Protect your pet from this insidious disease carried by mosquitoes
What are heartworms?
Heartworms are large worms that live in the hearts of dogs and cats. They are also found in
other species, including ferrets, foxes, wolves, sea lions, and horses. Dogs are the common
host for this parasite. This worm is also known as Dirofilaria Immitis. It is a long, spaghetti-like worm that can be anywhere from 6 to 10 inches in length (~17 - 27 cm).
How are heartworms transmitted?
In addition to the animal 'host', heartworms need a mosquito to complete their life cycle.
1. A mosquito bites a heartworm-infected animal.
2. The mosquito is then carrying microscopic versions of the heartworm, called
3. When the mosquito bites another dog or cat, that animal is now infected with the
4. Within 70 to 90 days, the microfilariae have made it through the tissues to the animal's
heart, where they reproduce (providing both male and female worms are present) and live for several years. If both sexes of worms are present, they wil be producing their
own little microfilariae within 6 - 7 months after that mosquito bite.
What are the signs of heartworm disease?
The signs vary according to number of worms present, stage of life cycle, age and species of
host. The heartworms live primarily in the right side of the heart and lung, and can cause significant damage and even death. Here are some general signs for the most common
DOG - possible heartworm signs.
Acute disease - usually no clinical signs (the dog just acquired the disease)
Mild to moderate - cough, reluctance/inability to exercise
Severe - marked shortness of breath, coughing, fainting episodes, weight loss, fever,
CAT - possible heartworm signs
The signs of heartworm disease are different in the cat than the dog. Cats can present
with sudden death (no other signs) or can live with the disease free of clinical signs. Most commonly, heartworm disease in the cat mimics feline asthma - coughing and difficulty
breathing. Vomiting can be another sign of feline heartworm disease (vomiting is a common sign in many feline diseases).
Could my dog or cat be at risk?
Yes, depending on your geographic location. Heartworm disease is now worldwide, and mosquitoes are too.
Diagnosis is most commonly done by a blood test in your Veterinarian's office. Additionally, x-ray, ultrasounds, or other tests may be performed.
Treatment for heartworm is not without some risk. Bloods tests are used to assess kidney
and liver function before initiating treatment. The worms are kil ed slowly, so as not to cause
a sudden blockage in the heart or lungs, and the patient must be kept quiet. The next phase is medication to kil the remaining microfilariae.
Your veterinarian wil first test your pet and find the heartworm status to be negative. You
can then begin heartworm prevention. Annual re-testing is recommended. Prevention is in the form of a chewable daily or monthly tablet, given in the summer months or year round,
depending on the climate where you live. The most commonly prescribed oral heartworm preventatives are: and
A topical treatment, by Pfizer is effective against heartworms,
fleas, ear mites, sarcoptic mange (dogs), hookworms (cats), roundworms (cats), and the American Dog Tick (Dermacentor variabilis) (dogs). The American Dog Tick is the principal
vector for a Rickettsial disease, Rocky Mountain Spotted Fever, in dogs and humans. Revolution™ is typically applied once a month for parasite control.
Revolution™ works by absorbing through the skin to the bloodstream, where it prevents
heartworms and treats intestinal parasites. Revolution™ also disperses from the blood to the sebaceous glands (microscopic oil glands in the skin) to act as a reservoir of drug for
protection against fleas, ticks, and mites.
Drug precautions. This drug should not be used in animals that are sick, malnourished, debilitated, or underweight. For more information about this drug, please see th
There are a lot of misconceptions about One of the most
common misconceptions is that using ivermectin-based heartworm preventive medications for a "slow kil " is the preferred way to treat canine heartworm disease.
Options for the Treatment of Heartworm Disease in Dogs
Essentially, there are two distinctly different methods of treating heartworm disease in dogs.
Treatment with melarsomine (Immiticide®), which kil s the adult heartworms, is one
method of treatment. There are different protocols that are used under different
circumstances but the bottom line with this method of treatment is that the adult
heartworms are kil ed in a relatively short timeframe. With this method of treatment, ivermectin-based preventives are also administered concurrently on a monthly basis to
Monthly administration of ivermectin-based heartworm preventive medications alone are
sometimes used as a second method of heartworm treatment. This is referred to as the
"slow kil " or "soft kil " method.
There is risk of complications occurring with both treatment methods.
What Are the Advantages of the "Slow Kill" Ivermectin Method of Canine
Often, the "slow kil " method of heartworm treatment is used because of financial considerations. Unfortunately, the melarsomine treatment method is quite expensive.
However, monthly ivermectin is affordable.
There are situations in which melarsomine treatment cannot be pursued due to other health
issues. In these situations, in addition to monthly ivermectin adminstration functioning as a
"slow kil " way to rid the infected dog of heartworms, it also clears the infected dog's blood stream of the larval form of heartworms (microfilaria). These microfilaria have the ability to
infect mosquitoes which feed on the infected dog. The infected mosquito can then spread heartworms to other dogs. Monthly ivermectin administration stops this from happening and
helps to protect other dogs in the area.
What Are the Disadvantages of the "Slow Kill" Ivermectin Method of Heartworm
Treatment in Dogs?
Thdoes not recommend the use of monthly ivermectin
products to treat dogs infected with heartworm disease. There are several reasons that using melarsomine to kil the adult heartworms is safer and more effective for your dog than using
The adult heartworm is responsible for the damage to heart and lungs that causes the
Melarsomine is the only medication we have available that can kil these adult worms.
Ivermectin kil s the larval stages but not the adult worms. It also does not shorten their
With time, as long the larval stages do not survive and no new infections occur, the adult
heartworms wil die of "natural causes." However, this may take as long as two years to
As long as there are adult heartworms living in the heart and pulmonary arteries, the
damage to these organs wil continue. That means that while your dog is receiving only
the monthly ivermectin medication, his heartworm disease wil continue to progress and his heart and lungs can suffer severe damage.
Another reason that monthly ivermectin treatment is not recommended for heartworm-
infected dogs is that some parasitologists believe that the "slow kil " method has
contributed to the development of strains of heartworms that are resistant to heartworm
preventive medications. (Dr. Byron Blagburn, webinar, Emerging Issues in Heartworm
Prevention, presented by DVM360, 4/20/2011)
In cases where melarsomine treatment is not practical for a dog with heartworms, monthly ivermectin is preferable to no treatment. However, it should be remembered that this
method of heartworm treatment has serious short-comings and is not the preferred method
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