Metastrongyloid lungworms

Host range: Cats and wild felids serve as definitive hosts.  Numerous species of terrestrial gastropods (slugs, land snails) serve as intermediate hosts. Various amphibians, birds, reptiles and rodents serve as paratenic hosts. 

Geographic range: Worldwide – reported from every continent except Antarctica. In Canada it has been documented in Ontario but it is known to also occur in BC, NB, NL and NS. 

Life cycle: Adult worms dwell in the terminal bronchioles and alveolar ducts of infected cats. Female worms lay undifferentiated eggs which develop and hatch releasing first-stage larvae (L1). The L1 are coughed up and swallowed to be passed in the feces. Terrestrial gastropods feeding on the feces ingest the L1, which undergo 2 moults to reach the infective third-stage (L3) in about 3-4 weeks. Cats become infected by ingesting L3 contained in the tissues of gastropods or paratenic hosts. The prepatent period is 5-6 weeks.

Diagnosis: Detection of L1 in the feces, sputum, or transtracheal wash and bronchoalveolar lavage samples.  Detection of larvae in feces is best achieved through use of the Baermann technique. Though much less sensitive, larvae may be detected in some cats by direct smear or centrifugal fecal flotation. L1 are identified based on size (360-400 microns in length) and morphology (cephalic button, kinked tail with a dorsal spine). In general, the fecal larval shedding pattern of metastrongyloids tends to be sporadic resulting in an increased likelihood of obtaining false negative fecal exam results. Examination of 3 fecal samples (collected on 3 consecutive days or within a 7-10 day period) will increase detection sensitivity. Infected cats often show no signs, or they may present with dyspnea, coughing, and anorexia. 

Management: Infected cats can be treated with emodepside, eprinomectin, fenbendazole, moxidectin, or selamectin. Preventing cats from hunting by denying outdoor access greatly reduces exposure.

Host range: Dogs and various wild canids serve as definitive hosts. Red foxes are the natural definitive host. Numerous species of terrestrial gastropods (slugs and land snails) and frogs can serve as intermediate hosts. Frogs and chickens can serve as paratenic hosts.

Geographic range: Endemic foci occur in Africa, Europe, North America and South America.  In North America, infection occurs throughout Newfoundland.  Recently, infection was reported in red fox in West Virginia in the USA.  The danger of spread within Canada (particularly to the Maritimes) is a concern.

Life cycle: Adult worms reside in the pulmonary artery of dogs and foxes. Adult female worms lay undifferentiated eggs. The eggs develop and hatch in pulmonary capillaries, releasing L1 which break out into the alveolar air space. They are coughed up and swallowed to pass in the feces. Canids acquire infection by ingesting L3 contained in the tissues of gastropods, frogs or chickens (and presumably other birds).  The prepatent period is 28-108 days (but usually occurs in 7-8 weeks).

Diagnosis: As above for A. abstrusus in cats. The L1 are identified based on size (310-399 microns in length) and morphology (cephalic button, kinked tail with a dorsal spine).  There are qualitative differences in the tail morphology sufficient to allow differentiation between the L1 of A. vasorum and those of A. abstrusus, which may be recovered from dog fecal samples due to coprophagy. Presently available only in Europe, commercial kits for use in the detection of circulating adult A. vasorum antigen can be used in the diagnosis of infection. Clinical signs are similar to those caused by Dirofilaria immitis, including coughing, dyspnea, and exercise intolerance; neurological signs and bleeding disorders may also occur.

Management: Fenbendazole, milbemycin oxime and moxidectin have been used to treat dogs infected with A. vasorum; efficacies of 85% were reported for all 3 anthelmintics.  However, post-treatment complications (severe dyspnea, ascites) can occur.  Milbemycin oxime and moxidectin, available for monthly prevention of D. immitis infection, also can be used as monthly preventive treatments for A. vasorum. When used as a preventive, an efficacy of 100% was reported for moxidectin. When used at dosages of 0.6 – 1.2 mg/kg, efficacies of 95-99% were reported for milbemycin oxime. Due to issues of efficacy, potential treatment complications and the possibility of permanent cardiopulmonary damage, prophylactic treatment is the preferred option. When feasible, preventing dogs from roaming or hunting will reduce the risk of exposure.

Host range: Dogs, wild canids, bears, badgers and martens. Red fox is the natural definitive host.  Numerous terrestrial gastropods (slugs, land snails) serve as intermediate hosts. 

Geographic range: Asia, Europe and North America. In North America, it is restricted to the northeastern quarter of the continent including the provinces of NB, NL, NS, PEI, QC and ON.

Life cycle: Adult worms reside in the bronchioles, bronchi and rarely the trachea of infected canids. Female worms lay larvated eggs which hatch shortly after deposit.  The L1 are coughed up and swallowed to pass in the feces.  Dogs acquire infection by ingestion of gastropods. The prepatent period is about 3 weeks.

Diagnosis: As above for A. abstrusus, for the most part.  The L1 are identified based on size (264-340 microns in length) and morphology (cephalic button, tail comes to a simple point lacking a kink or spine but there is a slight deflection). Many infected dogs appear to shed only a low level of larvae, increasing the risk of false negative results.  Examination of 3 fecal samples greatly increases detection sensitivity. Additionally, due to the low shedding levels, detection of C. vulpis L1 by direct smear is very rare and even zinc sulfate centrifugal fecal flotation detects only about 10% of infections. The main clinical sign in dogs is a persistent cough.

