The American Heartworm Society (AHS) and the American
Association of Feline Practitioners (AAFP) have produced a warning
regarding heartworm disease in cats.
The American Heartworm Society (AHS) and the American Association of Feline Practitioners (AAFP) have produced a warning regarding heartworm disease in cats. They feel that the disease is greatly under diagnosed and that relatively simple prevention measures are being ignored and underutilized because the diagnostic tests are ineffective.
There are tests for both heartworm larvae and adult heartworms available, but they are not always effective in diagnosing heartworm disease in cats. While research in feline heartworm disease is moving at a rapid pace, it is still a complicated and difficult call in most cases. Negative tests for adult and larval forms of heartworms do not always rule out the disease in cats. This is because the small number of worms that cats get can fool the tests. The other problem with the diagnosis is that the disease acts somewhat differently in cats than in dogs.
In dogs the primary problem is congestive heart failure due to the presence of the adult worms in the chambers and arteries of the heart. In cats much of the problem can arise from the presence of immature worms (late stage larvae) in the lungs. In dogs it presents as heart failure. In cats it often presents as coughing, asthma or vomiting. It is now being referred to as HARD (Heartworm Associated Lung Disease) in cats.
When the larvae are present, but no adult females, then some tests will be positive and others will be negative. Xrays, ultrasound and cytology then become important tests in making the diagnosis. The cost of making the diagnosis accurately can go from about $100 to 200 for a dog to over $700 for a cat.
Treatment options are also very different. In dogs we use an arsenic compound delivered by intramuscular injection to kill the worms, which are six to twelve inches long. The dead worms then have to rot and be absorbed in the bloodstream. Even in dogs this can result in obstruction of blood vessels, causing stroke and heart attack like symptoms.
In cats, if adult worms are present, killing them frequently produces a life threatening crisis. The dead worms are very large (relatively speaking) and easily block arteries. Strokes, heart attacks and death are common results of attempts to kill adult heartworms in cats. Experts are moving more towards surgical removal of worms in proven adult heartworm infected cats; with its own set of costs and risks.
When the disease state is caused by the immature larval worms in the lungs (HARD), the only options for treatment are symptomatic control until the parasite dies a natural death and is reabsorbed by the body. This can take one to three years – during which coughing and asthma like symptoms may make your cats life miserable. The HARD designation is very appropriate.
There are five myths the AHS and the AAFP want us to bury when it comes to heartworm disease in cats:
MYTH: Heartworm is mainly a dogs disease. TRUTH: Feline heartworm disease is very serious.
MYTH: Indoor cats are not susceptible to heartworm disease. TRUTH: it only takes one mosquito to infect a cat.
MYTH: Heartworm is only a heart disease. TRUTH: Remember HARD – asthma, bronchitis and other respiratory diseases can actually be feline heartworm disease.
MYTH: Heartworm larvae does not affect cats. TRUTH: 50 percent of cats infected with heartworm larvae have serious lung and arterial disease.
MYTH: It is easy to test a cat for heartworm disease. TRUTH: See above.
Hopefully the information in this column will do its part to demythologize heartworm disease in cats.
The good news is that there is simple prevention for heartworm disease in cats and testing is not required before using the preventive (unlike the case in dogs). Prevention comes in two forms. Revolution is a topical treatment that kills heartworm larvae, fleas and roundworms in the intestine with a once monthly application. Interceptor is a once monthly, chewable, pill shaped treat that kills heartworm larvae, roundworms, hookworms, whipworms and their larvae in the intestine.
My preference is a combination of Interceptor and Frontline Plus (flea and tick control) providing an excellent spectrum for safe, effective and comprehensive parasite control in cats.
Interceptor and Revolution are prescription items available from your veterinarian. They are very safe, effective and cost effective. They also help in controlling other parasites on or in your cat. Check with your veterinarian on what they feel is best for your situation.
Dr. Quick has owned and operated the Animal Care Center in Morgan Hill for 25 years. He is a founder of WERC and Furry Friends Foundation and was Morgan Hill Male Citizen of the Year in 2003.
