Why Skipping Even One Month Puts Pets at Risk
When most North Carolina pet owners think about parasites, they think about spring. Warmer temperatures, blooming landscapes, and more time outdoors naturally bring fleas, ticks, and mosquitoes to mind.
But in our state, parasite risk does not disappear when the weather cools. Because of North Carolina’s mild winters and humid climate, many parasites remain active for much of the year. And skipping even one month of prevention — whether for a dog or a cat — can create a dangerous gap in protection.
Understanding how parasite risks differ between species is essential to protecting pets effectively.
Heartworm Disease in North Carolina: Primarily a Canine Threat — But Cats Are Not Immune
According to data from the American Heartworm Society and national veterinary testing surveys, North Carolina consistently ranks among the states with the highest number of reported canine heartworm cases in the country. These statistics are based primarily on testing in dogs, since routine annual heartworm testing is standard for dogs but not for cats.
Heartworm disease is transmitted by mosquitoes. When an infected mosquito bites a dog, microscopic larvae enter the bloodstream and eventually mature into worms that live in the heart, lungs, and surrounding blood vessels.
In dogs, heartworms can grow long and numerous, causing:
Chronic coughing
Exercise intolerance
Fatigue
Weight loss
Heart failure in advanced cases
Death
Treatment for dogs exists, but it is expensive, requires months of restricted activity, and carries medical risks.
In cats, heartworm disease behaves differently. Cats are not the natural host for heartworms, so infections typically involve fewer worms. However, even one or two worms can trigger severe inflammatory reactions in the lungs. Some cats show asthma-like symptoms, while others experience sudden collapse or death.
There is no approved treatment to eliminate adult heartworms in cats — only supportive care. For that reason, prevention is especially important for feline patients.
Because mosquitoes can become active during brief warm spells, even in winter, both dogs and cats remain at risk year-round in North Carolina. The American Heartworm Society emphasizes that in warmer southeastern states, heartworm transmission can occur during every month of the year.
Most monthly heartworm preventions are combination products that also protect pets against intestinal parasites. Though intestinal parasites are not covered in this article, they pose a significant health risk to both cats and dogs. Many are also “zoonotic,” transmissible to people. For this reason, heartworm prevention goes hand in hand with intestinal parasite prevention.
Why One Missed Month Matters
Monthly heartworm preventives work by eliminating immature larvae before they develop into adult worms.
In dogs, if a monthly dose is skipped, larvae can mature past the stage where preventives are effective. Once adult worms develop, treatment becomes significantly more complicated and medically intensive.
In cats, prevention works on the same principle: stopping larval development early. Since there is no approved adulticide treatment for cats, prevention remains the only reliable safeguard.
Owners mistakenly may think their pets are not at risk if they do not spend much time outside, but this is not true. Consistent, year-round administration is crucial for all cats and dogs.
Fleas: A Year-Round Problem for Dogs and Cats
Fleas affect both species equally, and often simultaneously, within the same household.
A single flea can lay up to 50 eggs per day. Those eggs fall into carpet fibers, bedding, and upholstery, where they hatch and continue the life cycle indoors. If you notice fleas on your pets, your home also needs to be treated for this parasite given that the majority of fleas live in the environment.
In dogs and cats, fleas can cause:
Persistent itching
Flea allergy dermatitis (a severe allergic skin reaction)
Secondary bacterial skin infections
In young puppies and kittens, heavy infestations can even lead to anemia due to blood loss.
Both dogs and cats may ingest fleas while grooming, which can result in tapeworm infections. If you notice itching, especially around the rump, flea allergy dermatitis can be diagnosed even if fleas are not seen during an exam. Veterinarians look for clues like pattern of hair loss near the rump, “flea dirt,” and of course, fleas.
