Articles for Vets Diseases of Small Animals

Dirofilariasis: Symptoms, Diagnosis & Treatment

Dirofilaria immitis,the dog heartworm, is a parasitic roundworm that is spread from host to host through the bites of mosquitoes.


Heartworm disease is defined in three classes, varying in severity.

  • Class I heartworm disease are often asymptomatic, meaning they exhibit no visible symptoms, or may only exhibit minimal signs such as an occasional cough. 
  • Class II patients usually exhibit coughing and unusual intolerance to exercise.    
  • Class III may show symptoms of anemia, exercise intolerance, fainting spells, and — in severely affected dogs, right-sided chronic heart failure.


Identification of  Dirofilaria worm in blood samples plus clinical signs and history, serological tests are also available.


Treating canine heartworm disease involves both killing the adult worms that live in the heart and pulmonary arteries and the larval stages (called microfilaria) that circulate in the bloodstream of the dog.

  • Ivermectin is the medication most commonly used to kill the microfilaria (larval stage)
  • The only medication currently available to kill the adult heartworms is melarsomine 
  • Steroids may be given to reduce anaphylaxis  
  • Acetylsalicylic acid plus prednisolone prevents thromboembolism.

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