Paw Prints
Spring arrives today. This happy season provides the fresh grass and outdoor play that pets and their owners enjoy. But it is not all fun and games.
Spring also heralds the onset of heartworm season. Most dog owners are well-versed in the heartworm routine. Monthly at-home prevention and annual blood tests are the norm for Fido. If Kitty is your only furry companion, though, you may not have given it much thought. After all, heartworm had traditionally been considered a parasite of dogs.
In the past few years, awareness of heartworm in other species has increased. Feline heartworm disease is now recognized as a distinct illness, with clinical signs different from those of dogs. The incidence is about 10 percent of that in unprotected dogs, and indoor cats account for about one-third of the feline cases. Wild canids (coyotes, foxes, wolves) can serve as a reservoir, keeping pets at risk for infection. We also know that ferrets, and in rare cases humans, can contract heartworms.
Heartworms are vermicelli-like worms that live in or near the heart. They are transmitted by mosquitoes. Mammals are infected when they are bitten by these pests and heartworm larvae are deposited in their skin. These larvae mature and migrate into the chest. Animals may become symptomatic during this maturation process, or months later.
Heartworm disease in dogs causes heart failure. Exercise intolerance, weight loss, fatigue, heart murmurs and arrhythmias are common. Some dogs cough or have difficulty breathing.
In cats with heartworm disease, however, heart failure is uncommon. Felines usually present with respiratory illness. Heartworm Associated Respiratory Disease is the term used to describe this disease process.
Cats diagnosed with asthma in the past may in fact have been affected by HARD. Any cat with asthma-like signs (coughing or intermittent difficulty breathing) should be considered for heartworm testing. Another classic sign of feline heartworm disease is chronic vomiting, especially when unrelated to eating. Weight loss, decreased appetite and lethargy may also occur. Some cats have no symptoms but may die suddenly. In these cases, the cat may have been clinically normal just one hour prior to death.
Cats mount an overwhelming immune response to heartworms. This is actually harmful to the cat and is often what makes him sick. In addition, heartworms live for only a few years in the cat. The process of worms dying in the cat's blood vessels can be risky. A dead worm fragment can cause an embolism or blood vessel blockage, resulting in sudden death.
Heartworm disease in dogs and cats is typically diagnosed with blood tests. The canine test is extremely accurate if adult worms are present. The adult worms are about 12 inches long and are the cause of clinical signs in dogs. Annual heartworm testing of all dogs is recommended, as early diagnosis is the key to successful treatment.
Unlike dogs, affected cats often become sick when these worms are still in their immature larval stage. Most cases of heartworm disease in cats are detected with a dual set of feline heartworm blood tests. These tests search for evidence of both larval and adult heartworms.
Although heartworm treatment is available, it can be dangerous, especially for cats. The problem is that cats have smaller vessels than dogs, so the risk of embolism from dying worms is exponentially greater for them. Therefore, the illness in cats is generally managed symptomatically. For example, if your cat is coughing due to heartworm, your veterinarian can prescribe medicine to treat the cough and is typically better off doing this than eliminating the parasite.
The good news is that heartworm disease is easy, safe and inexpensive to prevent in dogs and cats. The most popular preventives are administered by the pet owner every month, either orally or topically. There are also monthly preventives available for ferrets.
Most heartworm preventives also control common intestinal parasites, including roundworms and hookworms that can also be transmitted to people. This multi-parasite control is an added bonus with the once-a-month prevention. Some options control external parasites such as fleas, too. Talk to your veterinarian about which product is best for your pet.
Using heartworm prevention seasonally is not advisable. Weather patterns are unpredictable, especially in fall and spring. Skipping a month presents a window of opportunity for heartworms. Too often, pet owners forget to start the spring heartworm prevention until too late. Also, gastrointestinal parasites can be contracted any time of the year. The Centers for Disease Control, American Heartworm Society and Companion Animal Parasite Council all recommend year-round heartworm prevention.
Heartworm disease is certainly a situation where an ounce of prevention is worth a pound of cure. It's quick and easy to do, and Fido and Kitty will thank you for it.
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Dr. Heidi Bassler is medical director of the Veterinary Center of Greater Newburyport. Do you have questions for Dr. Bassler? Send them to ndn@newburyportnews.com.
