Is Only My Dog at Risk for Heartworm Infection? What About Cats, Ferrets Or Wildlife?

HEARTWORM FAQS

What is heartworm disease?

ANSWERHeartworm disease is one of the major health problems of dogs in the United States and throughout the temperate and tropical areas of the world. As well as being found in dogs and other species, it is now being found in cats in ever increasing numbers. The disease develops when a pet becomes infected with parasites calledDirofilaria immitisthat are transmitted through the bite of an infected mosquito. Dogs may be infected by a few or up to several hundred heartworms. Cats are similarly infected although usually by only a few worms. Heartworm infection often leads to severe lung disease and heart failure and can damage other organs in the body as well.

Is only my dog at risk for heartworm infection? What about cats, ferrets or wildlife?

ANSWERHeartworm infection primarily affects dogs, but infection may also occur in cats. While cats may not be infected as frequently as dogs, diagnosis in cats is on the rise. Ferrets, as well as other mammals such as wolves, coyotes, foxes and even sea lions can be infected with heartworms. Outdoor pets are at greatest risk for infection, especially in regions of the world with high mosquito populations. However, even indoor pets become infected by heartworms as infected mosquitoes can get into houses. In addition the disease has been found throughout the country.

How big is my pet's risk for heartworm infection?

ANSWERMany things must be considered even if heartworms do not seem to be a problem in a local area. If owners travel with their pets to heartworm-endemicareas, pets will be at risk of infection. Heartworm disease is spreading to new regions of the country each year. Uncared-for dogs and certain wildlife such as coyotes, wolves and foxes can be carriers of heartworms. Mosquitoes blown great distances by the wind and the transportation of infected pets to different geographic locations all contribute to the spread of heartworm disease to areas that may have previously been considered heartworm-free. The best way for easy, safe prevention of heartworm infection is to administer a year-round heartworm preventive as directed by your veterinarian.

How is heartworm disease transmitted from one pet to another?

ANSWERAdult female heartworms living in an infected dog or other host release their young, calledmicrofilaria, into the bloodstream. Mosquitoes become infected by themicrofilariawhile taking a blood meal from these infected animals. During the next 10 to 14 days,microfilariamature to the infective larval stage within the mosquito. When the mosquito then bites another dog, cat or susceptible animal, the infectivelarvaeexit the mosquito's mouth parts and are deposited onto the surface of the animal's skin. The infectivelarvaecan then actively enter the new host through the fresh bite wound.

Inside a new host, it takes a little more than six months for the infectivelarvaeto mature into adult heartworms. Once mature, heartworms may live up to five to seven years, and because of theirlongevity, each mosquito season can lead to an increasing number of worms in our pets.

What physical signs could my dog have?

ANSWERHeartworms may accumulate gradually over years, or quickly when conditions allow exposure to high numbers of mosquitoes carrying infective heartwormlarvae. Clinical signs of disease may not be easily recognized in pets that have been recently infected or in those with low numbers of heartworms as they may not yet exhibit outward signs of disease. However, pets heavily infected with heartworms or those with chronic disease often show prominent clinical signs.

In dogs, signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite and weight loss. As heartworm disease progresses, pets may develop heart failure commonly recognized by an accumulation of fluid in the abdomen giving the pet the appearance of a "swollen belly." Dogs infected with large numbers of heartworms can develop a sudden blockage of blood flow within the heart leading to a life threatening form ofcardiovascularcollapse called "caval syndrome." Signs ofcaval syndromeinclude a sudden onset of labored breathing, pale gums and dark bloody or "coffee-colored" urine. Without prompt surgical removal of the heartworm blockage, few pets survive.

Can you tell me more about heartworm testing in dogs?

ANSWERTwo common types of tests exist for diagnosing heartworm infection in dogs. Because adult heartworms release their young (microfilaria) directly into a dog's bloodstream, a relatively simple blood filter test can identify them. A positive test tells us adult worms are present. Positive means positive. Unfortunately, 15 to 20 percent of heartworm-positive dogs will not have "microfilaria" circulating in their bloodstream and a negative test will sometimes be falsely negative. The most accurate test for detecting heartworm infection in dogs is theantigentest. This test looks for the presence of small proteins released by adult female heartworms into the dog's bloodstream. A positive test tells us mature female worms are present. And, while false negative results are uncommon, they can occur if a pet has a "male-only" infection (since the test detectsantigenfrom females), if only one or two worms are present, or if the female worms are immature.

Your veterinarian may have reason to suspect a negative test result to be inaccurate and might recommend re-testing using other methods. Chest X-rays andultrasoundevaluation can help identify heartworm disease and may be indicated.

