What are Worms?


Worms are parasites that can be found living in different locations inside the bodies of dogs and cats. Some can even pose a risk to humans.


Often, pets become infected by picking up worm eggs and larvae from the soil, ingesting faecal matter, hunting rodents and by feeding or scavenging from raw meat or carcasses. Dogs and cats can become infected at any age. Puppies can become infected while in the mother's womb if the mother is already infected, and both puppies and kittens can become infected through the mother's milk.


Risk of infection can be reduced by talking to your vet or SQP about preventing and controlling worms in your pet. Appropriate anti-parasitic agents can be applied in a manner best suited to your pet. For example, cats and dogs which hunt should be wormed more frequently than those which don't. Help to reduce environmental contamination from worm eggs and larvae by always disposing of your pet's faeces in a responsible manner.


Most worms in the UK are relatively well tolerated by dogs and cats unless infection is heavy. However, there is a constant threat of new and dangerous worm infections entering the UK from abroad. Protection against these may involve more than the usual worm treatment, so be prepared and, if you plan to take your pet abroad, speak to your vet about how best to protect it and how to ensure that you don't bring any foreign worms into the UK.


Symptoms of infected cats and dogs can include loss of condition, lethargy, weight loss, anal irritation, diarrhoea and respiratory problems. In puppies and kittens, a heavy worm burden can also cause intestinal blockage with possible life threatening consequences. If you are concerned that your pet may be infected seek immediate advice from your vet.


Lifestyle


The risk of an animal carrying a worm infection will depend on a number of lifestyle factors such as:

  • Age
  • Reproductive status (pregnant or lactating)
  • Environment
  • Nutrition e.g. access to raw meat or offal
  • Geographical location
  • Presence of other parasitic infections
  • Travel abroad
  • History of parasite control
  • General health of the animal

These lifestyle factors are individual to each animal and influence whether that animal picks up parasites or not. This in turn can inform us of how often each pet needs to be treated for parasites. ESCCAP UK advises that pet owners consult their vet about parasite control to ensure that the worming product used, and the frequency with which it is given, is specifically tailored to their pet’s lifestyle and risk factors.


Worm Lifecycles


Direct Lifecycle:  This is where a dog/cat can be infected from eating a fully developed worm egg or larva in the environment which has been passed in the faeces of the same or another dog/cat. Parasite eggs or larvae when first passed are not infective and require a period of development in the environment before being infective for another animal.


Multiple host lifecycle:  This is where a parasite is dependent on more than one animal species to complete its lifecycle. Usually certain species of animal (the intermediate hosts) contain immature stages of a parasite and other species (the final hosts) contain the adult stage.


Knowledge of this more complicated life cycle is important when it comes to controlling multiple host parasites. For example, some worm control in pets can often only be achieved by limiting a pet’s access to the intermediate host as well as using products that kill adult worms within the pet.


Migrating worm larvae: These are immature larval worms which move through the tissues including the organs of an animal. Larval migration is a normal part of many worm species. Some of the larvae may lie dormant within an animal and are only mobilised again when the animal becomes pregnant or ill.


Zoonoses: Some worms can infect humans as part of their lifecycle and can cause serious disease. The technical term for an infectious disease in animals that can be transmitted to people is a zoonosis. ESCCAP UK advises pet owners to consult their vet to ensure that any parasite control programme they have put in place for their pet is adequate to control all the parasitic zoonoses that their pet may harbour. This is essential to ensure the health and wellbeing of all people who come into contact with that pet, and its faeces!


Prepatent periods: All worm lifecycles include a prepatent period, which varies between worm species. A prepatent period is the interval between when a parasite infection occurs and when the products of reproduction or multiplication of the parasite become apparent. It is these products of reproduction (usually worm eggs) that are often the infective stage of the parasite. When treating or preventing worm infections in pets, the objective is to manage the animal sufficiently that these worm eggs are not passed out into the environment to pose a hazard to other pets. The prepatent period is therefore an essential piece of information used to decide the frequency with which worm control products should be used.


