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Ask the Vet - Heartworm Disease and My Pet

Updated: Nov 11

Dr. Lopez, DVM:

Veterinarian, Dr. Lopez smiling with cat in her arms

"What is Heartworm and should I worry about it for my pet?"


Heartworm is a parasite that can often get overlooked in California. Historically, heartworm was deemed to not be as common in southern California as compared to other parts of the country (such as the south and midwest).  While this is still true, we are seeing an increase in cases over the years with the expectation that it will continue to become more prominent.


While treatment for heartworm can be costly, prevention is simple.  So what exactly is heartworm?  


Heartworm - this doesn’t ACTUALLY live in an animal’s heart, right? 

Sadly, it does! Heartworm is a thin, long white worm that lives in the heart of an infected animal. They reproduce in the body, and can prevent adequate blood flow in the heart. 


How does an animal get heartworm? 

Heartworm is transmitted by an infected mosquito. If a mosquito bites an animal with heartworm, it can carry the baby heartworm from that blood feeding, and transmit it to the next animal they bite. 


Can indoor-only animals get heartworm? 

Absolutely! Mosquitos can get indoors and transmit that way. 


What are the signs of heartworm disease? 

Dogs - Early in infection, the animal often does not show any signs. But, studies have shown that the heart starts to undergo negative changes soon after the adult heartworm takes up residence in the heart. Later in the disease we can see a cough, sometimes worse with exercise. Late term changes can be consistent with congestive heart failure. This includes severe exercise intolerance, fluid in the belly, pale gums and weight loss. In severe cases, collapse or death can occur. 


Cats - Cats are often asymptomatic, or we may see asthma-like coughing. Sometimes the signs are more vague like decreased appetite or weight loss. In severe cases, collapse or death can occur. 


Cats and heartworm disease 

Cats are more resistant to getting infected with heartworm than dogs, but it is still possible and prevention is still recommended.


So how do I prevent my pet from getting heartworm? 

Luckily, there is a monthly prevention to keep your pet free of heartworm. 


Preventative forms include topical liquid, a pill, a chewable treat, or some vet clinics offer injections (CAMP does not offer the injection form). Often, the topicals or chewables are combined with other preventatives such as flea, tick or deworming medication. 


How do you test for heartworm? 

In dogs, we take a few drops of blood. If we run the test in-clinic, we have the results back within 15-20 minutes. We recommend performing this test prior to starting preventatives, 6 months after starting, and then yearly thereafter, even if on preventatives consistently. 


In cats, testing is optional prior to starting prevention. If electing to test, we use the same in clinic blood test as for dogs. But, if your pet is showing concerning signs, your vet may recommend further testing. 


What preventatives does CAMP have? 

Currently, for dogs CAMP carries Simparica Trio. This prevents fleas, ticks, heartworm, roundworms and hookworms and is a once a month preventative. Your pet will need an exam by one of our veterinarians within the past year and a recent heartworm test. 


For cats, CAMP carries Revolution or Selarid. This prevents fleas and heartworms in cats, and is a once a month topical. Your cat will need an exam by our veterinarian within the past year in order to prescribe it. 


Your veterinarian may recommend another preventative based on your pet’s history or other health issues.


Where can I find more information?

The American Heartworm Society is a great resource for more information: 


In summary, heartworm disease can be dangerous, but luckily prevention can be simple. Talk with your veterinarian to determine which prevention is right for your pet. 

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