Parasitic worms cause heartworm disease—a potentially fatal but preventable infection. Heartworm disease causes lasting damage to an infected pet’s heart, lungs, and arteries, and can negatively impact their health and quality of life long after the parasites are gone. Fortunately, heartworm prevention is effective and can safeguard your pet from this potentially deadly condition. Learn why our Milford Animal Hospital team recommends year-round preventive administration and annual heartworm screening tests for all dogs and cats. 

Heartworm disease is serious and potentially fatal in pets

An infected mosquito’s bite transmits heartworms to an unprotected pet. When an infected mosquito feeds on your pet, they transmit microscopic parasite larvae (i.e., Dirofilaria immitis) into their bloodstream. The larvae slowly migrate to your pet’s large lung and heart vessels, where they mature and can grow to 6 to 12 inches in length. Adult worms inflame and irritate an infected pet’s heart and lung lining, leading to vessel thickening and dangerous—potentially fatal—blockages as the worms die off at various life stages and smaller arteries carry them away. 

Cats and dogs are at risk 

Infection rates are generally lower in cats than in dogs, because cats are not these parasites’ preferred hosts. However, both species are vulnerable to the disease. Cats suffer the same tragic consequences as their canine counterparts, but with no available treatment, heartworm disease is often fatal in affected cats, making preventives and annual testing their only protection. Only one to two adult worms are necessary to make a cat ill, and their subtle disease signs are commonly mistaken for a respiratory condition. As large worms die and form a vascular obstruction, sudden death may occur, which may be the first sign that a cat has contracted heartworm disease. 

Heartworm signs in pets can be subtle

For a pet who has contracted heartworm disease, early treatment is crucial, dramatically increasing their chance of survival. Although detecting an infected pet’s subtle signs can be challenging, to ensure you seek your infected pet’s treatment as early in the disease process as possible, learn to recognize heartworm disease signs. Heartworm-positive cats may be asymptomatic or experience respiratory difficulty that mirrors asthma or bronchitis. 

Dogs will not show signs until heartworm larvae have matured and begin to cause vascular inflammation. At that point, a dog’s early heartworm disease signs may include:

  • Persistent cough
  • Exercise intolerance
  • Lethargy or fatigue

To prevent your pet from contracting heartworm disease, ensure you administer their preventives each month. If your pet is infected, your veterinarian can detect the parasite at their annual wellness visit and provide treatment to prevent the worms from maturing. However, if you forgo either of these prevention strategies, your pet’s infection will go undiagnosed, leading to these additional severe signs:

  • Decreased appetite
  • Weight loss
  • Swollen abdomen 
  • Collapse
  • Heart failure

Pets’ heartworm treatment is complex and expensive 

Veterinarians can detect heartworm disease by performing a simple blood test designed to detect an adult female heartworm’s protein (i.e., antigen),  or heartworm antibodies’ presence. If a pet tests heartworm-positive, their veterinarian will retest their blood to check for microscopic larvae (i.e., microfilariae). 

While heartworm treatment is available for dogs, the process is complex, expensive, and potentially risky. Treatment often requires multiple veterinary visits for blood tests, X-rays, and injections, which can take several months. If your dog is clinically ill, your veterinarian will first stabilize your four-legged friend’s condition, to ensure they are healthy enough for treatment. To prevent excessive damage to your dog’s heart and lungs, you must completely restrict their activity before and during heartworm treatment. Activity restriction is especially important during the treatment phase when the dead and dying worms can form a life-threatening blockage. During the treatment process, your veterinarian will administer a series of deep intramuscular injections to kill off adult heartworms. In severe cases, your veterinarian may perform surgery to physically remove heartworms from your pet’s body.

Heartworm disease can be prevented in pets

By consistently administering your pet’s preventive medication, you can protect your four-legged friend from contracting heartworm disease. The American Heartworm Society encourages owners to give pets 12 months of heartworm preventives and have them tested for heartworms every 12 months. Heartworm preventives eliminate the circulating microfilariae, but do not kill adult heartworms, making heartworm disease testing essential before starting a prevention protocol. Heartworm preventives are typically administered monthly in oral or topical form, although long-term injectable medications are available. While pausing preventives during colder weather may be tempting, this leaves pets vulnerable to infection. For the greatest peace of mind and protection, ensure your pet receives heartworm preventives year-round.

Heartworm disease is a serious condition, but you can easily protect your pet. Your veterinarian can customize your pet’s heartworm prevention protocol, and will perform heartworm testing at each of your pet’s annual wellness examinations. If your pet does not currently have a heartworm prevention plan in place, schedule an examination and heartworm testing with our Milford Animal Hospital team.