Fungal infections occur more commonly in dogs than cats and even less frequently in large animals. Clinical signs include chronic cough, acute respiratory distress, and lethargy. Diagnosis can be made by serologic testing or detection of fungal antigens in urine (for Histoplasma and Blastomyces). Treatment includes systemic antifungal medication, oxygen, and sometimes anti-inflammatory medications.
Fungal infection of the lung may result in an acute to chronic active, pyogranulomatous pneumonia. Dogs are affected more than cats and may present with a chronic cough, acute respiratory distress, or lethargy. Cats may have facial swelling from sino-orbital infection, respiratory distress, or both, depending on the fungus.
Etiology of Fungal Pneumonia in Animals
Cryptococcus neoformans, Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatitidis, Pneumocystis jiroveci, Aspergillus spp, Candida spp, and other less common fungi have been identified as causative agents of fungal pneumonia in immunocompromised and non-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, an opportunistic fungus, is more common in dogs than cats and often affects middle-aged German Shepherds. It 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.
Clinical Findings of Mycotic Pneumonia
Fungal pneumonia is more commonly seen in small animals than in large. The most common course of disease is chronic. A short, productive cough and/or a thick, mucoid to mucopurulent nasal discharge may be present. As the disease progresses, dyspnea, emaciation, and generalized weakness may become evident. Respiration may become abdominal, with crackles on auscultation. Inflammation is a significant component of fungal pneumonia and, as with any inflammation, a prothrombotic state may be present.
Approximately 2/3 of the cases in dogs are disseminated (ie, eyes, skin, bone, CNS), with the remainder primarily pulmonary. Cutaneous and subcutaneous nodules with draining tracts may be seen with blastomycosis 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.
Lesions
Multifocal to coalescing lesions (resembling large masses on radiographs) of granulomatous to pyogranulomatous inflammation are present in the lungs or other affected organs. Abscess formation and cavitation may be seen in conjunction with yellow or gray areas of necrosis. Causative organisms are present within macrophages or areas of intense inflammation.
Diagnosis of Fungal Pneumonia in Animals
Serologic testing or urine antigen (for Histoplasma and Blastomyces)
Fungal pneumonia can be diagnosed by a combination of clinical signs and cytology when aspirates can be obtained. Urine antigen is more sensitive than serologic testing for Histoplasma and Blastomyces. Serologic or PCR testing is used in the absence of diagnostic fine-needle aspirates.
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, urine antigen (Histoplasma or Blastomyces), serologic testing, PCR, or CSF tap (cryptococcosis). Special stains can be used to highlight the organisms.
Treatment of Fungal Pneumonia in Animals
Antifungal medication, along with oxygen and anti-inflammatory medications in some cases
Fungal pneumonia is treated by systemic antifungal medications. Depending on the condition of the animal, hospitalization with oxygen therapy may also be required. In some cases, anti-inflammatory medications may be added during the first few days of therapy to mitigate the increased inflammation caused by the fungal die-off. Treatment is often lengthy.
Drugs of choice include itraconazole, fluconazole, lipid-complexed amphotericin B, and voriconazole or terbinafine (local treatment for aspergillosis). Newer-generation azole antifungals such as voriconazole or posaconazole are more effective for resistant infections or systemic aspergillosis but may be costly.
Key Points
Fungal pneumonia is more common in dogs than in cats.
Clinical signs may involve the respiratory system (eg, coughing, increased respiratory rate and effort), other organs (eg, eyes, skin, bones, CNS) or both. Diagnosis can be made by urine antigen (Histoplasma, Blastomyces), fine-needle aspirates with cytology, serology, PCR, or CSF tap.
Treatment may involve hospitalization with oxygen and a prolonged course of antifungal medications.
