signs of difficulty breathing and quick, shallow breathing.

The tuberculin skin test for diagnosis is considered unreliable in cats, so the diagnosis is typically made with x-rays and laboratory tests. Treatment of tuberculosis in cats is often not successful. If a cat is suspected of having tuberculosis, it must be reported to the appropriate public health authorities. To protect people, it is generally recommended that affected cats be euthanized.

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