Questions and Answers
November, 1999
Dear Dr. Mark Silverio:
I have several Beagles and Heartworm Preventive is very
expensive. I’ve heard of other Beaglers using IVERMETIN to
prevent Heartworms, can you help me get the correct [recipe] for
Heartworm Prevention and other Worms, it would be a great help
and greatly appreciated. If so please tell me how to mix, how
much to administer per pound, and all necessary ingredients.
With great appreciation,
Dewayne Hawkins
Dear Dewayne,
Please refer to past articles in SPO Magazine on this topic
(January 1996 and April 1996).
Heartworm disease is caused by a parasite called Dirofilaria
Immitis, which actually lives in the right ventricle of the heart
and the pulmonary artery that leaves that chamber as it delivers
blood to the lungs. The first signs of heartworm disease include
coughing and exercise intolerance. Left untreated, it can lead to
severe weight loss, labored breathing and poor appetite. Treating
a dog that has had chronic infection is often unrewarding,
because of permanent changes in the heart and lungs. When
infection is detected in a blood sample while the dog has few
symptoms or none at all, treatment can be a complete success.
Even in those cases, some side effects of treatment can occur,
either caused by the drug used or by the lung’s reaction to
too many dead and dying worms.
The disease can only be transmitted by a mosquito bite. Adult
heartworms produce first-stage larvae, called microfilaria, 6-7
months after the dog is infected. These microfilaria are found
throughout the bloodstream and can be picked up by a mosquito
when it bites an infected dog. After several weeks in the
mosquito the microfilaria mature to third-stage larvae. The
mosquito can then spread the infection by biting an uninfected
dog. Because the mosquito is a necessary part of the worm’s
life cycle, dogs cannot get heartworm disease from contact with
an infected dog or even from contact with the blood of an
infected dog.
There are several medications that can be given monthly to
prevent heartworm disease. They act by killing third and fourth
stage larvae before they become adults. It usually takes 4-6
weeks for the infecting larvae to migrate through tissues and
reach the small pulmonary arteries. The preventative medications
that are given once a month do not remain in the dog’s body
more than a few days. They are effective when given monthly
because the larvae they kill are susceptible for at least four
weeks.
The first monthly preventive pill on the market was Heartgard,
which contains the drug ivermectin. These pre-packaged chewable
tablets can be expensive, expecially when you own a number of
dogs. A cheaper alternative involves using an injectable
anti-parasitic medication for cows called Ivomec. It is a fairly
concentrated form of ivermectin. Very small amounts would need to
be measured to give to a dog for preventing heartworms only. A
higher dose is required for intestinal parasites. Ivemec can be
given orally to a dog for both heartworms and intestinal worms at
a dose of 0.1cc for every 10 pounds of body weight. This is
equivalent to 1/4cc for a 25 pound beagle and can be given once a
month to prevent diseases caused by heartworms, hookworms,
whipworms and roundworms. All dogs over 6 months of age should be
blood-tested for heartworm disease before starting a monthly
preventative. As mentioned previously, using the drug in this
manner has not been approved by the FDA.