Do Dogs Need Heartworm Medication in the Winter?

Heartworm is a very serious concern in pets. While cats also can suffer from heartworm, these pests are mostly associated with dogs. The treatment for a dog infested withheartworm is risky in itself so prevention is the best measure.

There are many medications that are used to prevent heartworm and although not terribly expensive the costs do add up, so reducing the number of treatments per year can have financial benefits to a pet owner. Additionally, and perhaps more importantly, there are concerns in regards to the over-medication of pets and potential risks (including cancer).

The question remains, should you treat your dog year round for heartworm or only in the months in which mosquitoes are active?

First let us understand how heartworm medications work.

Heartworm is spread to cats and dogs via mosquitoes. The mosquito must drink the blood of an infected pet and take up the very young heartworms at that time (larval stage 1) . The larva grow inside the mosquito and eventually travel to the mosquito's mouth and wait to be inserted into another pet. The heartworms develop in the pet's bloodstream eventually making their way to the heart. Heartworm prevention medication does not actually “prevent” the heartworm infections, but rather they kill the young heartworms at one larval stage which is about 30 to 45 days after the initial infection, but before the worms make their way to the heart. Heartworm prevention medication does not kill the mature heartworms in the heart.

In order for the heartworms to develop in the mosquito temperatures must be relatively warm. When temperatures drop below 57F (14C) the lifecycle of the heartworms in the mosquitoes is ended.

But recalling that the heartworm preventative medication is only effective on larvae that have been in the infected dog for more than 30 days, you can see that treating a dog in the fall (depending on how cold it gets in your area), after mosquitoes have died off, is still a good idea, however into the winter is not necessarily required unless you live in a warm weather area. As such if you live in an area where winters get cold you may find that you do not have to treat your dog with heartworm medication from December to February or March.

You may want to discuss the risks of heartworm with your vet before going on a heartworm medication prevention program. In warm areas where there are lots of dogs and mosquito's (areas with lots of water) the risk is certainly higher than in areas with desert conditions and a lower population of pets.

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If you are looking for places to buy heartworm medication for your dog (or cat) here are some great online places worth considering. They sell many other pet health products too and you should note that a healthy pet has a natural defense against heartworm.