Current Advice on Parasite Control:
Parasites of Other Systems - Lungworms
Aelurostrongylus abstrusus (feline lungworm)
Eucoleus aerophilus (feline and canine bronchial capillarid)
Eucoleus aerophilus (feline and canine bronchial capillarid)
Eucoleus boehmi (canine nasal capillarid)
Filaroides hirthi (canine lungworm)
Filaroides osleri (canine tracheal and bronchial nodular worm)
Crenosoma vulpis (fox bronchial worm)
Angiostrongylus vasorum (French heartworm)
- Aelurostrongylus abstrusus is common in the cat around the world. The cat appears to be the only definitive host.
- Eucoleus aerophilus (also known as Capillaria aerophila) is primarily a parasite of the respiratory tract of the fox; it has also been reported from the dog, cat, and other carnivores in North America, South America, and Europe.
- Eucoleus boehmi is the nasal capillarid of the dog. The adult worms live in the nasal cavity and paranasal sinues of dogs and related canids. It was originally described from the frontal sinuses of a fox.
- Filaroides hirthi lives threaded through the lung parenchyma of dogs and other canids.
- Filaroides osleri is a parasite that produces hemorrhagic or granular, wartlike nodules in the trachea and bronchi of the dog and other canids. It has been reported from many parts of the world.
- Crenosoma vulpis is a parasite of foxes that occasionally makes its way into dogs. It lives in the bronchi where it causes mild catarrhal inflammation but no nodule formation.
- Angiostrongylus vasorum is a parasite of foxes that also finds its way into dogs.
Overview of Life Cycles
- With Ael. abstrusus, eggs passed by adult female worms hatch in the lungs, and larvae pass up the trachea, down the intestinal tract, and out in the feces. Snails and slugs are the intermediate hosts, but the cat is probably infected by eating transport hosts, e.g., rodents, birds, amphibia, and reptiles. Ingested larvae are liberated in the intestine, penetrate the mucosa, and migrate to the lungs. Adult worms are found in the alveolar ducts and terminal bronchioles 8 to 9 days after infection. Egg-laying starts about 4 weeks after infection. First-stage larvae are found in the feces about 6 weeks after the infection is initiated. Adults live 9 months or longer.
- In E. aerophilus, the life cycle is direct. Eggs are in the sputum or feces and embryonate in 30 to 50 days. Larvae from ingested eggs hatch in the small intestine, penetrate the mucosa, and apparently migrate by the bloodstream to the lungs. This process takes 7 to 10 days. Larvae penetrate the alveoli, migrate up the air passages as they develop, and reach maturity about 40 days after infection. Adult worms inhabit the epithelium of the bronchioles, bronchi, and trachea where their thin bodies are threaded through the epithelial surface.
- In the case of E. boehmi, the adults live threaded through the mucosa of the nasal sinuses. The life cycle has not been worked out in detail but is believed to be direct.
- With F. hirthi, the adults live threaded through the lung parenchyma. Larvae in the feces or in the respiratory secretions of infected animals are immediately infective. Transmission can occur from the bitch or between littermates from the ingestion of first-stage larvae in feces. Ingested larvae reach the lungs within 6 hours via the hepatic portal circulation or the mesenteric lymphatic draining. Larvae appear in the feces of experimentally infected animals within 5 weeks after infection.
- In F. osleri, the adults live in nodules in the trachea and bronchi, usually at bifurcations. Filaroides osleri requires no intermediate host with the first stage larvae passed in the feces or in saliva being infective to another dog. Nodules in experimental F. osleri infections can be detected with the bronchoscope about 2 months after infection. The prepatent period is 6 to 7 months.
- Females of C. vulpis live in the bronchi and produce larvae that are carried to the intestine by the tracheal route. These larvae enter snails where they develop to the infective third stage. Dogs become infected when they eat the infected snails; the prepatent period is 19 days.
- In the case of Ang. vasorum, canids acquire infections by the ingestion of gastropod intermediate hosts. Gastropods eat the first-stage larvae while feeding on the feces of infected canids. In addition to infection though the ingestion of snails, dogs can also be infected by ingesting frog paratenic hosts. When the third-stage larvae in the snail or frog are eaten by the dog, they penetrate the gut wall and develop in abdominal lymph nodes before entering the portal circulation and moving to the pulmonary arteries and right ventricle. In the lungs, the worms mature, mate, and produce eggs that lodge and develop in capillaries. Larvae that hatch from the eggs move into an airspace, are coughed up and swallowed to be passed in the feces. The prepatent period is about 28 to 108 days.
- The female Ael. abstrusus is about 9 mm long, and the male about 4 to 7 mm long. The vulva lies just anterior to the anus, and the tail ends bluntly. The ellipsoid egg in the lung measures about 80 μm. First-stage larvae are passed in the feces. The larvae are about 400 μm in length and have undulating tail and a dorsal spine. The third-stage larvae in the snail or transport host are the stage that infects the cat.
