Canine systemic fungal infections.

The principal route of infection for the disseminated fungal diseases discussed in this article is inhalation. In some cases, direct wound contamination and ingestion may also have an important role in the pathogenesis of the disease, especially in histoplasmosis. Another common theme of these diseases is the response of the immune system. If the inoculum is small and the animal is not immunocompromised, the infection may be limited to the respiratory tract and may resolve with few or no clinical signs. Dogs are usually presented to the veterinarian when the fungus has disseminated throughout the body via the circulatory or lymphatic systems, thus causing clinical signs secondary to specific organ infection. Draining skin tracts and lymphadenopathy occur in several of the diseases. The ocular location that is frequently affected is the choroid, where the organisms cause cell-mediated chorioretinitis. Early detection of these changes is important for saving vision and for diagnosing the systemic nature of the disease. Treatment is often effective, especially early in the disease, although it is expensive and long-term, with many animals needing over a year of treatment. Sometimes the treatment must continue lifelong. Ocular disease may not respond to treatment even when respiratory and other organ system clinical signs are rapidly improving. This isolation of the eye is similar to that of the CNS and requires regular monitoring of ocular disease, especially in the fundus, to ensure that systemic drugs are penetrating into the eye. Once the disease progresses to the anterior segment, the ocular prognosis worsens. Better penetration of the blood-retinal and blood-aqueous barriers may be achieved with fluconazole when compared with the other antifungal drugs. Secondary inflammatory ocular disease must also be monitored and treated appropriately to prevent scarring, which may cause vision loss or glaucoma.