How long does it take before heartworm infection can be detected by blood tests?

ANSWERIt takes five to seven months from the time a dog is bitten by infected mosquitoes until a blood test can accurately detect the presence of adult worms.

My dog tested positive for heartworms. What does this mean?

ANSWERA positivemicrofilariaorantigentest indicates that your dog has adult heartworms in the heart and arteries of the lungs. Even if your dog is not showing any symptoms, there may already be damage to the heart, blood vessels and lungs. If not treated, this can lead to serious, even life-threatening disease. If treatment is started before symptoms are obvious, the chances are very good that your dog will not have any significant complications following treatment.

Do you need a prescription for heartworm preventive medication? If so, why?

ANSWERYes, heartworm preventives must be purchased from your veterinarian or with a prescription through a pet pharmacy. The U.S. Food and Drug Administration (FDA) labeling on heartworm preventives indicates that the medication is to be used by or on the order of a licensed veterinarian. This means a veterinarian must have a doctor-client-patient relationship in order to write a prescription. Typically, prior to prescribing a heartworm preventive, the veterinarian will perform a simple heartworm test to make sure your dog doesn't already have adult heartworms. It is not necessary to test very young puppies prior to starting preventives since it takes approximately six months for adult heartworms to develop to adulthood in a dog. If the pet is free of heartworms, prevention is prescribed. Giving preventives to dogs infected with heartworms can lead to rare but possibly severe reactions that could be harmful or even fatal to the dog.

There are many types of medications available for heartworm prevention. What is the difference between the daily and monthly tablets?

ANSWERUntil the late 1980s, the only medication available for the prevention of heartworms had to be given daily. These products work by killing the microscopic heartwormlarvaedeposited by the mosquito, but must be given every single day to be most effective. This is because infective heartwormlarvaequickly molt within two to three days into their fourth stage of development. This fourth stage can not be killed by the daily medication. Daily heartworm preventives have largely been replaced by monthly products and are no longer commercially available in the United States. Compounding pharmacies still formulate daily preventives on an "as needed" basis. An important note to keep in mind is that monthly medications are quickly eliminated from a pet's system and do not continue to work for 30 days. Instead they work "backwards" to eliminate thelarvaethe pet acquired the previous 30 days, in essence, "de-heartworming" our pets each month in many cases, these monthly preventives control other parasites too.

How do monthly heartworm preventives work?

ANSWERFortunately, there are many very effective once-a-month heartworm preventives available today. Some are chewable tablets and others are topically-applied solutions. Monthly heartworm preventives, because of their ease of use and effectiveness, have become the popular choice for prevention of heartworm disease. Unlike the daily products of the past, these compounds are capable of killing developing heartwormlarvae, and administering the preventive every month will effectively eliminate the chance of infection. Check with your veterinarian to see which product is right for your pet.

Why do dogs need to be blood tested before starting heartworm medication?

ANSWERBefore starting a preventive program, all dogs should be tested for heartworms. Giving preventives to dogs that have adult heartworm infection can be harmful or even fatal to the pet.

Adult heartworms produce millions of microscopic "baby" heartworms (calledmicrofilaria) into the bloodstream. When you give a monthly heartworm preventive to a dog with circulatingmicrofilaria, this can cause the sudden death ofmicrofilaria, triggering a shock-type reaction. Even if your dog does not have this type of reaction, heartworm preventives do not kill the adult heartworms (although they may shorten the worms' life expectancy). This means an infected dog will remain infected with adult heartworms.

Unfortunately, as long as a pet remains infected, heartworm disease will progress and damage the heart and lungs, which can lead to life threatening problems. Giving heartworm preventives to heartworm-positive dogs can mislead an owner into thinking everything is all right, while within a pet, heartworm disease is worsening.

How often should I have my dog tested for heartworm infection?

ANSWERAnnual testing is recommended for several important reasons. First, many of us do not take our own medications as directed let alone medicate our pets. We're busy; we forget; we miss a dose here and there. Second, even if you never miss a dose there is nothing to prevent your dog from eating some grass and vomiting up the medication you just gave. Your pet would be without protection for an entire month. Third, if your pet accidentally became infected with heartworms, your veterinarian needs to detect it as soon as possible before irreversible heart and lung damage occur. Early detection and treatment are always best. Finally, some heartworm tests now come combined with tests that monitor other significant diseases (Lyme disease, Ehrlichiosis and Anaplasmosis). With annual testing, you know your pet is heartworm free and not infected with these serious tick-borne diseases, some of which could affect family members. The tests are quick and accurate and make sure your pet is free from infection. Annual testing provides peace of mind in knowing that your pet is free of heartworms, and should your pet be infected, it assures you of early diagnosis.

