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Bronchopulmonary Parasite Infections

Robert Sherding United States

Primary bronchopulmonary parasites in dogs and cats include nematodes, trematodes, arthropods, and protozoa. These parasites are relatively uncommon and most infections are subclinical. Young animals are most frequently affected. When clinical signs occur, the most common sign is chronic cough. Heavy infestations can occasionally cause dyspnea or be complicated by secondary bacterial pneumonia. Animals with clinical disease often have radiographic abnormalities. A peripheral eosinophilia is often found on complete blood count. Bronchopulmonary parasites are usually diagnosed by identification of parasite ova or larvae in feces or airway washings.

Oslerus osleri

This metastrongylid nematode lives in granulomatous nodules located on the mucosal surface of the trachea, tracheal bifurcation, and large bronchi in domestic dogs (usually puppies and young dogs less than one year of age) and many wild canid species. Nematode larvae that are coughed up can be directly transmit the infection through regurgitative feeding, in saliva during grooming, or when swallowed and passed in the feces. The primary clinical sign is chronic cough, although large granulomatous nodules may cause signs of large airway obstruction (exercise intolerance, dyspnea, death) in some cases. The distinctive airway nodules can occasionally be detected radiographically as large, space-occupying masses in the tracheal lumen near the bifurcation. Bronchoscopic visualization is the best way to detect these nodules. The most reliable way to diagnose O. osleri is to identify embryonated ova (80 u) and larvae (230 u with kinked tail) in bronchoscopic biopsies and airway washings. Feces can be examined for larvae using zinc sulfate flotation or a Baermann technique, but fecal shedding is intermittent so that a negative exam is inconclusive. Limited experience suggests that O. osleri can be treated with fenbendazole (Panacur; 50 mg/kg q24h PO for 1014 days), albendazole (Valbazen; 25 mg/kg q12h for five days; repeated in two wks), or ivermectin (Ivomec; 0.4 mg/kg IV once; do not use in Collies).

Filaroides spp.

Filaroides hirthi and Andersonstrongylus milksi (formerly known as F. milksi) are small metastrongylid nematodes that live in the lung parenchyma (alveoli and terminal airways) of dogs. Filaroides usually cause subclinical interstitial pneumonia, but fatalities have been reported in severe infestations, especially in immunosuppressed or corticosteroid-treated dogs and in toy breed dogs. Nematode larvae that are coughed up, swallowed, and passed in the feces can cause direct horizontal transmission and even autoinfection; thus, a high incidence of infection has been found in some kennels and dog colonies. Animals with clinical signs generally have diffuse pulmonary broncho-interstitial and alveolar infiltrates. The diagnosis is based on finding thin-walled ova and larvae in airway washings or larvae in feces. The preferred method for examining feces is with zinc sulfate flotation. Baermann examination is less reliable. Filaroides can be treated with fenbendazole (Panacur; 50 mg/kg q24h PO for 1014 days), albendazole (Valbazen; 2550 mg/kg q12h for five days; repeated in two wks), or ivermectin (Ivomec; 0.4 mg/kg IV once; do not use in Collies). The inflammatory response is greatest to dead and dying worms; thus, signs may initially worsen after treatment.

Aelurostrongylus abstrusus

This metastrongylid nematode is the feline lungworm. Adults live in the terminal bronchioles causing bronchiolitis, interstitial pneumonia, and hypertrophy of the vascular tunica media hypertrophy. Larvae are coughed up, swallowed, and passed in the feces. The indirect life cycle involves terrestial snails and slugs as intermediate hosts. Cats are infected by ingesting infected snails or slugs, or by eating a paratenic transport host (such as a bird or rodent) that feeds on snails or slugs. Most infections are asymptomatic; however, severe infections can cause chronic cough, dyspnea, and debilitation. Pleural effusion occurs rarely.

The diagnosis should be suspected in cats that hunt birds and rodents and have radiographic evidence of diffuse broncho-interstitial and alveolar pulmonary infiltrates, sometimes appearing patchy or nodular. Eosinophilia is an inconsistent finding. Confirmation is based on identification of A. abstrusus larvae in airway cytology specimens or in feces using the Baermann technique. Aelurostrongylosis can be treated with fenbendazole (Panacur; 50 mg/kg q24h PO for 10-14 days) or ivermectin (Ivomec; 0.4 mg/kg IV once). Nonspecific adjunctive therapy can include corticosteroids and bronchodilators.

Crenosoma vulpis

This nematode lungworm mostly infects wolves, foxes, and raccoons, but it rarely can infect dogs causing a chronic cough and broncho-interstitial infiltrates on radiographs. The life cycle involves terrestial snails and slugs as intermediate hosts and small prey as paratenic hosts, similar to Aelurostrongylus in cats. The diagnosis depends on identification of larvae in airway cytology specimens or feces by zinc sulfate flotation of Baermann technique. The suggested treatment is fenbendazole (Panacur; 50 mg/kg q24h PO for 10-14 days).

Capillaria aerophilia

This nematode, also known as Eucoleus aerophilus, lives in the bronchial mucosa of young dogs and cats. The direct life cycle involves ingestion of eggs from an infected host that are passed in the feces after being coughed up and swallowed. Earthworms may serve as transport paratenic hosts. Most infections are asymptomatic, but Capillaria can cause chronic, nonresponsive cough in young animals. The diagnosis is based on identification of double-operculated ova in fecal flotation or airway cytology specimens. Capillaria ova must be differentiated from the similar-appearing ova of intestinal whipworms (Trichuris vulpis) and the nasal nematode, Eucoleus boehmi. The suggested treatment is fenbendazole (Panacur; 50 mg/kg q24h PO for 10-14 days).

Paragonimus kellicotti

This lung fluke (trematode) infects wild carnivores and occasionally dogs, especially in the Great Lakes and Gulf of Mexico regions of the United States. This parasite requires two intermediate hosts: the aquatic snail and the crayfish. The adult flukes live in pairs within a subpleural cyst that communicates with a bronchus. This allows eggs to be expelled into the airway where they are coughed up, then swallowed and passed in the feces. Asymptomatic infections are common. Clinical signs can include chronic cough, exercise intolerance, and weight loss. Acute dyspnea sometimes occurs from spontaneous pneumothorax from cyst rupture.

Diagnosis is suspected from radiographic findings of multiloculated penumatocysts in dogs and thick-walled cysts and large ill-defined nodular densities (granulomas) in cats. Confirmation is based on identification of large yellow-brown, single-operculated ova in feces (using fecal sedimentation or zinc sulfate centrifugation-flotation) or in airway cytology specimens. Paragonimiasis can be treated with Praziquantel (Droncit; 25 mg/kg q8h PO for 3 days) or fenbendazole (Panacur; 50 mg/kg q24h PO for 10 to 14 days).

Notes


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