Lungworm disease in Cats (Felis) | Vetlexicon
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Lungworm disease

ISSN 2398-2950


  • CauseAelurostrongylus abstrusus infection is relatively common in domestic cats and is the most important lungworm in cats but other lungworms are now being reported in cats, eg Troglostrongylus brevior, Capillaria aerophila.
  • Signs: many cases are not clinically important.
  • The parasites live in the terminal bronchioles and alveolar ducts (Aelurostrongylus), bronchi and bronchioles (Troglostrongylus) or under the tracheal and bronchial epithelium (Capillaria).
  • Heavy infections can cause dyspnea/hyperpnea and coughing.
  • Diagnosis: detection of larvae of Aelurostrongylus or Troglostrongylus in feces following Baermann examination; they can also be seen in routine fecal flotation and may be seen in bronchial washings or BAL fluid. Similar samples may reveal Capillaria eggs.
  • Treatment: fenbendazole, moxidectin, emodepside, selamectin, eprinomectin and milbemycin appear to be effective in eliminating infections. Routine treatment using these products may be useful to prevent symptomatic infections developing.
Print off the owner factsheet Lungworms in cats Lungworms in cats to give to your client.

Presenting signs

  • Coughing.
  • Dyspnea.
  • Increased tracheal hypersensitivity.
  • May have lethargy and weight loss.

Acute presentation

  • Occasionally sudden death.

Geographic incidence

Age predisposition

  • Common infection, often going undiagnosed.
  • All ages can be affected, but more common to see clinical signs in younger cats.

Special risks

  • Conditions producing immunosuppression may exacerbate effects.



  • Most cases are due to Aelurostrongylus abstrusus Aelurostrongylus abstrusus.
  • Most cats tolerate light infection with no clinical signs.
  • Occasionally severe clinical signs occur.
  • Less commonly reported, cases are due to Troglostrongylus brevior Troglostrongylus brevoir or Capillaria aerophila Capillaria aerophila.
  • Troglostrongylus has historically been regarded as a wild cat parasite but it is being increasingly reported in young cats, especially those with possible access to wild cats.
  • Capillaria has also been regarded as a wild cat parasite but more recently reports have occurred in domestic cats. Capillaria can infect other carnivores as well as humans.

Predisposing factors


  • Immunosuppressive factors.
  • General debility.
  • More common in cats with access to outdoors.


A. abstrusus

  • Infected cats may develop bronchial hyperplasia, focal alveolar lung disease and hypertrophy of pulmonary arterioles; a granulomatous or mixed inflammatory response occurs in affected tissues.
  • Secondarily, there is increased mucus in the airways and signs that are indistinguishable from feline asthma Allergic bronchitis.
  • Most natural infections, however, are subclinical.
  • Cats become infected by ingesting L3 in tissues of intermediate (eg slugs and snails, in which the larvae L1 develop to L3) or paratenic (eg rodents, frogs, lizards, snakes, birds, containing L3) hosts.
  • L3 released from tissues of prey penetrate gut wall and migrate to lung via peritoneal and thoracic cavities via hemolymphatic system.
  • After a pre-patent period of 5-6 weeks adult females in the bronchioles, alveolar ducts and alveoli begin laying eggs.
  • Eggs hatch and L1 migrate up trachea, are coughed up and swallowed.
  • L1 are excreted in the feces ready to be taken up by an intermediate host.
  • Effects attributable to host's immune response.
  • In most cases this is not intense.
  • Balanced host-parasite relationship.
  • Occasional clinical cases due to disturbance of this balance.
  • Migration of eosinophils and mast cells into respiratory tract.
  • Hypertrophy and disturbed architecture of pulmonary arterioles most consistent change.

T. brevoir

  • Life cycle of T. brevior very similiar to A. abstrusus with involvement of intermediate and paratenic hosts and L1 excretion in the feces.
  • Some evidence that T. brevior  may be directly transmitted from an infected queen to her kittens.
  • Adults live in the bronchi and bronchioles, causing more severe signs in younger cats with pulmonary edema, congestion, hemorrhage, etc.
  • Pulmonary hypertension Pulmonary arterial hypertension has been reported in a case of T. brevoir infection.

