Dog Health

How Often Should I Worm My Dog?

A dog with worms is an unhappy, unfulfilled and potentially very poorly dog. You might be surprised to learn that one of the more common queries we receive is from dog owners who want to know "how often should I worm my dog?". The frequency of worming is something that requires some further analysis on the topic of worms in dogs on a more general level. You'll see why when you read on.

Dog worms used to be considered as 'just something you have to accept'. Not any more. We know that dogs can actually pass on nasty illnesses to humans as a result of worm infection and if that's not enough to motivate the average dog owner to keep their dog free of worms, the very fact that a worm infestation can actually prove fatal should really do the trick.

Worms generally tend to be more prevalent in younger animals, but there is a common misconception that by simply treating worms in puppies the dog won't require regular worming as he or she grows. The fact is, a dog can be infected and reinfected with worms at any time. So even a dog who has been wormed very recently can still reinfect themselves within days, let alone weeks.

Zoonotic diseases are those that can be passed on by animals to humans. They can be very serious, in extreme cases can even cause blindness.

To find out more about the most common types of dog worms and how they can affect a dog's health, we spoke with vet Shula Waining who has worked at Springfield Veterinary Group since 2011.

In the UK, Shula tells us the most common canine intestinal worms are roundworms and tapeworms.

She says, "Hookworms and whipworms are present in the UK, but are very rare. Often a worm infestation has no outwards signs, which is why it’s so important to treat for them even if your dog seems fine. Some animals with a heavy worm burden may have weight loss, diarrhea, increased appetite, and a poor quality hair coat. Periodically, infected dogs may shed adult worms in their faeces. Roundworms are long and thin, best likened to noodles, while tapeworms break off in small segments, often compared to grains of rice. I hope nobody’s eating while reading!"

The two most common types of dog worms explained


Roundworms can produce thousands of eggs and are commonly seen in puppies. Ingestion of these eggs releases the immature worm, which leaves the gut and migrates around the body of the animal eventually ending up in the intestine, where they develop into egg laying mature adult worms. In older animals they usually stop migrating and become stuck in tissues as cysts where they do little harm. In pregnant bitches these dormant stages re-activate and migrate to the mothers intestine, the milk glands and also directly into the puppies in the womb.


All tapeworms are caught by a pet following the ingestion of raw animal flesh (such as mice or birds) containing tapeworm cysts.

One tapeworm found in sheep rearing areas of the UK is of particular concern. The worm lays eggs that, when eaten from contaminated pasture, develop into large cysts in sheep (hydatid disease). If a human accidentally eats one of these eggs then a similar cyst can develop in the liver or lungs, requiring extensive surgery and (very rarely) proving fatal.

Rising Concerns About Lungworm

A parasite many dog owners fear, Shula says a lungworm (Angiostrongylus vasorum) infection is much less common than round or tapeworm, but can be very serious or even fatal. It can cause varied signs such as coughing, weight loss and bleeding disorders.

how often should i worm my dog

Most responsible dog owners know that they should be worming their dog but there are many myths regarding why to worm, how often to worm and what to worm with. Here are the facts:

Why worm your dog?

Worms are masters of multiplication and survival so there are plenty of worms out there waiting to infect your dog.

Shula reminds us that the four most common ways dogs can get worms are:

  • Contaminated soil
    Infected dogs shed worm larvae or eggs in their faeces. If this isn’t picked up it can become mixed into the soil, where eggs can survive for several years. Dogs may become infected by swallowing soil when playing, or by grooming it off themselves after walks.
  • Infected carcasses
    Animals such as rabbits, rodents and birds may ingest roundworm eggs which then pass to dogs if the small animals are eaten. Some tapeworms need to pass through an intermediate host, which must be eaten by the dog for the lifecycle to complete. These are often rodents, however some tapeworms infect sheep – it’s important to prevent dogs scavenging carcasses when out walking.
  • Flea
    The eggs of the common canine tapeworm (Dipylidium caninum) are ingested by fleas. These can then infect a new canine host if the fleas are ingested, usually during grooming.
  • During pregnancy/via milk
    The roundworm Toxocara canis is unique in that the larval stages can pass across the placenta to puppies before they are even born. Larvae can also be transmitted via milk, infecting pups during lactation.

