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06 Oct, 2022
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Heartworms & Pets – H&S Pets Galore

Everything You Need To Know About Heartworms In Cats & Dogs

Every pet owner must know that heartworm disease is a serious disease that can be fatal, but, the good news is that it is entirely preventable. The worms are known as ‘heartworms’ as they live in the heart, lungs and associated blood vessels of your infected pet. The disease is caused by a parasitic worm ‘Dirofilaria Immitis’, which is spread through the bite of an infected mosquito. Cats when compared to dogs, are somewhat resistant to heartworm disease, having an infection rate of 5-20%. Cats are also known to have fewer adult worms usually less than 6 and live in a cat for about 2 to 3 years, and interestingly, about 1/3 of infected cats live indoors. However, infections are likely more lethal in cats than in dogs. In dogs, the average number of worms found are 15, but they can range anywhere from 1 to 250 worms and can live for 5 to 7 years. Remember, this is not a contagious disease and only spreads with the bite of an infected mosquito.

Clinical Findings, Detection, Testing, Treatment & Prevention Of Heartworms 

Dogs are more susceptible to getting heartworm disease as they make an ideal host and spend a lot more time outside, however, cats too can get even if they are indoors as mosquitoes can get through your balconies, windows, etc and as stated infection in cats is more lethal than in dogs.

Clinical Findings In Dogs & Cats:

Clinical Findings In Dogs: Heartworm infections are ideally identified in dogs by a simple blood test, before onset of signs & symptoms. If your dog is not tested or given prophylactic treatment, infection may progress undetected. Some of the signs may include cough, shortness of breath, ascites, collapse. Remember, not all infected dogs may show the signs. It’s therefore advisable to not wait or rely on this. Make sure your pet is on a prophylaxis by age 8 weeks, and if not then get your pet immediately to be checked by a vet!

Clinical Findings In Cats: Infected cats may either be asymptomatic or have the following symptoms: cough, shortness of breath, vomiting, lethargy, weight loss etc. Again it’s best not to wait for the signs to show, but rather have your cat on a prophylactic treatment by 8 weeks of age.

Detection & Testing:

For cats & dogs, Antigen Testing can be done.

Heartworm Detection In Dogs: Antigen testing is the most sensitive and specific diagnostic method. However, timing of the test is of paramount importance as it can only detect adult female worms. A reasonable interval is therefore, 7 months after last possible exposure. Annual antigen testing is also recommended.

Heartworm Detection In Cats: Diagnosis is mainly based on history along with clinical signs and tests. An antigen test alone, is considered unreliable in cats but is recommended in cats suspected of having heartworm infection. Thus antigen test for screening in cats is not the choice of test because of its low sensitivity. However the antibody test is the preferred test for cats as it detects heartworms.

Treatment In Cats & Dogs:

Unfortunately, there is no effective treatment for cats who test positive, the only hope is that a cat outlives the worms. Your vet may give symptomatic treatment, if your cat is in crisis, by treating with oxygen, steroids & diuretics to relieve the reaction within the pulmonary arteries and lungs. Once stable, steroids may be continued to reduce the signs and improve the quality of their life. But pet owners must be aware of the threat of acute crisis and sudden death.

On the other hand there is a treatment for dogs who have been tested positive. Melarsomine dihydrochloride, Doxycycline along with Ivermectin are used to kill adult worms. An alternative treatment where a macrolide along with Doxycycline too can be considered. But remember, the treatment is not easy on dogs. Treatment can be toxic leading to serious complications such as blood clots to the lungs. Exercise restriction is also insisted upon, post-adulticidal treatment to minimize pulmonary thromboembolic complications. The treatment can be expensive as it can go on for several months requiring multiple visits, blood test, x-rays, hospitalization etc.


It’s therefore important to start preventive treatment in puppies & cats by 8 weeks of age with macrolide prophylaxis, which is then continued lifelong. Puppies older than 6 months must get tested before starting the preventive treatment because preventive medication given to a puppy with heartworms can prove more harmful, as they don’t kill adult worms, but may kill the microfilariae suddenly triggering a shock-like response in your pet. There is no need for testing in cats before starting treatment, because cats have no or small numbers of microfilariae, and if present they are typically transient.

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