C. aerophila

  • Life cycle of C. aerophila is not thought to involve an intermediate host; earthworms may act as a facultative intermediate or paratenic host but this has not been confirmed.
  • Eggs are excreted in the feces and they become infective in the evironment over 1-2 months, most likely, and are then ingested by a cat.
  • Adults live under the epithelium of the bronchi and trachea.
  • Mostly subclinical infections but pathology includes lesions in the trachea and lung parenchyma.


  • Pre-patent period is 5-6 weeks.
  • Lifespan of adult worms is at least 1 year.


A. abstrusus and T. brevior

  • Transmission depends on cats ingesting intermediate or paratenic hosts.
  • These hosts are ubiquitous.
  • L3 remain viable for long periods in these hosts.
  • Cats are very likely to engage in hunting.
  • A. abstrusus is a common infection in domestic as well as wild cats whereas T. brevoir is particularly common in wild cats.

C. aerophila

  • Transmission by ingestion of eggs from environment but earthworms may act as a facultative intermediate or paratenic host but this has not been confirmed.
  • Particularly common in wild cats.


Presenting problems

  • Dyspnea.
  • Hyperpnea.
  • Tachypnea.
  • Eosinophilia.
  • Coughing.

Client history

  • Persistent coughing.
  • Dyspnea.
  • Hunting behavior.
  • Sudden and severe respiratory distress.
  • May have weight loss and lethargy.
  • Sneezing and/or wheezing may also be described.

Clinical signs

  • Abnormal breath sounds on thoracic auscultation.
  • Increased tracheal sensitivity.
  • Sudden respiratory distress with associated signs.
  • Suggested cause of anesthetic-associated death due to reduced gas exchange, etc.

Diagnostic investigation

Fecal analysis

  • Direct fecal smears and classical sedimentation and flotation methods are not very reliable in the detection of feline lungworms because of their low sensitivity, inadequate sample size and larval osmotic damage, but are occasionally performed. A. abstrusus and T. brevior L1 may be present whereas C. aerophila is represented by the presence of eggs. The Baermann test offers a more sensitive method of examination of the feces for L1 Fecal analysis: parasites; this involves separating out the live larvae from the feces by attracting them out of the samples by humidity (hydrotropism) but takes 12-48 hours. It can provide quantitative data on the number of larvae present too and this can correlate with clinical disease. However negative results will occur during prepatent infections and when the adults remain in the absence of egg/L1 shedding.
  • Skill is required to differentiate A. abstrusus and T. brevoir L1. Although A. abstrusus L1 tend to be longer than T. brevoir L1, they should be differentiated based on their head and tail features. Skill is also required to identify egg morphology as being representative of C. aerophila infection.

Fluid/aspirate analysis

  • A. abstrusus and T. brevior L1 can also sometimes be detected in bronchoalveolar lavage Bronchoalveolar lavage samples (and pleural effusions, tracheal swabs) although this is likely to show less sensitivity than fecal analysis but may be preformed when cases are investigated for lung disease.


  • Thoracic radiography Radiography: thorax.
  • Radiographic changes are variable but alveolar or interstitial lung patterns appear to be most common but bronchial thickening is also seen and changes can be identical to cats with asthma.

Computed tomography

  • Variable, eg mixed bronchointerstitialalveolar pattern, bronchointersitial pattern, bronchial wall thickening.



  • PCR PCR (Polymerase chain reaction) to distinguish the different lungworm infections in cats has been reported experimentally for use on feces and pharyngeal swabs, and may be available in the future.


  • Detection of A. abstrusus antibodies has also been reported in experimental studies, showing promising sensitivity and specificity.

Confirmation of diagnosis

Discriminatory diagnostic features

  • Clinical signs.
  • Absence of other causes of respiratory pathology.
  • Appropriate imaging findings.

Definitive diagnostic features

  • Demonstration of A. abstrusus or T. brevior L1 in feces by Baermann examination, fecal flotation, fecal smear or after performing a bronchoalveolar lavage Bronchoalveolar lavage (BAL): wet preparationBAL. BAL cytology usually has a mixture of eosinophils, neutrophils and macrophages.

