Heartworm in Dogs - Parasitic Infection of Heart and Lungs

Heartworm in Dogs - Parasitic Infection of Heart and Lungs

Important note: Fidello is not a veterinarian. This page is meant to inform you and does not help you reach a diagnosis. If you have doubts about your dog's health, or recognise the signs described below, always contact a veterinarian.

Heartworm, also known as dirofilariasis, is a parasitic infection in which a type of worm establishes itself in the pulmonary arteries and heart of the dog. The condition is not spread through direct contact between dogs, but exclusively through a mosquito bite. Left untreated, heartworm can place serious strain on the heart and lungs over time.

What is heartworm?

Heartworm is caused by the parasite Dirofilaria immitis. A mosquito that has previously fed on an infected dog picks up microscopic larvae and passes them on to another dog with a subsequent bite. From the skin, the larvae migrate through the body and, over the course of several months, develop into adult worms that eventually settle in the pulmonary arteries and the right side of the heart. Adult worms can remain there for several years and themselves produce larvae that circulate in the blood, allowing the cycle to continue via another mosquito.

Which dogs are at risk?

Heartworm is not breed-specific: in principle, any dog is at risk if bitten by an infected mosquito. The risk mainly depends on exposure to mosquitoes in an area where the parasite occurs, and on whether preventive medication is used. Dogs that travel to or stay in warmer, mosquito-rich regions, and dogs imported from areas where heartworm is more commonly reported, deserve extra attention. Heartworm has traditionally been uncommon in many parts of Northern Europe, but due to climate change and the import of dogs from abroad, it is increasingly recommended to take this into account, especially after travel abroad.

Symptoms

In an early stage, a dog often shows few or no signs. Early signs that may occur include a mild, persistent cough and slightly reduced stamina during walks or play. In a more advanced infection, this can progress to weight loss, reduced appetite, a swollen abdomen due to fluid build-up, and shortness of breath. Signs that require urgent action include sudden collapse, pale or bluish gums, dark-coloured urine, or clear breathing difficulty: this can indicate an acute, life-threatening complication caused by a heavy worm burden and requires immediate veterinary help.

When to see a vet

Contact a veterinarian for a persistent cough, a clearly reduced condition or stamina, or if your dog is not on preventive heartworm medication and has recently been abroad. In the case of sudden collapse, pale or bluish gums, dark urine, or severe breathing difficulty, an urgent visit to a veterinarian or animal clinic is necessary.

How is it diagnosed?

A veterinarian diagnoses heartworm using blood tests, including a test for antigens from the adult worm and, where relevant, microscopic examination for larvae in the blood. In addition, a chest X-ray or an echocardiogram may be taken to assess the severity of the infection and the damage to the heart and lungs. This page cannot determine whether your dog has heartworm; only a veterinarian can assess that after examination.

Treatment in outline

A treatment plan is always determined by the veterinarian and depends on the severity of the infection and the condition of the dog. The approach is generally aimed at gradually eliminating the adult worms, often combined with preparatory medication, and involves a period of strict rest: with too much movement, dying worms can block pulmonary blood vessels. In severe cases involving a heavy worm burden, surgical removal of the worms may be necessary. There is no treatment that is guaranteed to succeed in every case; the veterinarian determines the approach for each individual dog.

What you can do yourself

During and after treatment, strict rest is the most important thing you can provide yourself: no walks, running or jumping, even if your dog already seems to feel better. Give medication exactly as prescribed by the veterinarian, provide a calm environment, and contact the veterinarian if you have doubts about recovery. This does not replace medical treatment, but does support a safe recovery.

Prevention

Heartworm is not hereditary, so breeding plays no role in this condition. The most important prevention is monthly, veterinarian-prescribed preventive medication, especially for dogs that travel to or stay in mosquito-rich areas. Before starting preventive medication, a test beforehand is often recommended. Limiting exposure to mosquitoes, for example by keeping dogs indoors more in the evening and at night in risk areas, can help as an additional measure.

Living with heartworm

Dogs that have gone through an infection may be left with lasting damage to the heart or lungs. In that case, long-term adjustments may be needed, such as a calmer exercise pattern and regular check-ups with the veterinarian, to keep the strain on the heart and lungs manageable.

Frequently asked questions

Is heartworm contagious from dog to dog?
No, heartworm is not spread through direct contact, but exclusively through the bite of an infected mosquito.

Does heartworm occur locally?
Traditionally uncommon in many regions, but due to travel, the import of dogs, and climate change, it is increasingly considered relevant, especially for dogs that have been abroad. Discuss this travel-related risk with your veterinarian.

Can heartworm be cured?
Treatment is possible, but risky and lengthy, involving a period of strict rest. Success varies from dog to dog; only a veterinarian can say more after an examination.

Does my dog need to be tested every year?
This depends on your dog's travel patterns and where you live. Ask your veterinarian for advice suited to your situation.

Conclusion

Heartworm is a parasitic infection that can affect a dog's heart and lungs, and which is spread by mosquitoes rather than through contact between dogs. Preventive medication, vigilance when travelling to mosquito-rich areas, and timely veterinary attention for a persistent cough or reduced condition make the difference between an infection caught early and a dog that only shows signs at an advanced stage.

Finally

Finally: this article does not replace a visit to the veterinarian. Fidello does not provide diagnoses or prescribe treatments. If in doubt, or in case of persistent complaints or acute signs, a veterinarian is always the right next step.