Worming Your Dog or Puppy

Author: Danielle Fletcher
Published: Friday 4th October 2013
Updated: Tuesday 14th January 2014

Parasitic worms are forever a concern for pet owners causing dogs loss of condition and ill health, with some additionally posing problems for human health. Almost 100% of puppies are born with infections already established as some parasitic worms have acquired the ability to pass from infected bitches to puppies (transplacental and transmammary transmission). Many of the worms have complex life cycles requiring more than one host to reach sexual maturity, and multiple transmission stages with numerous symptoms in both dogs and humans linked to them. The control of worm infestations requires both good hygiene practice and regular worming of animals. There are two main groups of worms that parasitise dogs- Roundworms (Nematodes) and Tapeworms (Cestodes).

General symptoms of a worm infection

  • Worms in faecal matter and vomit: many worms live along the gut and rely on their eggs being passed out in faeces for transmission. Sometimes adult worms are passed out or thrown up, although some types are not visible to the naked eye.
  • Bloated belly: this is most common in puppies where large worm burdens cause the intestines to swell, producing a distented stomach or abdomen.
  • Worms around the anus: tapeworms are made of segments and broken-off sections of worms are often seen hanging from the anus or in faeces. Other smaller worms may be seen around the area and in the fur.
  • Rubbing the rear on the ground 'scooting': worms can cause irritiation and itching and dogs may drag themselves along the floor to relieve it. This can be confused with gland problems unrelated to a worm infection.
  • Vomiting and diahorrea: stools may contain blood, depending on the worms parasitising the dog. Some feed on blood and flesh, causing damage to the gut lining and bleeding.
  • Coughing: many worms have stages which pass through the lungs during development and migration through tissues. They travel up the windpipe and coughing propels them to the mouth where they are swallowed and mature further in the gut. Inflammation induced by lung stages can be severe enough to cause pneumonia.
  • Change in general health and well-being: weight loss and constant hunger is common with worms as some compete for resources, absorbing the food eaten before the dog can. Lack of nutrients can also lead to weakness, lack of energy, and a dull coat.

Recommended worming treatments (anthelmintics)

1) Drontal Wormer -the leading brand of effective worm control tablets, a first choice for many. Effective against roundworms and tapeworms at every stage of their life cycle.

Tablets are available in two sizes: Plus Flavour for Dogs, one tablet per 10kg body weight, and Plus Flavour XL for Dogs, one tablet per 35kg body weight. The tablets are palatable and flavoured to make administration easier, and scored to allow you to break them for more accurate dosing.Tablets may be used to treat infections in pregnant bitches without harming the foetuses; care must be taken not to exceed the stated dose. Suspensions are available for puppies from 2 weeks of age, 1ml of suspension per 1kg of body weight.

Active ingredients: Praziquantel, Pyrantel embonate (pamoate) and Febantel, described below.

2) Endogard -a more affordable copy of Drontal Wormers, made with the same ingredients, safe and effective. It too is effective against immature and mature forms of roundworms and tapeworms.

Active ingredients: Praziquantel is key for targeting tapeworms and is effective against both immature and adult stages. The drug is taken up through the surface of the worms and exhibits its anthelmintic activity, preventing tapeworm ability to avoid digestion by the host animal. Tapeworms are consequently broken down and passed out in faeces. Futhermore, Praziquantel causes contraction of tapeworm musculature and paralysis, detaching them from the gut wall so that any undigested worms are propelled by gut contractions and passed out in the faeces. Pyrantel embonate works synergistically with febantel to clear roundworms and ascarids as the former induces spastic paralysis allowing clearance from the gut (peristaltic gut contractions dislodge the worms) and Febantel blocks metabolism, causing death. Febantel targets and blocks energy metabolism and waste excretion in whipworms. The worms die after depleting all resources and suffering internal damage from waste products.