- Adults of E. aerophilus are long and thin and threaded through the mucosa. Males are 1.5 to 2.5 cm long and females 2 to 4 cm long. The male has two caudal lobes and a single spicule with a spiny sheath. The vulva of the female is near the posterior end of the esophagus. Eggs are brown, oval, and 60 µm long by 30 µm wide, with a granular shell and bipolar plugs. The larval stages are usually not observed.
- With E. boehmi, adults are small and similar in morphology to the adults of E. aerophilus. The worms are threaded through the mucosa of the sinuses in which they live. The eggs of E. boehmi may be found in nasal discharges or feces and are about 50 μm in length. The surface of the egg of is pitted whereas that of E. aerophilus is covered with anastomosing ridges. The egg is passed in a partial stage of embryonation, and the developing morula in the egg often appears square or rectangular; the eggs of E. aerophilus will contain a single cell when passed.
- Filaroides hirthi adults are difficult to dissect out of fresh lung tissue. On the male, the spicules are short and stout, the cuticle appears inflated, but a bursa is not readily apparent. The vulva of the female is just anterior to the anus, and the uterus is full of eggs containing infective larvae. The larvae passed in the feces are 240 to 290 µm long, with the esophagus about 95 to 110 µm long.
- Adult F. osleri males are 5.6 to 7 mm long, and females are 10.0 to 13.5 mm long. The posterior end of the male is round, blunt, and almost nonbursate; the spicules are slightly unequal. The vulva and anus of the female are adjacent to one another in a cleft near the posterior end. The female is ovoviviparous; the uterus extends anteriorly to the esophagus and is filled with larvated eggs that measure 80 µm by 50 µm. The larvae passed in the feces are about 300 µm in length. The larvae of F. osleri and F. hirthi are virtually indistinguishable.
- Adult C. vulpis males are 3.5 to 8 mm long and the females are 12 to 16 mm long. The vulva is near the middle of the body. The anterior end of the body is marked by 18 to 26 cuticular folds that encircle the body and give the worms their crenated appearance. The female is ovoviviparous. The first-stage larvae shed in the feces are about 200 μm in length, with the oral ends bluntly conical and the tips of the tails tapering smoothly to the end without any kink, undulation, or spine. The esophagus is about one-third of the total body length.
- Adult Ang. vasorum are slender pinkish worms approximately 14 to 20 mm in length. The males are bursate, and the females have a “barber pole” appearance from the red intestine intertwined with the white reproductive tract. Females lay eggs that develop and hatch first-stage larvae that are 310 to 400 μm long with anterior cephalic buttons and tails with a dorsal spine.
- With Ael. abstrusus, clinical signs are usually absent. Sometimes in heavy infections, cats develop a chronic cough accompanied by progressive dyspnea, anorexia, and emaciation.
- In E. aerophilus, light infections are usually inapparent. Young animals are the most susceptible. Severe infections are characterized by a cough, nasal discharge, dyspnea, anorexia, and debilitation caused by tracheitis, bronchitis, and sometimes pneumonia.
- Light infections with E. boehmi are usually inapparent, and most cases are asymptomatic. Rhinitis may be present in heavy infections with infected dogs having chronic serous nasal discharge and occasional sneezing. If secondary infection occurs, the discharge can become purulent.
- An infection with Filaroides hirthi usually is not associated with clinical signs. Severe infections may show radiographic changes. Fatal cases of hyperinfection have developed in severely stressed and immunodeficient animals.
- With F. osleri, the major sign is the spasmodic attack of a hard, dry cough triggered by exercise or exposure to cold air. Attacks are not induced by pressure upon the larynx. Young dogs are most acutely affected and sometimes develop respiratory distress, anorexia, and emaciation.
- With C. vulpis clinical disease in dogs is seldom more than a persistent cough.
- Disease due to Ang. vasorum is an inflammatory reaction with the subsequent involvement of the surrounding lung tissue that may be accompanied by interstitial pneumonia, emphysema, thromboarteritis, coagulopathis, anemia, melena, hemoptysis, and congestive right heart failure. Aberrant migrations of adults (eye, left ventricle, femoral artery) and first-stage larvae (brain, spinal chord, eye, kidney, liver, skeletal muscle, intestine, stomach, pancreas, spleen, adrenal gland, thyroid gland) have occurred.
- Aelurostrongylus abstrusus is most common in cats that are allowed to hunt and is found fairly consistently in cats throughout the world.
- Eucoleus aerophilus seems to be found wherever there are dogs or cats.
- The prevalence of E. boehmi is not well known; it seems to be worldwide in distribution.
