Year Round Heartworm Prevention is Important by Dr. Michael Fagan
For twenty-plus years, we've enjoyed
the privilege of telling our clients that our heartworm preventative
medications were 100% effective in preventing heartworm disease if
given monthly throughout the entire mosquito season. Now we have to settle for telling you that they are Very
Effective.
Very Effective is still a good thing, but some
aspects of our overall prevention strategy have become even more
important. Over the past several years,
there have emerged a few strains of heartworms that are resistant to the entire
class of drugs used as heartworm preventatives (known as macrocyclic lactones,
or ML). So far, it appears that none of
the available products (Heartgard, Iverhart, Revolution, Interceptor, Advantage
Multi), are superior to any other:
while every product is still very effective, each has been documented to
be less than 100%.
What this means for our patients:
- It is very important to give monthly heartworm preventive year-round.
- Annual heartworm testing is essential to identify any dog that have acquired a resistant heartworm infection.
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| One of our patients, a year after heartworm treatment |
Dogs
that do become infected with ML-resistant heartworms tend to be infected with
lower numbers of worms than dogs that are not on preventatives at all. They still need to be treated with
injections of melarsomine to eliminate the adult heartworms for their own
health, but also to eliminate the source of resistant worms that could be
transmitted to other dogs.
Treating dogs that are infected is expensive and painful. The drug (melarsomine) is currently only available on a case-by-case basis from European production facilities. Melarsomine is injected deep into the muscle along the spine and it hurts! Dogs must be kept quiet for two months during treatment which means no running or playing. We are currently treating a really sweet black lab who moved here from the Southern U.S. where resistant heartworms have been identified.