3) Panacur Dog & Cat Paste -a broad spectrum anthelmintic containing fenbendazole, effective against immature and mature GI and respiratory worms. Available as individual 5g syringes or packs of 10. Panacur is suitable for worming puppies and kittens from two weeks of age.

Active ingredients: Fenbendazole starves parasites to death by blocking energy metabolism in the same way as febantel, as members of the same drug family. It is most active against egg and larval stages as they require the most resources because they are growing and developing thus their deaths are more rapid.

4) Advocate Spot On Solution -combats both internal and external parasites. Available in packs of 3 or 6 pipettes for a range of weights of dog and is easy and safe to use. One of the few products effective against lungworm. Suitable for puppies over 7 weeks of age, weighing over 1kg. Requires a veterinary prescription to buy.

Active ingredients: Moxidectin is absorbed through the skin, distributed systemically (throught the body via the blood) to target internal parasites and slowly eliminated over four weeks. It works by causing flaccid paralysis of the worms such that they are unable to maintain their postion in the gut/circulation or locomote and re-establish a position in the host. The parasites subsequently die and are expelled from the animal's body. The ectoparasites (skin dwelling) are targeted by imidacloprid.

5) Stronghold Spot On -like Advocate, Stonghold Spot On targets both internal and external parasites but contains just one active ingredient, selamectin, which is both a topical parasiticide and anthelmintic. A range of pipette sizes suitable for different weights are available in packs of 3 or 6, and puppies can be treated from 6 weeks. Requires a veterinary prescription to buy.

Active ingredient: Selamectin provides protection from heartworm, hookworm and roundworms in dogs by affecting their neuromuscular function. Selamectin causes impaired contraction of muscles and paralysis, eventually leading to the death of the worms encountered.

6) Program Plus Tablets -target fleas, mites and a wide range of worms including hookworm, roundworm and whipworm. Program Plus tablets are commonly used as a heartworm preventative in dogs travelling to or living in regions with high heartworm incidence. Program Plus tablets are safe for use in pregnant and lactating bitches and in puppies from 2 weeks of age over 1kg. There is a range of tablets available for tiny. small, medium and large dogs. For dogs over 45kg, a combination of tablets will be prescribed; for example, one tablet for large dogs and one tablet for tiny dogs. Requires a veterinary prescription to buy.

Active ingredients:Milbemycin oxime causes paralysis in the neuromuscular systems of worms and mites, resulting in death and or expulsion. Lufenuron prevents the proper development of eggs and developing larvae produced by adult fleas that bite a treated animal.

Information on the worms parasitising your pets


  • Ascarid, Toxocara canis: a gastro-intestinal (GI) parasite that causes vomiting and diarrhoea in dogs. Adult worms are thin and beige/white, measure up to 10cm in length, spaghetti-like in appearance and can be seen in faeces and vomit. T.canis worms typically present more problems in the very young (around three months) or elderly dogs, and those with weaker immune systems. In a healthy adult dog, the larvae tend to encyst in the muscles, evading the immune system and medication, only re-emerging when the dog's immune system is compromised through age, illness or pregnancy. T.canis is one of the helminths able to be transmitted to puppies via the placenta and then by an infected mother's milk after birth.

    Life cycle: dogs are the definitive host of these worms, passing unembryonated eggs (not containing an embryo) into the environment in their faeces, where we and other abnormal hosts can become infected with them. Eggs in the environment embryonate to an infective stage and are accidentally ingested by dogs, or ingested with infected abnormal host such as a rabbit. The larvae hatch from eggs in the stomach and penetrate the gut wall then migrate to the lungs where they travel up the trachea, are coughed up and swallowed. Mature adult worms arrive in the intestines and lay eggs. In immune-compromised dogs, (young, old or ill) they cause symptoms of the infection- vomiting and diarrhoea.

    Humans are paratenic hosts of T.canis, meaning that the larvae do not develop while inside us, however they do invade through our gut wall, migrate through our tissues and travel in the bloodstream, causing symptoms with varying severity- Covert Toxocariasis (the most common condition with milder syptoms, abdominal pain, headache and cough), Visceral Larva Migrans (affecting the lungs, liver and heart, producing abdominal pain, fever and shortness of breath), and Ocular Larva Migrans (the most serious, with larvae migrating to the eyes, causing blurred vision and even loss of sight completely, although it usually affects a single eye). Children under the age of four are most frequently affected because they often play outside and come into contact with soil contaminated with faeces containing the worm eggs. Children then put their fingers in their mouths without washing their hands, accidentally ingesting the eggs which then hatch, invade through the gut wall and travel in the bloodstream to various tissues.
  • Heartworm, Dirofilaria immitis: heartworms can grow up to 14 inches long and live for 5-7 years in dogs. Heartworms cause mechanical blockage of the right ventricle and twisting of the vessels carrying deoxygenated blood to the lungs. If blood is not provided to the lungs, the oxygen supply will not be replenished, having serious consequences for a dog's health. The worms also cause Endarteritis, damage-induced inflammation of arteries, where the body cannot heal itself faster than the damage is delivered. They are extremely dangerous to dogs if left untreated, and in extreme cases Vena Cava/ Caval Syndrome develops- a close to complete blockage of flow that is likely to result in death.

    Life cycle: dog heartworms are spread by mosquitos. Development of the worms involves four moults- two in the mosquito and two in the dog. The infective stages migrate to the salivary glands of mosquitoes and are injected into the dog when mosquitos bite. After two moults to reach sexual maturity in the dog, adult worms shed their eggs into the heart which circulate in the bloodstream and can be picked up in blood meals by new mosquitos and spread to other dogs. These parasites very rarely infect humans.

    While some worms are easily treated with anthelmintics and passed out of the body, heartworms continue to be a threat to a dog's health. The dead worms break down in the chambers of the heart and are gradually pushed through the circulatory system until they have been fully broken down in the blood stream by the dog's immune system. Pieces of worm may lodge themselves in small vessels of the heart and lungs and cause death, so dogs should not be allowed to exercise to get over-excited to reduce the risk of more dangerous blockages and pulmonary embolism. Veterinary checks and wormings are required regularly if a dog lives in 'risk regions' of the UK, and if they travel to Southern Europe with you. Prevention through regular worming is the best method to protect dogs from this devastating parasite.
  • Lungworm, Angiostrongylus vasorum: Lungworm is becoming more of a problem in the UK, causing cardio-respiratory problems in dogs, often with fatal consequences, but luckily awareness is rising. A.vasorum is commonly known as 'French Heartworm'; the title of 'lungworm' is slightly misleading. The worms do pass through the lungs during egg hatching and tissue migration as larvae, however the adults live in the heart and pulmonary arteries, similar to the heartworm D.immitis. Larvae in the lungs elicit inflammatory responses causing bronchitis and pneumonia. Survival of the adult worms relies on the ability to manipulate the blood of the host dogs, and the worms secrete factors to reduce the blood's clotting ability. Risk of internal bleeding or excessive bleeding upon injury soar with this lungworm, with the most dangerous forms causing neurological problems (brain haemorrhages producing ataxia, seizures and loss of vision), and rapid death in some cases.

    Life cycle: dogs pick up A.vasorum by ingestion of infected intermediate hosts, snails and slugs, while scavenging and playing. It is also possible to become infected after contact with their slime trails if fresh and containing larvae. Dogs contaminate the environment further with their faeces and infect more garden molluscs. Larvae in the dog invade the gut wall and migrate to the lungs where they mature while progressing to the gut again. Adult worms migrate from the gut to the heart and pulmoary arteries where they lay eggs and contribute to mechanical blockage and inflammation of the vessels. These worms do not affect humans.

