Heartworm disease in cats

mosquito heartworm cat

Heartworms (Dirofilaria immitis) are transmitted to cats by mosquitoes. Cats who travel abroad or who are adopted from outside the UK are most at risk and preventive precautions should be taken in these animals. Although heartworm is much more common in dogs than cats, it can cause serious illness and even death in both species. Here we will discuss how to prevent heartworm in your cat.

Are you concerned about your pet? Meet a vet online!
  • Included free as part of many pet insurance policies
  • Help, treatment and if you need it, a referral to your local vet
  • Open 24/7, 365 days a year


What causes a heartworm infection in cats?

What are the symptoms of heartworms in cats?

How is a heartworm infection in my cat diagnosed?

Can a heartworm infection in my cat be treated?

How can heartworms be prevented in cats?

What causes heartworm infection in cats?

Heartworms are blood-borne parasites, transmitted to cats through the bite of mosquitoes which are carrying heartworm larvae (microfilariae). The larvae then travel in the bloodstream until they reach the right side of the heart and heart pulmonary artery (the major artery supplying blood to the lungs). Here they mature into adult worms over 8 months before producing more larvae some of which enter the bloodstream. The females are around 15-36cm long and 3mm wide. The male parasites are half the size of females.

It is important to note that one-third of infected cats are indoor-only cats having been bitten by mosquitoes within the home. Cats seem to be more resistant to heartworm infection than dogs. However, with increasing numbers of cats travelling abroad the number of cases reported is increasing.

Since mosquitoes are essential to transmission of heartworms, there is currently no risk to cats that are UK residents and have never travelled abroad.

What are the symptoms of heartworm?

The symptoms of heartworm disease are mainly associated with disturbances of the heart and lungs as this is where the adult worms live. These include:

  • Coughing

  • Laboured breathing

  • Vomiting

  • Abnormal heart beat or the presence of a heart murmur

  • Weakness

The symptoms will depend on how long the cat has been infected, the number of heartworms and the individual immune response of the cat.

How is a heartworm infection diagnosed?

Diagnosis of heartworm in cats can be difficult as the signs are non-specific. It is important to make your vet aware of any travel outside of the UK if you have noticed vomiting, coughing or breathing difficulties in your cat after being abroad. There is a blood test that can help to diagnose a heartworm infection but it is not always reliable in cats as heartworm-specific markers are not always present in the blood.

Screening blood tests, chest x-rays and a heart scan are often advised to rule out other diseases that have similar symptoms, as well as to look for changes that would suggest a heartworm infection.

Can a heartworm infection in my cat be treated?

Unfortunately, there is no specific treatment for heartworms in cats. The drug that is used to treat heartworms in dogs has severe side-effects in cats and is not usually recommended. The lifecycle of the heartworm in cats is shorter (2-3 years) than in dogs (5-7 years) and treatment is based on supporting and treating any symptoms associated with the breathing and circulatory system that occur during this time. Some cats mount an immune response strong enough to kill the worms and can recover without any treatment. However, there is a risk of sudden death in cats with a heartworm infection, even if they appear to be doing well.

In severe cases surgery may be recommended to physically remove the worm burden. Although, since the worms live within the heart and important arteries this is a risky procedure.

How can heartworm disease be prevented?

Use of preventative medication for heartworm is the best method of protection for cats that travel abroad or who have been adopted from outside the UK. Since diagnosis and treatment of heartworm in cats is so difficult and risky, it is important to prevent a heartworm infection in the first instance. This is usually a monthly treatment and it is important to keep up to date with regular preventative treatments for the entire time your cat is at risk. Your vet can advise you on a treatment protocol and give you additional treatment if your cat is abroad and at risk for a longer period of time. Consistent protection is required and missing one dose can increase the risk of heartworm infection. The risk of heartworm infection increases if a cat has not been given preventative heartworm medication and has visited a region where there are heartworms and mosquitoes.

When to see your physical vet

  • You are planning a trip abroad with your cat - be sure to read our cat travel advice!

  • Your cat has breathing problems, is coughing or vomiting

Still have questions?

You can always book a video call with a vet at FirstVet if your cat is lame to get an initial assessment and advice about how to proceed!

More articles about cat

Contact a UK vet online right now!

What can we do for your furry friend?

  • Assess how they are in that exact moment
  • Answer your questions, offer advice, and make a plan about your concerns
  • Recommend easily available, over-the-counter pet health products when sufficient
  • Make a referral to a local vet when necessary
Book an appointment
  • Included free as part of many pet insurance policies Included free as part of many pet insurance policies
  • Help, treatment and if you need it, a referral to your local vet Help, treatment and if you need it, a referral to your local vet
  • Open 24/7, 365 days a year Open 24/7, 365 days a year