Heartworm Infection in Cats and Dogs

Treatment and Prevention of Dirofilaria Immitis Parasites in Pets

Jul 19, 2008

Cat, Magnus Rosendahl, public-domain-photos.com

Heartworm parasites can be fatal for cats and dogs. However, with preventative treatment, most animals make a full recovery.

Heartworm is common in tropical, semitropical and temperate climates throughout the world including North America and southern Europe. Animals can succumb to heartworm at any age.

Heartworm larvae are carried by mosquitoes, which transmit the organisms when they bite an animal. These organisms infest the lungs, heart and blood vessels, and if the larvae reach the adult stage, they can cause serious health problems.

Many cats rid themselves of the parasites on their own, with fewer than 26% of worms making it to the adult stage in cats, whereas 40-90% reach this stage in dogs. Additionally, heartworms tend to live just 2-3 years in cats, compared to 5-7 in dogs.

In both cats and dogs, the disease can be fatal if not treated. However, cats are more likely to die if the larvae have the opportunity to grow to the adult stage because their blood vessels and hearts are smaller and so the damage caused by the worms is greater.

Symptoms in Cats

Heartworm Associated Respiratory Disease (HARD) is often misdiagnosed as allergic bronchitis or asthma. Symptoms may also mimic other feline diseases, so it tends to be more difficult to diagnose in cats than in dogs. Common heartworm symptoms in cats include:

Intermittent vomiting
Lethargy
Loss of appetite and/or weight
Coughing
Panting, open-mouthed breathing or other signs of intermittent breathing difficulties
Gagging

Symptoms in Dogs

Dogs with heartworm present a different clinical picture. Symptoms, which are usually far more severe in very active dogs, include:

Abnormal lung sounds
Intolerance for exercise
Coughing
Abnormal heart sounds
Failure to grow
Laboured breathing
Bluish or purplish skin discoloration
Spitting up blood
Bleeding nose
Temporary loss of consciousness

In contrast to active dogs, inactive “couch potato” dogs may show few if any symptoms when they have been infected with heartworms.

Preventative Treatment

Free roaming cats and dogs housed outdoors face a greater risk of heartworm infection, though indoor pets are not free from risk. There are several medications that have been approved by the FDA to prevent larvae from developing into adult heartworms. The American Heartworm Society recommends implementing year-round prevention, particularly in areas where heartworm is common. Preventives for dogs and cats only need to be administered once per month, so it is relatively easy to keep your pets safe.

Late-Stage Treatment for Cats

There are no approved treatments for feline heartworm infection when the heartworms have been left to reach the adult stage. If the disease is affecting the blood vessels and lungs, x-rays should be taken every 6-12 months and a veterinarian may prescribe prednisone. In some cases heartworms can be extracted surgically.

When severe symptoms are present, a cat may require intravenous fluid, oxygen therapy, bronchodilation, antibiotics, cardiovascular medications and nursing care. Only 25-50% of cats survive adult heartworms.

Late-Stage Treatment for Dogs

For dogs, there are a few different late-stage treatments available. The first is an FDA-approved organic arsenical compound. Another treatment option is Merial’s Immiticide. This treatment is administered via intramuscular injection.

Destroying adult heartworm parasites can lead to serious complications such as pulmonary thromboembolism. Additionally, dogs must be confined and their movement restricted during and for at least one month following treatment to reduce the risk of respiratory problems as a result of the dead worms in their systems. In some cases, a second round of treatment is required. Given the severity of late-stage treatment, preventative treatment is by far the better option.