In the early stages of the disease, many dogs show few symptoms or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced clinical signs.
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 and the appearance of a swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop a sudden blockages of blood flow within the heart leading to a life-threatening form of cardiovascular collapse. This is called caval syndrome, and is marked by a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworm blockage, few dogs survive.
Heartworm disease is a serious, progressive disease. The earlier it is detected, the better the chances the pet will recover. There are few, if any, early signs of disease when a dog or cat is infected with heartworms, so detecting their presence with a heartworm test administered by a veterinarian is important. The test requires just a small blood sample from your pet, and it works by detecting the presence of heartworm proteins. Some veterinarians process heartworm tests right in their hospitals while others send the samples to a diagnostic laboratory. In either case, results are obtained quickly. If your pet tests positive, further tests may be ordered.
Dogs. All dogs should be tested annually for heartworm infection, and this can usually be done during a routine visit for preventive care. Following are guidelines on testing and timing:
No one wants to hear that their dog has heartworm, but the good news is that most infected dogs can be successfully treated. The goal is to first stabilize your dog if he is showing signs of disease, then kill all adult and immature worms while keeping the side effects of treatment to a minimum.
Whether the preventive you choose is given as a pill, a spot-on topical medication or as an injection, all approved heartworm medications work by eliminating the immature (larval) stages of the heartworm parasite. This includes the infective heartworm larvae deposited by the mosquito as well as the following larval stage that develops inside the animal. Unfortunately, in as little as 51 days, immature heartworm larvae can molt into an adult stage, which cannot be effectively eliminated by preventives. Because heartworms must be eliminated before they reach this adult stage, it is extremely important that heartworm preventives be administered strictly on schedule (monthly for oral and topical products and every 6 months for the injectable). Administering prevention late can allow immature larvae to molt into the adult stage, which is poorly prevented.
The risk of puppies getting heartworm disease is equal to that of adult pets. The American Heartworm Society recommends that puppies be started on a heartworm preventive as early as the product label allows, and no later than 8 weeks of age.
Yes. The U.S. Food and Drug Administration (FDA) labeling on heartworm preventives states that the medication is to be used by or on the order of a licensed veterinarian. This means heartworm preventives must be purchased from your veterinarian or with a prescription through a pet pharmacy Prior to prescribing a heartworm preventive, the veterinarian typically performs a heartworm test to make sure your pet doesn't already have adult heartworms, as giving preventives can lead to rare but possibly severe reactions that could be harmful or even fatal. It is not necessary to test very young puppies or kittens prior to starting preventives since it takes approximately 6 months for heartworms to develop to adulthood. If the heartworm testing is negative, prevention medication is prescribed.
No. At this time, there is not a commercially available vaccine for the prevention of heartworm disease in dogs or cats. However, research scientists are looking at this possibility. Right now, heartworm disease can only be prevented through the regular and appropriate use of preventive medications, which are prescribed by your veterinarian. These medications are available as a once-a-month chewable, a once-a-month topical, and a once or twice-a-year injection. You should determine the best option for your pet by talking with your veterinarian. Many of the medications have the added benefit of preventing other parasites as well.
For 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. Mosquito species are constantly changing and adapting to cold climates and some species successfully overwinter indoors as well. Year-round prevention is the safest, and is recommended. Remember too that many of these products are de-worming your pet for intestinal parasites that can pose serious health risks for humans.
As with all drugs or pharmaceutical products, heartworm preventives should be used before the expiration date on the package, because it is impossible to predict if it will be effective or safe. The expiration date is established by a series of tests mandated by the U.S. Food and Drug Administration to provide assurance that the product is effective and has undergone no significant deterioration.
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