Canine Heartworm Disease
Canine heartworm disease is a potentially deadly infection, caused by worms (Dirofilaria immitis) that may grow to be 14-inch-long adults. These worms live in the right side of the heart and arteries of the lungs. Dogs of any age and breed are susceptible to infection. Heartworm infection can cause potentially serious damage to these arteries, eventually leading to heart failure, and in severe cases, damage other organs such as the liver and kidneys. In extreme cases, a dog can be infected with several hundred heartworms. Cats are also susceptible to the disease.
Who can get heartworms?
Dogs are considered the definitive host for heartworms (Dirofilaria immitis). However, heartworms may infect more than 30 species of animals (e.g., coyotes, foxes, wolves and other wild canids, domestic cats and wild felids, ferrets, sea lions, etc.) and humans as well. When a mosquito carrying infective heartworm larvae bites a dog and transmits the infection, the larvae grow, develop, and migrate in the body over a period of several months to become sexually mature male and female worms. These reside in the heart, lungs, and associated blood vessels. Even as immature adults, the worms mate and the females release their offspring (microfilariae), pronounced: (micro fil ar ee), into the blood stream. The time elapsed from when the larvae enter the dog until the minute offspring can be detected in the blood (pre-patent period) is about six to seven months. The male heartworms (four to six inches in length) and the females (10-12 inches) become fully grown about one year after infection, and their life span in dogs appears to be at least five to seven years.
How is it transmitted?
Coinciding with mosquito season, heartworm disease is spread by mosquitoes that become infected with microfilariae while taking a blood meal from an infected dog. The microfilariae mature into the infective larval stage within the mosquito. When the mosquito then bites another dog, cat, or susceptible animal, it then passes the larvae into the animal's blood stream through the bite wound, resulting in heartworm infection. It then takes a little over six months for the infective larvae to mature into adult worms that can live for five to seven years in the dog.
Distribution in the U.S.
Canine heartworm infection is widely distributed throughout the United States. Heartworm infection has been found in dogs native to all 50 states. All dogs regardless of their age, sex, or habitat are susceptible to heartworm infection. The highest infection rates (up to 45%) in dogs (not maintained on heartworm preventive) are observed within 150 miles of the Atlantic and Gulf coasts from the Gulf of Mexico to New Jersey and along the Mississippi River and its major tributaries. Other areas of the United States may have lower incidence rates (5% or less) of canine heartworm disease, while some regions have environmental, mosquito, and dog population factors that allow a higher incidence of heartworm infection. Regions where heartworm disease is common have infections diagnosed in dogs as young as one year of age, with most areas diagnosing infections primarily between the ages of three and eight years. Although there are differences in frequency of infection for various groups of dogs, all dogs in such regions should be considered at risk, placed on prevention programs and frequently examined by a veterinarian.
The American Heartworm Society (AHS) estimates that 27 million dogs in the U.S. are currently not on a heartworm preventative, needlessly exposing them to potential infection from heartworm. Heartworm disease is a serious canine health concern that threatens animals in all 48 contiguous states and Hawaii, as well as throughout the temperate regions of the world.
What are the signs of heartworm?
For both dogs and cats, clinical signs of heartworm disease may not be recognized in the early stages, as heartworms tend to accumulate gradually over a period of months and sometimes years and after repeated mosquito bites. In dogs, recently infected animals may exhibit no signs of the disease, while heavily infected animals may eventually show clinical signs, including mild, persistent cough, reluctance to move or exercise, tiredness after only moderate exercise, reduced appetite, and weight loss. Cats may exhibit clinical signs that are very non-specific, mimicking many other feline diseases. Chronic clinical signs include vomiting, gagging, difficulty breathing or rapid breathing, lethargy and weight loss.
How can heartworms be detected?
Detection of heartworm infection in apparently healthy animals is usually made with blood tests for microfilariae or a heartworm substance called an "antigen," although neither test is consistently positive until about seven months after infection has occurred. Heartworm infection may also be detected through x-ray and/or ultrasound images of the heart and lungs, although these tests are usually used in animals that are known to be infected.
How can I prevent heartworm disease?
Because heartworm disease is completely preventable, the AHS recommends that pet owners take steps now to talk to their veterinarian about how to best protect their pets from this dangerous disease. According to the AHS, heartworm prevention is safe, easy and inexpensive compared to treating a dog or cat after worms have matured into adults. While treatment for heartworm disease is possible, it is a complicated and expensive process, taking weeks for infected animals to recover.
There are a variety of options for the prevention of heartworm infection for dogs, including daily and monthly tablets and chewables, monthly topicals or an injectable administered by your veterinarian that provides protection for six months. For cats there are monthly tablets or a topical solution. All of these methods are extremely effective and when administered properly on a timely schedule, heartworm infection can be completely prevented.
Currently, there are no products in the United States approved for the treatment of heartworm infection in cats. Cats have proven to be more resistant hosts to heartworm than dogs, and often appear to be able to rid themselves of infection spontaneously. In severe cases of the disease, veterinarians will treat an infected cat with supportive therapy measures.
Paw's Place has a heartworm test done on every dog that comes to the shelter. Unfortunately, because the general public is not aware that all dogs in our area will get heartworm disease and how inexpensive it is to prevent the disease, most of the dogs we get test "positive" for heartworm disease. The "low positive" dogs are in the early stages of the disease. The "high positive" dogs are in the later stages of the disease. All dogs that test positive (high or low) are treated by the veterinarian. Heartworm prevention is very inexpensive, but for dogs infected with heartworms, heartworm treatment is very costly (from $300 to $1,200 depending on the vet) and is successful in 9 out of 10 cases. Some of these "high positive" animals are already too weak from the effects of the disease to be able to fight to survive.
Every dog at Paw's Place is on heartworm prevention medication!
And we routinely spray for mosquitoes all year long!
It's common sense:
Mosquitoes are found in all 50 states! A mosquito becomes infected when it bites an infected dog. Infected mosquitoes then bite and infect an uninfected dog!
Canine heartworm disease has been found in dogs in all 50 states!
Dogs that do not receive consistent periodic preventative measures for heartworm disease may only live for two to five years after they are infected.
Keeping your pet inside will not guarantee that it will not get heartworm disease! Mosquitoes will eventually get inside your home (they have an opportunity to come in every time you open the door)!
Is your dog on heartworm preventive medication?
WARNING: Before you rush out and buy HeartGuard, Interceptor, Sentinel, Ivomec, or some other brand, have your pet tested for the disease. It is possible that if you give your pet these medications by yourself, prior to having your pet tested at your vet, you might kill the animal! If the pet was actually "high positive," heartworms killed by the medication may collect in one spot in a blood vessel, and may clog the flow of blood (an embolism) which may cause the animal's sudden death.
