What you should know about Heartworm disease, testing and the monthly preventative.
1. What is heartworm disease?
Heartworm 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 called Dirofilaria immitis that are transmitted through the bite of an infected mosquito. Heartworms are “foot long” worms that live in the heart and major blood vessels of the lungs. Heartworm disease is spread by mosquitoes to both dogs and cats as well as other animals, such as foxes, coyotes, and wolves, which act as reservoirs and help spread the disease. While dogs can be infected with just a few to hundreds of worms, cats generally have low worm counts. Even one or two heartworms, however, can be life threatening to a cat. While there is a treatment for infected dogs it is time consuming and costly. There is NO treatment approved for cats so prevention is critical. Heartworm infection often leads to severe lung disease and heart failure and can damage other organs in the body as well.
2. How can I tell if my pet has heartworms?
Early on, many dogs show little or no symptoms. The longer the infection persists, the more likely symptoms will develop. Clinical signs depend on the number of these “foot-long” worms in the dog’s heart and major blood vessels, the dog’s lifestyle, and any other health issues the pet has. More active dogs, 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 of cardiovascular collapse called caval syndrome. Signs of caval syndrome include 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.
In cats the presence of just one or two worms can lead to severe respiratory symptoms and even death. The symptoms in a cat can easily be confused with a respiratory infection like pneumonia or “asthma-like” symptoms with wheezing or shortness of breath. Other than supportive care, there is no approved, safe treatment for heartworm-infected cats. Prevention is critical!
3. Can you tell me more about heartworm testing?
Two 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% 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 the antigen test. 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 detects antigen from females), if only one or two worms are present, or if the female worms are immature.
In cats, there are two different tests that can be helpful in determining if a cat has a heartworm infection. The antibody test can tell us if a mosquito has infected the cat with microscopic baby heartworms called larvae. This is important because the arrival and death of even these baby heartworms can cause respiratory disease in the cat (wheezing, coughing, “asthma-like” symptoms). The antibody test has the advantage of being able to detect infection by both male and female worms, as larvae of either sex can give a positive test as early as 2 months after infection. A “positive” antibody test confirms exposure to heartworm disease!
While the antigen test is the “gold standard” in diagnosing heartworms in dogs, it can commonly give a “false-negative” result in cats. This finding is more common than in dogs because infected cats generally have only a few adult heartworms present, because “single-sex” infections may consist of only male worms, and because immature but symptomatic infections are more common in cats. A positive antigen test does indeed mean that adult female heartworms are present but a negative test does not rule out an infection!
In both dogs and cats your veterinarian may have reason to suspect a negative test result to be inaccurate and might recommend follow-up testing, chest x-rays, and/or cardiac ultrasound to help identify heartworm disease.
4. How often should I have my dog tested for heartworm infection?
All dogs should be tested for heartworms every 12 months. This usually takes place during a pet’s annual visit for routine preventive care and is your insurance policy against what could turn out to be a serious illness.
Nothing is perfect. People miss doses of medication or fail to give it the same day each and every month. Pets vomit frequently and at times “lose” their dose of prevention. At times they spit it out. Heartworm preventives are “nearly” perfect, but nothing is perfect and the danger of not testing is in not knowing.
If you administer heartworm prevention to your pet as scheduled, the chance of your pet developing an infection is extremely low. Your veterinarian’s job, however, is to ensure your pet’s good health by detecting problems before they progress into serious issues. Heartworm disease is a serious issue and when present, should be detected and treated as soon as possible. Testing annually is important.
5. How long should my dog be on heartworm prevention?
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.
Home FurEver has four heartworm positive dogs right now. If you’d like to make a tax deductible donation toward their care, please click here: https://www.youcaring.com/hfevetbills