Treatments


There are a number of important factors owners must understand about worm treatments:


  • Many modern wormers are very effective at eliminating adult worms in the intestine but not all are equally as good at eliminating all the migrating larval stages, therefore repeated treatment may be necessary.
  • Many worming treatments given by mouth have no lasting action. The medicine is absorbed from the intestine; it eliminates worms present at that time but once the medicine has been excreted from the body there is no residual action. This means that a pet can be re-infected almost immediately after being wormed if it gains access to ground contaminated by worm eggs or larvae that are ready to cause an infection, if it has access to raw meat containing the intermediate stage of a tapeworm or if the pet has a flea infestation at the same time.
  • Not all products used for treating worms are effective against all species of worms.

Roundworms


Roundworms are the most common worm in dogs and cats. They are so called because they are circular in cross section and have openings at both ends. They are found in either the intestines, the airways or the around the heart.


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Toxocara canis



Zoonotic: capable of causing sight impairment and a variety of other symptoms in infected humans

No signs and symptoms with a light infection

Direct lifecycle with dogs infected from eating a worm egg in the environment which has been passed in the faeces of the same or another dog (once the worm larvae has fully developed inside the egg). These microscopic eggs are invisible to the naked eye and can live in the environment for 2-3 years, thus remaining a health risk long after dog faeces have disintegrated..

Infection can also occur:

* through eating uncooked meat or prey containing worm larvae

* across the placenta to unborn puppies and in milk to suckling puppies.

The vast majority of puppies carry this infection at birth and have egg-laying worms in their small intestine by three weeks of age. Infection also occurs in older dogs.



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Toxascaris leonina



Zoonotic

No signs and symptoms

Dogs are infected by eating eggs containing fully developed larvae or by eating prey containing larvae. Adult worms are large and found in the small intestine.



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Uncinaria stenocephala



No signs and symptoms

Dogs are infected with this hookworm when they eat fully developed larvae, possibly as they eat grass. The larvae can also penetrate skin causing dermatitis and inflamed skin. The adult worms are found in the small intestine and cause protein to be lost in the faeces.



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Ancylostoma caninum



No signs and symptoms with a light infection

This hookworm is less common than U. stenocephala in the UK, but capable of causing more severe disease. Infection can occur through the skin or by a dog eating larvae from the environment. Larvae are capable of infecting puppies through milk as they suckle and so disease may be seen in very young puppies. The adult worms in the intestine feed off blood and some blood may pass in the faeces which typically turns faeces a blackish colour.



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Trichuris vulpis



Adult whipworms live in the large intestine with the worm's narrow front end embedded in the intestinal wall. A few worms are well tolerated but a heavy infection can result in bloody diarrhoea.



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Toxocara cati



Zoonotic: capable of causing sight impairment and a variety of other symptoms in affected humans.
No signs and symptoms with a light infection

Direct lifecycle with cats infected from eating a worm egg in the environment which has been passed in the faeces of the same or another cat (once the worm larva has fully developed inside the egg). These microscopic eggs are invisible to the naked eye and can live in the environment for at least a year, thus remaining a health risk long after cat faeces have disintegrated. Infection can also occur: * through eating uncooked meat or prey containing worm larvae * in milk to suckling kittens. This is a common infection of kittens and occurs in older cats as well.



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Toxascaris leonina



Zoonotic

No signs and symptoms

Cats are infected by eating eggs containing fully developed larvae or by eating prey containing larvae. Adult worms are large and found in the small intestine.



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Ancylostoma tubaeforme



No signs and symptoms with a light infection

This hookworm uncommon in the UK, but capable of causing severe disease. Infection can occur through the cat eating larvae from the environment. The adult worms in the intestine feed off blood and some blood may pass in the faeces which typically turns faeces a blackish colour.



Tapeworms


Tapeworms have a two host life cycle. Adult tapeworms live in the intestine of the final host (e.g. dog) and the immature stage of the tapeworm (usually a cyst) lives in another species of animal (e.g. sheep, fleas, rabbits or mice). The dog ingests the cyst by eating an infected part, or the whole, of the other animal containing the cyst.


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Dipylidium caninum



Zoonotic but does not cause serious harm

Signs and symptoms: Dogs appear visually unaffected by the infection although the tapeworm segments emerging from the anus of a dog are unsightly.

The immature tapeworm occurs in fleas and lice. Dogs are infected when they groom and ingest infected fleas or lice. Control fleas and you control Dipylidium infection.



