In the past, heartworms were thought to be a threat mostly affecting dogs, commonly causing canine heartworm disease. In recent years, we have discovered that cats also can suffer from heartworm disease. According to the American Heartworm Society, feline heartworm disease has been found in "each of the contiguous 48 states, Hawaii, Puerto Rico, U.S. Virgin Islands and Guam".
Transmission of Heartworm Disease
Heartworms are spread by mosquitoes and cats become infected when bitten by an infected mosquito. Cats are susceptible to heartworm disease whether they are housed indoors or indoor/outdoor because mosquitoes frequently find their way inside. It takes only one mosquito bite to spread the disease.
Infected mosquitoes carry a larval form of heartworms and when the mosquito bites to take its blood meal, the larval heartworm is introduced to the cat. The larval heartworms invade the blood vessels inside of the lungs as they mature. Larval heartworms develop into adults which are capable of reproduction within 8 months.
Symptoms of Feline Heartworm Disease
Symptoms of heartworm disease most frequently occur when the larval heartworms arrive in the lungs or when the adult heartworms die. The syndrome which develops due to the damage caused in the lungs by the larval heartworms is commonly know as Heartworm Associated Respiratory Disease, or HARD.
Many cases of feline heartworm disease are chronic in nature. Symptoms include:
- coughing
- asthma-like symptoms
- difficulty breathing
- rapid breathing
- gagging
- vomiting
- fluid in the chest
- lack of appetite
- weight loss
- lethargy
Some cases may be more acute and may display symptoms such as:
- collapse
- fainting
- diarrhea
- vomiting
- difficulty breathing
- rapid breathing
- convulsions
- blindness
- sudden death
Diagnosis of Feline Heartworm Disease
Diagnosis of feline heartworm disease is difficult. Commonly used blood tests (including those for heartworm antibodies, antigens and microfilaria) can often be falsely negative. Radiographs can show non-specific changes that can mimic those seen with other diseases, such as feline asthma. Echocardiography can also be performed and can sometimes but not always allow visualization of the feline worms.
Treatment for Feline Heartworm Disease
There is no medical "cure" for feline heartworm disease. Surgical extraction of the worms has been performed but is very invasive and not appropriate for all cases of heartworm disease in cats.
In most cases, treatment is based on relieving the symptoms of heartworm disease and may include:
- prednisolone (or prednisone)
- bronchodilators such as terbutaline or albuterol, often administered by an inhaler
- cardiovascular drugs
- oxygen therapy
- intravenous fluids
- antibiotics
- cage confinement
Prevention of Feline Heartworm Disease
Prevention of feline heartworm disease is simple and requires monthly administration of a heartworm preventive medication. These medications include:
- Revolution
- Heartguard Plus for Cats
- Interceptor
- Advantage Multi for Cats
All of these medications are very effective in preventing heartworms and heartworm disease in cats. Revolution and Advantage Multi are topical medications which are applied to the skin. Heartguard Plus and Interceptor are tablets. These products should be started early in life and should be given monthly year round even in colder weather.
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