Fungus Among Us, Part 3: Coccidiodomycosis

Posted by Dr. Kim Smyth on Nov 29 2012

Coccidiodomycosis is the systemic fungal disease caused by the organism Coccidiodes immitis or Coccidiodes posadasii. Unlike the other two fungal diseases we have already discussed, this organism is found primarily in the southwestern United States, as well as Mexico and Central America. Southern California, Arizona and southwest Texas are common states where these incidents occur, and they seem to increase in late fall and winter. This organism seems to favor dry conditions, and high winds help it to spread.

Like the previous two fungal infections we’ve discussed, Coccidiodomycosis occurs when spores are inhaled. Pulmonary disease occurs as the spores spread to local lymph nodes, then to the bones, eyes, skin, heart, testicles, central nervous system and major abdominal organs. The incubation period is typically one to three weeks, although the disease can remain dormant for up to three years before causing symptoms.

Sometimes, dogs and cats are exposed to the disease and develop mild respiratory signs that resolve without treatment. Other times, more serious symptoms develop, like:

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  • Fever
  • Inappetence and weight loss
  • Lethargy
  • Lameness
  • Enlarged lymph nodes
  • Draining skin lesions
  • Blindness
  • Lameness
  • Heart failure

Diagnosis can be made by a number of ways. X-rays of the chest may show specific signs, and evidence of the organism can show up on microscopic examination of the fluid from the lungs or draining tracts. Unlike histoplasmosis, blood tests for coccidiodomycosis are a good way to diagnosis disease.

Male young adult dogs are most commonly affected, and strictly outdoor dogs are five times more likely to be affected than their indoor cousins. Cats are more resistant to coccidiodomycosis than dogs. They tend to develop mild respiratory signs with spontaneous recovery, and disease that has spread through the body is rare in cats.

Treatment with anti-fungal medication must be sustained for a minimum of three months (two months past resolution of clinical signs). Prognosis is fairly good – 90% of cases with localized pulmonary disease respond to treatment, and about 60% of more severe cases respond, though response in these specific cases is unpredictable. In all cases, relapses can occur, so continued treatment is important, as it carrying pet insurance that can help cover repeat cases, like Petplan.

Coming up next, we’ll wrap up this series on systemic fungal diseases with a look at one that tends to affect cats more than dogs – cryptococcosis.

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