HEARTWORM FAQs
What is heartworm disease?
ANSWER 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.
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.
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. 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.
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 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.
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.
My cat never goes outside. Should I put her on heartworm preventive medication?
ANSWERWhether living indoors or outdoors, cats can be exposed to mosquitoes carrying heartworm disease. While the outdoor cat is more likely to be bitten by a higher number of mosquitoes, mosquitoes do get into our homes and are capable of biting our indoor pets. It is important to realize that a single heartworm can cause severe consequences. Multiple studies have reported a significant number of heartworm infections in cats living exclusively indoors. If heartworms are found in dogs in your area, cats are also at risk and should be placed on preventive medication.
Can people get heartworm disease from a mosquito bite?
ANSWERYes, it is possible. Fortunately, people are not natural hosts for heartworms. However, there have been cases in which thelarvaemigrate to the person's heart and lung arteries. In these cases, thelarvaedied before they matured into adult worms and the person's body produced "scar tissue" around the worm. This can look like a spot on the lungs on an X-ray.
According to medical reports, most people (over 50 percent) infected with a heartworm or two never had symptoms, but some people (33 percent) had chest pains, some (20 percent) had a cough, and fewer (15 percent) had a fever. About 1 percent experienced spitting up blood or difficulty breathing. Most people that are diagnosed with heartworms are "smokers." When the physician sees the white spot (called a "coin lesion") on the chest X-ray, they are also concerned that it might be primary lung cancer. Additional testing or even surgery (to remove the suspect spots) may occur. It is after surgical removal and microscopic evaluation of the spot that some of these cases have been identified as heartworm, rather than cancer. Unfortunately, there is no reliable diagnostic test for heartworm disease in humans.
I have missed two months of heartworm prevention for my dog. Should I worry?
ANSWERYes, you should worry. You need to consult your veterinarian, and immediately start your dog back on monthly preventive and retest in seven months. The reason for testing seven months later is that heartworms must be approximately seven months old before the infection can be diagnosed.