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Heartworm Disease in Dogs

Heartworm Disease in Dogs

Unfortunately, the area we live in has a high prevalance of heartworm disease so this post is going to focus on the basics of this disease in dogs ~ what it is, how to prevent it and even the treatment. (Cats can get heartworm disease too, but the diagnosis and symptoms are dramatically different.) At Best Friends, we see 20 - 30 cases of heartworm disease in dogs a year! Granted, some of these dogs came from shelters, but many are from households where the owners didn't give preventative at all, or skipped several doses. So please, please, please - give your pet a heartworm preventative year-round.

  • So what is a heartworm? The heartworm is a parasite that spreads through the blood of the infected host (here, the dog). Heartworms can mature up to 10 – 12 inches in length, making their home in the right side of the heart or the lung arteries.
  • How is the worm spread? It is spread thru mosquitos. The life cycle of the heartworm starts when a mosquito bites an infected animal, ingesting the young heartworm (microfilariae) along with the blood. The microfilariae mature for the next 10 to 14 days developing into infective larvae inside the mosquito. When the mosquito bites another dog, the larvae are left behind to enter the fresh wound. It takes about 6 or 7 months for the larvae to make their way to the heart and vessels of the lungs, where they mature and reproduce. The offspring start the cycle again when picked up by a mosquito.
  • Who can get the disease? The most common carriers are dogs, foxes, coyotes, wolves and ferrets. Cats can also get heartworm disease (HWD), but the disease manifests itself differently in cats. Human cases of heartworm disease are extremely rare. Dogs are most commonly diagnosed with heartworms.
  • Are there heartworms in this area? Based on previous years' research, we are able to forecast the prevalence of heartworm disease for the United States. Our region (St. Louis and surrounding areas), has a history of high to very high infection rates in dogs.
  • Can heartworm disease be prevented? YES! There are a number of products available to prevent heartworms in your dog (and cat too)! All approved heartworm preventatives are highly safe, easy to use, relatively inexpensive and often provide treatment for additional parasites. We carry both Heartgard & Sentinel in-house, and many other products on our online store.
  • How does heartworm prevention work? Monthly heartworm prevention interferes with the central nervous system of the larva. It’s not effective against the adult form of the worm, but is sometimes given to heartworm-infected dogs to prevent further growth if supervised by your veterinarian.
  • Why is heartworm prevention a prescription? The drug that is in heartworm prevention, can affect some types of dogs in very bad ways. It's important to never give heartworm prevention to any pet that has not been tested for heartworm disease. This is because if there are any present heartworms in your pet, the medicine will kill the adult heartworms, which can cause serious heart failure and even death. That is why most products are given as a preventative, which kill the larvae before they turn into adult heartworms.
  • Do I have to give it year-round? Some people believe that heartworm medication should only be given during the warm months of the year, but the medication only works on parasites your pet has been exposed to in the preceding month, so the American Heartworm Society recommends that heartworm prevention be used year round.
  • How do I know if my pet has heartworm disease (HWD)? A simple blood test annually is a good start to detecting whether there are heartworms present in your dog. If the heartworms are young, if there are too few to be detected or if the pet is carrying only male worms, the test may not detect the infection.
  • What are the symptoms? Some dogs can be infected for years without displaying any physical symptoms. But for most dogs, as heartworms slowly cause damage to the pulmonary arteries of the lungs, signs of disease may include:

o A mild persistent cough

o Reluctance to exercise

o Fatigue after moderate activity

o Decreased appetite

o Weight loss

Severe or prolonged infections can lead to heart failure. Symptoms often include:

o A sudden onset of labored breathing

o Pale gums

o Dark red or “coffee colored” urine

o Inability or unwillingness to move

  • If my pet tests positive for HWD, how is it treated? Adult heartworms in dogs are killed using a drug called an adulticide that is injected into the muscle through a series of treatments. Treatment may be administered on an outpatient basis, but hospitalization is usually recommended.
  • Why is HWD treatment so expensive? Office visits, pre-treatment tests, hospitalization, and drug costs all contribute to the cost of treating your pet for heartworms and may vary significantly from dog to dog. Treatment for adult heartworms is very expensive and does vary according to weight, age, and overall health status and may be based on individual client needs and expectations.
  • What if I don't get my HWD positive pet treated? Because HWD is very complex and may affect many vital organs including the heart, lungs, kidneys, and liver, the outcome of infection varies greatly among patients. The adult worms cause inflammation of the blood vessels and can block blood flow leading to pulmonary thrombosis (clots in the lungs) and heart failure. HWD can also lead to liver or kidney failure, causing death by one or a combination of these problems.

Dogs that are exposed to a large number of infective larvae all at one time are at great risk of sudden death due to massive numbers of developing larvae bombarding the vascular system.

Other animals may live for a long time with only a few adult heartworms and show no clinical signs unless faced with an environmental change (extreme increase in temperature, for example) or other significant health problem.

For more information, please visit The American Heartworm Society or the Companion Animal Parasite Council.

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