Dorsal view of an adult female western blacklegged tick, Ixodes pacificus (Wikimedia)

Ticks collected along Umbrella Tree Trail at North Sonoma Regional Park came back positive in pooled tests for Borrelia burgdorferi — the bacterium that causes Lyme disease — at a minimum infection prevalence of 7.41%, meaning two pooled samples tested positive out of 27 adult ticks tested in the Marin/Sonoma Mosquito & Vector Control District’s recently released 2025 Vector Surveillance Report.

If that sounds like a dry lab statistic, here’s the part you’ll actually remember: Lyme is one of those infections that can make you feel like you got hit by a truck. Feverish. Wiped out. Achy. Foggy. And it can start as the kind of “I’m just run down” stretch that people blow off for a week or two — especially when it’s winter and everyone’s tired anyway.

That’s why a little, very local number from a very normal park matters.

Because the whole reason we do surveillance isn’t to give you a perfect, park-wide “Lyme percentage.” It’s to answer a more useful question: Are infected ticks showing up where people actually go? This report says yes — at a named Sonoma County trail that plenty of us treat like an easy, low-drama option.

It’s enough to care.

First, the number they report is minimum infection prevalence (MIP), and the “minimum” part is doing real work. The District explains exactly how they calculate it: “*Minimum Infection Prevalence (MIP) = (number of positive tick pools/total ticks tested)100.” That’s a conservative way to report pooled testing.

Here’s what “pooled” means: adult ticks aren’t always tested one-by-one. The District writes, “A maximum of five ticks were placed in each pool.” So if a pool tests positive, you don’t know if one tick in that tube was infected or if all of them were — you only know at least one was. That’s why MIP is the floor, not a dramatic overstatement.

At Umbrella Tree Trail, their table shows 27 adult ticks tested, grouped into seven pools, and two pools came back positive. That math is where the 7.41% comes from — and even as a conservative number, it’s higher than the “low single digits” people often think of when they think about adult tick infection rates in Northern California.

It’s also a small sample — and we should be honest about that. Twenty-seven ticks is not “the whole park,” and it’s not “every season.” But that’s the point: even with a small sample and a method designed not to overclaim, the signal popped. That’s exactly how surveillance is supposed to work: spot the signal, then nudge people toward simple, cheap prevention.

Why this is a “now” story, not a “sometime in spring” story

A lot of us have a mental calendar that goes: • Winter: ticks are basically sleeping • Spring: maybe ticks • Summer: definitely ticks

The District makes it plain: “Throughout the year, District laboratory staff collect ticks of different species and life stages from trails … around Marin and Sonoma counties.” That line matters because it tells you they’re not just running a “tick season” project. They’re tracking what’s out there, across the year, in places people use.

So yes, this can be a February story. Especially when we get those sunny winter weekends and the parks fill up with hikers, runners, mountain bikers, kids, and dogs who do not stay politely on trail edges.

The tick in question — and why your socks are part of this plot

In our part of the world, the main Lyme vector is the western black-legged tick, Ixodes pacificus. The report is blunt about it: “Ixodes pacificus is the common tick species in the area that can transmit Borrelia burgdorferi, the bacterium that causes Lyme disease.”

And here’s the visceral truth about ticks that makes people underestimate them: this is not a “deep wilderness” problem. It’s a “normal places, normal days” problem.

This is the tick that climbs onto your pant leg when you step off the trail for 10 seconds because someone needs to tie a shoe. The tick that rides home tucked in a sock cuff. The tick that falls off in your car or your

hallway and becomes a gross little surprise. The tick your dog collects in its fur on a quick loop and then shares with your couch.

And because it’s Sonoma County, it’s also the tick that catches you when you’re not taking the situation seriously — because the trail feels familiar, the outing feels routine, and the risk doesn’t feel like a headline until the report hands you one.

What “minimum infection prevalence” really means for a person on a trail

It does not mean you’re doomed if you hike Umbrella Tree Trail. It does not mean “7.41% chance you’ll get Lyme” or anything close to that.

It means something much more practical: • Infected ticks are present in that environment. • You don’t get to assume “this park is safe” just because it’s popular and well maintained. • Your prevention habits matter more than your optimism.

And if you’re thinking, “OK, but I’ll see a tick if it’s on me,” I have more bad news: the tick life stage matters.

The District notes: “Nymphal ticks were tested individually, while adult ticks were pooled by collection date, location, and sex.” Adults are bigger and easier to find. Nymphs are tiny — easy to miss — and part of the reason tick checks are the whole game. Even if this particular headline is about adult tick pools, the broader message is: tick country is tick country, and “I would’ve noticed” is not a plan.

If you’ve never had it, it’s easy to file Lyme under “treatable, not a big deal.” And yes — caught early, it’s typically treatable. That’s exactly why the goal is to catch it early.

The problem is what happens when it’s missed or shrugged off.

Early Lyme can look like a flu-ish fog: fatigue, fever, headaches, muscle aches, joint aches. Sometimes there’s a classic expanding rash. Sometimes there isn’t, or it’s in a spot you don’t see. People keep going to work, keep training, keep pushing through, assuming they’re just tired or fighting something off — and meanwhile the infection has more time to spread.

Untreated Lyme can turn into a longer, more complicated mess: neurologic issues, facial palsy, heart rhythm problems, or stubborn joint inflammation that doesn’t politely resolve on your schedule. And even after appropriate treatment, some people deal with prolonged fatigue or pain that can drag on for months. The details get complicated fast. The point is simple: this is a preventable detour you don’t want.

Not panic. Not cancel the parks. Not turn every hike into a horror movie.

Just act like grown-ups who live in a gorgeous county full of brush, grass, deer trails, and perfect tick habitat.

Here’s the stuff that works because it’s boring: • Use a real repellent when you’re in trail-edge vegetation or tall grass. • Stay on trail, especially when the vegetation is brushing your legs. • When you get home, do the tick check like it’s part of the routine — behind knees, along sock lines, around waistbands, under bra straps, anywhere warm and tucked-in. Check your kids. Check your dog. • If you find an attached tick, remove it promptly and properly (steady pull, close to the skin).

And here’s a hyper-local detail most people don’t know until they need it: Sonoma County’s Public Health Regional Laboratory accepts ticks for testing, with a schedule that can matter if you’re trying to make sense of what happened. (Tick testing isn’t a substitute for medical advice, but it can provide information.)

The point of all of this isn’t to make you afraid of your favorite park. It’s to make you a little less casual about something that’s easy to prevent and annoying to treat.

Because I want to hear people say, “Hey, I read in the Gazette that Umbrella Tree Trail had positive tick pools,” and then do the simplest, most unglamorous thing in public health: take 60 seconds after a hike to check for hitchhikers.

Keep enjoying Sonoma County. Just don’t bring home passengers.