Management: Febantel, fenbendazole, milbemycin oxime and moxidectin are available for treatment of dogs infected with C. vulpis. Complete clinical cure occurs in most dogs within 7-10 days of deworming. Since infections are nonfatal and easily treated, it is doubtful that a great deal of expenditure in time, effort and resources are appropriate for the prevention of infection by this parasite.

Host range: Infections have been reported in laboratory research colony beagles and rarely in client-owned pet dogs.

Geographic range: Asia, Australia, Europe, North America (USA, Canada). In Canada, it has been reported in ON.

Life cycle: The life cycle is direct and the L1 is the infective stage. Adult worms occur in bronchioles and are embedded in lung parenchyma. Female worms lay larvated eggs. L1 larvae and unhatched eggs are coughed up and either pass out in saliva/sputum or are swallowed and pass out in the feces. Larvae passed in the feces lack vigour and are shortlived. Dogs acquire infection by ingestion of L1 in very fresh feces or in sputum, saliva or vomitus. The prepatent period is about 35 days.

Diagnosis: Diagnosis is challenging. Baermann examination has low detection sensitivity due to the lack of vigour of the L1.  L1 may be detected by zinc sulfate centrifugal flotation, however, false negatives are common. Fecal sedimentation may detect L1 but the technique is time consuming and the larvae quickly degenerate and become unrecognizable. L1 are best recovered from examination of saliva, sputum, or transtracheal wash or bronchoalveolar lavage samples. The larvae are 240-290 microns in length with a bluntly rounded head and a tail that has a kink but lacks a spine. The larvae are very similar to those of Oslerus osleri. F. hirthi infections are usually asymptomatic.

Management: Treatment involves ivermectin or prolonged (14-21 days) administration of fenbendazole. Most infections reported in research beagles have been subclinical.  Infections reported in pet dogs have involved severe signs of respiratory disease and are usually associated with an underlying immunosuppression (corticosteroid therapy, demodectic mange) or serious disease condition (distemper infection, neoplasia, and severe trauma). 

Host range: Dogs and wild canids serve as definitive hosts.

Geographic range: Worldwide – reported from all continents except Antarctica. In Canada, infection has been reported in AB, BC, MB, NS, ON, QC and SK. It is also known to occur in NB and PEI.

Life cycle: Adult worms occur in wart-like nodules attached to the epithelial surface of the lumen in the trachea and bronchi, clustered at the tracheal bifurcation. Larvated eggs are deposited into the lumen by female worms.  Canids acquire infection by the ingestion of L1. Dogs acquire infection primarily as pups from exposure to L1 in saliva from dams during cleaning/grooming. Wild canids become exposed as pups from regurgitative feeding from dams. The prepatent period is 70-126 days.

Diagnosis: As above for F. hirthi. The L1 recovered from mucus are 232-266 microns in length and those recovered from feces are 326-378 microns in length. The morphology is very similar to that of F. hirthi. The nodules are easily detected at the bifurcation of the trachea through bronchoscopy. Infected dogs present with a dry cough associated with exercise or cold air.

Management: Extra-label fenbendazole and ivermectin have been used to treat infected dogs.   

Diagnosis of lungworm infection in dogs or cats in Canada On a worldwide basis, dogs are susceptible to infection with 7 helminth parasites (6 nematodes, 1 trematode) of the respiratory system. Canada is the only country in the world where endemic infection in dogs has been reported for all 7 of these lungworms. The nematodes include 2 capillarids (Eucoleus aerophilus, Eucoleus boehmi) and 4 metastrongyloids (Angiostrongylus vasorum, Crenosoma vulpis, Filaroides hirthi, Oslerus osleri). The trematode is Paragonimus kellicotti. Of these “lungworms”, the most that might be endemic (at the present time) in any one region in Canada is 6 (ie all but P. kellicotti in Atlantic Canada; all but A. vasorum in Ontario).

A thorough diagnostic evaluation in a case where “lungworm” infection was suspected in a dog would be to perform a direct smear (may detect all of the above but has overall poor detection sensitivity), zinc sulfate centrifugal flotation (eggs of E. aerophilus, E. boehmi; larvae of F. hirthi, O. osleri but has poor detection sensitivity for nematode larvae), Baermann examination (larvae of A. vasorum, C. vulpis) and fecal sedimentation (operculate eggs of P. kellicotti). Additionally, examination of sputum or a transtracheal wash sample may be useful to detect larvae of F. hirthi or O. osleri. Due to the sporadic fecal larval shedding patterns typical of metastrongyloid infection, multiple fecal examinations (3 examinations conducted on 3-consecutive-day samples or 3 samples collected over a 7-10 day period) greatly increases detection sensitivity of the Baermann examination.

In Canada, cats are susceptible to infection with 1 capillarid (E. aerophilus), 1 metastrongyloid (Aelurostrongylus abstrusus) and the lungfluke (P. kellicotti). In cases of suspected “lungworm” infection, the direct smear, Baermann examination, zinc sulfate centrifugal flotation and fecal sedimentation should be performed.