It can be difficult to know if your dog is infected with one of these common intestinal worms. Your dog can appear totally healthy and may not pass worms in their faeces as is often thought. Symptoms of worm infection can include scooting their bottom on the ground, vomiting, diarrhoea, weight loss and a distended abdomen. However, it is better to treat your dog for worms before they start to damage their health.

In addition to this a dog with worms poses a health risk to other animals and humans.

How often to worm?

To answer that age old question we hear: 'how often should I worm my dog?' Shula says:

"I generally suggest adult dogs are treated at least every 3-6 months, dependent on individual risk level.  However dosing schedules vary dependent on which product you are using; many combined flea and worm treatments need to be administered or applied every month to remain effective.  This is also the case for lungworm preventatives.

Is it true dogs can be re-infected with worms soon after treating for worms?

Something we have wondered about with our own dogs, we took the opportunity to ask vet Shula whether this was true.

"Yes, this is true; wormers work by killing the parasites present at the time of dosing, but don’t have any residual activity.  This means a dog could pick up a new infection within days of being dosed.  Regular worming prevents worms building up to the point where an infection causes a clinical problem; small numbers of worms rarely cause an issue.  This is why it is important to try and prevent exposure to worm eggs (pick up faeces, prevent scavenging and so on) and to dose based on individual risk."

How can worms affect a dog's health?

Knowing a dog can be re-infected we asked Shula how worms affect a dog's health if untreated.

She says, "Small numbers of worms are usually not problematic, however if untreated the worm burden will increase.  Eventually worms will absorb a disproportionate amount of nutrients from the intestines, causing weight loss, poor body condition and diarrhea. In young puppies this can be fatal if left untreated.  Rarely, large numbers of worms can cause intestinal obstruction.  The roundworm (Toxocara canis) can also pose a health risk to people, especially young children."

Should the frequency of worming change based on a dog's age?

Keen to explore more about worming very young dogs, we asked vet Shula to tell us more.

"Young puppies are at the greatest risk both due to possibility of infection from their mum and because they are the most likely to suffer serious symptoms. Puppies should be wormed at 3, 5 and 7 weeks of age then monthly until 6 months of age.  Ideally, bitches should be wormed during pregnancy with a licensed product."

Can you worm an older dog?

Having heard that sometimes older dogs find it harder to process chemicals, we asked Shula for her advice.

"It very much depends on their risk level.  All licensed worming products are safe to use in animals of any age; however elderly animals that have reduced mobility may be at decreased risk of contracting infection.  That said, they are more likely to become unwell from worms if they do pick them up.  I would advise discussing your dog’s worming protocol with your vet if in doubt."





  1. Emma

    December 6, 2013 at 12:59 pm

    I wormed my 5month old Collie 2weeks ago but I think that he may have another tapeworm. Is it too soon to worm him again at this stage. I would really appreciate some advice. Thank you.

  2. Brooke

    March 13, 2017 at 5:49 am

    My dod didn’t eat all her food her medican was in and then threw up after she did eat it. She got her full dose yesterday and today. Should I go get more deworming medican and do it again? If so should I wait 2 weeks. We are not able to see a vet so I just got the medican from pet smart

  3. Brooke

    March 13, 2017 at 5:51 am

    Please email and post answer Emma December 6, 2013 at 12:59 pm
    I wormed my 5month old Collie 2weeks ago but I think that he may have another tapeworm. Is it too soon to worm him again at this stage. I would really appreciate some advice. Thank you.
    Brooke March 13, 2017 at 5:49 am
    Your comment is awaiting moderation.

    My dog didn’t eat all her food her medican was in and then threw up after she did eat it. She got her full dose yesterday and today. Should I go get more deworming medican and do it again? If so should I wait 2 weeks. We are not able to see a vet so I just got the medican from per smart

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