Humans abhor mosquitoes—arguably the worst summer pests—and hate their itchy bites. But, in pets, mosquitoes cause more than itchy welts—they also transmit deadly heartworms. If your pet contracts a heartworm infection, treatment can be painful, costly and lengthy, restricting your pet’s activities for months. Fortunately, heartworm disease is preventable. 

April is National Heartworm Awareness Month, and your Towne Centre Animal Hospital team is here to answer your most frequently asked questions about heartworms and preventing possible life-threatening disease in your pet .

Question: What are heartworms?

Answer: Heartworms are parasitic worms that live in the pet’s blood vessels around the heart and lungs. These parasitic worms are different from intestinal worms, and cannot be killed with a standard deworming treatment. Heartworms can grow to a foot in length, and prefer to live inside canine hosts, including dogs, wolves, coyotes, and foxes. They can also infect cats, but they are considered “dead-end” hosts (i.e., a species in which the worms cannot reproduce). Heartworms cause inflammation and permanent damage to the host’s heart and lungs, and may cause death if left untreated. 

Q: How do heartworms reach your pet?

A: Adult worms live and reproduce inside their preferred canine hosts, who are a reservoir for infection. Microscopic immature worms (i.e., microfilariae) circulate in the reservoir’s blood, where mosquitoes ingest them through bites. The worms mature inside the mosquito before being transmitted to the next suitable host through a bite. The immature worms take months to make their way through body tissues to reach the heart and lungs, where they become reproductive adults. Heartworm disease has been found in all 50 states, and only one unfortunate mosquito bite can transmit disease.

Q: What are dogs’ heartworm signs?

A: Dogs are heartworms’ preferred hosts. Heartworms reproduce and increase quickly, making it possible for a dog to host anywhere from 30 to several hundred heartworms at one time—and the more worms, the worse the clinical picture. After they first infect dogs, the worms reach adulthood in about six months, causing no signs during this time. Signs may not be seen for months or years, and may include:

  • Coughing
  • Exercise intolerance
  • Weight loss
  • Fluid in the abdomen
  • Heart failure
  • Death

Q: What are cats’ heartworm signs?

A: Cats are not heartworms’ preferred hosts, and can usually host only one to six worms, many of which will die before reaching adulthood. Heartworms that do survive in a feline host cause serious inflammation and heartworm associated respiratory disease (HARD). Despite hosting fewer worms than dogs, cats are more likely to die suddenly from heartworm infection, which may be the infection’s first and only sign. Cats’ disease signs can be misleading, because they mimic conditions like asthma, hairballs, or intestinal problems. Signs may include:

  • Weight loss
  • Vomiting
  • Coughing, wheezing, or difficulty breathing
  • Seizures

Q: Can my pet be screened for heartworms?

A: A simple blood test can indicate whether a dog has adult heartworms. A different blood test indicates a cat has heartworms, and because a cat may have only one worm, additional testing may be required for confirmation. Although your veterinarian will recommend the best schedule for your pet, dogs should have an annual heartworm screening that may be done more frequently for those who are newly adopted, have had a heartworm infection, or have missed monthly preventives. Your veterinarian will recommend a feline heartworm screening if your cat’s signs are confounding. 

Q: What happens if my pet gets heartworms?

A: Adult heartworms are difficult to kill, and only one approved canine treatment is available.  During a several-month period, a dog receives two deep spinal muscle injections, and then is hospitalized and closely monitored. Most dogs also receive steroid and antibiotic medications during treatment to prevent allergic reactions caused by the dying worms, and to kill their associated bacteria.

Unfortunately, cats are unable to tolerate canine heartworm medication, and no feline treatment is available. Cats infected with heartworm receive medications to reduce inflammation and heart and lung damage, and will need close monitoring by your veterinarian for a few years until their heartworms have died. These cats must receive preventive medication to ensure they are not infected with additional worms. Some cats may die, despite supportive care.

Q: Is my pet uncomfortable during heartworm treatment?

A: Canine heartworm treatment injections are painful and can cause discomfort for several days, or longer. This treatment’s most challenging aspect is the exercise restriction for its duration. Dogs must remain calm and avoid exertion, meaning no playing, running, dog park visits, or anything fun for several months. For most pet owners, this is a challenging time—logistically and emotionally. In addition, canine heartworm treatment can be costly.

Q: How do I prevent my pet from getting heartworms?

A: Monthly preventives retroactively kill immature worms. Your veterinarian will prescribe medication after confirming your pet is negative for infection, and will help determine which formulation is right for you. Heartworm preventives are inexpensive, easy to administer, and a far better alternative to treatment. These medications can also protect your pet from intestinal parasites that pose a threat to humans. Your pet must receive monthly preventives year-round to be effective.

Q: Does my indoor cat need heartworm prevention?

A: One in four heartworm-infected cats lives indoors. Remember, mosquitoes can easily enter your home, and therefore all pets, including those who stay indoors, should receive preventives. Heartworm disease is especially devastating in cats, because no treatment is available, making prevention the only option.

Your pet, like you, no doubt finds mosquitoes a nuisance, but do not allow heartworm disease to threaten their health, as well. If your pet is due for a wellness examination and heartworm screening, or they need to begin a heartworm prevention protocol, schedule a visit with our Towne Centre Animal Hospital team.