Why Should I Treat My Pets Year-Round with Heartworm, Flea, and Tick Prevention?

It is that time of year again when we will start to see insects flourish, this includes fleas, ticks, bees, and mosquitoes. We’ve already seen our first cases of tick infestation and bee sting reactions in the middle of April this year. So, have you been giving heartworm, flea, and tick prevention through the winter?

Heartworm disease requires a ‘middle man’ which is the mosquito in order for the microfilaria (baby heartworms) to mature to the infective L3 larva stage. Heartworm disease is spread when a mosquito bites a dog which has microfilaria, the microfilaria then mature, and the mosquito goes and bites an unprotected dog or cat. It then takes 6-7 months for the microfilaria to mature before the adult worms start producing microfilaria of their own. This also the time frame it takes for adult female worms to produce the antigens that are picked up in our standard heartworm tests.

We’ve been talking about year-round heartworm prevention for over a decade. I hear a lot of clients who are still only giving prevention during the warm months. But anymore, we are seeing mosquitos into November. Unfortunately, heartworm prevention does not kill all the circulating microfilaria with one dose. It can take 2-3 months before preventatives will kill all the microfilaria. Several specialists are even talking about resistant microfilaria which take more doses to control. If you are traveling south with your pets, that is also going to affect the disease risks. Year-round prevention which also covers intestinal parasites is going to ensure that your pet does not pick up a parasite that can passed to people.


This year-round recommendation applies to flea and tick prevention as well. We see many cases of flea infestation over the winter despite a good freeze outside. Flea eggs can lie dormant in areas of the garage, basement, in the furnace filter, and even on wildlife in the backyard. When these areas warm up, the eggs start to hatch. When heartworm, flea, and tick prevention become a monthly habit all year-round, it helps insure we don’t miss a dose or get off the monthly schedule when our pets do need the protection the most.

So what about cats? Yes, they can get heartworm disease as well but it works a little differently than in the dog. In the cat, only a handful of adult worms mature and so there is a very low level of microfilaria, if any. But it only takes a few worms to make a cat very sick because of the difference in body size. Unfortunately, there is no current treatment for heartworm disease in cats. Since we live in an area where heartworm disease is prevalent in dogs, we recommend heartworm prevention in cats year-round as well.

By: Dr. Haag-Eggenberger
Skinner Animal Clinic
Dwight Veterinary Clinic