    There is a shortage of treatments for lungworm, with Advocate being the only effective product available at present.
  • Hookworm, Ancyclostoma caninum: Are thin, small worms, less than an inch long. They feed on blood and flesh in the GI tract and move around regularly to find new food, leaving ulcers at each site which may contribute to blood in stools and development of anaemia in heavily burdened dogs or puppies. These worms also encyst in muscles in healthy adults animals and re-establish active infections when the immune system is weaker. They are transmitted from bitches to puppies via milk (transmammary).

    Life cycle: hookworms are transmitted indirectly through contact with infected faeces and contaminated soil/grass. Like many other parasites, hookworm larvae migrate to the lungs and up the trachea until they are swallowed for a second time and reach the gut as mature adult worms. Here they attach to the intestinal walls to feed on gut tissue and blood.

    A.caninum larvae can penetrate the skin on humans, producing Cutaneous Larva Migrans, effectively meaning 'wandering larvae in the skin'. They are unable to penetrate below the outer layers of human skin but as they move around beneath the surface, they generate red, itchy, traceable patterns.
  • Whipworm, Trichuris vulpis: whipworms cause bloody diarrhoea in dogs which can either be acute, chronic or intermittent. The eggs passed out in faeces can persist in the environment for a number of years, making long-term treatment necessary to prevent reinfection.

    Lifecycle: whipworm eggs require a minimum incubation period of a month in the environment before they become infective to dogs. When swallowed in contaminated food or water, the eggs hatch and develop in the gut, and adults embed their thinner whip-like anterior end into the intestinal wall. The reproductive end is left in the gut lumen and eggs passed out in faeces.


Tapeworms may require an intermediate host for a stage of development but do not undergo a tissue migratory phase in their definitive hosts like many roundworms, and they mature on route to the large intestine, and establish themselves upon arrival. They can be difficult to treat properly since the heads are buried within the intestinal wall and if they are not destroyed, the rest of the worms will regenerate! Tapeworms are made up of the head or 'scolex' and many segments called 'proglottids' which each contain reproductive systems, allowing for mass egg production. These break off naturally and are replaced.

  • Dipylidium caninum: this tapeworm is transmitted by fleas and one of the reasons that worming and flea treatments are often combined. Accidental ingestion of an infected flea may occur when a dog grooms itself. Although the usual definitive host is a dog, these worms will develop into adult tapeworms in humans and will also be seen in human faecal matter.
  • Taenia spp.: dogs and canids are the definitive hosts for many Taenia species, with rodents, bovine and ovine animals infested as intermediate hosts. Humans may be infected by various Taenia species, not only those related to dogs.
  • Echinococcus granulosus and E.multilocularis: intermediate rodent hosts are required for egg development into cysts which in turn infect definitive hosts when the rodents are eaten. Infected dogs pass eggs in the faeces and contaminate the ground that rodents feed upon. Infestation of a dog by Echinococcus spp. commonly results in diarrhoea and is rarely severe enough to cause major disease problems unless the burden is extremely high. These worms are much smaller than other tapeworms, thus unlikely to cause blockage or out-compete the host for food resources.

    Humans may become infected by handling infested animals or ingesting contaminated food or water, producing 'Echinococcosis' disease. Hyatid cysts (larval cysts) similar to those formed in rodents spread throughout the internal organs of humans, causing life threatening disease in some cases. E.granulosus produces large cysts, predominantly in the liver, with fewer in the lungs, liver and brain. E.multilocularis produces many small cysts that spread more erratically like a cancerous tumour. General symptoms are coughing, itching, abdominal pain/swelling and jaundice if the liver function is severely disrupted. Thankfully, Echinococcus are rarely found in dogs so human risk of contracting Echinococcosis is low.

    Lifecycle: tapeworm eggs are eaten by an intermediate host (commonly flea larvae or rodents) and hatch into larval worms. These are passed onto dogs when they ingest the intermediate host. Adult tapeworms develop from the larvae once in the final (dog) host's intestines and eggs are produced and excreted in faeces.