I heard that certain heartworm prevention medications will also protect against intestinal parasites. Is this true?

ANSWERCertain heartworm preventive products are also effective in removing specific intestinal (and external) parasites and are labeled for such uses. They either contain a single active ingredient that is effective against several parasites including developing heartworm or a combination of ingredients to achieve control of many different parasites. Such products have been tested and meet the same safety requirements as the heartworm-prevention-only products.

I heard that the heartworm prevention medication is toxic to certain breeds of dogs, particularly collies. Is this true?

ANSWERWhen given as prescribed, all of these medications are safe. It has been found, however, that some dogs are genetically predisposed to be more sensitive when doses dramatically exceed the recommended amount. Problems can occur when products designed for large animals (horses, cattle, pigs) are inappropriately used in dogs, or when dogs are dosed incorrectly. Heartworm preventives are safe for all breeds of dogs when used as directed.

Is a puppy born with immunity to heartworm disease?

ANSWERNo, even nursing puppies are at risk for heartworm infection. Puppies of any age exposed to mosquitoes carrying infectivelarvaecan become heartworm-infected, so it is important to begin prevention early. Puppies can be started on heartworm preventive as early as four to eight weeks of age, depending on the label recommendations of the preventive.

I live in Minnesota. How long should my dog be on heartworm prevention?

ANSWERFor a variety of reasons, even in regions of the country where winters are cold, the American Heartworm Society is now recommending a year-round prevention program. Dogs have been diagnosed with heartworms in almost every county in Minnesota, and there are differences in the duration of the mosquito season from the north of the state and the south of the state. Year-round prevention is the safest, and is recommended.

I live in Arizona where it is very dry and there are very few mosquitoes. My vet says I should use monthly prevention. What should I do?

ANSWERThere are different climates in Arizona, including micro-climates such as irrigated fields, backyard ponds and man-made golf courses, which affect the severity and duration of the mosquito season. We also know that areas can have heartworm infection in wild species such as coyotes, and these infected wild animals can be a source of infection to your dog or cat as well. Despite the fact that heartworm disease may not be diagnosed as often in Arizona as in some other states, it is definitely present.

The American Heartworm Society is now recommending year-round prevention, even in states like Arizona. And remember, if your dog or cat travels out of state with you or to another part of Arizona where mosquitoes are common, they may be at higher risk of exposure.

Are heartworms more common in certain areas of the United States?

ANSWERHeartworms have been found in all 50 states. Certain areas have a higher risk of heartworm. Some very high risk areas cover large regions, such as near the Atlantic and Gulf coasts and along river tributaries. Most states have "hot spots" where the heartworm infection rate is very high compared to other areas in the same state. Factors affecting the level of risk of heartworm infection include the climate (temperature, humidity), the species of mosquitoes in the area, presence of mosquito breeding areas and presence of animal reservoirs (such as infected dogs or coyotes).

Is there an effective natural prevention for heartworm?

ANSWERNo, there is no natural prevention for heartworms.

Is it OK to have surgery on a heartworm positive dog or cat?

ANSWERIf surgery can be postponed, it is better to treat a dog for the heartworms first. If this isn't possible, your veterinarian can assess your dog and make appropriate recommendations. Since cat are not routinely treated for heartworm infection, your veterinarian can assess your cat and make appropriate recommendations.

How often should I have my cat tested for heartworms?

ANSWERHeartworm infection in cats is easily overlooked and harder to detect than in dogs. The preferred method for screening cats include, the use of both anantigenand an antibody test. Your veterinarian may also use X-rays orultrasoundto look for heartworm infection. Your cat should be tested prior to starting a preventive, and annually thereafter. Remember, since there is no approved treatment for heartworm infection in cats, prevention is critical.

What are the signs of heartworm disease in cats?

ANSWERSigns of heartworm disease in cats can be very subtle and misleading. Signs may include coughing,asthma-like attacks, intermittent vomiting, lack of appetite, or weight loss. Occasionally ataxia (difficulty walking), seizures, fluid accumulation in the abdomen (ascites) andsyncope(fainting) have been reported as well. Unfortunately, the first sign in some cases is sudden collapse of the cat, or sudden death.

My cat goes outside daily. Should I put her on heartworm preventive medication?

ANSWERThe prevalence of feline heartworm infection parallels that found in the local dog population, but at a somewhat lower rate. If heartworms are found in dogs in your area, cats are also at risk and should be placed on preventive medication. The products that prevent heartworm disease also remove intestinal parasites that are potentially contagious to family members. Intestinal parasites are a year-round problem and require year-round treatment and prevention.