Heartworm disease starts as a simple mosquito bite, and can develop into something fatal if not checked through regular use of preventative treatments. First, a mosquito bites an infected animal, taking up embryonic heartworm larvae (microfilariae) along with its meal. Over the next 10 to 14 days, the microfilariae mature into infective larvae inside the mosquito. Then, the mosquito bites your pet, transfering the larvae into its bloodstream. Over the next six months, the larvae mature into adult worms, and begin producing their own microfilariae.
Heartworm preventatives are only effective during the one to two months that larvae are developing in your pet, and well before he or she shows symptoms. So it’s critical to start administering preventatives as soon as mosquitos start buzzing around every year.