These bacterial organisms can be found in lesions on cats that result from bites, scratches or other puncture wounds. The wounds are usually located on the head, neck or extremities. Sometimes the organisms enter the abdomen or thorax and produce severe systemic infections resulting in fever, weight loss, depression and difficulty breathing.

The lesions produced by these organisms are similar in appearance and treatment for either infection requires prolonged antibiotic therapy over weeks to months. In other ways these are very different organisms and the differences influence the diagnosis and treatment of these infections.

Actinomyces species are anaerobic (grow without oxygen) organisms that can be found in the mouths of normal cats. These bacteria can be difficult to isolate because they are frequently associated with multiple other organisms growing in culture. They are sensitive to high doses of penicillin and related antibiotics, but require long-term antibiotic therapy.

Nocardia species are aerobic (need oxygen to grow) organisms found in soil, water, and on plants. These bacteria are easily cultured and usually sensitive to sulfonamides and related antibiotics. Sometimes treatment involves multiple antibiotics. Response to therapy can be very slow and prognosis is guarded for severe infections.

Diagnosis of Actinomyces-Nocardia infection is based on cytologic examination of exudate or aspirates from nodules. Special stains may be needed to reveal the organisms. Culture and sensitivity is the most definitive way to determine which organism is present and the appropriate antibiotic to use. Radiographs may also be needed to determine the extent of pleural involvement.

Once antibiotic sensitivity has been determined, long-term antibiotic therapy should be instituted and continued for several weeks after the lesions have resolved. Some lesions may need to be surgically drained and debrided. Response to therapy can be very slow, over weeks to months, especially if there is underlying immune suppression. Prognosis is guarded particularly for systemic disease.

No cases of human disease have been acquired by direct contact with lesions on a cat but people can acquire the disease from a cat bite. People with suppressed immune systems are more susceptible to these infections and caution is advised.