- Filaroides hirthi occurs sporadically and periodically appears in some kennels or in individual dogs.
- Filaroides osleri tends to occur sporadically and in certain regions; it is relatively common in Israel and South Africa.
- Crenosoma vulpis is widely distributed around the world in the fox population and therefore in dogs that share the same environment.
- Angiostrongylus vasorum is mainly a parasite of continental Europe, Africa, and South America, but it has recently entered England and Ireland and found its way over to the Atlantic provinces of Canada.
Host Associations and Transmission Between Hosts
- Aelurostrongylus abstrusus is a parasite of felidae. Other animals in a household are usually not at risk of obtaining infections due to the need for an intermediate host.
- Eucoleus aerophilus is a parasite of foxes, dogs, and cats. Foxes are thought to serve as the reservoir for infections in domestic animals.
- Eucoleus boehmi is a parasite of foxes and dogs, and the life cycle is poorly known. It is possible that transmission may occur between family pets.
- Filaroides hirthi is a parasite of dogs, and transmission occurs easily in kennels because the larvae are infectious when passed.
- Filaroides osleri, like F. hirthi, is easily transmitted between dogs because the larvae are infectious when passed.
- Crenosoma vulpis is a parasite of foxes and dogs; transmission requires the ingestion of an intermediate host.
- Angiostrongylus vasorum has been reported in the red fox, African desert fox, crab-eating zorro, hoary fox, and dog.
Prepatent Period and Environmental Factors
- With Ael. abstrusus, first-stage larvae are found in the feces about 6 weeks after a cat is infected.
- For E. aerophilus, the prepatent period is about 40 days.
- The prepatent period for E. boehmi is unknown.
- With F. hirthi, the larvae appear in the feces of experimentally infected animals within 5 weeks after infection.
- For F. osleri, the prepatent period is 6 to 7 months.
- The prepatent period of C. vulpis is 19 days,
- The prepatent period for Ang. vasorum is 28 to 108 days.
Site of Infection and Pathogenesis
- The adults of Ael. abstrusus live in the lungs with the mature worms found at the terminal parts of the bronchioles. Typical gross lesions consist of gray nodules, 1 to 10 mm in diameter, scattered over the surface of the lungs or arranged in clusters. Incised nodules exude a milky fluid that contains many eggs and larvae.
- Eucoleus aerophilus lives threaded through the mucosa of the trachea, bronchi, and bronchioles. Tracheobronchitis, pulmonary edema, hemorrhage, and sometimes pneumonia may be seen at necropsy.
- Eucoleus boehmi lives threaded through the mucosa of the nasal sinuses. Inflammation of the epithelia of the sinuses is caused by the presence of the worms and eggs within the epithelium.
- The adults of F. hirthi that live in the alveoli and bronchioles provoke a focal granulomatous reaction and other pulmonary changes, some of which suggest drug-induced and neoplastic lesions.
- Filaroides osleri lives in nodules in the trachea and bronchi. The gray-white, wartlike submucosal nodules range in size up to 18 mm in diameter and commonly occur at the bifurcation of the trachea. The nodules are usually transparent, and the coiled worms inside are clearly visible.
- The adults of C. vulpis live in the lumen of the bronchi where they may cause mild inflammation.
- The adults of Ang. vasorum live in the pulmonary arteries. Infections are associated with chronic cough, dyspnea, exercise intolerance, and anorexia; gagging and weight loss are the most common clinical signs of infection. Pulmonary hemorrhage can occur as larvae migrate into airspaces. Granulomas develop in response to eggs and larvae, and fibrosis occurs. Pulmonary vascular lesions include thromboarteritis and intimal proliferation; pulmonary hypertension can lead to congestive right heart failure.
- Diagnosis of Ael. abstrusus can be considered in cats with respiratory signs. Infection is easily confirmed by the demonstration of the first-stage larvae in the feces.
- For E. aerophilus diagnosis is made by identification of the eggs in the sputum or feces. The eggs in the feces of dogs must be differentiated from Trichuris vulpis eggs (which are larger), Eucoleus boehmi eggs (which contain a partially developed embryo when passed), and Pearsonema plica and P. feliscati eggs (which can be present in feces contaminated with urine).
- In E. boehmi, diagnosis is made by identification of the eggs in nasal discharges or feces. The eggs in the feces of dogs must be differentiated from Trichuris vulpis eggs (which are larger), Eucoleus aerophilus eggs (which contain a single cell when passed), and Personema plica and P. feliscati eggs (which can be present in feces contaminated with urine).
- Diagnosis of F. hirthi is made by finding the characteristic larva in the feces. The larva has a constriction and a kink just posterior to the end of the tail. The larva of F. hirthi is virtually indistinguishable from that of F. osleri. The first-stage larva of Filaroides spp. lacks the caudal spine present on the tail of the larva of Angiostrongylus spp. and has a rounded anterior end that differentiates it from the larva of C. vulpis, which has a conical anterior end and a tail that ends in a sharp point without a constriction.
