Gazette Vet: Down But Not Out


By John Andersen, DVM

November is here! Gone is the hot summer and fall we’ve been having, as well as the bugs and humidity! Besides being a very pleasant time of year for us, this is a great time of the year to be a dog. I think every dog has been waiting for 30-degree mornings and 50-degree highs. Wearing their thick coats, Virginia summers are simply harsh on our furry domestic best friends.

One of the most common mistakes I see, however, is that people tend to think that just because it’s cool outside, the threat of fleas, ticks, and other parasites goes away.

Unfortunately, here in Virginia there are many parasites that are a threat year round that you should be aware of as you continue to enjoy the outdoors with your dog in our relatively mild fall and winter.

Which parasites do we still need to worry about? Should we give heartworm and flea/tick preventatives year round?

Let’s take this question parasite by parasite:

Fleas:  The very worst time of year for fleas is from August through late October.  During this time, their eggs that are falling into your yard or environment are hatching at an exceptionally efficient rate, and many of our pets are facing huge “flea pressure” every time they go outside. But once we get a week or so with solid overnight freezes, these eggs in the environment will die.

However, if just one flea gets inside your home, you will definitely have a flea infestation, no matter how cold it is outside. Fleas live all of their adult life on your pet, but they lay eggs that are slippery and that fall off the furry animal and land all over the environment.  If this environment is your home, they will be happy as can be to hatch in your carpet, under your couch, and even between the tight boards of your hardwood floors. So, although flea pressure outside is very low from mid November through February, your pets can definitely still get fleas if they hang with the wrong pets or if you’ve got some flea-ridden wildlife that comes close to your home.

Ticks:  Contrary to popular belief, ticks are active year round in Virginia. The worst time of year for ticks is from April through August.  During this time, all life stages of ticks are active and there are many waves of hatchings of eggs, which will produce thousands of tick larvae, which are the very very small ticks, the size of the period at the end of this sentence. It is important to know that all ticks have these different life stages; they all have a larval stage and a “seed tick” stage before they turn into adult ticks.

There is no good tick. You don’t have to worry about identifying different species of ticks because they all carry different diseases that can make us sick.  Lyme Disease, Ehrlichiosis, Anaplasmosis, Rocky Mountain Spotted Fever—both humans and dogs can succumb to these tick-borne diseases, which seem to become more common each year.

But what about when it’s cold outside? When it is currently below freezing outside, you don’t really need to worry about ticks. But when its 35 degrees and you’re in the fields and woods, the adult ticks that have survived through the summer are still hungry and they are willing and able to find a new host in you or your pet. I have personally pulled ticks of my dog when there was a foot of snow on the ground after hiking in the woods. Ticks are survivors!

Intestinal Parasites:  Many different intestinal parasites affect our dogs here in Virginia, with hookworms and whipworms being the most common. These cause weight loss, diarrhea, and intestinal problems. They have a sometimes very complex life cycle, but ultimately adult worms living in an infected dog/canine will shed eggs in that animal’s feces.

The eggs of hookworms and whipworms are stable and infectious in the environment for years.  That means that during the winter, when it’s 20 degrees outside, those frozen whipworm eggs are still infective if your dog happens to ingest them.

Common routes of infection are from our dogs eating fox or coyote poop while hiking in the woods/fields. They also may get some dirt that has eggs on their paws, and then ingest the eggs when they groom themselves clean.

Heartworms:  Heartworms are a major problem in infected dogs. They are literally spaghetti-sized worms that live in the heart and lungs of infected dogs! Heartworms are transmitted by mosquitoes, so the active season for transmission here is from March through October. The risk of getting infected in December through February is very low, however not impossible if we have some of those rare 70 degree weeks in the wintertime.

As you can see, overall the risk of acquiring internal and external parasites certainly goes down in the late fall and winter, but unfortunately it never goes away, and I do commonly see dogs with these parasites all year long at our office.

The best way to avoid them? Use preventatives year round.

Heartworm prevention is extremely safe and easy—it is a chewable pill given once a month and not only does it do a fantastic job preventing heartworms, but it also does a very good job preventing new infections with intestinal parasites as well. The latter reason is why I never miss a dose of heartworm prevention in my own dogs over the winter.

Flea and tick preventatives are also very safe and do a great job of killing fleas and killing ticks before they’ve had a chance to spread disease. There are many different types of flea and tick prevention, and a discussion with your vet can lead you to choosing the best option for you and your pet.

I always tell new clients from out of town that “here in Virginia, we’ve got all the parasites, and we’ve got ’em year round.” Despite that, we live in an awesome climate and the fall and winter are the best time to get outdoors with your dogs!


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