What is heartworm disease?

Heartworm disease is one of the major health problems in dogs in the United States and other parts of the world. The disease develops when a pet becomes infected with parasites called Dirofilaria immitis that are transmitted through the bite of an infected mosquito. Dogs may be infected by a few or up to several hundred heartworms. Heartworm disease often leads to severe lung disease and heart failure and can damage other organs in the body as well which can be fatal.

How is heartworm disease transmitted from one pet to another?

Adult female heartworms living in an infected dog or other host release their young, called microfilaria, into the bloodstream. Mosquitoes become infected by the microfilaria while taking a blood meal from these infected animals. During the next 10 to 14 days, microfilaria mature to the infective larval stage within the mosquito. When the mosquito then bites another dog, cat, or susceptible animal, the infective larvae exit the mosquito’s mouth parts and are deposited onto the surface of the animal’s skin. The invective larvae can then actively enter the new host through the fresh bite wound.

Why do dogs need to be blood tested before starting heartworm treatment?

Before starting a preventative program, all dogs should be tested for heartworms. Giving preventives to dogs that have adult heartworm infection can be harmful or even fatal to the pet.

Adult heartworms produce millions of microscopic “baby” heartworms (called microfilaria) into the bloodstream. When you give a monthly heartworm preventative to a dog with circulating microfilaria, this can cause the sudden death of microfilaria, triggering a shock-type reaction. Even if your dog does not have this type of reaction, heartworm preventives do not kill the adult heartworms (although they may shorten the worms’ life expectancy). This means an infected doge will remain infected with adult heartworms.

Unfortunately, as long as a pet remains infected, heartworm disease will progress and damage the heart and lungs, which can lead to life threatening problems. Giving heartworm preventives to heartworm-positive dogs can mislead an owner into thinking everything is all right, while within a pet, heartworm disease is worsening.

How often should I have my dog tested for heartworm infection?

Annual testing is recommended for several important reasons. First, many of us do not take our own medications as directed let alone medicate our pets. We’re busy; we forget; we miss a dose here and there. Second, even if you never miss a dose there is nothing to prevent your dog from eating some grass and vomiting up the medication you just gave. Your pet would be without protection for an entire month. Third, if your pet accidently became infected with heartworms, your veterinarian needs to detect it as soon as possible before irreversible heart and lung damage occur. Early detection and treatment are always best. Finally, no medication is 100%. If your pet happens to be infected with heartworm while on our prescribed heartworm preventative medication, our manufactures will pay for the treatment through their guarantee program.

I live in Ohio. 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 Association is now recommending a year-round prevention program. Dogs have been diagnosed with heartworms in Ohio in almost every county in Ohio, and there are differences in the duration of the mosquito season from the north of the state and the south of the state. Our hospital has diagnosed heartworm positive dogs that get heartworm prevention in the spring, summer, and fall months, but not in the winters. Year-round prevention is the safest, and is our recommendation.

What is the treatment for heartworm disease in dogs?

If a dog is infected with heartworms, the treatment needs to kill the adult and immature worms. Currently, only one product is approved by the FDA for this purpose (Immiticide® - melarsomine hydrochloride). It is given by deep injection into muscle. A series of injections are given, either over a 24-hour period or two treatment periods, one month apart. While treatment may be administered on an outpatient basis, hospitalization for the procedure is often recommended. Other medications may be given at the time of treatment depending on the stage of heartworm disease.

This treatment is expensive and may have serious side effects. Also, depending on the duration a dog is infected with heartworm disease, there may be irreversible damage to lungs and other organs.

Annual heartworm testing and monthly prevention is the safest and the most cost effective way to battle heartworm disease.