- For F. osleri, the lesions observed by bronchoscope are pathognomonic. The infection can also be diagnosed by finding the larva in fecal flotation using zinc-sulfate centrifugation. The larva has a constriction and a kink just posterior to the end of the tail. The larva of F. osleri is virtually indistinguishable from that of F. hirthi.
- For C. vulpis, diagnosis is made by finding the characteristic larva with a conical head and pointed tail in the feces or by finding the worms in the bronchi at necropsy.
- For Ang. vasorum, larvae are detected in feces using the Baermann technique or fecal flotation. Larvae are less reliably detected on fecal flotation. Multiple fecal samples may need to be examined. Radiographic changes may include diffuse peribronchial, interstitial and alveolar densities. Multiple nodular-like densities may occur in the peripheral regions of the caudal lung lobes, and enlargement of the right heart and pulmonary artery may also be visible.
- Cats have been treated for Ael. abstrusus with fenbendazole for extended periods. Ivermectin has also been used, but there have been mixed results as to efficacy. Moxidectin (in a European formulation similar to Advantage Multi and Emodepside in Profender, have been shown to have good efficacy in the treatment of Ael. abstrusus.
- Both E. aerophilus and E. boehmi have been successfully treated with ivermectin or fenbendazole.
- Filaroides hirthi is difficult to treat. Drugs that have been used include ivermectin, albendazole, and other anthelmintics.
- The treatment of choice for F. osleri seems to be injectable doramectin. Some veterinary practitioners also remove as many nodules as possible with the aid of the bronchoscope.
- Crenosoma vulpis has been successfully treated with fenbendazole, ivermectin, and febantel.
- Angiostrongylus vasorum has been treated with levamisole, fenbendazole, ivermectin and moxidectin. Severe dyspnea and ascites may be seen after treatment; bronchodilators, expectorants, and diuretics may be required to manage these post-treatment reactions.
- Monthly year-round treatment of dogs and cats with moxidectin in the topical formulation seems as though it would prevent infection with Ael. Abstrusus and possible A. vasorum.
Control and Prevention
- For dogs and cats, routine preventives are probably not protective against these parasites. Pets can be protected by minimizing the amount of hunting that the animals do. Fencing and mollusk control could also help to minimize the infection in dogs.
- In the case of F. hirthi, it may be very difficult to clear breeding kennels, and it may require that puppies be derived by caesarean section and reared by foster mothers. Similarly, the infectious nature of F. osleri makes it difficult to ensure that puppies are not infected.
Public Health Considerations
- Most of these nematodes do not infect people. There have been rare reports of human infections with E. aerophilus in Russia and Morocco.
- Traversa D, Cesare A di, Milillo P, Lohr B, Iorio R, Pampurini F, Schaper R, Paoletti B, Heine J. Efficacy and safety of imidacloprid 10%/moxidectin 1% spot-on formulation in the treatment of feline aelurostrongylosis. Parasitology Research 105(Suppl. 1): 55-62; 2009
- Traversa D, Milillo P, Cesare A di, Lohr B, Iorio R, Pampurini F, Schaper R, Bartolini R, Heine J. Efficacy and safety of emodepside 2.1%/praziquantel 8.6% spot-on formulation in the treatment of feline aelurostrongylosis. Parasitology Research 105(Suppl. 1): 83-90; 2009
- Burgess H, Ruotsalo K, Peregrine AS, HanselmanB, Abrams-Ogg A. Eucoleus aerophilus respiratory infection in a dog with Addison's disease. Canadian Veterinary Journal 49: 389-392; 2008
- Yao CQ, O'Toole D, Driscoll M, McFarland W, Fox J, Cornish T, Jolley W. Filaroides osleri ( Oslerus osleri): two case reports and a review of canid infections in North America. Veterinary Parasitology 179: 123-129; 2011.
- Morgan E, Shaw S. Angiostrongylus vasorum infection in dogs: continuing spread and developments in diagnosis and treatment. Journal of Small Animal Practive 51: 616-621; 2010
- Schnyder M, Fahrion A, OSsentP, Kohler L, Webster P, Heine J, Deplazes P. Larvicidal effect of imidacloprid/moxidectin spot-on solution in dogs experimentally inoculated with Angiostrongylus vasorum. Veterinary Parasitology 166: 326-332; 2009
- Willesen JL, Kristensen at, Jensen AL, Heine J, Koch. Efficacy and safety of imidacloprid/moxidectin spot-on solution and fenbendazole in the treatment of dogs naturally infected with Angiostrongylus vasorum (Baillet, 1866). Veterinary Parasitology 147: 258-264; 2007