Heartworm in cats

Heartworm disease in cats is a serious and life threatening illness. Mosquitoes carry the heartworm parasite and transmit infection when they bite. Heartworm isn’t present in the UK, but it’s a hazard to cats living or travelling abroad with their owners.

Heartworm disease in cats is different to dogs. Cats are not the ‘chosen’ host of the heartworm parasite, so immature larvae rarely develop into adult worms inside cats’ hearts. But they still cause a nasty illness called heartworm associated respiratory disease (HARD). Symptoms of HARD range from mild to life-threatening. They include coughing, vomiting and difficulty breathing. And unlike dogs, there’s no treatment for heartworm infection in cats. Heartworm is preventable, with regularly monthly prescription medicine. Talk to a vet for early advice if planning travel to countries with heartworm

Overview

What is heartworm in cats?

Heartworm is caused by the parasite Dirofilaria immitis. Mosquitoes pick up heartworm larvae (baby worms) from the blood of infected cats, foxes or ferrets when they bite and take a blood meal. Then they transfer the infective larvae to cats they bite afterwards.

Immature parasites migrate through your cat’s tissues and into their blood vessels, heart and lungs.
Larvae take around 6 months to mature. But in cats they die before becoming adult worms.
Dead and dying larvae can trigger a severe immune or allergic reaction, causing severe damage to your cat’s heart and/or lungs.
Unlike dogs, severity doesn’t depend on how many worms are present. A few worms can cause fatal illness in a cat.
The disease is most common in Southern and Eastern Europe. Colder weather keeps heartworm disease out of the Northern countries at the moment. But Global Warming is changing this.

Symptoms

What are the symptoms of heartworm in cats?

Symptoms of heartworm result from damage by migrating larvae and the body’s immune response. They range from mild to life-threatening. Mild or early symptoms may be mistaken for asthma or an infection.

Coughing and difficulty breathing
Asthma-type attacks, wheezing
Vomiting and going off food
Weakness, fainting, seizures
Swollen tummy due to fluid build-up
Sudden death

Risk

Which cats are at risk of heartworm infection?

Cats of any breed, age or sex can get heartworm. They only have to be bitten by a mosquito carrying infective heartworm larvae.

Higher risk cats include:

Cats who’ve been abroad
Imported cats, including rescue pets
Cats who live outside
Cats not getting regular heartworm preventives

Are humans and other pets at risk?

Humans and other pets are not at risk of infection from cats with heartworm.
However, animals travelling together will be equally at risk of infection
Heartworm infection in humans can cause benign, non-cancerous nodules in the lung. These are occasionally mistaken for cancerous changes, but they don’t cause serious illness

Diagnosis

How do vets diagnose heartworm in cats?

Diagnosing heartworm in cats is challenging:

Most tests target adult worms but these are rarely present in cats.
Symptoms may be mild and escape diagnosis. Or result in sudden death, before testing.

Vets will first consider your cat’s symptoms and any history of living or travelling abroad.

Special blood tests: often multiple tests needed to confirm. Tests for worms won’t become positive until 6 or 7 months after infection.
Endoscopy: passing a special camera into the windpipe and airways.
Echocardiography: chest ultrasound.

A cat that misses a dose of preventive treatment will need to be tested 6 months after the date of the missed dose. And again 6 months after preventive treatments started up again.

Vet treatment

How do vets treat heartworm in cats?

There’s no treatment to cure heartworm in cats. The usual treatment for dogs, called melarsomine, is poisonous to cats. Vets will treat the symptoms in an emergency and later to improve your cat’s quality of life.

Supportive care for very sick cats:

Treatment for shock
Steroid anti-inflammatory injections
Fluids given directly into your cat’s veins
Oxygen therapy
Bronchodilators: medicine to open up the airways and help breathing

Ongoing medication for heartworm-related symptoms:

Prednisone: steroid anti-inflammatory medicine. A higher starting dose for 2 weeks is gradually reduced as symptoms improve.
Treatment can be repeated if clinical signs come back.

Home treatment

How to care for a cat with heartworm at home

There are no home remedies for heartworm. It’s a very serious illness, needing intensive treatment by a vet. However homecare during and after treatment is an essential part of recovery.

Follow your vet’s instructions carefully.
Give all medicines as prescribed, at the correct times and dose.
Let your cat rest when they need to. An indoor lifestyle will be safer.
Attend regular follow-ups with your vet.

Prevention

How to prevent heartworm infections in cats

Prevention is far and away the best treatment for heartworm.

Preventing infection:

Treat any cat travelling to an area with heartworm once a month with a licensed product to prevent infection. Treatment options include drops or tablets.
It’s important not to miss any doses. These drugs kill the early stages of infection. If the treatment lapses by a few weeks and the parasite starts to matures, they’ll no longer be effective. If you’re going abroad for less than a month, give the treatment as soon as you come back to the UK.

Are mosquito/insect repellents safe for cats?

Unfortunately none of the mosquito repellents used for dogs is safe for cats. They are all poisonous to cats.

Are my family and other pets at risk?

Heartworm will not spread between cats and other animals or between cats and humans. However, humans and other pets at the same risk of mosquito bites will be equally at risk of getting heartworm.

When to worry