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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • Primary fungal pneumonia is caused by pathogens with discrete geographic restrictions
  • Secondary fungal pneumonia is caused by ubiquitous environmental fungal agents such as Aspergillus and affects horses with immune compromise or with significant gastrointestinal comorbidities such as colitis

Signalment!!navigator!!

  • Horses with fungal pneumonia may be any age
  • Pneumocystis jiroveci (previously Pneumocystis carinii) has only been reported in foals 1.5–4 months of age

Signs!!navigator!!

  • Fungal pneumonia—weight loss, exercise intolerance, and cough are common and fever, tachypnea, hemoptysis, and nasal discharge have also been noted
  • Foals with P. jiroveci pneumonia typically present with severe respiratory distress and pneumonia

Causes and Risk Factors!!navigator!!

  • Primary fungal pneumonia is caused by inhalation of the infectious form of pathogen fungi such as Blastomyces dermatitidis, Coccidioides immitis, Cryptococcus neoformans, and Histoplasma capsulatum
  • Secondary fungal pneumonia is caused by environmental (ubiquitous) fungi, and occurs only in horses profoundly immunocompromised by other diseases or the use of immunosuppressive drugs. Agents identified in horses with secondary pneumonia include Aspergillus, Phycomycetes, Rhizopus, Mucor, Acremonium, Paecilomyces, and P. jiroveci in foals

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Bacterial pneumonia/pleuritis
  • Equine multinodular fibrosis
  • Severe equine asthma
  • Intrathoracic neoplasia

CBC/Biochemistry/Urinalysis!!navigator!!

Nonspecific inflammatory leukogram.

Other Laboratory Tests!!navigator!!

  • Serology for C. neoformans, C. immitis, and H. capsulatum can be supportive of the diagnosis, but previous exposure can cause titers in unaffected animals
  • Panfungal PCR assays are available to identify fungal DNA in fluid or tissue samples

Imaging!!navigator!!

Thoracic radiographs typically show significant abnormalities. Interstitial, miliary, nodular, and patchy bronchoalveolar patterns have all been described.

Other Diagnostic Procedures!!navigator!!

  • Special care should be taken not to overdiagnose this disease in the field; up to 70% of transtracheal washes have evidence of fungal elements which are considered normal
  • Lung biopsy is frequently diagnostic. Special stains are often needed to visualize fungal organisms
  • Fungal culture may identify specific pathogens but 16% of healthy horses will have fungal growth on transtracheal wash culture

Treatment ⬆ ⬇

TREATMENT

  • Antifungal medications form the mainstay of treatment
  • Supportive care for pneumonia is indicated

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Itraconazole, fluconazole, ketoconazole, and voriconazole have all been investigated in horses. Voriconazole is the newest (4 mg/kg PO SID) and is considered broad spectrum; itraconazole (5 mg/kg PO SID) is effective against Aspergillus spp. Fluconazole (loading dose of 14 mg/kg followed by 5 mg/kg PO SID) is ineffective against the filamentous fungi such as Aspergillus and Fusarium
  • Amphotericin B (0.1–0.5 mg/kg IV every 48 h) has been used when other drugs are ineffective
  • Iodides and 5-fluorocytosine (flucytosine) have also been used
  • For Pneumocystis infection in foals, trimethoprim–sulfamethoxazole (25 mg/kg PO BID) can be used. Oral dapsone can be an alternative treatment

Contraindications/Possible Interactions!!navigator!!

  • Fluconazole (and other azole drugs) have been associated with hepatoxicity, but are generally well tolerated
  • Amphotericin B is potentially nephrotoxic; kidney function should be monitored closely

Follow-up ⬆ ⬇

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FOLLOW-UP

Patient Monitoring!!navigator!!

  • Repeated radiographs are useful for monitoring course of disease
  • Decreasing serum titers (where applicable) may also be helpful

Prevention/Avoidance!!navigator!!

Horses should be housed in areas with low dust levels, as the majority of dust particles are of fungal origin.

Possible Complications!!navigator!!

Most complications are associated with the chronic, severe pneumonia, or the primary cause of immunodeficiency.

Expected Course and Prognosis!!navigator!!

  • The prognosis for fungal pneumonia is generally poor, although mild infection with some of the primary pathogens may be self-limiting
  • Treatment is often unrewarding and expensive, and involves long-term (2–4 months) administration of antifungal agents and supportive care

Miscellaneous ⬆ ⬇

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MISCELLANEOUS

Associated Conditions!!navigator!!

Many of the primary fungal pathogens also cause disease of other organs such as the skin, liver, meninges, or bone.

Age-Related Factors!!navigator!!

P. jiroveci has been diagnosed in foals only.

Zoonotic Potential!!navigator!!

Organisms are of low virulence to humans. Nonetheless, immunocompromised humans should be advised to avoid contact with these patients.

Pregnancy/Fertility/Breeding!!navigator!!

H. capsulatum and C. neoformans are associated with abortion in mares. Many antifungals are teratogens, and should be avoided during pregnancy.

Abbreviations!!navigator!!

PCR = polymerase chain reaction

Suggested Reading ⬆ ⬇

Stewart AJ, Cuming RS. Update on fungal respiratory disease in horses. Vet Clin North Am Equine Pract 2015;31(1):43–62.

Author(s) ⬆

Author: Rose D. Nolen-Walston

Consulting Editors: Daniel Jean and Mathilde Leclère