I do not give heartworm medication during the winter. After a mosquito bites an infected dog, it must be above 57 degrees for two weeks for the larva to develop to the stage that causes heartworm. If the temperature drops below 57 degrees the cycle is halted and must start over. The larva must mature in a mosquito for it to be transmitted (a mosquito bite is the only way it is transmitted). So if you see a mosquito during a few warmer days in winter, don't worry, there hasn't been enough time for the stages the larva must go through.
I'm not trying to convince anyone not to give the meds all year long, heartworm disease is very serious. It is up to you and your vet to decide what is best for your dog. I'm just explaining why it is safe if you choose not to in cold weather. I discussed it with my vet, read up on it and have my dogs tested each year. There is a ton of information about this online alone.
If anyone is wondering why I just wouldn't give it all year long, it's because the medication is a toxic chemical - some say one that is completely harmless to dogs, others disagree - one I feel I can safely take my dog off of for almost half his lifetime.
Also, you have to remember to give the medication if you do any travelling with your dog to warmer climates. |