Heartworm Disease and Prevention

pet heartworm prevention

Spring is right around the corner, and with it comes warmer weather, more outdoor time – and of course, creepy, crawly bugs. Among the most annoying can be the flying variety, namely, mosquitoes. And although the bite of a mosquito can be uncomfortable, it can also pose serious and even deadly risks for your pet.

All is takes is one mosquito bite to transmit heartworm to pets. Once thought of as only a problem in the southern states, heartworm disease is now found in all 50 states and Canada. An infected pet faces permanent organ damage to the heart and lungs, or death. So what’s a conscientious pet owner to do?

Let Berks Animal Emergency and Referral Center walk you through the basics of heartworm disease and prevention.

What Is Heartworm Disease?

Heartworm disease is caused by the mosquito borne parasite, Dirofilaria immitis. The mature heartworm is up to 12 inches long and lives in the heart and pulmonary arteries of infected pets and wildlife (coyotes are a main carrier).

The basic steps to infection are:

  • A mosquito bites an infected animal and takes up heartworm larvae, or microfilariae, into its body
  • The microfilariae develop in the mosquito’s boy for 10 -30 days
  • The mosquito bites an uninfected animal, and injects the microfilariae into the pet’s bloodstream
  • The microfilariae circulate in the pet’s bloodstream and develop further over the course of several weeks.
  • Microfilariae find their way to the pet’s heart and pulmonary arteries, where they mature into adult heartworms.
  • After 6-7 months, the adult heartworms release new baby microfilariae into the bloodstream. The pet can now pass the disease on to other animals with a new mosquito bite.

Signs of Heartworm Disease

The signs of heartworm disease may be subtle at first, and resemble signs of other diseases. For these reasons, diagnosis is rarely made based on clinical signs.

Signs of heartworm in dogs:

  • Soft, dry cough
  • Exercise intolerance
  • lethargy
  • Weight loss
  • Rapid breathing
  • Bulging chest
  • Collapse

Signs of heartworm in cats:

  • Wheezing
  • Sudden onset cough
  • Rapid breathing
  • Vomiting
  • Weight loss
  • Sudden death


In dogs, diagnosis is usually made with a combination of diagnostic tests. Cats are resistant hosts for heartworm, which makes diagnosis extremely challenging if not impossible. The American Heartworm Society states that cats are underdiagnosed, and even those few worms present cause heartworm associated respiratory distress (HARD) and other life threatening complications.

Treatment and Prevention of Heartworm Disease

In dogs, treatment includes injections that kill the adult worms over a period of several weeks. The dead and dying worms pose a great risk to the dog, as fragments can block pulmonary arteries, impacting blood and oxygen flow to the heart and lungs. Most dogs need to be hospitalized for monitoring post injection due to the risk of respiratory distress or sudden collapse. All dogs should be on exercise restriction during the entire course of treatment to mitigate these risks at home.

Sadly, the same drug has not been approved for use in cats. This drug can have serious side effects in cats, including pulmonary failure and death. Some choose to treat anyway, and hope there is no reaction. Others treat the symptoms of heartworm disease with a combination of oxygen therapy, corticosteroids, and other medications if needed. Surgical removal of heartworms is a relatively new technique that may become more common in the future.

Prevention – Your Best Medicine

You may be convinced by now that prevention is the best way to tackle the heartworm problem, and we couldn’t agree more! Prevention is simple, effective, and cost effective compared with the costs of treatment and managing disease complications.

Year-round protection against heartworm is essential. Once you and your veterinarian choose a preventive medication, it’s important that it be given on schedule. Microfilariae take about 51 days to mature to the adult worm stage, and it’s critical to interrupt this process every month to avoid organ damage and the other serious consequences of the disease.  And with iCal and other electronic reminders, it’s easy for everyone to remember when their pet’s dose is due.

If you have questions or concerns about heartworm disease and your pet, please don’t hesitate to contact us.