Keeping your pet healthy requires regular preventive health care. Timely administration of heartworm preventive medication is one of the preventive measures that all dog owners should be practicing.
What are heartworms?
Heartworms are mosquito-borne parasites that live in the heart and blood vessels of an infected dog. These worms cause damage, often significant damage, to the cardiovascular structures and can lead to serious illness in the infected dog. In severe cases, heartworms can be fatal. Their scientific name is Dirofilaria immitus.
What are the symptoms of heartworm disease?
Heartworms can damage both the pulmonary arteries and the heart. Symptoms seen may include:
- exercise intolerance
- hemorrhage from the nose
- right-sided heart failure
- cardiac arrhythmia, which may lead to sudden death in some cases
How can heartworms be prevented?
Numerous medications are available that prevent heartworm infections from occurring in a susceptible dog. Most of these medications are either tablets or topical medications that must be applied monthly. Though the risk of side effects can occur with any medication, these drugs are generally safe and are very effective in preventing heartworm infections if used correctly.
Alternatively, there is an injection that can be administered every 6 months which is also capable of preventing heartworm.
Why prevent heartworms rather than treat the infection if it occurs?
- Heartworms can cause significant damage to the circulatory system before they are detected and this damage is likely to be irreversible.
- Heartworm treatment (treating an existing infection) carries the risk of complications, even though the medications used today are safer than those used in the past.
- Strict cage rest is required for long periods of time while the dog undergoes treatment, sometimes as long as 6-8 weeks or longer.
- Heartworm treatment is not guaranteed to kill all of the infecting heartworms.
Monthly preventive medications only address the immature form of the heartworm. They do not kill the adult worms directly. With time, the adult worms will age and die of natural causes. Therefore, monthly heartworm preventive medications can eventually be effective in eliminating heartworm infections. However, elimination may take up to 2 years to occur. Meanwhile, the worms remain in the heart and blood vessels causing additional damage and disease.
In some instances, such as when a dog is debilitated or suffering from concurrent disease, he may not be considered a good candidate for heartworm treatment with a medication that kills adult worms. In these cases, treatment with a monthly preventive may be the optimal form of treatment. However, in most cases where the dog is otherwise healthy and deemed a fit candidate for treatment, the drug of choice is Immiticide® (melarsomine dihydrochloride).
Immiticide® is the only drug available that will kill adult heartworms. The major risk with Immiticide® injection is embolization of dying worms to the lungs, which can cause serious side effects for the dog being treated. Strict cage rest is necessary to minimize these complications. Before treatment with Immiticide®, a monthly preventive medication is usually administered to remove the immature heartworms before addressing the adults.
Lorie Huston has been practicing veterinary medicine for over 20 years. Besides a successful career in a busy small animal hospital in Providence, RI, Lorie is also a successful freelance writer specializing in pet care and pet health topics. Currently, she is the feature writer for the Pet Care section at Suite101.com and the National Pet Health Examiner at Examiner.com. Lorie also publishes her own blog, The Pet Health Care Gazette and manages an increasingly popular facebook page, The Voice of Pet Care. In addition, she co-moderates DogTalk, a weekly twitter chat that focuses on a variety of dog topics.