Heartworm disease is an infectious disease caused by the parasite Dirofilaria immitis that can occur in dogs and cats but is less common in cats. An infected mosquito that bites your cat can transmit Dirofilaria immitis. Below we will give you information about heartworm symptoms as well as information about the diagnosis, treatment and prevention of heartworm disease. We will also cover other diseases that can cause similar symptoms and be confused with feline heartworm disease.
There are key differences in heartworm disease and in heartworm symptoms in cats vs. dogs. The cat is not the typical host for heartworms. It is believed that dogs get heartworm disease 10 times more commonly than cats. Many cats with heartworm disease go undiagnosed.
Heartworm disease in cats can occur in any breed and at any age. Male cats are more commonly infected and outdoor cats are at increased risk. It is estimated that approximately one-third of cats with heartworm disease are indoors only.
The numbers of worms that develop in cats are generally much less than dogs. In fact, some cats infected with heartworms may have only one to three worms. These worms will live in pulmonary vessels and cause the symptoms we will identify below.
Heartworm Symptoms in Cats
The symptoms of heartworm disease in cats can be vague to critical. Some cats will appear normal on physical examination while others will have a history of vomiting, a cough, trouble breathing, or even sudden death.
Symptoms of heartworm disease in cats may include:
- Coughing (dry)
- Coughing up blood
- Difficulty or trouble breathing – Learn more about How to Recognize Fluid in a Cat’s Lungs
- Increased respiratory effort
- Occasional vomiting
- Sudden death
- Decreased appetite
- Weight loss
- Collapse or fainting
- Decreased activity or playfulness
- Sleeping more
- Abnormal neurologic symptoms such as seizures, circling, blindness, trouble walking or incoordination
- Sudden death – Learn more about Sudden Cat Death: Understanding Why it Happens
Why and How Cats Get Heartworms
The following are the steps of how a cat can get heartworm disease:
- Transmission of heartworms to a cat occurs when a mosquito bites an infected dog or cat and ingests heartworm larvae (baby heartworms) that live in the bloodstream. The parasite is known by the scientific name of Dirofilaria immitis.
- The infected mosquito then bites a normal healthy cat and when this happens some of the larvae are injected under the skin.
- Over the following 3 to 4 months, the larvae grow in the cat and eventually make their way into the heart where they develop into adult worms. As little as 2 or 3 worms can be fatal to an adult cat.
- The process is then ready to repeat itself.
Figure 1. Graphic of a heart with heartworms in the heart and pulmonary blood vessels. The heartworms appear as light colored thin spaghetti type structures. This heart shows many heartworms. Cats with heartworms may only have one to three worms.
Other Diseases that Can Look Like Heartworm Disease in Cats
Many cat owners are concerned that their cat has heartworm disease when they see signs of difficulty breathing or labored breathing. Trouble breathing in cats can be caused by heartworm disease but it is more common for the cause to be from heart disease or feline asthma.
Causes of heart disease in cats include Hypertrophic Cardiomyopathy in Cats, Dilated Cardiomyopathy (DCM) in Cats and Chronic Valvular Heart Disease. The increased respiratory effort associated with heart disease is often caused by pulmonary edema (fluid in the lungs) or pleural effusion (fluid around the lungs) that is secondary to congestive heart failure.
There are several causes of an enlarged heart in cats. Learn more about What Does an Enlarged Heart Mean for Cats?
Asthma in cats, also known as “Feline Allergic Asthma” or “Feline Allergic Bronchitis”, and is a lung condition associated with airway obstruction caused by sudden narrowing of the bronchial tubes. These symptoms are caused by the spasmodic constriction of the bronchial tubes and increased production of secretions from the bronchial tree. Some cats may have an acute onset of signs while other cats may have signs that come and go. Common symptoms in cats include coughing, difficulty breathing, increased respiratory effort, fast respiratory rates, wheezing breathing, lethargy, weight loss, weakness, withdrawing from social activities around the house, and/or an abnormal posture. As some cats struggle to breathe, they may sit with their head extended and elbows back.
Diagnosis of Heartworm Disease in Cats
Tests that can diagnose heartworm disease in cats include serum heartworm antibody test, serum heartworm antigen test, and or Microfilaria test (looking for larva in the blood).