Gross autopsy findings

  • Presence of adult worms in small bronchioles and alveolar ducts (Aelurostrongylus), bronchi and bronchioles (Troglostrongylus) or under the tracheal and bronchial epithelium (Capillaria).
  • Eggs in alveoli.
  • Eggs and L1 in tracheal mucus.

Histopathology findings

  • Hypertrophy of muscular layer of pulmonary arterioles.
  • Eosinophils migrating throughout lung tissue.
  • Proliferation of vascular endothelium.

Differential diagnosis


Initial symptomatic treatment

A. abstrusus

  • Fenbendazole Fenbendazole 50 mg/kg PO for 3 days reported to be 99.29% effective in one study.
  • Moxidectin Moxidectin 1% (and imidacloprid Imidacloprid 10%) spot-on parasiticide showed 100% effectiveness in the same study.
  • Emodepside 2.1% and praziquantel Praziquantel 8.6% spot-on parasticide showed 99.38% effectiveness in the same study.
  • Selamectin Selamectin reduced clinical signs of infection after a single spot-on administration whereas a second dose 1 month later was accompanied by improvement in imaging findings too.
  • Milbemycin oxime Milbemycin oxime (with praziquantel) PO at 2 week intervals has also been effective at stopping L1 shedding and resolving clinical signs of infection.
  • The topical formulation of eprinomectin Eprinomectin 0.4% (with fipronil Fipronil 8.3%, S-methoprene 10% and praziquantel 8.3%) has also been shown to be effective for A. abstrusus.
  • A short course of prednisolone Prednisolone commencing at the time of treatment may be helpful to treat the secondary eosinophilic inflammation.


  • Fecal monitoring for L1 larvae.
  • Resolution of clinical signs.
  • Reversal of radiographic changes.

T. brevoir

  • Limited data on treatment of T. brevior exists.
  • Imidacloprid 10% and moxidectin 1% spot-on parasiticide was not successful in one case but this may have been due to treatment being instigated too late in infection/disease; it has been effective in another published case report.
  • Emodepside 2.1% and praziquantel 8.6% spot-on parasiticide shows some promise for treatment.
  • Eprinomectin 0.4% (with fipronil 8.3%, S-methoprene 10% and praziquantel 8.3%) also appears to be effective in treatment of T. brevior.

C. aerophila

  • Very limited data on treatment of C. aerophila exists.
  • Moxidectin 1% (and imidacloprid 10%) spot-on parasiticide appears to be effective.
  • Eprinomectin 0.4% (with fipronil 8.3%, S-methoprene 10%, and praziquantel 8.3%) is also effective.



  • Generally impractical to prevent hunting in cats who display this behavior.
  • Periodic routine anthelmintics treatment advisable. Monthly administration of parasiticides (eg emodepside, eprinomectin, moxidectin, milbemycin, selamectin) may be able to prevent patent infections developing but confirmatory studies in the field are required.


  • Periodic routine anthelmintic treatment as discussed above.



  • General debilitating factors, senility, immunosuppression compromise outlook.

Expected response to treatment

  • Adequate anthelmintic treatment usually leads to rapid resolution of clinical signs and reversal of radiographic changes, if treatment instigated early enough.

