Heartworm Disease in Dogs & Cats

What is heartworm disease?

Heartworm disease is caused by a worm called Dirofilaria immitis. Mosquitoes pick up tiny young worms, called microfilariae, when they bite an infected dog, and pass them on when they bite another animal. The young worms grow into adult worms that live in the heart and the large blood vessels of the lungs. Over time they damage the lungs, blood vessels and heart.

Dogs are the main host, and adult worms can live in a dog for years and produce microfilariae. Cats can be infected too, but they usually carry only a few worms, often have no microfilariae, and may react strongly even to a small number of worms. This makes heartworm harder to find in cats.

Signs to watch for

Common signs include:

• A soft, dry cough
• Tiring easily on walks
• Weight loss
• Fast or difficult breathing
• A swollen belly in advanced cases
• In cats, coughing, breathing trouble or vomiting

Many infected animals show no signs at first, and some cats collapse suddenly.

Which lab tests help

For dogs, the Canine Heartworm Antigen (Rapid Test) looks for antigen, a protein made by adult female heartworms. The Snap 4Dx (Ehrlichia / Lyme / Heartworm / Anaplasma) checks for heartworm antigen along with antibodies to some tick-borne germs. Antigen tests only turn positive several months after infection, so a very recent infection can be missed.

The Microfilaria Detection (Knott's Method) concentrates a blood sample so the lab can look for microfilariae under the microscope. A positive result shows that young worms are in the blood, but a negative one does not rule heartworm out. The Dirofilaria immitis (Heartworm) RT-PCR can confirm heartworm and tell it apart from other worms whose young look similar.

For cats, the Feline Heartworm Ag (Rapid Test) is used, but cats often carry too few female worms to give a positive result. A negative test does not rule heartworm out in a cat, so your vet may combine blood tests with X-rays or a heart scan.

A Complete Blood Count (CBC) may show raised eosinophils, a type of white cell linked to parasites and allergy. For dogs, heartworm screening is also part of the Pro Tick Bone Safety Panel and the Pro Max Panel, through the Snap 4Dx kit.

A registered veterinarian interprets each result in the light of your pet's signs and history.

When to see your vet

See your vet promptly if your dog or cat has a lasting cough, tires easily or loses weight. Trouble breathing, a swollen belly or collapse need a vet the same day. Ask your vet about heartworm prevention, and about testing before prevention starts.

Testing in Bhopal

Pashupatinath Vet Lab is at C-200, C Sector, Shahpura, Bhopal, and provides free sample collection anywhere in Bhopal. From other districts, blood samples can be sent by courier, by bus parcel or through your local vet; call or WhatsApp +91 88175 01118 to plan it. The lab confirms the method, sample needs and reporting time when you book. Reports reach you on WhatsApp, by e-mail and in My Reports on the website.