Heartworm Prevalence

As the temperatures continue to increase, is your pet protected against heartworms and other vector-borne diseases? Mosquitos are now out in full force thanks to an early spring. These mosquitos can infect your pets with heartworms. Dogs are the natural host for heartworms, but cats can also become infected. One single bite is all it takes for your pet to become infected. Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microfilaria (baby worms) that circulate in the bloodstream. When a mosquito bites an infected animal, it picks up these baby worms, which then develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, cat, or wild animal, the infective larvae enter the new host through the mosquito’s bite wound. Once inside a new host, it takes approximately 6 months for the larvae to develop into sexually mature adult heartworms which can produce more microfilaria (baby worms). Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

Each year, the number of heartworm cases seen in the country progressively increases, and there are now confirmed cases in all 50 states. This map demonstrates the difference that just a few years can make in the number of cases. The white areas have no cases, while the dark red areas have many cases.

Due to the mild winter and early spring, the number of heartworm cases is predicted to increase significantly this year if pets go unprotected. The following map displays the predicted number of heartworm cases for 2020. Blue represents a lower number of positive cases; red represents a higher number of positive cases.

In the early stages of heartworm disease in dogs, you might not see any symptoms. However, the longer they are infected, the more likely they are to develop symptoms. Signs of heartworm disease might include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss (not an exhaustive list). As heartworm disease progresses, pets might develop heart failure, and the appearance of a swollen belly might reveal itself due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop sudden blockages of blood flow within the heart, resulting in a life-threatening form of cardiovascular collapse called Caval Syndrome. Caval Syndrome is marked by a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworm blockage, few dogs survive.

For cats, symptoms of heartworm disease are sometimes subtle, but often they can be very serious. Other symptoms can include (but are not limited to) the following: coughing, asthma-like attacks, periodic vomiting, lack of appetite, or weight loss. Occasionally, an affected cat might have difficulty walking, experience fainting or seizures, or suffer from fluid accumulation in the abdomen. Unfortunately, the first sign in some cases is the sudden collapse of the cat, or even sudden death.

So, what can you do to keep your pet safe? It is recommended to test your dog and/or cat for heartworms annually and keep your pet (dogs and cats) on a heartworm preventative year-round—regardless of whether they are predominantly indoor or outdoor, since mosquitos can easily come into the house through an open door. Here are a few different varieties of heartworm medications available:

  • Chewable tablets given monthly: These are flavored, and many pets enjoy them.

  • 6- or 12-month injection: Great if your pet does not prefer to eat a tablet, or if your pet has food allergies. This is also a great option if you have a difficult time remembering monthly treatments.

  • Topical liquid between shoulders given monthly: This may not be the best option if the patient swims often or is bathed frequently, as medication can wash off.

If you are unsure which is the best option for your pet, contact your veterinarian. They will be happy to guide you to the choice that is the best option to keep your pet safe and protected!