If you assume heartworm disease only affects pets in warm climates, you may be surprised to learn that infections have been reported in all 50 states. Heartworm disease is transmitted by mosquitoes infected with heartworm larvae, and the parasites thrive in a variety of conditions. Heartworms can cause devastating disease in pets, but there is good news—the disease is easily prevented. April is National Heartworm Awareness Month, and our Stack Veterinary Hospital team wants to ensure your pet is protected. Learn why pets need year-round prevention to stay safe. 

Heartworm transmission in pets 

Understanding how your pet can be infected with heartworms is essential to protect them. The disease transmission cycle occurs in the following stages:

  • Initial infection — The transmission of heartworms begins when a mosquito bites an animal already infected with heartworm larvae (i.e., microfilariae). Dogs and wild canids, such as wolves, coyotes, foxes, and raccoons, are natural hosts for heartworms. When the mosquito bites an infected animal, it ingests microfilariae along with the blood. These microfilariae are tiny, immature heartworms that circulate in the bloodstream of the infected animal. Eventually, the microfilariae mature and develop into infective larvae within the mosquito’s body.
  • Transmission to pets — When an infected mosquito bites your pet, the microfilariae enter their bloodstream through the wound, and travel through the bloodstream.
  • Migration to the heart — Over time, the microfilariae migrate to the heart and large lung vessels, where they can grow up to 12 inches long. As the worms reproduce and compete for space, they irritate the vessel lining and restrict blood flow, leading to cardiovascular complications, respiratory difficulties, and death in untreated pets.

Your pet’s risk factors

Many pet owners recognize heartworm disease as a canine health concern but do not realize that cats are equally vulnerable. Dogs are the preferred hosts and can be infected with hundreds of worms, but the disease can affect any mammal, including humans. Since cats are not preferred heartworm hosts, they are usually infected with only two or three worms. However, only a few worms can significantly damage a cat’s small heart and lungs. Certain areas of the country carry a higher risk for heartworm disease. Risk factors include:

  • Climate (i.e., temperature and humidity) 
  • Mosquito species in the area
  • Presence of mosquito breeding areas

Heartworm disease can occur in both indoor and outdoor pets. For instance, indoor dogs who go outside to use the bathroom and to exercise are vulnerable to mosquito bites and can also carry feeding mosquitoes back indoors. Because every pet is at risk, the American Heartworm Society recommends year-round heartworm preventives for all pets no matter where they live. 

Heartworm disease signs in pets

The severity of heartworm disease in pets depends on the number of worms, how long the pet has been infected, and how their body responds to the infection. Because heartworm disease progresses slowly, an infected pet may not show visible signs until they are severely affected, which can be six or more months after infection. Signs may include:

  • Coughing or difficulty breathing
  • Decreased appetite
  • Lethargy, fatigue, or unwillingness to exercise
  • Enlarged abdomen 
  • Collapse 

Because most worms in cats do not survive to the adult stage, not all cats with heartworm disease show signs. If they do, the signs will include:

  • Vomiting
  • Decreased activity 
  • Decreased appetite and weight loss
  • Respiratory problems (e.g., trouble breathing, increased respiratory rate, and cough) 

Heartworm treatment for pets

A test is available to determine if a pet has a heartworm infection, with follow-up tests to determine disease severity. Heartworm treatment for dogs includes medication to kill larvae, antibiotics to eliminate heartworm-associated bacteria, and anti-inflammatory medications. During treatment, dogs require strict exercise restriction to prevent the dying heartworms from causing deadly blood flow obstructions. Unfortunately, cats are unable to tolerate canine heartworm medication, and no feline treatment is available.

Heartworm prevention in pets

Heartworm prevention is the best way to guard against heartworm disease. Preventive medication works by destroying microfilariae before they can mature into damaging adult worms. You can also reduce your pet’s likelihood of mosquito bites by using flea and tick preventives that contain pet-safe mosquito repellent. A heartworm test is recommended annually for dogs, including those receiving a heartworm preventive. This is a simple and easy way to ensure their medication is effective and a breakthrough infection has not occurred.

Heartworm disease can be devastating, and prevention is the best strategy to protect your pet. Schedule your pet’s next wellness visit, heartworm test, or heartworm prevention consultation with our team at Stack Veterinary Hospital.