Parasites are major causes of respiratory tract disease in the dog and cat. Recent advances in therapy of these diseases
have been made providing the practicing veterinarian with a more rational treatment modality. This review will discuss the
biology, diagnosis, disease, and treatment of respiratory parasites (protozoan, nematode, trematode, and arthropods) of the
dog and cat emphasizing chemotherapeutics.
PARASITES OF THE LUNG PARENCHYMA
1. Aelurostrongylus abstrusus.
Epidemiology: Metastrongyloid nematode parasite of cats.
• Adult female (9 to 10 mm long) and males (4 to 6 mm) worms coil in the terminal respiratory bronchioles and alveolar
ducts. The females lay eggs that contain a single cell when laid and which embryonate within the alveolar ducts and the surround
alveoli. The larvae hatch from the eggs, are carried up the ciliary escalator, swallowed, and passed in the feces.
• Larvae: approx. 360-390 um long, characteristic dorsal spine on the tail.
• Cats infected when ingest infected snail intermediate host or, more likely, paratenic hosts (mice, birds).
Clinical signs: Heavy infestations (100 larvae) can cause severe pulmonary disease and radiographic changes by 2-wks PI. Most severe disease
occurs 5 to 15 weeks after infection.
• Presents as alveolar lung disease (no pulmonary hypertension or associated RVH disease).
• Most infections are asymptomatic with the cat recovering uneventfully.
• May get signs of severe bronchopneumonia (rapid open-mouthed abdominal breathing with) - eosinophilia rare. - radiographs:
diffuse interstitial pattern. After a week of treatment, the radiographic pattern may appear worse (more peribronchial infiltrates
with areas of alveolar consolidation) in spite of clinical improvement in signs.
Diagnosis: Identifying typical larvae in the feces or in a trans-tracheal wash.
Treatment: Fenbendazole (20 mg/kg, PO, q24h, for 5 days, then repeat after 1 week).
• Ivermectin (400 μg/kg, PO, once, followed by a second dose of 400 μg/kg, PO, one week later).
• Prednisone (1 mg/kg, PO, q12h, 5 days) alleviates signs during recovery.
2. Eucoleus aerophilus (Capillaria aerophila)
Epidemiology: Trichuroidea parasite with bi-operculate eggs. Direct life cycle.
• Eggs – easily confused with those from other Capillarids (Eucoleus boehmi of the nose, and Pearsonema plica in the urinary bladder) and whipworms of dogs (Trichuris vulpis).
• Adult worms – embed in the mucosal lining of large airways expelling eggs into the respiratory passages. Eggs - coughed
up the trachea, and swallowed to be passed in the feces.
• Infection – occurs by ingesting L1 larvae (take about 40 days to mature in eggs).Infections - can last as long as a
year. PPP = 3 to 5 weeks.
Clinical Signs: Fairly common infection in both cats and dogs.
• Most infections are asymptomatic - rarely causes clinical signs.
• When signs occur:- mild wheezing, chronic cough can occur. Very rarely produces weight loss. When complicated with
bacterial pneumonia, can cause death.
• Thoracic radiographs may show diffuse mild bronchoalveolar pattern but are not pathognomonic.
• Diagnosis made by finding bi-operculate eggs in feces or tracheal wash fluids.
Treatment: Assymptomatic cases do not require treatment.
• Fenbendazole (50 mg/kg, PO, q24h, 14 days). Treatment of choice in dogs.
• Ivermectin (200 μg/kg, PO, once). Efficacy is unknown but is effective against nasal capillariasis and indications
are that it is effective against E. aerophilus as well.