Feline Histoplasmosis

1 Feline Histoplasmosis

Epidemiology

Histoplasma capsulatum grows in soil and infects mainly by nasal inhalation, not by contact. Once in cat tissue it grows as yeast. Infection can spread from the primary site via blood or lymph to the liver, adrenal glands, spleen, central nervous system, skin and bone. Primary infection is often self-limiting.

Clinical symptoms

Generally cough or diarrhea or both, with irregular fever, anorexia, emaciation, vomiting and dermatitis. Some cases last for months.

Differential diagnosis

(1) Feline histoplasmosis vs. feline toxoplasmosis

Both show fever, anorexia, cough, sometimes diarrhea and emaciation.

Difference: toxoplasmosis is caused by Toxoplasma. Temperature above 40°C, lethargy, anemia, sometimes conjunctival/iris inflammation. At necropsy congestion and hemorrhage on hind limbs, abdomen and ears; pulmonary edema with pale areas and irregular red centers; cut surfaces ooze yellow transparent fluid; scattered lung nodules; impression smears Gram-stained show Toxoplasma.

(2) Feline histoplasmosis vs. feline viral rhinotracheitis

Both show fever, anorexia, cough and dermatitis.

Difference: viral rhinotracheitis shows pulmonary nodules on X-ray, sneezing, serous nasal discharge, conjunctival congestion and edema, dendritic corneal congestion, tearing, sometimes generalized skin ulcers. Necropsy shows focal necrosis of nasal, laryngeal and bronchial mucosa; multinucleated giant cells and intranuclear inclusions in upper respiratory epithelium.

(3) Feline histoplasmosis vs. feline tuberculosis (pulmonary)

Both show fever, anorexia and cough.

Difference: pulmonary tuberculosis is caused by Mycobacterium tuberculosis, usually chronic, with rales, dry then productive cough, later purulent viscous sputum that is grayish-white or slightly green. Necropsy shows liver purulent foci that form cavities after drainage; pulmonary lesions are nodular, with caseous areas draining to form cavities, some calcified. X-ray shows broncholymphadenitis and interstitial pneumonia, later pulmonary sclerosis and calcified nodules. Acid-fast smears reveal red, medium-sized, straight and curved tubercle bacilli.

(4) Feline histoplasmosis vs. feline coccidioidomycosis

Both show fever, cough, diarrhea, anorexia and emaciation.

Difference: coccidioidomycosis causes persistent cough; bone involvement leads to lameness and muscle atrophy. Necropsy shows swollen bronchial/mediastinal nodes and granulomas in pleura, pericardium, heart, lungs, liver, spleen and stomach; the coccidioidin test is positive.

(5) Feline histoplasmosis vs. feline paragonimiasis

Both show cough, diarrhea and fever.

Difference: paragonimiasis causes severe morning cough, dry then productive, sputum initially white then rust-colored or brown. Fecal examination may reveal the parasite.

Notes

The disease mainly shows irregular fever, anorexia, emaciation, cough or diarrhea. X-ray shows pulmonary nodules and enlarged bronchial and visceral lymph nodes. An intradermal test, immunodiffusion or immunofluorescence can aid diagnosis.

Prevention and treatment

(1) Prevention

1. If the disease has occurred locally, keep cats out of endemic areas.

2. For sick cats, carefully handle feces, urine and vomit, and deep-bury or incinerate them.

(2) Treatment

Treatment centers on antiparasitic, anti-inflammatory and symptomatic care.

1. Azithromycin: cats 5-7 mg/kg orally twice daily for 5-7 days; dogs 5-10 mg/kg orally 1-2 times daily for 5-7 days.

2. Amphotericin B: cats 0.125-0.5 mg/kg, made into a 1% solution with 5% glucose, IV drip, every other day, 4-8 weeks per course.

3. Rifampin: cats 10-30 mg/kg orally in 2-3 divided doses, combined with amphotericin B for a synergistic effect.