Filaroides hirthi

This metastrongyloid lungworm is related to O. osleri and is apparently a very rare lungworm of dogs.  The adult parasites live in the lung parenchyma. F. hirthi has a direct life cycle in which the first-stage larvae are infective. Filaroides hirthi was first discovered in laboratory housed beagles in the USA and has since been reported from several areas of the world in pet dogs with clinical signs of respiratory disease. Many of the affected pet dogs had a history of some form of immunosuppression. Filaroides hirthi has been found once in Canada, in an immunosuppressed dog with respiratory signs in Saskatchewan.  Diagnosis can be challenging as larvae are sporadically shed; larvae may be detected on Baermann examination of feces (low sensitivity) or on cytology of bronchoalveolar lavage fluid. Treatment requires multiple rounds of extralabel fenbendazole or macrocyclic lactones.

Crenosoma vulpis

This metastrongyloid lungworm of dogs and wild canids has a typical  indirect life cycle involving a gastropod intermediate host. In Canada, Crenosoma vulpis has been reported in coughing dogs in the maritime provinces, Ontario, and Quebec. Diagnosis relies on detection of characteristic first stage larvae on Baermann sedimentation of feces,  or visualization of adult lungworms in the airways on bronchoscopy.  A single dose of milbemycin oxime appears to be highly effective.  Other macrocyclic lactones or fenbendazole can be used off label.

Eucoleus aerophilus (Capillaria aerophila)

The nematode Eucoleus aerophila is a tracheal worm that infects primarily foxes and occasionally other free-ranging carnivores, dogs, cats and people.  It occurs worldwide, including in Canada. .  Adult male E. aerophila are approximately 24mm and females 32mm in length.  The oesophagus occupies 1/3 to 1/2 of the body length.  This nematode is in the same family as Trichuris sp., and the eggs of E. aerophila resemble Trichuris spp. eggs with bipolar plugs.  They are less pigmented, and measure approximately 65 µm by 30 µm.   The outer surface with characteristic anastomosing ridges distinguishes eggs of E. aerophilus from E. boehmi, adults of which are present in the nasal and frontal cavities of dogs and wild canids.

Like other capillarid nematodes, Eucoleus aerophilus can have either a direct or an indirect life cycle.  Adult females lay eggs in the trachea and bronchi of the definitive host.  The eggs are coughed up, swallowed and passed with the feces.  Like Trichuris, the infective stage is, unusually, the first stage larvae within the egg. Development of the infective first-stage larva in the egg take 5-6 weeks and eggs can survive for months in the environment.  In the direct life cycle, a definitive host ingests the infective egg from the environment, the larva hatches and travels through the small intestine wall, travels via lymphatics or bloodstream to the lungs, breaks out into the airways and completes its development to adult.  In the indirect life cycle, the eggs are ingested by an earthworm intermediate host in which the eggs hatch to release the infective first stage larva.  A definitive host then ingests the earthworm and the larva follows the same path as in the direct life cycle.  The prepatent period is 6 weeks.

Light infestations with E. aerophilus are usually asymptomatic.  Moderate to severe infections can result in bronchitis, nasal discharge, wheezing cough, sneezing, dyspnea, bronchopneumonia, abscesses in the lungs, emphysema, or secondary bacterial infections which can be fatal in younger animals.  The larva and adult nematodes can cause irritation of the respiratory mucosa and constricted air passages.  Diagnosis is usually made by detecting E. aerophilus eggs on cytology of broncho-alveolar lavage fluid, or on fecal flotation. In a recent national study of shelter animals across Canada, capillarid eggs were detected in 0.7% of dogs and 2.5% of cats.  The parasite has been implicated in respiratory disease in shelter cats and anesthetic deaths elsewhere in the world. Eucoleus aerophilus infection can be treated with fenbendazole and probably ivermectin or milbemycin.

Villeneuve, L. Polley, E.J. Jenkins, J.M. Schurer, J. Gilleard, S. Kutz, G. Conboy, D. Benoit, W. Seewald, F. Gagné. 2015. Parasite prevalence in fecal samples from dogs and cats across the Canadian provinces. Parasites and Vectors 8:281 doi:10.1186/s13071-015-0870-x  

Hoopes, J., J.E. Hill, L. Polley, C. Fernando, B. Wagner, J. Schurer, E. Jenkins. 2015. Enteric parasites of free-roaming, owned, and rural cats in prairie regions of Canada.  Canadian Veterinary Journal 56(5): 495-501.