Heartworm (Dirofilaria immitis) is a parasite that lives in the heart and the pulmonary arteries of a dog. This disease has been reported in every state and is most prevalent in areas where mosquitoes are in high numbers. Dogs get Heartworms from mosquito bites. These larval stages enter the skin through the bite and then migrate through the body to the blood vessels, where they are carried up to the heart. Dogs are not infected directly from dog to dog, but from dog to mosquito to dog.
Clinical Signs
Once the larva have developed into adult worms (this takes about 6 months), clinical signs may or may not be seen. Dogs that have a cough, breathing difficulty, exercise intolerance, or syncopal (fainting episodes) should be evaluated for Heartworm disease. If a dog is only infected with the larva, they usually do not show any signs at all. This is part of the reason this disease can be so deadly. By the time we are seeing clinical signs for Heartworm disease, they not only have Heartworm Infection but also have Heartworm Disease, which must be treated far more aggressively. Heartworms, in the adult stage, can do a lot of damage to the body.
Heartworm and its effect on the body
Worms living in the pulmonary arteries do a tremendous amount of damage. They damage the lining of the artery and cause an inflammatory response to ensue. This results in immune cells that try to destroy the parasite, but cannot kill it. This inflammation and continued inflammation, casue more damage to the surrounding tissue. These arteries become dilated from the inflammation and appear tortuous on an x-ray. This can also result in abnormal blood clotting and dogs can develop embolisms, which block the arteries. This results in shunting of blood to other arteries that are not blocked by worms. What happens in effect, is an overtaxed plumbing system and the pressure and inflammation cause fluid to accumulate in the lungs around the arteries. The complicating result is that blood is not appropriately oxygenated in the lungs and cannot deliver adequate oxygen to the rest of the body. This commonly results in coughing and exercise intolerance. Some dogs can cough up blood or fluid and it is not uncommon to see secondary infection in the lungs. With this kind of pressure in the arteries, the heart has to work harder to pump blood where it needs to go. This leads to a higher blood pressure and can have drastic effects on the right side of the heart. Worms can create even less space in the right side of the heart as they fill the ventricle. Obviously, the can tax the heart to a point of no return. Sometimes, a heart murmur or arrhythmia can be ausculted on physical exam if this is the case. As with any murmur, sudden death can occur. When this right sided heart failure occurs, fluid can back up in the abdominal cavity, which can result in a distended abdominal appearance and difficulty breathing. The immune system does not stop trying to control all of this and the inflammatory response becomes systemic, causing irritation and damage throughout the body. As a result, these dogs become very uncomfortable.
Treatment for Heartworm Disease
Treatment depends on staging of the disease, the area of infection and the dog’s clinical signs. This means your vet will need to decide how to treat the disease. This process is usually costly and is not without pain and involves crating/kenneling your dog for several weeks. This is not an easy process for owners to go through. It is important to note that even though treatment for Heartworm disease exists, this disease can be fatal.
Heartworm Prevention
There are lots of different types of heartworm preventive that you can use for your dog. Please discuss this with your vet and decide which one might be best for your dog. Some not only cover heartworms, but also cover gastrointestinal parasites and protect against fleas and ticks. Some of the more popular brands include Heartgard, Advantage, Interceptor, Sentinel, Revolution.
Heartworm in Cats
Heartworm disease in cats is quite a bit different from dogs. Cats are so small that only one adult worm can be enough to cause heart failure. Cats also appear to have more inflammation with immature worms than dogs do. Commonly, cats that are Heartworm positive will not show many clinical signs and often death is seen before anything other clinical signs. Please contact your vet for more information on Heartworm disease in cats.
Prevention
The good news is that feline heartworm infection is 100% preventable and there are currently four products on the market that are reliably effective. Keep in mind that cats need a higher dose of ivermectin than dogs, so it is important that you buy a product marketed for cats. It is also important that your cat be tested prior to administration of the preventive.
i have a 9 year old female lab. for the past week she hasnt been eating well at all. she is drinking ALOT of water and she is very lethargic. she also is spotting when she lays down. it is a pinkish color.and she is licking herself alot. i think she may be in heat,but usually it is red in color.she has never "leaked" when she lays down like she has been. she seems to have a loss in energy and she is coughing. .not alot ..but frequent enough for concern. i did get her to eat some boiled chicken and rice.when she has went into heat in the past it hasnt quite been like this? any suggestions?
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Questions Answered By:
Dr. Lauryn Spohn, DVM
