South Carolina ranks sixth among states with the highest rates of heartworm-positive pets—perhaps because the Palmetto State is home to at least 61 mosquito species. An infected mosquito that bites your four-legged friend can do more than cause an itchy welt, because they can harbor heartworms, which can significantly damage your pet’s heart and lungs. Fortunately, medications are available that are extremely effective in preventing infection. Our Safe Harbor Animal Hospital team wants to help you protect your furry pal from these dangerous parasites, and we offer information about heartworms and explain how you can safeguard your pet. 

Heartworm transmission in pets

A mosquito that bites a heartworm-infected dog or wild canid ingests baby heartworms, called microfilariae. The immature parasites develop into infective larvae while in the mosquito, and can cause disease after about two weeks. If the mosquito bites your four-legged friend after this time, they can transmit the infective larvae. 

During the first three months after your pet is infected, the parasites migrate throughout your pet’s body, eventually reaching the blood vessels that supply the lungs, where they settle and continue to mature. Females can grow up to 14 inches in length. If male and female heartworms are present, they mate, produce microfilariae, and create a new source of infection for other pets. 

Heartworm consequences in pets

Heartworms are problematic for cats and dogs, but affect each species differently.

  • Dogs — Canines are natural hosts for heartworms, meaning the parasites can complete their life cycle while parasitizing dogs. If left untreated, numerous heartworms can accumulate, causing extensive damage to the dog’s heart, lungs, and vasculature.
  • Cats — Cats are atypical hosts for heartworms, but infection can still result in significant health problems. The cat’s immune system mounts an intense response to the infective larvae, causing a condition known as heartworm-associated respiratory disease (HARD). In addition, if one or two heartworms reach adult size, they can easily block blood flow through the cat’s small heart.

Heartworm signs in pets

Heartworm-infected pets typically don’t show signs until they have significant health problems. When present, signs include:

  • Dogs — Signs in dogs may include a soft, persistent cough, decreased energy, tiring quickly on walks, decreased appetite, and weight loss. As the condition worsens and heart failure develops, the dog’s belly may appear swollen from accumulated fluid. The buildup of worms may block blood flow through the heart, causing a condition called caval syndrome that causes labored breathing, pale gums, dark bloody urine, collapse, and potentially sudden death. This is an emergency situation that requires immediate surgical removal of the worms to save the pet.
  • Cats — HARD causes signs such as coughing, difficulty breathing, increased respiration rate and effort, vomiting, and weight loss. Unfortunately, the first sign in some heartworm-infected cats is sudden collapse or death. 

Heartworm diagnosis in pets

The American Heartworm Society recommends annual heartworm testing for all dogs. These tests are also important for dogs on year-round heartworm prevention, because doses can be missed or your dog may surreptitiously spit out a flavored chew. Annual testing helps detect heartworm infections early when they are easier and safer to treat. Heartworm testing in dogs involves looking for circulating microfilariae and testing for circulating heartworm antigen from adult female worms.

Testing in cats is more difficult, since felines usually don’t have adult worms or circulating microfilariae. In cats, heartworm testing typically involves an antibody test to detect exposure to heartworm larvae. Ultrasounding the heart is also usually helpful. 

Heartworm treatment in pets

No heartworm treatment is available for cats, which means that prevention is the only way to protect your feline friend. Treatment for dogs is available, but the process is costly and dangerous. Heartworm treatment for dogs involves a multi-step process to stabilize the dog’s condition and kill the heartworms at every life stage. The process must be slow, because if a large amount of the worms die all at once, severe complications can occur. All heartworm-infected pets must be kept strictly confined, because during physical exertion, the heartworms further damage the pet’s heart and lungs. 

Heartworm prevention in pets

The good news is that heartworm disease can easily be prevented with year-round heartworm prevention medication. Multiple options that make administration easy and convenient are available. Heartworm preventives include:

  • Chewable pill — You can give your pet a flavored chewable heartworm pill once a month.
  • Topical medication — If your pet turns their nose up at the chewable pill, you can administer a topical, spot-on medication once a month.
  • Injection — If you have difficulty remembering to treat your pet once a month, your veterinarian can administer an injection every 6 to 12 months to protect your furry pal. This option is available only for dogs. 

If your dog is due for their annual heartworm test, or you would like to discuss the best heartworm prevention for your cat, contact our Safe Harbor Animal Hospital team to schedule an appointment.