Feline Lungworms

Filed Under: Cats, Parasites

Has your cat been coughing lately?  Have you noticed weight loss in your pet or periods with difficulty breathing?  You may be dealing with a parasitic infection rather than a respiratory disease, feline heartworms, or feline asthma.  Any cat with clinical signs of respiratory disease that is over 3 months of age should be screened for the feline lungworm, or Aelurostrongylus abstrusus, which is a nematode (type of roundworm) capable of infecting the lungs of cats. 
Feline lungworms are contracted through the ingestion of infected snails or slugs, which are intermediate hosts of A. abstrusus.  Lungworms may also be acquired through the consumption of a bird, reptile, amphibian, or rodent that has fed upon an infected snail or slug, and they are referred to as a “transport” or “paratenic host”.
Adult lungworms reside in the bronchioles and alveoli of the lungs where the female nematode lays its eggs approximately 25 days following ingestion of the paratenic host.  The eggs, or ova, hatch and become larvae which migrate to the bronchi and trachea where they are coughed up, swallowed again, and are then passed through the host in the infected individual’s feces.  Once the eggs are shed on the ground they are picked up by snails and slugs to infect yet another host cat, thereby completing its lifecycle
Many infected cats will be asymptomatic (showing no clinical signs of illness), while others will show clinical signs of bronchial and pulmonary (lung) disease.  Common clinical signs include coughing, possible harsh lung sounds on auscultation, and in rare cases pleural effusion (fluid in the chest).  The cat may become dyspnic (have difficulty breathing), and often the host will appear depressed and lethargic.  Some cats will lose weight, have a rapid heart rate (tachycardia), and rapid respiration (tachypnea).  In rare instances death may occur.  Often the infection will be self-limiting (run its course with the cat appearing to improve), and is therefore often an overlooked diagnosis.  The most commonly infected cats are free-roaming and stray to semi-feral.
 Serologic testing may demonstrate an elevation in eosinophil levels on a CBC, or complete blood count.  Eosinophils are a type of white blood cell that is characteristically found in elevated levels with parasitic and allergic conditions.  Serum globulin levels may also be slightly elevated which is characteristic of an infection. A serum antibody test is available for the detection of third-stage larvae.  This test is highly specific for feline lungworms but will not differentiate between current and past infections.
The condition is definitely diagnosed through microscopic fecal analysis, and the test is simple, but it lacks sensivity, by only detecting 21.7% of infected cats. Use of the Baermann technique can increase the sensivity to 63.6%.  When seen, the ova (eggs) have a football-like appearance with opercula at apposing ends. The larvae measure 360 to 390 µm in length and have a curved tail which is characteristic of the parasite. Larvae are shed intermittently therefore when suspected serial fecal analysis should be conducted.    
Treatment consists of fenbendazole at a dose of 25 to 50 mg/kg orally every 12 hours or one dose of ivermectin at 0.4 mg/kg by subcutaneous injection or orally.  Supportive treatment should include the administration of corticosteroids and the use of bronchodilators to ease breathing and decrease the lung inflammation.  Although ivermectin is used for treatment, it is not considered as effective as fenbendazole. 
The prognosis for A. abstrusus infection is generally thought to be good with treatment.  Some cases of infection may be self-limiting (resolve on their own).

Ettinger, Stephen and Edward Feldman.  Textbook of Veterinary Internal Medicine. Vol 2. W.B. Saunders.  5th Edition  2000.  Pp. 1068-1070.
Freeman, William.  “Feline Lungworm.”  Veterinary Forum.  May 2007.  Pp. 74-75.
Lacorcia, Lauren and Robin Gasser et al.  “Comparison of bronchoalveolar lavage fluid examination and other diagnostic techniques with the Baermann Technique for detection of naturally occurring Aelurostrongylus abstrusus infection in Cats.”  JAVMA, Vol 235, No. 1, July 1, 2009.  Pp. 43-49.
Norsworthy, Gary.  The Feline Patient.  3rd Ed.  Blackwell Publishing.  2006. P. 175-176.

Topics: lungworms

Symptoms: difficulty breathing, weight loss

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