Worms in Dogs: How to Identify Them and Why Puppies Are Born With Them
Last reviewed: August 2026
Intestinal Worms Quick Answer
Four common types. Only two are ever visible, and most puppies are infected before they are born.
Most people go looking for worms in the stool, which works for two of the four common types and not at all for the other two. Hookworms and whipworms cause the most serious disease and are essentially never seen — which is why a dog can be carrying a significant burden while everything looks normal.
The Four You Are Dealing With
| Worm | What you'd see | How dogs get it | Typical signs |
|---|---|---|---|
| Roundworm | Spaghetti-like, pale, several inches, may be coiled | Before birth through the placenta, and in milk; also from eggs in soil | Pot-bellied puppy, poor growth, vomiting, diarrhoea |
| Hookworm | Rarely seen — too small to spot in stool | Larvae in soil penetrate skin, or in the mother’s milk | Pale gums, weakness, dark or bloody stool |
| Whipworm | Rarely seen; eggs found on faecal test | Eggs swallowed from contaminated ground | Chronic large-bowel diarrhoea, mucus, fresh blood |
| Tapeworm | Rice-grain segments near the anus or in bedding | Swallowing an infected flea, or eating prey | Often none; scooting, visible segments |
Why Puppies Are Almost Always Infected
This is the part that surprises owners, and it changes how you think about deworming. Roundworm infection in puppies usually occurs by transfer into the developing fetus through the placenta. Puppies can also be infected while nursing.
The mechanism is that dormant larvae sitting encysted in the mother's tissues reactivate during late pregnancy and travel to the puppies. A spotlessly clean, well-cared-for bitch can still deliver infected puppies, because the worms were already in her and nothing she encountered during pregnancy is responsible.
That is why puppies are dewormed on a schedule starting at a couple of weeks old rather than when somebody spots a worm. Waiting to see evidence means waiting through the period the burden does most harm. For hookworms specifically, fenbendazole given daily to the pregnant bitch from day 40 of pregnancy until two days after whelping greatly reduces transmission through the milk.
A pale, weak puppy is an emergency
Hookworms feed on blood from the intestinal wall, and a heavy burden in a small puppy can cause severe anaemia quickly. Pale gums, weakness or collapse in a young dog needs same-day veterinary care rather than an over-the-counter wormer.
What Can Pass to People
Worth being straight about, because this is a parasite group where the human risk is genuine rather than theoretical.
Toxocara canis, the dog roundworm, is considered the most important species precisely because its larvae can migrate in people. Swallowing infective eggs — from soil, sand or unwashed hands — can cause visceral and neural larva migrans. Hookworm larvae, particularly Ancylostoma braziliense, can penetrate human skin and cause cutaneous larva migrans, the itchy tracking rash people pick up walking barefoot on contaminated ground.
None of that is a reason for alarm, but it is a reason for the boring measures: pick up faeces promptly, wash hands after handling soil, keep sandpits covered, and keep puppies on their deworming schedule. Eggs need time in the environment to become infective, so prompt pickup does most of the work.
Why the Vet Wants a Sample
Because what you can see is a poor guide. Two of the four types are invisible, roundworms are passed only intermittently, and tapeworm segments dry out and disappear from bedding within hours. A faecal examination looks for eggs, which is a far more reliable signal than what turned up in the garden. If your dog has ongoing diarrhoea and a clear faecal test, the conversation usually widens to giardia, dietary causes and inflammatory bowel disease.
What Bloodwork Adds
Not the diagnosis — that comes from the faecal test — but the consequences. A complete blood count shows whether blood loss has caused anaemia, which is the thing that actually threatens a puppy with hookworms. Raised eosinophils are a common finding with parasites and sometimes the first hint on a routine panel. Chemistry picks up low protein where a heavy burden has been present a while.
Bloodwork back after a worm diagnosis?
Upload your dog's panel and see red cell count, eosinophils and protein levels explained in plain English — the values that show what the parasites have actually cost.
Check My Dog's ResultsFrequently Asked Questions
How do I know if my dog has worms?
Only tapeworms (rice-grain segments) and roundworms (pale spaghetti) are reliably visible. Hookworms and whipworms are found on a faecal test. Watch for diarrhoea, a pot belly in puppies, poor growth, pale gums and scooting.
Can puppies be born with worms?
Yes, and most are. Roundworm larvae cross the placenta into the developing puppies, and more are passed in milk. That is why deworming starts on a schedule, not when worms are seen.
Can people catch them?
Some. Swallowed roundworm eggs can cause visceral and neural larva migrans, and hookworm larvae can cause cutaneous larva migrans through skin contact with contaminated ground.
Can a dog have worms with nothing visible in the stool?
Routinely. Two types are never visible and roundworms are shed intermittently. The faecal test is what settles it.
Can worms cause anaemia?
Hookworms can, and it is their main danger. Pale gums and weakness in a puppy is an emergency, not a case for an over-the-counter wormer.
Related Reading
Giardia in Dogs
The parasite that testing misses, and why it keeps coming back
Blood in Dog Stool
What red versus black tells you about where the bleeding is
Pale Gums in Dogs
The sign that makes a worm burden an emergency
High Eosinophils in Dogs
The blood value that often rises with parasites
Dog & Cat Diarrhoea
When diarrhoea needs a vet rather than watching