Why Parasite Prevention is no Longer Seasonal

Inside Sales | March 2026

Written by:

Dawn Singleton-Olson has more than 25 years of experience in the animal health industry, including distributor sales, manufacturing, practice management and as a zoo supervisor. She is a volunteer, fundraiser and board trustee for several humane organizations and the Omaha (Neb.) Police Mounted Patrol.

The weather we had in my region of the Midwest this past winter made a strong argument for year-round parasite protection. Mild temperatures for most of December, a record high of 67 in early January and ten days above 60 in February created ideal conditions for pests. When I spotted a bee in the backyard in January, I knew parasitic insects were likely active too.

Tick activity is influenced by temperature and humidity, but studies show ticks are far more active in winter than once believed. Common species such as black-legged (deer) ticks can emerge when temperatures reach 40 to 45 degrees, including during winter thaw events.

More concerning, black-legged ticks infected with the pathogen that causes Lyme disease (Borrelia burgdorferi) tolerate below-freezing temperatures and may remain active throughout winter.

In North America, Lyme disease is the most commonly diagnosed tick-borne disease in humans. When identifying new regions of high human risk, canine Lyme prevalence can serve as an early warning for increased human exposure. As tick species expand their range, new pathogens continue to emerge. The Asian longhorned tick, first discovered in the United States in 2017, has now been found in 24 states as far west as Oklahoma. This species carries the protozoan Theileria orientalis, which causes the disease theileriosis in cattle.

Other common tick-borne diseases affecting both dogs and humans include anaplasmosis, babesiosis, ehrlichiosis, Rocky Mountain spotted fever and Powassan virus disease.

One tick, multiple threats

One of the biggest diagnostic challenges is that ticks can transmit multiple diseases simultaneously. Their life cycle includes larval, nymphal and adult stages, each requiring a blood meal from different hosts such as rodents, ground-nesting birds, deer and even lizards in the southern states.

As ticks move through their life cycle, they can accumulate pathogens capable of infecting pets or people. Just one attached tick can transmit disease, and the longer it remains attached, the greater the risk of transmission. Larvae and nymphs are much smaller and harder to detect than adult ticks, but pets can be infected with dozens of these tiny “seed” ticks. Without the ability to attach and feed, ticks cannot transmit disease, which is why products that kill quickly and prevent attachment provide
the best protection.

Heartworm rates in pets are trending upward nationwide, even though this life-threatening parasite is preventable. Many pet owners believe heartworm risk is limited to summer, but mosquitoes begin emerging from hibernation at temperatures above 50 degrees. Heartworm diagnosis rates remain relatively steady year-round, reinforcing the need for continuous prevention.

Ticks and mosquitoes are expanding their range and activity, but effective parasite control options have expanded as well. In recent years, both stand-alone isoxazolines and combination products pairing this ectoparasiticide with endoparasiticides have been introduced. These endectocides provide broad-spectrum protection in a single monthly dose, improving convenience and owner compliance.

Currently, three isoxazoline combination preventives are available in the United States. All are labeled for the four widespread tick species commonly found on pets — black-legged ticks, lone star ticks, American dog ticks and brown dog ticks — as well as heartworms, roundworms, hookworms and fleas for dogs as young as 8 weeks. Each has demonstrated safety in microfilaremic dogs infected with heartworm and in dogs with the MDR1 gene mutation.

Simparica TRIO (Zoetis) is labeled to prevent transmission of Lyme disease by killing the tick vector before transmission and to prevent tapeworm transmission by eliminating the flea vector. Both Simparica TRIO and Simparica have added the Asian longhorn tick to their labels and are the only isoxazoline preventives to include the Gulf Coast tick — important for clinics in the Southeast and for pets traveling to the region.

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NexGard Plus (Boehringer Ingelheim) has also added the Asian longhorn tick to its label and is the only isoxazoline product labeled for three different hookworm species. Another label highlight is its ability to improve signs of flea allergy dermatitis as a direct result of eliminating fleas.

Credelio Quattro (Elanco) is the newest combination preventive in the U.S. market and the only isoxazoline-containing product that includes praziquantel for prevention and treatment of tapeworms. Like the other brands, it is a chewable tablet, though it must be administered with food.

With so many vector-borne pathogens affecting both pets and people, parasite prevention is not just a pet owner issue but a year-round public health concern. Isoxazoline combination preventives offer effective control of multiple parasites in a single product, improving compliance and supporting the health of pets and people.

Year-Round Tick Threat
Canadian biologist Dr. Laura Ferguson conducted a study showing that infected ticks “have a huge boost in survival through the winter” with nearly 80% surviving temperatures as low as -0.4 degrees Fahrenheit and becoming far more active after a cold spell than uninfected ticks. Her findings show that fluctuating winter conditions increase ticks’ activity and their ability to find hosts and spread disease year-round. This boosts the odds of even higher infection rates in the spring for both pets and people.

Image Credit:

istockphoto.com/Andrey Maximenko

istockphoto.com/Thanawath Seangsuriyapone

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