Every spring, the calls pick up at Douglas Animal Hospital. Pet owners across Osseo and the surrounding Hennepin County communities start finding ticks on their dogs after walks, or they realize it’s been a few months since they last gave a heartworm preventive. The timing makes sense. Warm weather returns, and so does the visible evidence that parasites are active. But what catches many people off guard is that the risks don’t start and stop when the weather feels like it should.
Minnesota’s parasite season is longer than most pet owners assume, and the consequences of gaps in prevention can be serious, expensive, and in the case of heartworm, potentially fatal.
Tick-Borne Disease in Hennepin County Is Not Hypothetical
Ticks are not a rural problem. They’re a suburban one too, and Hennepin County has the numbers to prove it. The blacklegged tick (also called the deer tick) is well established across the Twin Cities metro area, including the wooded parks, trails, and residential yards that Osseo pet owners use every day. This species transmits Lyme disease, anaplasmosis, and ehrlichiosis, all of which are diagnosed regularly in Minnesota dogs.
The American dog tick, another common species in the state, carries Rocky Mountain spotted fever and can cause tick paralysis in rare cases. Both species are active from roughly April through November, though blacklegged ticks have a quirk that extends their season: adult deer ticks remain active into late fall and can survive mild winter days when temperatures climb above freezing. It’s not unusual to find a deer tick on a dog in December in Minnesota during a warm stretch.
Lyme disease gets the most attention, and for good reason. Infected dogs can develop joint pain, fever, lethargy, and kidney complications that range from manageable to life-threatening. But anaplasmosis is arguably just as common in Minnesota and causes similar symptoms, including lameness, fever, and decreased appetite. We test for both at Douglas Animal Hospital as part of our annual wellness screening, using a simple in-house blood test that also checks for heartworm and ehrlichiosis in a single draw.
The Minnesota Department of Health tracks tick-borne disease in humans, and their surveillance maps consistently show Hennepin County as an area with documented Lyme and anaplasmosis cases. The tick populations affecting people are the same ones biting your dog in the backyard.
Heartworm Transmission: Shorter Season, Same Consequence
Heartworm works differently than tick-borne disease, and the timeline matters. Heartworm is transmitted through mosquito bites. When an infected mosquito feeds on your dog, it deposits microscopic larvae into the skin. Those larvae migrate through the body over several months, eventually reaching the heart and pulmonary arteries, where they mature into adult worms that can grow up to a foot long.
Minnesota’s mosquito season typically runs from late May through September, though it shifts depending on the year. The larvae need a sustained period of warm temperatures (above 57°F) to develop inside the mosquito to an infective stage, which is why transmission peaks in midsummer. But here’s the catch: the worms your dog picks up in August won’t show up on a test until roughly six months later. Heartworm has a long latency period, and by the time it’s detectable, the damage has already begun.
Treatment for heartworm disease exists, but it’s not simple. It involves a series of injections with an arsenic-based drug, strict exercise restriction for months (because exertion with worms in the heart can be deadly), and a total cost that typically runs into the thousands. Prevention, by comparison, costs a fraction of that. A monthly preventive given consistently is one of the most clear-cut cost-benefit calculations in veterinary medicine.
Why the “Seasonal Only” Approach Has Gaps
Many pet owners in Minnesota still give heartworm prevention only from June through November, reasoning that mosquitoes aren’t active in winter. The math seems logical. The problem is that this approach assumes a perfectly consistent start date every year, zero missed doses, and a mosquito season that doesn’t start early or end late.
In practice, doses get missed. Mosquito activity in Minnesota has started earlier in warm years. And some preventive products also protect against intestinal parasites like roundworms and hookworms, which can be transmitted year-round through contaminated soil and feces regardless of temperature.
The American Heartworm Society recommends year-round prevention for all dogs, everywhere in the country. Their reasoning is straightforward: the cost of 12 months of preventive is far less than the cost of treating a single heartworm infection, and consistent dosing eliminates the risk of accidental gaps. At Douglas Animal Hospital, we’ve adopted that same recommendation. It’s simply the safer approach.
Building a Year-Round Prevention Plan at Douglas Animal Hospital
Parasite prevention isn’t one product that fits all. The right plan for your pet depends on their lifestyle, age, health status, and what risks they’re realistically exposed to.
A dog that hikes off-leash in Elm Creek Park Reserve every weekend has a different tick exposure profile than one that sticks to sidewalk walks in downtown Osseo. A cat that goes outdoors, even onto a screened porch, has mosquito exposure that a strictly indoor cat may not. We factor these details in when making recommendations.
For most dogs in the Osseo area, we recommend a combination approach: a monthly heartworm preventive that also covers common intestinal parasites, plus a separate tick preventive (either a monthly topical or chewable, or a longer-duration product like a tick collar that lasts several months). Some newer combination products cover fleas, ticks, and heartworm in a single dose, and we can discuss whether those are a good fit at your pet’s next wellness visit.
Annual testing is the other non-negotiable piece. Even dogs on consistent prevention should be tested for heartworm and tick-borne diseases once a year. No product is 100 percent effective, vomited doses happen, and tick-borne infections can occur despite prevention if a tick feeds long enough before the product kills it. The annual 4Dx test we run at our clinic screens for heartworm, Lyme, anaplasmosis, and ehrlichiosis from a single blood sample, and results are back within minutes.
Don’t Wait for the First Tick to Show Up
The best time to start or restart parasite prevention is before you need it. If your dog or cat isn’t currently on a year-round prevention plan, or if you’ve had gaps over the winter, schedule a wellness visit at Douglas Animal Hospital so we can test, update, and get your pet covered. Call (763) 424-3605 or book through our website. Parasites don’t send advance notice, and the diseases they carry are far easier to prevent than to treat.
