By Bert S. Gaddis, Jr. D.V.M.

Heartworm prevention and treatment has come a long way in the past 10 years. The products available for prevention (and treatment) are safe, effective and provide flexibility in administration. Heartworms are transmitted to dogs by mosquito bites. The mosquito feeds on a dog with heartworms and later feed on your dog. This transmits the larvae to your dog.

The larvae stage of the heartworm migrates through the dog's body and goes through several larval stages before it ends up in the dog's heart. Adult worms cause the dog's heart to work harder in order to pump blood through the body. This eventually causes premature heart failure.

To detect heartworms requires a small blood sample be drawn to run in-clinic tests that detect the presence of adult worms and looks for the microfilaria ("baby" heartworms). Treatment of heartworm disease typically involves pre-treatment lab work and several days in the hospital after the treatment has be given. The drug used to treat for heartworms has been improved to be both safer and more effective with fewer side effects. It is very important to restrict activity for about a month after treatment to allow the body to break down and remove the dead worms from the body.

The most common side effect of the treatment is the result of too much activity too soon after release from the hospital. Severe side effects can lead to sudden death. Prevention of heartworms has advanced over the years. We now have several options of medications to prevent heartworm disease. These options include daily or monthly tablets and injections given every 6 months. In the south it is imperative that heartworm prevention (HWP) be given year-round because our climate is mild enough that mosquitoes may be seen any given time of the year. HWP can be discontinued for several months in northern areas where there is a solid period of cold weather from late fall to early spring.

Check with your local veterinarian for the exact recommendations. The "old" daily HWP still exists. These are chewable tablets that MUST be given every day, ideally at about the same time. When given as directed they are effective for prevention of heartwoms, but do not prevent or treat internal parasites. It is the least convenient method for most owners.

There are several monthly HWPs available. They typically contain either Ivermectin or Milbemycin oxime and are usually chewable. These drugs are 100% effective in prevention of heartworms when used about the same day each month. Some manufacturers have guarantees pertaining to the 100% effectiveness. One big difference between Ivermectin and Milbemycin oxime is the prevention/treatment of internal parasites.

Milbemycin oxime prevents or removes three of the four common internal parasites (roundworms, hookworms and whipworms) while Ivemectin does not. Some of the Ivermectin products have a de-wormer added to treat for roundworms and hookworms only. An injectable HWP was introduced a couple of years ago. The injection must be given every 6 months and is 100% effective in the prevention of heartworms when given as recommended.

The effectiveness is guaranteed by the manufacturer. The "down side" of the injectable is it doesn't prevent/treat the internal parasites like the monthly products. The cost is typically comparable to the monthly preventions. Heartworm prevention is an important part of a complete health care program for any dog. The prevention of heartworms and internal parasites is not only healthier for your pet but also helps maintain peak performance in working dogs. It is also a great example of "it is easier (and better) to prevent something than to treat for it".

Dr. Gaddis, a veterinarian, is owner of Indian Springs Animal Clinic located at 1583 Cahaba Valley Road in North Shelby County across from Indian Springs School. Questions can be sent him at ISACVETS@aol.com or by phone at 205-988-8654.