Do I REALLY need to give heartworm prevention year-round? By Dr. Dawnetta Woodruff

This is a question I am asked on a regular basis by clients and friends. In my part of the country (central Midwest), the answer is a resounding YES!! I have seen well-meaning owners give heartworm prevention 9 or 10 months out of the year, and their dog tests positive from exposure during the 2-3 months they skipped during the winter that they thought were “safe.” To understand why this can happen, it is important to know a little more about heartworm disease.

“First, adult female heartworms release their young, called microfilariae, into an animal's bloodstream. Then, mosquitoes become infected with microfilariae while taking blood meal from the infected animal. During the next 10 to 14 days, the microfilariae mature to the infective larval stage within the mosquito. After that, the mosquito bites another dog, cat or other susceptible animal, and the infective larvae enter through the bite wound. It then takes a little over 6 months for the infective larvae to mature into adult worms. In dogs, the worms may live for up to 7 years. Microfilariae cannot mature into adult heartworms without first passing through a mosquito.” (Quoted from the American Heartworm Society.)

Heartworm Lifecycle

Copyright 2007 American Heartworm Society

So heartworms are carried by mosquitoes…  and during a mild winter, we could see those annoying little critters pop up even in January or February! Since you can’t tell when we might have a spell of warmer-than-normal weather, I recommend that my clients give heartworm preventative to their pets each and every month, year round.  (I also recommend purchasing your heartworm prevention through a veterinary clinic, not an online source or a local pharmacy – but that’s another subject for a separate blog post!)

If you don’t live in the central Midwest, the answer to this question might be different for you.  Most parts of the country have enough warm, moist weather that mosquitoes (and heartworm disease!) are a problem… but are they a problem year round?  And which preventative is best for you and your pet?  The best way to answer these questions is to ask your own personal veterinarian!  He or she is familiar with the incidence of heartworm disease in your area, and can help you make an educated choice that keeps your pet as safe as possible!  If you are interested in more information on heartworm disease incidence, check out the map below.

Heartworm Incidence 2007
The severity of heartworm incidence as shown in this map is based on the average number of cases per reporting clinic. Some remote regions of the United States lack veterinary clinics, therefore we have no reported cases from these areas. Copyright American Heartworm Society

You can also find a lot more information about Heartworm disease, its incidence, prevention, and treatment on the American Heartworm Society’s webpage under the “Pet Owner Resources” tab - http://www.heartwormsociety.org/pet-owner-resources/heartworm.html

Written by Dr. Dawnetta

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Read more or contact Dr. Dawnetta:
Dawnetta Woodruff, DVM
Dr. Dawnetta assists families with in home hospice and euthanasia in Missouri & Illinois areas including:

• MISSOURI - Serving St Louis and portions of the St Louis Metro: South County / Fenton / Chesterfield / Kirkwood / Webster Groves / Town & Country / Ellisville 
• ILLINOIS - Serving Monroe County and portions of Randolph & St Clair counties: Waterloo / Columbia / Smithton / Millstadt / Belleville / Fairview Heights / O'Fallon