Reasons for treatment failure

  • Occasionally cases are non-responsive or exacerbate following treatment.
  • Undefined factors rendering some individuals prone to severe disease.
  • Immunosuppression.
  • Debility.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Lacava G, Zini E, Marchesotti F et al (2016) Computed tomography, radiology and echocardiography in cats naturally infected with Aelurostrongylus abstrusus. J Feline Med Surg 19 (4), 446-53 PubMed.
  • Traversa D & Di Cesare A (2016) Diagnosis and management of lungworm infections in cats. Cornerstones, dilemas and new avenues. J Feline Med Surg 18 (1), 7-20 PubMed.
  • Di Cesare A, Veronesi F, Frangipane di Regalbono A et al (2015) Novel molecular assay for the simultaneous identification of neglected lungworms and heartworms affecting cats. J Clin Microbiol 53 (9), 3009-3013 PubMed.
  • Pennisi M G, Hartmann K, Addie D D et al (2015) Lungworm disease in cats: ABCD guidelines on prevention and management. J Feline Med Surg 17 (7), 626-636 PubMed.
  • Varcasia A, Brianti E, Tamponi C et al (2015) Simultaneous infection by four feline lungworm species and implications for the diagnosis. Parasitol Res 114 (1), 317-321 PubMed.
  • Brianti E, Giannetto S, Dantas-Torres F et al (2014) Lungworms of the genus Troglostrongylus (Strongylida: Crenosomatidae): neglected parasites for domestic cats. Vet Parasitol 202 (3-4), 104-112 PubMed.
  • Di Cesare A, Castagna G, Otranto D et al (2012) Molecular detection of Capillaria aerophila, an agent of canine and feline pulmonary capillariosis. J Clin Microbiol 50 (6), 1958-1963 PubMed.
  • Foster S F, Martin P, Allan G S et al (2004) Lower respiratory tract infections: 21 cases (1995-2000). J Feline Med Surg (3), 167-180 PubMed.
  • Naylor J R, Hamilton, J M & Weatherley A J (1984) Changes in the ultrastructure of feline pulmonary arteries following infection with the lungworm Aelurostrongylus abstrusus. Br Vet J 140 (2), 181-190 PubMed.
  • Losonsky J M, Thrall D & Prestwood A K (1982) Radiographic evaluation of pulmonary abnormalities after Aelurostrongylus abstrusus inoculation in cats. Am J Vet Res 44 (3), 478-482 PubMed.

Treatment studies include the following:

  • Böhm C, Wolken S, Schnyder M et al (2015) Efficacy of emodepside/praziquantel spot-on (Profender®) against adult Aelurostrongylus abstrusus nematodes in experimentally infected cats. Parasitol Res 114 (Suppl 1), S155-164 PubMed.
  • Giannelli A, Brianti E, Varcasia A et al (2015) Efficacy of Broadline® spot-on against Aelurostrongylus abstrusus and Troglostrongylus brevior lungworms in naturally infected cats from Italy. Vet Parasitol 209 (3-4), 273-277 PubMed.
  • Knaus M, Shukullari E, Rapti D et al (2015) Efficacy of Broadline against Capillaria aerophila lungworm infection in cats. Parasitol Res 114 (5), 1971-1975 PubMed.
  • Knaus M, Chester S T, Rosentel J et al (2014) Efficacy of a novel topical combination of fipronil, (S)-methoprene, eprinomectin and praziquantel against larval and adult stages of the cat lungworm, Aelurostrongylus abstrusus. Vet Parasitol 202 (1-2), 64-68 PubMed.
  • Rehbein S, Capári B, Duscher G et al (2014) Efficacy against nematode and cestode infections and safety of a novel topical fipronil, (S)-methoprene, eprinomectin and praziquantel combination product in domestic cats under field conditions in Europe. Vet Parasitol 202 (1-2), 10-17 PubMed.
  • Iiannino F, Iannetti L, Paganico D et al (2013) Evaluation of the efficacy of selamectin spot-on in cats infested with Aelurostrongylus abstrusus (Strongylida, Filariodidae) in a Central Italy cat shelter. Vet Parasitol 197 (1-2), 258-262 PubMed.
  • Traversa D, Di Cesare A, Di Giulio E et al (2012) Efficacy and safety of imidacloprid 10%/moxidectin 1% spot-on formulation in the treatment of feline infection by Capillaria aerophila. Parasitol Res 111 (4), 1793-1798 PubMed.
  • Traversa D, Milillo P, Di Cesare A et al (2009) Efficacy and safety of emodepside 2.1%/praziquantel 8.6% spot-on formulation in the treatment of feline aelurostrongylosis. Parasitol Res 105 (Suppl 1), S83-9 PubMed.
  • Traversa D, Di Cesare A, Milillo P et al (2009) Efficacy and safety of imidacloprid 10%/moxidectin 1% spot-on formulation in the treatment of feline aelurostrongylosis. Parasitol Res 105 (Suppl 1), S55–62 PubMed.