Importantly, fleas survive extremely well indoors. Even if outdoor temperatures drop, climate-controlled homes allow flea populations to persist through winter. Stopping flea prevention during colder months often leads to indoor infestations that become noticeable only once scratching intensifies. Once a flea infestation is established, the home environment and all pets in the household must be treated for three months to break the flea life cycle.
Ticks: A Significant Canine Risk, With Feline Exposure Possible
Ticks are most commonly found on dogs, largely because dogs spend more time outdoors in wooded areas, tall grass, and parks.
In North Carolina, ticks can transmit several diseases that primarily affect dogs, including:
Lyme disease
Ehrlichiosis
Anaplasmosis
Rocky Mountain spotted fever
These illnesses can cause joint pain, fever, lethargy, kidney complications, and long-term immune issues in dogs. Veterinary surveillance data across the Southeast has shown steady exposure rates in dogs, particularly in suburban and wooded communities.
While cats can carry ticks and be bitten by ticks, they are less frequently diagnosed with tick-borne illnesses compared to dogs since most cats live indoors. However, outdoor cats remain at risk for exposure.
Ticks become active whenever temperatures rise above freezing. In North Carolina, that can occur in nearly every month of the year.
Indoor Pets: Lower Risk Is Not No Risk
Many owners of indoor cats — and even small-breed indoor dogs — assume parasite prevention is unnecessary. However:
Mosquitoes enter homes, putting indoor dogs and cats at risk for heartworm disease.
Fleas can hitchhike indoors on shoes, clothing, or visiting animals. Indoor cats are often infected with fleas by other dogs in the household who go outdoors.
Ticks may be carried inside by people or other pets.
Indoor pets may have lower exposure risk, but they are not fully protected without prevention.
Climate Patterns and Expanding Parasite Seasons
Veterinary parasitology experts have noted that milder winters and expanding suburban development are contributing to longer parasite activity seasons across the Southeast.
As neighborhoods expand into wooded areas, dogs in particular encounter increased tick exposure. Wildlife such as deer and coyotes serve as hosts for ticks and help sustain parasite populations in suburban environments.
Warmer winters also extend mosquito activity, lengthening the potential transmission period for heartworm disease—especially in dogs, who are the primary host species.
A Species-Specific Prevention Plan
An effective parasite prevention plan should be tailored to each pet’s individual risk factors, including:
Whether the pet is a dog or a cat
Whether they live strictly indoors or spend time outdoors
Whether they travel outside the region
Whether they share a home with other pets
Dogs typically require:
Monthly heartworm and intestinal parasite prevention
Monthly broad-spectrum flea and tick protection
Annual heartworm testing
Cats typically require:
Monthly heartworm and intestinal parasite prevention (particularly in mosquito-prone regions like North Carolina)
Monthly broad-spectrum flea and tick protection
Routine veterinary exams allow early detection and adjustments to prevention strategies as needed.
Spring Is a Reminder—Not a Starting Point
Spring often brings increased exposure to ticks and mosquitoes, but parasites do not adhere to a strict calendar in North Carolina. Infections acquired during winter may not be detected until spring testing. Flea populations established indoors in December can become overwhelming by March. Year-round prevention eliminates these seasonal gaps.
Protecting Dogs and Cats Through Every Season
Dogs and cats experience parasite diseases differently, but both species are vulnerable in our region. For dogs, heartworm and tick-borne diseases pose significant risks. For cats, heartworm prevention is critical because treatment options are limited. For both, fleas remain a persistent, year-round threat.
Parasites may be common in North Carolina—but they are also highly preventable with consistent protection. Skipping even one month may seem insignificant. From a biological standpoint, however, it can be enough to allow disease to take hold.
When it comes to parasite prevention, steady protection — not seasonal reaction — is what keeps pets safest.
Dr. Molly Shelton is a veterinarian at Harmony Animal Hospital, Pet Resort & Spa in North Carolina. She has a special interest in preventive medicine and is passionate about educating families on proactive strategies that support lifelong health for both dogs and cats.
