Heartworm Disease in Pets

Heartworm disease is a serious, but preventable problem for dogs and cats worldwide.  The disease is transmitted by mosquitos, so any pet that goes outdoors is at risk, and even indoor pets are at risk since mosquitoes can easily sneak into the house and bite your pet.  The worms are 12 inches long and live in the heart and lungs of the host.


Symptoms of Heartworm Disease in Pets

The symptoms of heartworm disease can vary in presentation from animal to animal and/or depending on the severity of the infection.

Unfortunately, most dogs do not show any signs of heartworm infection until they are in heart failure.  Dogs may lose weight, act tired or reluctant to exercise in the early stages of the disease.   Worms living in the blood vessels of the lungs can cause damage leading to shortness of breath or coughing.  If there are enough worms to cause blockage in the right side of the heart, then right heart failure will develop.  Fluid will build up in the dogs abdomen and the dog will be too weak to move and can die.  Heartworms can also cause sudden collapse and death if the worms create a blockage in the vena cava, a huge blood vessel that exits the heart.  Kidney and liver failure are also a possibility. In cats, heartworm disease is a little different.  Worms rarely grow to adults but can still cause severe respiratory disease and permanent lung damage. 

Cats may have no symptoms, symptoms similar to dogs, or different symptoms like vomiting, diarrhea, blindness, head tilt, circling, seizures, and sudden death.

Diagnosis of Heartworm Disease

After a mosquito bites your dog or cat, it has to grow from a larval stage into an adult before the pet can be tested positive for heartworms.  The growth and development process of the heartworm takes about 6 months, which is why puppies under 6 months of age are not tested.  The test itself, however, is a simple blood test.

Adult dogs should be tested prior to taking heartworm prevention and then annually even if they are on prevention, so the disease can be detected as early as possible.  If your dog or cat has less than three worms or only male worms, the test could be falsely negative.  The more worms your pet has, the more likely they are to get sick. Cats can be difficult to diagnose since they usually only have 1-4 worms at a time.

Treatment of Heartworm Disease

Heartworm treatment is only available for dogs, and the treatment method selected depends on the stage of the disease.  Your vet will want to run blood tests to check all the major organs and xrays or additional tests to see how much damage has occurred to the heart and lungs.  A dog who already has heart failure, lung issues (pneumonitis), liver or kidney problems will need extra medications to treat these issues prior to treatment for heartworms.

Two or three injections of immiticide will be given by the vet to kill the adult worms.  These worms have to die and break apart, and be resorbed by the body, a process which takes 2-4 weeks.   Exercise needs to be restricted for up to 2 months after treatment, and additional medications may be required, depending on the severity of the infection. 

Side effects of the adulticide are rare, usually just transient pain and swelling at the injection site.  Some veterinarians will give an antibiotic in cases of severe infection and/or a separate dose of medicine to kill any "baby" heartworms (microfilariae) the adults have produced. 

There is currently no treatment available to kill adult heartworms from cats, but they should be placed on monthly prevention if they test positive because many of them will naturally  eliminate the heartworms from their bodies within a few years.  

Heartworm Prevention

There are many products on the market which can be given to prevent heartworm infections in dogs and cats.  The once-a-month medications are given as a pill or as a topical fluid that is applied to the skin between the shoulder blades. There is also an injection which can be given every 6 months. Preventatives may seem expensive to some pet parents, but they are much cheaper than the heartworm treatment and can save your pet from a fatal disease!

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