Flea, Tick, and Heartworm Preventatives – Don’t Stop Yet!

By Sharon Billings, CVT
Associate Veterinary Information Specialist at Pet Poison Helpline®

In April of this year, Pet Poison Helpline®’s CVT Darlene Hanenburg wrote an excellent blog article regarding things you should know about flea and tick topical solutions (read Darlene’s original blog post here:  http://petpoisonhelp.wpengine.com/2014/04/four-things-know-flea-tick-topical-solutions/).

In this blog post we will build on that information to explain the importance of continued “coverage” as we head toward the end of the calendar year.  Perhaps, if you live in a northern climate area, you are enjoying cool evenings and beautiful foliage, breaking out the sweaters, jackets, and mittens.  Perhaps, if you live in a southern climate area, you are just glad to give the air conditioner a bit of a break!  No matter where you live, cooler temperatures and shorter days may tempt you to stop your flea, tick, and heartworm preventives “for the season”.  Not so fast!

The bugs that we battle – fleas, ticks, and mosquitoes – can survive and persist even in dry, cold temperatures.  While it may be difficult to find a mosquito flying around when it’s twenty degrees below zero outside (yes, it really gets that cold here in Minnesota), it possible to find fleas and ticks year round.  So, you may be wondering, why is this such a big deal?  Well, there’s much more at stake than just itching and scratching.  Let’s take a closer look at each of these all-too-common pests.


Adult fleas bite animals to take a blood meal.  Bites from fleas can cause allergic dermatitis in some animals.  Heavy flea burdens may rob animals of so much blood they become anemic.  When they bite, fleas may transmit a number of bacterial diseases and intestinal parasites to the animals they bite.  Adult fleas lay eggs everywhere – not just on your pet —  that mature to larvae and later pupae (similar to a butterfly’s cocoon) before becoming adult fleas.  In the pupae form, fleas are immune to insecticides; adults may emerge from the pupae form in as little as 13 days or up to 50 weeks depending on temperature and other stimuli.  Flea eggs laid in August, for example, may result in persistent flea problems throughout the winter, long after cold weather arrives!


As with fleas, ticks bite animals to take a blood meal; ticks attach by burying their mouth parts just under the animal’s skin and stay attached while they feed.  During this process they may transmit a variety of bacterial diseases.  Most well known of these diseases is Lyme Disease.  Once your pet is infected with Lyme Disease, even if treated, symptoms may recur later in life and in some instances may be life-threatening.  Ticks, both adults and nymphs (immature ticks), are active and looking for a blood meal well into cooler weather.


Mosquito bites are an itchy nuisance for everyone but for companion animals,  such as dogs and cats, a mosquito bite may also transmit heartworm microfilariae, the immature larval form of the heartworm.  Your pet’s heartworm preventative works by killing these microfilariae.  If they are not killed, microfilariae travel to the heart and mature to adult heartworms during a months-long process.   Female adult heartworms reach 10 to 12 inches in length and live up to 7 years.  Adult heartworms damage the heart muscle and your pet’s heartworm preventative cannot kill these adult heartworms.  That late-summer or early-fall mosquito bite could spell big trouble for your pet!  Of course, heartworm disease is treatable, but treatment carries much greater risk, difficulty, and cost compared with prevention.

To quote Benjamin Franklin, an ounce of prevention is worth a pound of cure!  So before you stop your pet’s preventatives “for the season’, consult  with your pet’s veterinarian to ensure you’re doing everything you can to prevent  bug-borne maladies from affecting your pet.  For more information, visit these websites: