Filaroides osleri

Also known as: Dog lungworm — Oslerus osleri

Filaroides osleri
Class	Nematoda
Super-family	Metastrongyloidea
Species	Filaroides osleri

Introduction

Filaroides osleri is a metastrongyloid nematode that lives in granulomatous nodules located on the mucosal surface of the distal trachea, tracheal bifurcation and first division bronchi in dogs and wild canid species.

Identification

The adults are pale, thin nematodes. The female is larger than the male, at around 9-15mm in length.

Life Cycle

This is a direct life cycle, so forms the exception in the superfamily Metastrongyloidea. The females are ovo-viviparous. The eggs are laid, and hatch within the trachea. They then transform into the larvae, which are coughed up and swallowed. They enter the intestine, and are passed out in the faeces.

The bitch may transfer the larvae to the pup during grooming, or infection may come about via ingestion of the larvae. The larvae mature and travel to the lungs.

The prepatent period is 10-18 weeks.

Clinical Signs

The primary clinical sign is a chronic cough. Progressively enlarging granulomatous nodules may obstruct airflow and lead to signs such as exercise intolerance, dyspnoea or even death.

Spontaneous pneumothorax can occur extremely rarely.

Diagnosis

The tracheobronchial nodules may occasionally be detected radiographically as large, space-occupying masses protruding into the tracheal lumen near the bifurcation.

Bronchoscopic visualisation is the best way to detect the mucosal nodules.

Bronchial washings may then reveal larvated ova and larvae with a kinked tail.

Faeces can be examined for larvae, but this is less rewarding.

Zinc-sulphate centrifugation/flotation is preferred to the Baermann method as the larvae are lethargic and do not migrate out of the faecal mass.

Treatment

Endoscopic examination and removal of the nodules is essential for a successful outcome.

A good clinical response may be seen using extended courses of ivermectin, fenbendazole, albendazole and levamisole. This does not always clear the nodules on follow-up bronchoscopy.

In a breeding colony, bitches should be treated before whelping, and pups should be separated from older infected dogs to prevent horizontal transmission by ingestion of infected faeces. In infected dogs, good hygiene is essential, and pups could be hand-raised or foster-reared on uninfected bitches.

Filaroides osleri Learning Resources
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References

Taylor, M.A, Coop, R.L., Wall,R.L. (2007) Veterinary Parasitology Blackwell Publishing

King, L. (2004) Textbook of respiratory disease in dogs and cats Elsevier Health Sciences

Pinckney, R. D. (2000) Canine Filaroides infection in Companion and Exotic Animal Parasitology IVIS publication

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