Parasites of the lower respiratory tract of dogs and cats (Proceedings)

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.

3. Filaroides hirthi.

Epidemiology: Metastrongyloid nematodes found in the lung parenchyma of dogs. Direct life cycle.

     • Infection of pups probably occurs during nursing. After ingestion, larvae migrate to lungs via hepatic-portal or mesenteric lymph system. Prepatent period is 5 weeks. Larvae appear in the feces.

     • Most cases reported in beagles in research colonies.

Clinical signs: Nonproductive cough ± increased respiratory rate.

     • Severe infestations: respiratory distress and exercise intolerance, looks like "kennel cough."

     • Radiographs: diffuse interstitial lung opacities and mixed alveolar patterns with consolidation

Treatment: Albendazole (25 mg/kg, PO, q12h, 5 days, then repeat treatment 2 wks later).

     • Fenbendazole (50 mg/kg, PO, q12h, 14 days), or Ivermectin (0.2 mg/kg, PO, q24h, 3 days).

     • Prednisone (1.25 mg/kg, PO, q24h, 14 days)

4. Paragonimus kiettiella

Epidemiology: Trematode (fluke) normally found in mink, but occasionally in the lungs of dogs and cats.

     • Adult pairs live in subpleural cysts that communicate with bronchiole. Eggs produced in the cysts are carried into the bronchiole, swept up airways and swallowed.

     • Carnivores infected by eating 2nd intermediate host (crayfish).

Clinical signs: Most are asymptomatic but those with disease present with a chronic cough (unresponsive to most treatments) and rarely pneumothorax.

Diagnosis: Identifying eggs (large, operculated) in feces or tracheal wash. Radiology; multiloculated cysts (dogs), and interstitial nodules (cats).

Treatment: Praziquantel (23 mg/kg PO, q8h, 3 days), or fenbendazole (50 mg/kg PO, q24h, 10-14 days).

TRACHEA AND BRONCHI

1. Crenosoma vulpis.

Epidemiology: Metastrongyloid nematode of bronchi (dogs and other canids). Adult worms (males; 4 to 8 mm long, females; 12 to 16 mm long) parasitize the terminal bronchi of the respiratory tract where eggs are laid, develop and hatch, larvae then coughed up and swallowed to be passed in the feces.

     • Dogs infected when ingest gastropod (snails) intermediate hosts. Larvae migrate to the lungs by way of the visceral lymphatic or via the hepatic portal system: prepatent period about 18 to 21 days.

Clinical signs: Infection occurs during summer in dogs living or visiting rural areas frequented by foxes, the more usual definitive host. - dry, nonproductive cough easily elicited by tracheal palpation. Cough may be chronic and productive.

Radiology: Diffuse bronchial patterns with prominent interstitial markings.

     • Bronchoscopy: Moderate mucoid to mucopurulent discharge in the airways. Cytology of tracheal wash: reveal inflammatory cells, mainly eosinophils (matching a peripheral eosinophilia).

Diagnosis: Larvae (pointed tail, 250 - 300 um) in feces or tracheal wash sample.

Treatment: Fenbendazole (50 mg/kg PO, q24h, 3 days, or 20 mg/kg, PO, q24h, 14 days).

     • Levamisole (7.5 mg/kg, PO, once, followed by a second dose 2 days later).

2. Oslerus osleri.

Epidemiology: Metastrongyloid nematode: causing nodules in the terminal trachea and bronchi of dogs and other canids (coyotes, foxes). Adult worms found in subepithelial fibrous nodules usually close to the bifurcation of the trachea and extending down into the mainstem bronchi. Thin-shelled eggs or larva (L1 - infective stage and very similar to F. hirthi) are coughed up, swallowed, enter feces, or coat regurgitated food.

     • Direct lifecycle. Pups infected by L1 in sputum (infected when cleaning, or coating regurgitated food.

Clinical signs: Dry cough (often precipitated by exercise or tracheal palpation) unresponsive to antibiotics or steroids.

     • Severe respiratory distress due to upper airway obstructive disease.

Diagnosis: L1 in fecal samples or in transtracheal washes. Bronchoscopy: identifies the brown reddy nodules at the tracheal bifurcation. Radiology may reveal soft tissue nodular densities at the tracheal bifurcation.

Treatment: Physical removal of nodules via bronchoscopy can be life saving.

     • Oxfendazole (10 mg/kg PO, q24h, 28 days). Only drug known to work.

     • Prednisone (0.5 - 1 mg/kg PO, q12h, 5 days post-nodule removal). Removes inflammation with worm death.

References

1. Glass EN, Cornetta AM, deLahunta A, et al. Clinical and clinicopathologic features in 11 cats with cuterebra larvae myiasis of the central nervous system. J Vet Intern Med 1998;12:365-368.

2. Gunnarsson LK, Moller LC, Einarsson AM, et al. Clinical efficacy of milbemycin oxime in the treatment of nasal mite infection in dogs. J Am Anim Hosp Assoc 1999;35:81-84.

3. Barr SC. Feline Lungworm (Aelurostrongylus). In: Canine and Feline Infectious Diseases and Parasitology. Barr SC and Bowman DD (eds). Ames Ia: Blackwell Publishing. 2006. p. 233.

4. Peterson EN, Barr SC, Gould WJ, et al. Use of fenbendazole for treatment of Crenosoma vulpis in a dog. J Am Vet Med Assoc 1993;202:1483-1484.

5. Kelly PJ, Mason RP. Successful treatment of Filaroides osleri infection with oxfendazole. Vet Rec 1985;116:445-446.

6. Barr SC, Lavelle RB, Harrigan KE, et al. Oslerus (Filaroides) osleri in a dog. Aust Vet J 1986;63:334-336.