Overview of Mycotic Pneumonia

Cryptococcus neoformans, Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatiditis, Pneumocystis jiroveci, Aspergillus spp, Candida spp, and other less common fungi have been identified as causative agents of mycotic pneumonia in immunocompromised hosts (also see Fungal Infections). Infection is typically caused by inhalation of spores, which can lead to hemolymphatic dissemination. Pulmonary tissues and secretions are an excellent environment for these organisms. Aspergillosis is most commonly associated with sinonasal infection in dogs or sino-orbital infection in cats, with systemic infection being quite rare and seen only in immunocompromised individuals. Cryptococcosis most commonly affects the nasal cavity in cats, with CNS infection less commonly encountered in dogs and cats. The source of most fungal infections is believed to be soil-related rather than horizontal transmission.

Mycotic pneumonia is more commonly seen in small animals than in large. The most common course of disease is chronic. A short, productive cough is often present. A thick, mucoid to mucopurulent nasal discharge may be present. As the disease progresses, dyspnea, emaciation, and generalized weakness become increasingly evident. Respiration may become abdominal, with crackles on auscultation. Generalized lymphadenopathy is common in dogs. Multiple cutaneous and subcutaneous nodules with draining tracts may be seen with blastomycosis in dogs. Blastomycosis is often associated with emaciation and diarrhea in dogs, with skin lesions common in cats. Coccidiomycosis is often associated with severe bone pain due to osteomyelitis in dogs, with skin lesions common in cats. Uveitis or granulomatous chorioretinitis may accompany dimorphic fungal infections. (Also see Fungal Infections.)

Thoracic radiographs often disclose a diffuse pattern with tracheobronchial lymphadenopathy in dogs or large focal pulmonary granulomas in cats. If bone pain is present, skeletal radiography shows osteolysis with periosteal proliferation and soft-tissue swelling at infected sites. Abdominal radiography may reveal granulomas or lymphadenopathy. The clinical diagnosis can be confirmed with impression smears of cutaneous draining tracts, fine-needle aspirate of the lung, lymph node aspirates, or CSF tap (cryptococcosis). Special stains can be used to highlight the organisms.

Treatment of mycotic pneumonia is often lengthy. Drugs of choice include itraconazole, fluconazole (cryptococcosis), lipid-complexed amphotericin B, and terbinafine (aspergillosis). Newer generation azole antifungals such as voriconazole or posaconazole are more effective for resistant infections or systemic aspergillosis.