According to the Companion Animal Parasite Council’s 2024 Pet Parasite Forecast, the heartworm population is expanding across the United States, and the disease has now been diagnosed in all 50 states. Our Rustebakke Veterinary Service team wants your pet to be protected, and we provide information about heartworm disease and how to safeguard your four-legged friend.

How heartworm disease is transmitted to pets

Heartworms are transmitted by infected mosquitoes. When a pesky mosquito takes a blood meal from an infected dog or wild canid, they ingest baby heartworms—microfilariae. The immature parasites develop inside the mosquito and are passed to your pet when the bloodsucking insect chooses them for its next meal. 

Coyotes are prevalent in Washington state, with the population increasing. The wild canid acts as a heartworm reservoir, which puts your four-legged friend at risk since a hungry mosquito can easily feed on your pet after ingesting microfilariae from an infected coyote.

Heartworm consequences in pets

Once inside your pet, microfilariae travel through your furry pal’s body, eventually establishing themselves in the blood vessels that supply the lungs. Heartworms affect dogs and cats differently:

  • Dogs — Dogs are definitive heartworm hosts, which means that the parasites can mature to adulthood and reproduce while in your canine friend’s body. If your dog’s heartworm disease is left untreated, 100 worms or more can infect their heart. The inflammation caused by the parasites’ presence leads to vessel thickening, making the heart less able to effectively pump blood throughout the body. In addition, if enough worms are present, they can cause a blockage inside the heart, causing caval syndrome, which is a life-threatening condition that requires the worms’ prompt surgical removal to prevent the affected dog’s death.
  • Cats — Cats are atypical heartworm hosts, and their immune system typically reacts strongly to the microfilariae, which can lead to a severe inflammatory response that causes heartworm-associated respiratory disease (HARD). Heartworms don’t typically grow to adulthood inside cats, but if even one or two worms grow large, they can significantly block the cat’s tiny heart. 

Heartworm signs in pets

Most pets show no signs in the initial heartworm infection stages, and in some cases, particularly in cats, the first sign is death. When signs manifest they can include:

  • Dogs — Weakness, exercise intolerance, soft, persistent cough, excessive panting, and distended abdomen
  • Cats — Vomiting, open-mouthed breathing, increased respiration rate and effort, difficulty breathing, and collapse

Heartworm diagnosis in pets

The American Heartworm Society (AHS) recommends that all dogs 7 months of age and older be tested for heartworms annually even if they are on year-round heartworm prevention. This is the best way to detect infection early when the parasites are easier to treat. Heartworm testing is more difficult in cats and may include blood tests and imaging such as X-rays and ultrasound.

Heartworm treatment in pets

All pets diagnosed with heartworms must be strictly confined because activity can exacerbate the damage done by the parasites. For dogs, treatment involves administering medications over several weeks or months to slowly kill the heartworms at every life stage. The process can cause severe health complications as the worms die off, and your pet must be monitored carefully. Treatment is often successful, but your dog may have permanent heart or lung damage that must be managed long-term. No treatment is available for cats, and management focuses on supportive care.

Heartworm prevention in pets

Fortunately, heartworm disease is easily prevented in pets by providing year-round heartworm preventive medication. You can administer oral or spot-on products monthly, or our veterinary team can give your pet an injection every 6 to 12 months to prevent the parasites. 

Don’t leave your four-legged friend at risk for heartworm disease. Contact our Rustebakke Veterinary Service team today to determine the heartworm preventive that would be most effective for your pet.