A single mosquito bite can transmit heartworms to your pet, and year-round prevention is necessary to protect your four-legged friend from these harmful parasites. Our Stanton Pet Hospital team strives to maintain every pet’s health and we provide information you should know about heartworm disease and prevention.

Heartworm transmission to pets

Dogs and wild canids, such as coyotes, wolves, foxes, and raccoons, are natural heartworm hosts, and when a mosquito bites an infected natural host, the insect ingests baby heartworms (i.e., microfilariae). The microfilariae incubate inside the mosquito for several weeks, and when they are ready, they migrate to the mosquito’s mouth. When the mosquito takes its next blood meal, the microfilariae are deposited in the insect’s saliva, and they swim through the mosquito bite to infect the new host. Heartworms are most comfortable infecting canine species, but cats and ferrets can also be infected. Initially, the microfilariae circulate through the pet’s body, and after five to seven months, they find their way to the heart and pulmonary arteries in which they make themselves at home. Inside their natural hosts, heartworms mate and produce microfilariae, providing another heartworm infection source.

Heartworm disease signs in pets

Pets often don’t exhibit signs during early heartworm disease. The parasites affect each species differently:

  • Dogs — In dogs, heartworms lodge in the blood vessels that supply the lungs, and they can grow to about 12 inches in length. A dog’s immune system recognizes the worms as foreign and creates inflammation, resulting in enlarged pulmonary arteries, which can lead to lung vasculature scarring that creates a high-pressure area, inhibiting the heart’s ability to pump blood effectively. In addition, when the worms die, their bodies break apart and can lodge in vessels, obstructing blood flow. As the disease progresses, a dog’s signs may include coughing, heavy panting, exercise intolerance, lethargy, nose bleeds, abdominal fluid accumulation, and sudden death. If many worms are present, they can completely obstruct blood flow through the heart (i.e., caval syndrome), causing collapse, labored breathing, muddy mucous membranes, and coffee-colored urine. In these cases, prompt surgery to remove the worms is necessary to save the dog’s life.
  • Cats — Cats are not natural heartworm hosts, and their immune system clears many of the microfilariae. However, a cat’s heart is small, and a single worm can take up significant room in the tiny space. In addition, an affected cat can experience heartworm-associated respiratory disease (HARD), which occurs when the microfilariae reach the pulmonary arteries, and the cat’s immune system reacts strongly, resulting in severe inflammation and lung disease. Of cats who have heartworm disease, the first sign 10% to 20% of them exhibit is sudden death. Cats’ other potential heartworm disease signs include coughing, wheezing, difficulty breathing, and vomiting.

Heartworm disease diagnosis in pets

Diagnosing heartworm disease is not always straightforward, especially in cats. Our Stanton Pet Hospital team may perform one or more of the following tests to check for heartworms:

  • Antigen testing — This test detects circulating antigens produced by adult female worms and can provide a positive result 6.5 to 7 months after infection. Antigen tests will produce a false negative if:
    • The infection is present for fewer than five months.
    • The worms are all male.
    • The worm load is low.
  • Microfilariae testing — If microfilariae are present in the bloodstream, we can observe them in specially prepared blood smears. False negatives can occur if:
    • No adult worms are present.
    • All adult worms are one sex, so mating can’t occur.
    • Microfilariae numbers are too low.

  • Antibody testing — The antibody test detects exposure to the heartworm larvae and is the preferred method for heartworm testing in cats, because they often don’t have enough adult worms to produce heartworm antigens or microfilariae. 
  • Imaging — X-rays and ultrasound are also helpful when diagnosing pets’ heartworm disease. 

Heartworm disease treatment in pets

No approved heartworm disease medication is available for cats, and treatment focuses on supportive care and decreasing parasite-induced inflammation. Treatment for dogs can be dangerous and involves:

  • Stabilization — If your dog has heartworm disease, we must first stabilize them to ensure they are prepared for heartworm treatment.
  • Exercise restriction — Physical activity can exacerbate the damage heartworms cause, and you must confine your affected dog.
  • Anti-inflammatories — Our team will prescribe anti-inflammatory medications. These drugs are necessary to control parasite-induced inflammation.
  • Antibiotics — Heartworms are infected by the bacteria Wolbachia, which intensifies the inflammatory response. Our team prescribes antibiotics to kill these pathogens.
  • Microfilariae treatment — We prescribe medications to clear microfilariae.
  • Adult heartworm treatment — If your dog has adult heartworms, we must administer multiple intramuscular injections deep in their lower back muscles. Embolism-related problems can occur as the worms die, and strict confinement is critical during the first few days after this treatment.
  • Retesting — Approximately nine months after treatment, we retest your dog to confirm that the treatment has been effective in eliminating all the heartworms.

Heartworm prevention in pets

The best way to protect your pet from heartworms is to provide year-round heartworm prevention. Preventives are available in many forms, including topical applications and chewable pills that you administer monthly. If you prefer, you can schedule a veterinary visit every 6 to 12 months, so our team can administer your pet’s injectable preventive medications. 

Contact our Stanton Pet Hospital team, so we can test your pet for heartworms and determine what heartworm preventive is most effective for your four-legged friend.