Fungal pulmonary infections occur more commonly in dogs than in cats, and even less frequently in large animals. Clinical signs include chronic cough, acute respiratory distress, ocular lesions, skin lesions, and lethargy. Diagnosis can be based on serological testing or the detection of fungal antigens in urine (for Histoplasma and Blastomyces). Treatment includes systemic antifungal medications, 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 develop a chronic cough, acute respiratory distress, or lethargy. Cats may have facial swelling from concurrent sino-orbital infection, respiratory distress, or both, depending on the causative fungus.
Also see Blastomycosis, Histoplasmosis, Coccidioidomycosis, Antifungal Agents, Azoles, Candidiasis, Cryptococcosis, Aspergillosis, and Pneumonia in Dogs and Cats.
Etiology of Fungal Pneumonia in Small 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 immunocompetent hosts. Also see Fungal Infections.
Fungal pneumonia is typically brought on by the inhalation of spores, which can lead to hemolymphatic dissemination. Pulmonary tissues and secretions are an excellent environment for these organisms.
Aspergillosis, an opportunistic fungal disease, more commonly affects dogs than cats, and it often affects middle-aged German Shepherd Dogs. Aspergillosis is most commonly associated with sinonasal infection in dogs or sino-orbital infection in cats. Systemic aspergillosis is quite rare, occurring in only immunocompromised individuals.
Cryptococcosis most commonly affects the nasal cavity in cats; CNS infection is less common in both dogs and cats.
Most fungal infections are believed to be acquired from the soil rather than through horizontal transmission.
Clinical Findings of Fungal Pneumonia in Small Animals
Fungal pneumonia is more common in small animals than in large animals. The most common course of disease is chronic. A short, productive cough or a thick, mucoid to mucopurulent nasal discharge may be present.
As fungal pneumonia progresses, dyspnea, emaciation, and generalized weakness may become evident. Respiration may have an abdominal component, with crackles heard on auscultation. Inflammation is a major component of the disease and, as with any inflammation, a prothrombotic state may also result.
Approximately two-thirds of fungal pneumonia cases in dogs have other systemic involvement (ie, eyes, skin, bone, CNS); the remainder are primarily pulmonary.
Cutaneous and subcutaneous nodules with draining tracts can occur with blastomycosis in dogs, and skin lesions are common in cats.
Coccidioidomycosis is often associated with severe bone pain due to osteomyelitis in dogs, and skin lesions are 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 in cases of fungal pneumonia. Abscesses and cavitation may occur 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 Small Animals
Serological testing or urine antigen testing (for Histoplasma and Blastomyces)
The diagnosis of fungal pneumonia can be based on a combination of clinical signs and cytological examination when aspirates can be obtained. Urine antigen testing is more sensitive than serological testing for Histoplasma and Blastomyces. Serological testing or PCR assay is conducted in the absence of diagnostic fine-needle aspirates.
Thoracic radiography in fungal pneumonia cases often reveals a diffuse pattern with tracheobronchial lymphadenopathy in dogs or large focal pulmonary granulomas in cats. If signs of bone pain are present, radiography shows osteolysis with periosteal proliferation and soft tissue swelling at infected sites. Abdominal radiography may reveal granulomas or lymphadenopathy.
The clinical diagnosis of fungal pneumonia can be confirmed with impression smears of cutaneous draining tracts, fine-needle aspirates of the lung, lymph node aspirates, urine antigen testing (for Histoplasma or Blastomyces), serological testing, PCR assay, or CSF collection and analysis (for Cryptococcus). Special stains (eg, periodic acid–Schiff and Grocott-Gomori methenamine–silver nitrate) can highlight the organisms.
Treatment of Fungal Pneumonia in Small Animals
Antifungal medications
Supplemental oxygen therapy
Anti-inflammatory medications
Fungal pneumonia is treated by systemic antifungal medications. Depending on the patient's condition, hospitalization with oxygen therapy may also be required. In some cases, anti-inflammatory medications may be added during the first few days of treatment to mitigate the increased inflammation due to the fungal die-off. Treatment is often lengthy.
Drugs of choice to treat fungal pneumonia 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; however, they can be costly. See Azoles.
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 based on urine antigen testing (for Histoplasma or Blastomyces), fine-needle aspirates with cytological evaluation, serological testing, PCR assay, or CSF analysis.
Treatment requires a prolonged course of antifungal medications and may require hospitalization and supplemental oxygen.
