Tick season is running 2–4 weeks ahead of schedule this spring. A mild 2025–26 winter across most of the US means nymphal ticks are emerging well before the calendar suggests, and standing snowmelt water is creating prime leptospirosis exposure zones on trails that looked clean just weeks ago.

Most spring prep guides treat these threats separately. This one doesn’t. Before Rocky’s first real trail day this season, I sat down with our vet to run through every parasite and spring hazard in one shot. What came out of it reshaped how I’m approaching the whole pre-season window, and it starts earlier than most people think.

Spring 2026 Parasite & Safety Readiness: Quick Reference

Threat	Active Window	Risk Level	Pre-Season Action
Ticks / Lyme / Anaplasmosis	March–November (nymphs: April peak)	High	Prescription preventative active before first hike
Fleas	March–November	Medium	Confirm tick product covers fleas
Heartworm (mosquitoes)	April–October	High	Year-round prevention + annual test
Leptospirosis (standing water)	Peak spring/fall	High	Vaccine + avoid standing water on trail
New World Screwworm	Border regions	Low-Medium	NexGard EUA; vet consult if traveling near border
Rattlesnakes	March–October	High	Avoidance training + leash control
Foxtails	March–June	High	Dog boots through dry grass

Bottom line: Spring 2026 is running early. If your preventatives aren’t current by the end of March, you’re already behind.

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Tick and Flea Prevention: Update Before the First Hike

This is where most trail dog owners get it wrong. They wait until they pull the first tick to call the vet. By then, the dog has already been exposed.

Nymphal ticks are the primary Lyme disease transmission threat in spring. They emerge when soil temperatures hit roughly 45°F, which happened weeks earlier than average across the mid-Atlantic, Great Lakes, and Pacific Northwest this year. Nymphs are the size of a poppy seed. You won’t spot one on a dark-coated dog at the trailhead.

The American Kennel Club recommends checking your dog thoroughly within a few hours of returning from any trail to reduce transmission risk. The CDC confirms that prompt removal (ideally within 24 hours) is one of the most effective defenses against Lyme transmission, though some tick-borne diseases can transmit in far less time.

What to do right now:

• Call your vet this week if tick/flea prevention has lapsed since fall. Don’t wait until the first warm Saturday.
• Confirm your preventative covers both ticks and fleas. Products like Bravecto, Simparica Trio, and K9 Advantix II cover both, but check your specific product and its coverage window.
• If your dog hasn’t had a heartworm test in the past year, schedule that at the same vet visit. The American Heartworm Society’s updated guidelines require a negative test before starting or resuming prevention. You can’t just restart without it.

Post-hike body check protocol:

Run fingers through the coat from head to tail before your dog gets in the truck. Focus on: between the toes, under the collar, around the ears (both inside the flap and the base), armpits, groin, and the base of the tail. A fine-toothed comb helps on double-coated dogs. If you find a tick, use blunt-tipped tweezers, grasp close to the skin, pull straight up without twisting, and clean the site with isopropyl alcohol.

Rocky’s a 50 lb Aussie mix with a medium-length double coat. Tick checks after trails through tall grass take about four minutes. That’s a reasonable trade for not pulling a swollen nymph off him two days post-hike.

For a more thorough breakdown of specific 2026 tick products and the full post-hike protocol, see our tick prevention guide.

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Leptospirosis: The Spring Hazard That Snowmelt Creates

Leptospirosis risk spikes in spring for one main reason: snowmelt creates exactly the standing water conditions the Leptospira bacteria needs to survive. Puddles on muddy fire roads, shallow creek crossings, flooded meadow paths: these are all exposure opportunities.

The AVMA explains that dogs typically get infected through contact with contaminated water via mucous membranes or skin wounds. Wildlife (raccoons, skunks, rodents, deer) urinate near water sources and leave behind bacteria that can survive in soil and standing water for weeks to months.

Trail dogs face higher exposure than backyard dogs because they’re drinking from creek crossings, wading through meadow puddles, and sniffing at mud holes. That’s the terrain.

Your options:

• Vaccination. The lepto vaccine is the primary protection tool. The standard protocol is two initial doses, four weeks apart, followed by annual boosters. If your dog isn’t vaccinated and you hike in wet terrain regularly, talk to your vet this week. It takes about 4 weeks for full protection to develop from the initial series.
• Water management on trail. Carry enough water and use a collapsible bowl so your dog isn’t drinking from puddles or slow-moving creek water.
• Know the symptoms. Sudden lethargy, vomiting, decreased appetite, increased thirst or urination, and jaundice are the warning signs. Leptospirosis responds well to antibiotics when caught early. Delayed treatment can mean kidney or liver failure.

Leptospirosis is also zoonotic. Your dog can pass it to you, and vice versa. That adds a practical urgency to the vaccination conversation.

We went deeper on the spring leptospirosis picture (including regional risk maps and what your vet actually needs to know about your trail frequency) in our leptospirosis hiking guide.

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NexGard and the Screwworm EUA: What Trail Dog Owners Need to Know

On February 18, 2026, the FDA issued an Emergency Use Authorization for NexGard (afoxolaner) to treat New World screwworm infestations in dogs. This isn’t a standard seasonal parasite story. It’s specific to dogs near the US-Mexico border or traveling to countries with active screwworm cases.

New World screwworm (Cochliomyia hominivorax) lays eggs in open wounds or soft tissue. The larvae cause severe myiasis. As of the EUA date, NWS has not been confirmed in the US, but cases have been documented in livestock in northern Mexico, including Tamaulipas, which borders Texas.

