“Home is where the heart is.”
— Pliny the Elder
No truer words were spoken when it comes to heartworm disease in pets, as these spaghetti-like parasites enjoy making their home in and around your pet’s heart. Via an infected mosquito’s bite, your pet can acquire a serious, potentially fatal, infection of worms that can completely block the large blood vessels surrounding the heart and lungs, and spread to the heart itself. To help protect your pet from this fate, learn about how heartworm disease spreads, signs to watch for, and how you can best protect your furry pal.
What causes heartworm disease in pets?
Heartworm disease is a parasitic infection that is not transmitted directly between pets. Rather, the heartworm must go through a mosquito to complete its life cycle and advance to the infective stage. If we lived in a wonderful mosquito-free world, no heartworms would exist, but unfortunately, that is not the case. Once an infected mosquito bites your cat or dog, immature heartworms (i.e., microfilariae) wriggle their way through your pet’s body to reach their preferred location—the large blood vessels around the heart and lungs. During this migration process, which takes five to six months, the microfilariae cause a massive amount of damage to your pet’s body. By the time the heartworms have reached their final destination, they have matured into adults, and begin reproducing, creating more microfilariae to infect other mosquitoes.
In dogs—the heartworm’s preferred host—adult heartworms can live for five to seven years. However, heartworms don’t find cats as hospitable, and usually survive only two to three years. Despite this shortened lifespan, heartworms can cause tremendous damage to the cat’s heart, lungs, and blood vessels.
What signs will my pet show if they have heartworm disease?
In the beginning stages, you likely won’t see any changes in your pet. Heartworms are insidious creatures, and cause damage long before the pet shows visible signs. Dogs may seem fine for months, and sometimes years, before they show their first sign of heartworm disease, while cats may show no signs.
However, in dogs, keep an eye out for the following signs that may appear as their heartworm disease progresses:
- A dry, persistent cough
- Exercise intolerance
- Fatigue, especially after exercise
- Decreased appetite
- Weight loss
Your dog may eventually develop heart failure, which can be seen with a fluid-filled abdomen and a more pronounced cough. In severe cases, dogs can develop caval syndrome, where the heartworms invade the heart and cause a life-threatening blockage that requires emergency surgical removal.
Since cats are not ideal heartworm hosts, their disease signs are different. Cats may:
- Breathe rapidly
- Lose weight
- Be lethargic
- Struggle to walk normally
In some cases, cats will show no signs, but may suddenly collapse or die.
How will my veterinarian determine if my pet has heartworm disease?
Several factors make an accurate heartworm disease diagnosis difficult to obtain. These include:
- An immature heartworm infection — Standard in-hospital heartworm tests detect only adult heartworms, so if your pet was bitten by an infected mosquito four months ago, they likely won’t test positive for heartworms yet.
- A same-sex heartworm infection — Heartworm tests look for the presence of female adult heartworms, so if your pet has a male-only heartworm infection, their test result will be a false negative.
- A small heartworm infection — If your pet has too few heartworms to produce enough antigen for a test to detect, they’ll receive a false negative result.
- A robust immune response to heartworms — Cats in particular often clear their heartworm infections before the parasites reach adulthood, but this doesn’t mean they are unaffected by immature heartworms.
Annual testing is the best way to screen your pet for potential heartworm disease, and to ensure no gaps are missed. We recommend this screening as part of your pet’s annual wellness examination—with a few drops of blood, we can determine if your pet has heartworm disease, in addition to other serious illnesses.
Can my pet be treated for heartworm disease?
While your dog can be treated for heartworm disease, no approved treatment is available for cats, and symptom management is their only course of treatment. And, while dogs can be treated, the process is tough on their body and can have serious side effects. The treatment process consists of a series of injections administered deep into the lumbar muscles, which can cause pain, lethargy, nausea, and general discomfort. During the injection series, which can take a month, your dog must not participate in any exercise other than going outside to eliminate. After the injections have been completed, your dog will still be exercise-restricted for a month, to help prevent clots of dying worms from forming.
How can I protect my pet from heartworm disease?
Although treatment is difficult—and nonexistent for cats—heartworm prevention is a cinch. A variety of heartworm preventives not only make administration easy, but also often protect against other parasites, such as intestinal worms, fleas, and ticks. Choose from topical liquids applied to the skin, oral pills, or chewable tablets for a tasty treat.
Contact our Companion Veterinary Clinic team to see which heartworm preventive is right for your pet, and to schedule your pet’s heartworm test.
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