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Heartworm disease

Heartworm disease is caused by an infection with parasitic worms that live in the right side of the heart and the pulmonary vessels, and sometimes will extend into the major veins supplying the heart. These worms are introduced into the animal's cardiovascular system by the bite of a mosquito that is carrying the infective larval worms. When the worms have been in the animal's system for a long enough period of time, they will cause a number of different problems with the lungs, heart and liver. Pulmonary hypertension is the biggest problem we see with heartworm infection, and will shorten your animal's life span, as well as cause it to become weakened, and experience chronic lung and breathing problems.

These heartworm larvae that are in the mosquitoes' mouth parts need to have an average outdoor temperature of 67 F. for a sufficiently long enough period of time to be able to mature to the infective larval stage. Then, when they bite a susceptible host, the larvae are transmitted into the host's bloodstream, and they go on to mature to adult worms. These adult worms create the disease, but they also breed with each other inside the dog's heart and create more larvae, which are picked up by a mosquito feeding on its blood, and then begin the process of maturation in the mosquitoes' mouth parts to its infective stage. As a result of this temperature requirement, climates that are have average outdoor temperatures of less than 67 F for the majority of the year do not have a high incidence of heartworm disease.

States such as Colorado, Wyoming, Utah, Nevada tend to be too cold for much of the year, and too dry during much of their warm seasons to provide mosquitoes a breeding place. If the risk is sufficiently low, heartworm prevention and treatment may not be necessary. In his nearly 20 years as a veterinarian in private practice in Colorado, Dr. Silver has seen only 7 heartworm positive cases. And, up until this year Dr. Silver did not think that the risk of heartworm was great enough to warrant preventative measures at all, or at least for only 6 months of the year, during the warm season. (April-November). However of those six cases (to date) 5 of them have been in the last 12-month period (8/99-8/00).

As a result of an increased risk for heartworm in Colorado, BNA now recommends that you give your pet the once a month heartworm preventative pill for 6 months out of the year. The once monthly heartworm preventative is safe to give to most animals (patients with liver disease may not be able to tolerate the preventative, and Collies have been found to be sensitive to ivermectins, which are only one of several types of heartworm preventative.

The preventative is so effective, that if it is given as directed has nearly a 100% rate of prevention. For this reason, the American Heartworm Association recommends that your animal be tested for heartworm disease every other year for the presence of the disease. This is a simple blood test that costs $27.50 at BNA. The test also checks for the presence of Lyme's Disease and Ehrlichiosis, which are two tick-borne infections. Lyme's Disease is very rare or non-existent in Colorado.

There is a new injection for heartworm protection that only needs to be given every six months. BNA does no recommend this form of protection. Statistically, it has the highest death rate of all of the forms of protection. The spot-on drops, Revolution™, which are given monthly, have the second highest death rate of all of the

It is recommended that if your dog has never been tested for heartworm disease that you do so to be certain that it does not have the disease before you start the preventative. There is a delay time between the infection of your animal with heartworm disease and the time that it will be able to be tested of six months. This is the time it takes the heartworm to grow to sexual maturity and produce its infective offspring.