Parasites
Worms, fleas, ticks and heartworm: what does my puppy need?
By Dr. Steve Pelton, DVM, a small-animal vet since 2000.
The short answer
- Most puppies come home with worms, usually from mom before birth. It's nobody's fault and it's very treatable.
- Prevention for heartworm, intestinal worms, fleas and ticks runs every month, all year. Around Houston there's no off season.
- One stool test at the first visit, and a recheck if it finds something.
- No heartworm test needed to start. The first one comes after 7 months, then once a year.
Tap one
Meet the freeloaders
Six roommates who didn't sign the lease. Tap each one to see how puppies get it, what it does, and how it's stopped.
Pick a freeloader above to see its file.
Giardia. A tiny single-celled bug, not a worm, from contaminated water or other dogs' poop. Causes soft, smelly, on-and-off diarrhea. Your vet picks the test and treatment.
Coccidia. Another single-celled bug, very common in puppies from busy kennels and shelters. Can cause diarrhea. Not every dewormer covers it, so your vet chooses.
Try to skip a month
Every month, all year
Around Houston, fleas, ticks and mosquitoes don't take winter off. Go ahead, tap a month and try to turn it off.
All 12 checked. That's the plan for heartworm, intestinal worms, fleas and ticks.
Your puppy
What's due right now?
Monthly prevention: every month, all year
Heartworm, intestinal worms, fleas and ticks, all 12 months. Around Houston there's no off season.
Stool test: at the first visit
Bring a fresh sample to the first puppy visit.
Heartworm test: not yet
No test needed to start prevention, and there's no reason to test before 7 months. No 6-month test if he's been on prevention from the start.
Deworming: every 2 weeks until monthly prevention takes over
Most puppies are born with roundworms from mom. It's nobody's fault.
Your vet picks the product by your puppy's age, weight and where you live.
Keeping the freeloaders away from your kids
- Pick up poop every day, in the yard and on walks.
- Make poop duty a grown-up job, and never bare-handed.
- Wash hands after cleanup, after puppy play and before snacks.
- Cover the sandbox when nobody's using it.
- Keep your puppy on his schedule. A dewormed puppy on monthly prevention isn't spreading eggs in your yard.
After a dose, call your vet if...
He vomits soon after a dewormer, or seems unusually sleepy, drools a lot, vomits or is a little unsteady after a flea, tick or heartworm product. Seeing worms in the poop for a day or two after deworming is normal.
Go now if...
He has a seizure, can't stand, or his face swells. Head to your vet or the nearest emergency clinic, and call on the way.
What to ask your vet
- Which preventive is right for his age and weight, and what does it cover?
- Can you check a stool sample at the first visit?
- If the stool test finds something, when do we recheck?
- When is his first heartworm test?
- Do the cat and our other pets need flea prevention too?
- I'm late with a dose. What do you want me to do?
Questions I get every day
Is it the breeder's fault my puppy has worms?
Almost never. Roundworms pass from mother to puppies before they're born, and deworming the mother doesn't stop all of it. That's why every puppy gets dewormed on a schedule, starting young.
My puppy lives indoors. Does he really need heartworm prevention?
Yes. Mosquitoes get inside, and it only takes one. Texas topped the American Heartworm Society's list for heartworm for the first time, and around Houston there are mosquitoes nearly every month of the year.
Can I stop flea and heartworm prevention in the winter?
Not around Houston. A mild winter barely slows fleas and mosquitoes down, and a few warm days are all they need. The parasite guidelines recommend year-round prevention for every dog anyway.
How many stool tests does my puppy need?
Dr. P's plan is one at the first visit. If it finds worms or other gut bugs, he treats and rechecks. Once your puppy is on a good monthly preventive that covers worms, repeat tests on top of it usually aren't needed. Your vet may prefer a different plan.
When does my puppy need a heartworm test?
Puppies don't need one to start prevention. For a puppy on prevention since his first visit, the first test comes after 7 months, then once a year. No 6-month test is needed if he started on time with no gaps.
Where this comes from
- Companion Animal Parasite Council (CAPC). General Guidelines, updated April 24, 2025; Ascarid, Giardia, coccidia, hookworm and tapeworm guidelines.
- American Heartworm Society (AHS). Canine Heartworm Guidelines, revised 2024.
- AAHA Trends. Latest AHS heartworm incidence map shows troubling trends. April 21, 2026.
- Centers for Disease Control and Prevention. About toxocariasis.
- Merck Veterinary Manual. Fleas and flea allergy dermatitis; ticks.
General education, not veterinary advice. Your vet's plan for your puppy comes first.