What this means for your trail dog:

• If you hike in southern Texas or near the US-Mexico border, ask your vet about the NexGard EUA specifically.
• For most US trail dogs (Colorado, Utah, Pacific Northwest, Southeast), this is background information, not an immediate action item.
• The news keeps parasite prevention top of mind with vets right now, which makes spring 2026 a good time to have a full prevention conversation at your annual visit rather than a narrow tick-only discussion.

See our full breakdown: NexGard screwworm FDA EUA guide.

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Heartworm: Don’t Let the Prescription Lapse

Mosquito season starts earlier in warmer springs. In the Gulf Coast states, mosquitoes are already active. In the mountain West, you have a few more weeks, but not many.

The American Heartworm Society’s updated guidelines are clear: year-round prevention, annual testing. The “only give it in summer” approach is outdated and leaves gaps that adult heartworms can fill. Treatment costs $1,500 to $4,000 and requires 60 days of strict crate rest. Prevention is $60–$120 per year depending on the product.

If your dog’s prescription lapsed over winter, you need a current negative heartworm test before restarting. Your vet can’t refill without it, and that’s the right call, because giving heartworm preventatives to an already-infected dog can cause severe reactions.

Combo products that cover heartworm, ticks, fleas, and intestinal parasites (like Simparica Trio or Interceptor Plus with a flea product) can simplify the spring protocol. One conversation with your vet, one prescription, most of the parasite bases covered.

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Spring Water Hazards: Standing Water and What Grows In It

Beyond leptospirosis, spring water on trail carries two other risks worth mentioning.

Giardia and Cryptosporidium. Both are protozoan parasites that live in contaminated water. Dogs that drink from stagnant pools, puddles, or slow-moving streams can pick these up. Symptoms are GI: soft stools, vomiting, weight loss. Both are treatable but require a fecal test to diagnose properly. Carry enough clean water for your dog on every spring hike.

Blue-green algae. Cyanobacteria blooms can appear in slow-moving ponds and lakes as temperatures rise in spring. Blooms look like green or blue-green paint floating on the water surface. They can be fatal within hours of ingestion. If you see any unusual discoloration in still water, keep your dog out. There’s no antidote.

For the full spring water safety picture, including filtration options and trail hydration gear, see our spring water safety guide.

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The Complete Spring 2026 Pre-Season Parasite Checklist

Run through this before your first trail day. Every item, every year.

Veterinary (do these in the next two weeks)

• Confirm tick/flea prevention is current. If it lapsed since fall, call your vet today.
• Schedule heartworm test if it’s been more than 12 months. Required before restarting prevention.
• Update or start leptospirosis vaccine. Allow 4 weeks for initial series protection to develop.
• Discuss screwworm EUA if you’re hiking in south Texas or planning cross-border travel.
• Review your dog’s full preventative protocol as a single conversation, not piecemeal. Cover ticks, fleas, heartworm, intestinal parasites, and lepto in one appointment.

On-Trail Protocols (before every spring hike)

• Full tick body check within a few hours of returning. Toes, ears, armpits, groin, tail base.
• Carry clean water for your dog. Don’t let them drink from standing water, puddles, or slow-moving streams.
• Scan for blue-green algae before letting your dog near any pond or lake.
• Collapsible bowl in your pack. Not optional in spring.
• Blunt-tipped tweezers accessible, not buried in the bottom of the pack.

Gear Checks (before the first spring hike)

• Dog boots fitted and broken in if you hike through dry grass or foxtail country.
• First aid kit restocked. Styptic powder, gauze, antiseptic wipes. See our first aid kit guide if yours needs rebuilding.
• GPS collar charged and tracked. Spring conditions change fast; having a location fix on your dog matters more when trails are wet and unfamiliar. Our GPS collar guide covers the 2026 options.

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What the 2026 Spring Is Doing Differently

Two factors are compressing the prep window this year.

Earlier parasite activity. The mild winter means tick nymphs, mosquitoes, and fleas are emerging ahead of schedule across most of the continental US. The trails that felt safe in early March last year may not be safe in early March this year. If you’re using the calendar rather than your local conditions to decide when to update prevention, recalibrate.

More standing water. Where the winter was mild, snowpack was reduced, and spring melt is running faster and pooling more. Leptospirosis bacteria need standing water to survive. More spring puddles on your regular trails means more lepto exposure opportunities, even on routes you’ve done dozens of times.

Neither of these is catastrophic. They’re manageable with a vet visit and an earlier-than-usual prep timeline. The dogs that get in trouble in spring are almost always the ones whose owners assumed the season started the same week it did last year.

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The One Thing to Do Today

If you haven’t already: call your vet and book a spring parasitology appointment. Cover tick prevention, heartworm testing, lepto vaccination status, and any border-region screwworm questions in one visit.

That conversation, done before your first spring hike, handles the majority of what’s on this checklist. The gear and on-trail protocols are straightforward. The vet step is the one that requires lead time, especially the leptospirosis vaccine series, which needs four weeks to establish full protection.

Spring trail time with dogs is worth the pre-season work. Rocky and I have some serious miles planned between now and October. None of that happens smoothly if we skip the homework in March.

Do the homework now. The trails will be there when you’re ready.

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Field experience with Rocky (50 lb Australian Shepherd mix) on Colorado and Utah trails, spring 2023–2026. Tick transmission data from CDC and AKC. Leptospirosis guidance from AVMA and UC Davis School of Veterinary Medicine. Heartworm information from the American Heartworm Society updated guidelines. NexGard/screwworm information from FDA Emergency Use Authorization, February 18, 2026. Consult your veterinarian for dog-specific prevention decisions.