Heartworm disease is a potentially life-threatening mosquito-borne parasitic infection that affects dogs, cats, and ferrets. Fortunately, diligent preventive care can protect your pet from this dangerous disease. Learn the truth—and consequences—about heartworm disease in this guide from Safe Harbor Animal Hospital.

Truth: Heartworm disease is preventable in pets

Heartworm disease in dogs can be prevented by administering heartworm preventives year-round and performing annual heartworm screening tests. Preventives are safe, convenient, and effective, and many modern products provide up to 100% protection against heartworm infection when used as directed. Heartworm preventives for dogs are available in oral chews and tablets, topical liquid applications, and a long-acting injectable medication. Unlike flea and tick medication, heartworm preventives are available only by prescription and not over-the-counter.

Consequence: Heartworm-positive pets can experience significant suffering and death

Adult heartworms invade the major vessels, lungs, and heart and cause damaging inflammation and dangerous blockages that obstruct blood flow, which forces the heart to work overtime and ultimately strains the heart muscle. Heartworm-positive pets may also experience heart failure, respiratory compromise, and worm emboli (i.e., sudden, lethal, clot-like blockages formed by migrating or dying worms).

Truth: Early heartworm disease signs aren’t obvious in pets

For the first four to six months after infection, heartworm-positive pets may look and behave normally, and show no visible illness signs or only vague nonspecific changes. As the juvenile heartworms (i.e., microfilariae) reach your pet’s major vessels, lungs, and heart, and mature into adult worms, their full wrath becomes apparent.

Consequence: Clinical signs indicate an established heartworm infection in pets

Clinical signs in pets reflect the internal lung and cardiovascular inflammation caused by migrating microfilariae and mature adult worms. These signs may include:

  • Persistent cough
  • Respiratory distress 
  • Exercise intolerance
  • Weakness or fatigue after brief physical activity
  • Inappetence
  • Abdominal swelling (i.e., pot-bellied appearance)
  • Weight loss
  • Vomiting
  • Collapse
  • Sudden death

Truth: Feline heartworm disease looks different

Unlike dogs, cats are not natural heartworm hosts, meaning that their internal environment is less hospitable to the growing parasite. Cats can mount an immune response to microfilariae and clear many of the juvenile worms from circulation. Unfortunately, this immune response and the dying microfilariae can result in additional inflammation in the small lung passages (i.e., bronchioles) and a collection of respiratory signs known as heartworm-associated respiratory disease (HARD).

Also, cats and ferrets have relatively minor infections (i.e., one or two adult worms) compared with dogs, but a single adult worm can fatally damage their small hearts.  

Consequence: Feline heartworm disease is underdiagnosed

Feline heartworm disease is more common than veterinary experts previously believed, but has been frequently misdiagnosed because the presentation is atypical. For example, the persistent coughing, gagging, and difficulty breathing associated with HARD is outwardly identical to feline asthma.

Alternatively, some heartworm positive cats are completely asymptomatic (i.e., show no visible signs) and the only clinical sign is unexplained, sudden death.

Truth: Year-round prevention is essential for pets

Despite common belief, heartworm disease is not a seasonal threat. Although mosquito populations surge during warm and humid months, they can emerge from winter hibernation on mild weather days and feed on your unprotected pet. Infected mosquitoes can also sneak inside and overwinter in your garage or basement, lying in wait for their next blood meal. 

Continuous heartworm preventive administration is the only way to outsmart this persistent parasite and prevent dangerous gaps in your pet’s prevention.

Consequence: One missed dose can leave your pet vulnerable to heartworm disease

Consistent dosing is essential to prevent heartworm disease, because preventives work retroactively, eliminating any circulating microfilariae from the past 30 days. If you pause your pet’s preventives, forget to give a dose, or—unbeknownst to you—your pet vomits their oral medication, any circulating microfilariae can mature to the next growth stage where prevention medication will no longer affect them and they will mature into adult worms. Remember—always give your pet’s oral medication with a full meal to prevent digestive upset.

Set in place a system for success that will ensure you never miss a dose. This can include phone reminders, calendars, or email notifications from preventive manufacturers.

Truth: Heartworm treatment is available only for dogs

Canine heartworm disease is treatable, but not without significant risks and costs. Heartworm treatment is an expensive and prolonged process (i.e., up to six months) during which dogs receive a series of deep, intramuscular injections to kill circulating adult heartworms and are kept on strict crate rest to prevent potentially life-threatening complications.

Prognosis is generally related to disease severity, with early diagnosis ensuring the best possible outcome, and advanced disease likely causing permanent cardiovascular damage.

Consequence: Heartworm prevention is the only option for cats and ferrets

Unfortunately, no safe heartworm treatment is available for cats or ferrets. However, affected pets can benefit from supportive care measures that may reduce inflammatory damage, minimize clinical signs, and provide an improved quality of life for as long as possible. Without an effective cure, prevention truly is the best and only option for these pets.

Heartworms may seem a distant threat until your pet is directly affected by this horrible and heartbreaking disease. Understanding the truth about heartworm disease and the consequences of inadequate prevention are the first steps toward ensuring a strong defense—and a long and healthy life—for your four-legged friend. 

Let us help you protect your pet. Contact Safe Harbor Animal Hospital, which is an Animal Hospitals of the Low Country practice, to schedule an appointment for an examination that includes heartworm testing and prevention advice.