Diagnosing feline heartworm disease.
Heartworm disease is very difficult to detect in the early stages, as most cats are asymptomatic at that point. At the 1998 American Heartworm Society Symposium, ten papers were presented on the topic of serologic testing for feline heartworm infection. The results show that serologic testing is not as accurate or definitive in cats as it is in dogs. The antibody tests proved to be the most sensitive, but they only test for exposure to heartworms and not to actual heartworm infection. Antigen tests are less effective in cats due to low worm numbers, immature worms and more single sex infections.

In a lecture on feline heartworm disease at the Toronto Academy of Veterinary Medicine, Dr. Joseph Taboda recommended thoracic radiography as the best screening test. He suggests looking for pulmonary artery enlargement (1.6 times greater in width than the ninth rib at the ninth intercostal space) which is present in greater than fifty percent of affected cats. He adds that echocardiography may also be of value in diagnosis. As cats are generally amicrofilaremic and most have very low numbers of heartworms, microfilaria tests are therefore of little value.

According to Dr. Taboda, the most sensitive test for feline heartworm disease is an Elisa antibody test (Heska Corp.). This test detects heartworm antibody in cases greater than sixty days post infection. False positives may occur due to ectopic infections where worms (immature or adult) are spontaneously cleared. Because of this, a positive antibody test must be supported by one or more of the following tests: a positive antigen test, supportive clinical signs, or laboratory data including radiographs. A negative test in a cat showing clinical signs can be used to rule out heartworm disease.

Clinical signs of feline heartworm disease.
Heartworm disease is also difficult to detect after the disease has progressed, because the signs may vary from cardiac to respiratory, gastrointestinal or central nervous system.

In his lecture, Dr. Taboda also discussed a variety of clinical signs indicating feline heartworm disease. He said, "Cats that show signs of heartworm disease usually do so when the heartworms arrive at the pulmonary arteries or as the worms die, causing thromboembolic events. Acute signs range from sudden death to acute onset dyspnea, haemoptysis and collapse, as well as neurologic signs varying from ataxia to head tilt, blindness and seizures (due to aberrant migrations). More common than acute presentations are chronic cases. Heartworm disease should be considered in any cat with a chronic intermittent cough (the most consistent sign), chronic intermittent vomiting, lethargy, weight loss, tachypnea, dyspnea or central nervous signs."

Feline heartworm disease versus canine heartworm disease.
According to information gathered from an AAHA Conference, heartworm infection in cats varies considerably from that in dogs. Cats are generally only very transiently microfilaremic, typically have lower numbers of heartworms than dogs, a shorter worm life-span, and more commonly have aberrant migrations and suffer death as sequelae to infection.

Dr. Taboda also points out that "the prepatent period in cats is longer than in dogs, being approximately eight months."

Interceptor® is now approved for cats.
Over the years, many clients have trusted Interceptor® Flavor Tabs^TM to protect their dogs against heartworm and other harmful worms. Now, Interceptor provides cats with the same proven protection against heartworm, as well as treats and controls roundworm and hookworm.