Getting to Know the Enemy: Protecting Pets from Heartworm Disease

May 01

Categories: Pet Care

Getting to Know the Enemy: Protecting Pets from Heartworm Disease

We’ve all heard “knowledge is power.” The phrase rings true when it comes to our pets, because more knowledge can help us make better decisions about their health. With the risk of heartworm infection increasing every year, the Cherry Hill Animal Hospital team wants to teach you about these dangerous pests.


Lifecycle of a heartworm

  1. A mosquito bites a heartworm-positive dog and ingests a few larvae.
  2. Inside the mosquito, the larvae develop into the infective stage.
  3. The infected mosquito bites a pet and transfers the infective larvae into her tissue.
  4. The larvae develop in the pet’s tissues during the next four to six weeks. At this stage, the larvae are vulnerable to heartworm preventives.
  5. The worm develops into a juvenile adult, or microfilaria, and moves into the bloodstream, where it spends another four to six months growing into a mature heartworm. Worms can grow up to 12 inches long. The microfilariae are no longer vulnerable to preventives and must be killed with different medication.
  6. After reaching adulthood, the heartworm can live up to seven years. If at least one adult male and one adult female are present, they will breed and create new larvae, and the lifecycle can continue.

How heartworm disease affects pets

Of domestic pets, heartworms can infect dogs, cats, and ferrets. After any victim is infected, the worms set up residency in the pulmonary artery, the blood vessel that connects the heart with the lungs. There the worms start creating new worms, which grow into adult worms that also live in the pulmonary artery and the heart. Infection signs start to show when enough worms are inside the blood vessel to affect blood flow. In dogs, these symptoms include:

  • Mild, persistent cough
  • Reluctance to exercise
  • Being unusually tired after moderate exercise
  • Decreased appetite
  • Weight loss
  • Heart failure
  • Fluid in the abdomen
  • Labored breathing

In cats, symptoms can include:

  • Coughing
  • Asthma-like attacks
  • Occasional vomiting
  • Decreased appetite
  • Weight loss
  • Difficulty walking
  • Fainting or seizures
  • Fluid in the abdomen
  • Collapse
  • Sudden death

Treating heartworm disease

Unfortunately, no treatment is available for heartworm infection in cats, and owners can only keep them safe by giving a heartworm preventive. Dogs are better able to handle the medication needed to kill the adult worms, but treatment is lengthy and tightly controlled because of the potential complications caused by the dead worms in the bloodstream.

Here’s what to expect if your dog tests positive for heartworm disease:

  1. Because the first test can sometimes produce a false positive, a second, different type of test is performed to confirm heartworm infection. Treatment is lengthy and difficult, making confirmation crucial in case treatment can be avoided.
  2. Exercise restriction is important as soon as the diagnosis is confirmed. Depending on infection severity, the heart and lungs may be damaged. Exercise increases the risk of signs from infection, as well as side effects from treatment.
  3. Before treatment, your veterinarian may need to test for and treat any other health issues. Heartworm treatment should begin only when your dog is in otherwise excellent health.
  4. Once your veterinarian determines it’s safe to begin treatment, medication injections will be administered 30 days apart. Exercise restriction should continue for six to eight weeks following the last injection.
  5. Retesting is recommended twice—at 30 days and nine months after the last injection to confirm successful treatment.

The best way to minimize risk of heartworm infection is keeping your pet on year-round heartworm preventive medication. An annual heartworm test is recommended, because missed or late doses can leave a small window open for the developing worm to reach the bloodstream. Also, small pockets of resistant heartworms have been found in the United States. Make an appointment with our team to test your pet for heartworm disease and to stock up on preventive.

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