Is your pet at risk of heartworm?

In many countries across the world, the word “heartworm” is enough to make vets and pet owners shudder. This potentially fatal parasite has infected pets all over the world. While mosquitoes don’t carry infections in the UK, that doesn’t mean our pets are off the hook from heartworm. With the numbers of people and their pets travelling internationally picking up since Covid AND significantly increased numbers of pet adoption outside the UK, our pets are all but safe from heartworm infection. So if you’re travelling abroad with your pet or have adopted them from a warm climate, keep an eye out for Heartworm. 

What is heartworm?

Heartworm is the general term used to describe infection with the parasitic worm Dirofilaria immitis. This worm makes its home within the heart, as well as the blood vessels in the heart and lungs. 

*While heartworm can have a similar end location and clinical signs as lungworm (Angiostrongylus in dogs, Aelurostrongylus in cats), these are different parasites and have differing life cycles. For more on lungworm, check out our lungworm blog!

How do pets get infected with heartworm?

Unlike many of our other common worms, heartworm is NOT TRANSMITTED DIRECTLY from pet to pet via faeces. Heartworm is spread via mosquito bite. A mosquito bites an infected animal and consumes the blood containing intermediate heartworm larvae. The mosquito then moves to take its next blood meal from another pet and transmits the larvae into this animal’s bloodstream. The larvae mature and travel to the heart/lungs where adult heartworms make themselves at home and begin causing problems.

What are signs my pet might be infected with heartworm?

Signs of heartworm infection can range from mild to severe. It may be as simple as lethargy or decreased appetite. More severe signs can include vomiting, diarrhea, coughing, exercise intolerance, and even collapse. These clinical signs are a result of damage to the heart and vessels from adult heartworms. In cases of advanced untreated infection, pets can die from this dangerous parasite.

Can my vet test my pet for heartworm?

Absolutely! There are a few ways your vet can test for heartworm, all primarily via blood. The simplest version is a test looking for heartworm antigen in the blood. This means the lab is looking for evidence of what heartworm produces that the immune system responds to. If this comes up positive, then another fresh blood sample is submitted looking for microfilariae in the blood. Microfilariae are the immature larval form of heartworm that float freely in the bloodstream. 

Oftentimes, x-rays of the chest are also performed looking for enlargement of the heart and pulmonary blood vessels to help determine how advanced the infection may be. 

Can heartworm be treated?

Heartworm can be treated, but it is a majorly time consuming and costly process. The treatment regimen also comes with risks. Pets that are positive for heartworm are treated with injections of a strong adult worm immiticide deep in the muscles of the back. They must also be placed on steroids to decrease the inflammation that the body will create in response to the major killing off of the worms. In addition, pets are placed on an antibiotic to kill the bacteria Wolbachia, which is released by heartworms into the blood when they die. Lastly, pets are also placed on monthly heartworm preventatives as a part of the treatment protocol. Pets are required to be restricted to a cage or small confined space during treatment, as exerting activity like playing or running may exacerbate release of dead worms that travel into the lungs and block small blood vessels. 

Help! What can I do as a pet owner?

We can’t emphasize enough how important year round consistent parasite prevention is. Prevention is always better than treatment, especially in the case of heartworm. Particularly, if you have adopted a pet from another European country OR if you are traveling internationally with your pets from the UK, it is important to ensure these animals are tested for heartworm and on the appropriate prevention. A negative test is recommended prior to beginning regular prevention.

Fortunately, most of the prescription preventatives/treatments that cover LUNGWORM will also cover HEARTWORM, so if you are using a monthly treatment that gets lungworm it’s likely your pet is also protected against heartworm. That being said, it is important to check the product label to see if the drug is licensed to prevent maturation of Dirofilaria immitis. These preventatives must be given every 4 weeks consistently year round to be effective. Missing one dose in areas endemic for heartworm can result in infection. 

VetBox Top Tip: 

Once again our favorite theme rings true, consistent responsible parasite prevention is essential for healthy pets! 

Dr. Kirsten Ronngren, DVM MRCVS

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