Most cat owners are unaware of this fatal disease. Heartworm disease was found in cats as early as the beginning of the 20th century, but few cat owners or veterinarians were concerned about it. Recent studies have shown that 26% of cats from the Gulf Coast have signs of heartworm infection at some point in their lives and 10% have actual adult worms. These prevalence rates are significantly higher than rates for Feline Leukemia or for the Feline Immunodeficiency Virus. Yet, according to the American Heartworm Society, only about 5% of cat owners use any sort of heartworm preventative for their cats! Like dogs, cats acquire the parasite from mosquitoes but this is when any similarity ends!
Heartworms continually evolve to exist in their canine hosts, but cats are abnormal hosts and these heartworms will live stunted and shortened lives. You might think that this is a good thing, but due to our cat’s strong immune systems, heartworms actually can cause more serious and severe disease than they do in dogs. It is not unusual for a dog to live for years with 20, 30, or even 50 worms in their heart. But a cat with a single heartworm can die suddenly, often with no apparent clinical signs whatsoever. In addition, your “inside only” kitty is just as susceptible as the outdoor tomcat.
Upon infecting a cat, the heartworm larva will travel to the blood vessels of the heart and lungs, where it will grow to be about two inches long. At this time, cats may exhibit respiratory symptoms that are often misdiagnosed as bronchitis or asthma. Veterinary scientists studying heartworm disease in cats have given this stage of the disease a name: Heartworm Associated Respiratory Disease, or HARD.
As the heartworms mature, signs of their presence will often diminish. In fact, evidence suggests that the live heartworms can actually suppress the cat’s immune function and the cat appears to tolerate the infection. However, when the mature worms start dying, massive inflammation can occur, leading to acute lung injury and even sudden death. Your cat can literally die within an hour!
So, what signs should you look for to keep your cat safe? Cats with heartworms may exhibit difficulty breathing, coughing, vomiting, weight loss, sudden collapse, or even sudden death. Because this disease can cause such a terrible outcome in a short period of time, we should immediately examine any cat exhibiting these signs. Tests are available to screen for heartworm disease, but again, unlike dogs, testing cats is a complex, often confusing, endeavor. To make matters even worse, there is no effective or approved way of treating adult heartworms in cats. So prevention is really the key!
And on that front there is good news! Heartworm preventatives are available for cats and are as easy to give as the medications designed for dogs. We recommend Revolution by Pfizer. Revolution is the first-ever topically applied medication for cats that prevents heartworm disease, kills adult fleas, treats and controls ear mites, roundworms and hookworms.
We can also help you make sense of heartworm testing options for your cat. Although the Heartworm Society does not mandate testing healthy cats prior to using preventatives, we may recommend a test if clinical signs are evident.
Preventing heartworm disease in cats is only one step to helping our feline friends live long and healthy lives. Yearly physical exams, blood tests and appropriate vaccinations can all do their part to insure your cat’s health. To learn more about how heartworms can affect your cat, visit www.heartwormsociety.org More
For many years we have been fighting a battle against heartworms. We have great products on our side to prevent this disease, but recent findings about heartworm resistance have many pet owners and veterinarians concerned.
Microfilaria in blood of dog
Heartworm disease has been known to veterinarians for more than 120 years. The heartworms are transmitted from any of more than 70 known species of mosquito, and the disease attacks the pulmonary arteries and right side of the heart in dogs. Heartworms are spread directly to the dog from the mosquito, with no dog-to-dog transmission.
For more than 4 decades, heartworm disease has been effectively prevented in dogs by using available products. But recent research indicates this might be changing. At a veterinary conference in 2010, information was released detailing a genetic mutation in heartworms that appears to confer slight resistance to current preventives. Anecdotal reports in the last 4-5 years also point toward an increase in heartworm prevention product failures in the Mississippi delta region of the U.S.
While lack of efficacy (LOE) to heartworm preventives remains geographically limited, research is ongoing to determine the extent of this problem. Historically, the LOE was attributed to poor owner compliance in the geographic area, the effects of Hurricane Katrina, increased heartworm numbers within the mosquito vector, and/or the increased sensitivity of heartworm testing.
Two prominent veterinary groups, the Companion Animal Parasite Council (CAPC) and American Heartworm Society (AHS) concluded at a recent council strategy session that most credible reports of LOE are geographically limited at this time. In addition, the extent of this problem is not truly known.
The lack of conclusive evidence to LOE could also be due to several factors:
• Poor Owner Compliance.
o Are pet owners accurately following the veterinarian recommendations?
o Is the pet given the preventive medication consistently without missing or delaying any treatment?
o Is the pet ingesting the medication? (vomiting, pets spitting out or hiding the medications, swimming or bathing immediately following application can cause a missed treatment).
• Imperfect Clinical Testing & Education
o Dogs with inconsistent heartworm testing are at greater risk and must be tested more often.
o Delayed maturity of heartworms can potentially indicate a “negative” antigen test. This may lead to a false sense of security with dog owners and reluctance to retest.
o Heartworm tests may also have become more sensitive (i.e. more accurate), than older generation tests.
Whether there is indeed resistance to heartworm, this same study group (CAPC and AHS) concludes: “The potential for lack of efficacy of traditional control products is not a reason to abandon their use. ” They place additional emphasis on the importance of annual heartworm testing.
Although research into heartworm resistance is on-going, the veterinary industry does recognize the dire consequences if resistance is confirmed. The American Heartworm Society will continue to support and monitor research in this area. And if resistance is confirmed, changes to preventive and therapeutic strategies may need to be implemented in the future.
Key recommendations for veterinarians include:
• Proper use of current heartworm preventives remains effective in the vast majority of dogs.
• Prevention strategies should not be abandoned.
• In the case of confirmed heartworm disease, stage-specific medical management should be implemented.
• CAPC and AHS guidelines should be followed in the “face of reports of lack of efficacy”.
Key recommendations for dog owners include:
• Annual testing for heartworm disease; more often if preventives are missed or high risk.
• Don’t vary from label directions on the dose and frequency.
• Make sure the dog ingests the medication.
• Reduce exposure to mosquitoes
• Get examined by veterinarian immediately if symptoms appear in your dog…i.e. persistent cough, exercise intolerance, body wasting.
• Follow veterinary recommended treatment if dog is diagnosed with heartworm disease.
Heartworm disease is a complex issue. Until more is known about the extent of the issue, pet owners should trust that current heartworm products are still the best choice for prevention in the vast majority of dogs.
No matter where you live, following your veterinarian’s recommendations and giving heartworm prevention every month, year-round as well as annual testing gives you the peace of mind that you are protecting your pets. More