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Heartworm Disease Article

Heartworm Disease

Heartworm disease is a preventable, but potentially fatal condition caused by parasitic worms living in the arteries of the lungs and occasionally in the right side of the heart of dogs, cats, ferrets, and other species of mammals. While dogs and cats of any age or breed are susceptible to infection, dogs are primarily at risk. Cats, while susceptible, have proven more resistant hosts to heartworm than dogs. Heartworm can damage the heart muscle, the circulation, and the kidneys of an infected animal. Once infected, treatment is also a dangerous, painful process which can result in lung embolism and sudden death. Prevention is critical for susceptible animals.

Infection: Heartworm is transmitted from one animal to another by mosquitoes. Mosquitoes become infected with microfilariae when taking blood from an infected animal. Microfilariae mature to the infective larva stage within the mosquito. When the mosquito bites another susceptible animal, the infective larvae enter through the bite wound. It takes approximately six months for the infective larvae to mature into adult worms. In dogs, the worms may live for up to seven years.

Signs of Heartworm Disease: Clinical signs of heartworm disease may not be recognized during the early stages of heartworm development in cats and dogs. Once adult worms have developed, dogs and cats may show clinical signs:


  • Mild, persistent cough
  • Exercise intolerance
  • Fatigue after only moderate exercise
  • Reduced appetite and weight loss


  • Vomiting
  • Gagging
  • Difficulty or rapid breathing
  • Lethargy and weight loss

Detection: Heartworm infections are usually detected with a blood test for a heartworm substance called an antigen or microfilariae. Ultrasound and x-ray images of the heart and lungs may also be used on animals with a positive heartworm test and that are already exhibiting clinical signs.

Prevention: There are a variety of safe heartworm preventatives for dogs and cats. When administered properly, infection can be completely prevented. Consult your veterinarian for the appropriate medication for your pet. Before animals can take heartworm preventative, it is imperative that they test negative for the infection due to potentially harmful side effects for infected animals.

Treatment: While prevention of heartworm is easy and affordable, treatment is a complicated, expensive process and requires an animal to be confined for six to eight weeks. Adult heartworms in dogs are killed using a drug called an adulticide that is injected into the muscle through a series of treatments and the recovery period can last from one to two months. There is no effective treatment for heartworm disease in cats.

For more information on heartworm disease visit the Heartworm Society