Cytomegalovirus in Cats: Understanding and Managing the

Characteristics of the Disease

Capsular histoplasmosis, a type of fungal infection, primarily grows in soil and is transmitted to cats through inhalation, not through direct contact. Once inside a cat's body, the fungus exists in a yeast form within the tissues. The infection can spread from the primary site to the liver, adrenal glands, spleen, central nervous system, skin, and bones via the bloodstream or lymphatic system. The primary infection is often selflimiting.

Symptoms

Cats with this disease typically exhibit symptoms such as coughing, diarrhea, or a combination of both, along with intermittent fever, loss of appetite, weight loss, vomiting, and dermatitis. Some cases can last for several months.

Differential Diagnosis

(1) Feline Histoplasmosis vs. Feline Toxoplasmosis

Both conditions present with fever, loss of appetite, coughing, and sometimes diarrhea and weight loss. However, feline toxoplasmosis is caused by Toxoplasma gondii, with symptoms including a body temperature above 40°C, lethargy, anemia, and sometimes conjunctivitis and uveitis. Postmortem examination may reveal petechiae and hemorrhages in the hind limbs, abdomen, and ear flaps, pulmonary edema, and irregular, pale areas with red centers in the lungs. The lungs may exude a yellow, clear fluid, and there may be scattered nodules. On examination, tachyzoites can be seen under a microscope after Gram staining.

(2) Feline Histoplasmosis vs. Feline Viral Rhinotracheitis

Both diseases share symptoms like fever, loss of appetite, coughing, and dermatitis. However, feline viral rhinotracheitis is characterized by nodules in the lungs visible on Xray, sneezing, purulent nasal discharge, conjunctival congestion and edema, corneal dendritic keratitis, and lacrimation. Postmortem examination may reveal localized necrosis in the nasal, pharyngeal, and bronchial mucosa, with multinucleated giant cells and intranuclear inclusions in the respiratory epithelial cells.

(3) Feline Histoplasmosis vs. Feline Tuberculosis (Pulmonary Type)

Both conditions present with fever, loss of appetite, and coughing. Feline tuberculosis is caused by Mycobacterium tuberculosis and is often chronic, with pulmonary rales, initially dry coughing followed by productive cough with sputum that is thick, creamy, and grayish or slightly greenish. Postmortem examination may reveal suppurative lesions in the liver, with cavities forming after pus discharge. Pulmonary lesions are often nodular, with caseous areas that discharge pus to form cavities, and some may calcify. Xray may show bronchial lymphadenitis, interstitial pneumonia, and later pulmonary sclerosis and calcified nodules. The stained tissue smear can reveal acidfast, red, mediumsized, straight, and curved tubercle bacilli.

(4) Feline Histoplasmosis vs. Feline Coccidioidomycosis

Both diseases have fever, cough, diarrhea, loss of appetite, and weight loss. Feline coccidioidomycosis is caused by Coccidioides spp., with persistent cough and, when affecting the bones, limping and muscle atrophy. Postmortem examination may reveal swollen bronchial and mediastinal lymph nodes, granulomas in the pleura, pericardium, heart, lungs, liver, spleen, and stomach. A positive result in the Coccidioides sensitivity test can aid in diagnosis.

(5) Feline Histoplasmosis vs. Feline Paragonimiasis

Both conditions present with coughing, diarrhea, and fever. Feline paragonimiasis is characterized by severe morning cough, initially dry and then productive, with sputum that starts white and turns to rust or brownish. The presence of the worm can be detected in fecal examination.

Reminders

This disease is primarily characterized by irregular fever, loss of appetite, weight loss, coughing, or diarrhea. Xrays may show nodules in the lungs. Enlargement of bronchial and visceral lymph nodes can also be observed. A skin test can be used for diagnosis, as well as immunodiffusion and immunofluorescence tests, which can assist in diagnosis.

Preventive Measures

(1) Prevention

① If the disease has been reported in the area, cats should be kept out of the endemic region.

② If an infected cat is found, its feces, urine, and vomit should be carefully handled and disposed of by deep burial or incineration.

(2) Treatment

The treatment principle focuses on deworming, antiinflammatory, and symptomatic treatment.

① Azithromycin, 57 mg/kg body weight for cats, taken orally twice a day for 57 days; 510 mg/kg body weight for dogs, taken orally once or twice a day for 57 days.

② Amphotericin B, 0.1250.5 mg/kg body weight, prepared as a 1% solution in 5% glucose for intravenous infusion. Administered every other day, a course of treatment is 48 weeks.

③ Rifampin, 1030 mg/kg body weight for cats, taken orally in two or three divided doses, and used in combination with amphotericin B for synergistic effects and improved efficacy.