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Taenia species



Dogs are infected when they eat infected prey (e.g. rabbits) or have access to carcasses or uncooked meat. Treatment will eliminate the adult tapeworms but infection may recur if the dog has future access to prey or uncooked meat.



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Echinococcus granulosus



Zoonotic: causes Hydatid Disease in humans

No signs and symptoms

(Wales and the Welsh Borders and the Hebrides only). Dogs are infected when they gain access to offal from sheep carrying hydatid cysts. Humans can be infected if they accidentally eat eggs passed by the adult tapeworms living in the dog's intestine. This is an important zoonosis. Wales is conducting a control scheme at present. See this page for more information N.B. People holidaying in affected areas may not be aware of the risk of this tapeworm. ESCCAP UK advises that people living or holidaying in high Echinococcus granulosus risk areas should speak to their vet to ensure they use an appropriate worming frequency and to check that the product they are using is effective against this tapeworm (it must contain the medicine 'praziquantel').



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Echinococcus multilocularis



Zoonotic: causes alveolar echinococcosis in humans

No signs and symptoms

(Found in Continental Europe, also found in foxes). Dogs are infected when they eat small rodents carrying the immature tapeworm. Adult tapeworms develop in the dog's intestine in approximately 4 weeks. Dogs are unaffected by the infection. If a human accidentally eats an egg passed by the tapeworms and present in a dog or fox faeces, severe disease can result. N.B. People from the UK holidaying with their pet in Echinococcus multilocularis affected areas need to be aware of the risk of this tapeworm and consider worming their pet more frequently (at least monthly) and check that the product they are using is effective against this worm (it must contain the medicine 'praziquantel').



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Dipylidium caninum



Zoonotic

Signs and symptoms: Cats appear visually unaffected by the infection although the tapeworm segments emerging from the anus of a cat are unsightly.

The immature tapeworm occurs in fleas and lice. Cats are infected when they groom and ingest infected fleas or lice. Control fleas and you control Dipylidium infection.



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Taenia taenaieformis



Cats are infected when they eat infected prey (mice). Treatment will eliminate the adult tapeworms but infection may recur if the cat contuse to hunt.



Lungworm


Lungworm is the common name for the parasitic worm Angiostrongylus vasorum which infects dogs. It is so called because it lives near the heart and in the blood vessels supplying the lungs. This parasite is also known as 'French Heartworm'. There are also other types of lungworms but none of these are referred to as the Lungworm:


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Angiostrongylus vasorum



This lungworm has been in the news recently as it has infected dogs from many parts of England, Wales and now Scotland. Infected dogs may show a variety of signs but most commonly abnormal bleeding patterns and respiratory signs such as coughing are seen. Dogs acquire the infection when they ingest a slug or snail that carry the larvae. Adult worms develop in the arteries leading to the heart after about 5 weeks. These worms lay eggs that travel through the animal's lungs and hatch allowing the young larvae to be coughed up and swallowed.



Heartworm


Heartworm is the common name for the parasitic worm Dirofilaria immitis which infects cats and dogs. It is so called because it lives in the pulmonary artery of the heart.


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Dirofilaria immitis



Zoonotic

Signs and symptoms are not seen for a long time

(Located in Southern Europe). Dogs are infected when they are bitten by a mosquito carrying the immature stages of the worm. The larvae migrate to the dog's heart and major arteries, where they mature into adult worms. These worms are up to 30 cm long and infection can result in coughing and loss of condition. Occasionally acute signs such as collapse are seen. Infection can be prevented by regular administration of a heartworm preventive taken when a dog is travelling to these areas at times of year when mosquitoes are active. Heartworm prevention needs to start well before travel to infected areas so ESCCAP UK advises clients to make a travel clinic appointment with their vet at least a month before the date of travel.






Key preventative measures


Many worms are transmitted to pets (and sometimes humans) by the passage of eggs or larvae in the faeces. Therefore hygiene measures will greatly reduce environmental contamination with infective parasite stages:


  • Clean up pet faeces immediately and dispose of them in a responsible manner - do not dispose of the faeces or cat litter in recyclable waste or compost
  • Practice good personal hygiene - always wash your hands after handling your pet and before eating food
  • Groom dogs regularly to minimise the risk of coat contamination
  • Avoid facial contact with your pet and never kiss your pet
  • Always wash your hands after gardening as soil can be contaminated by worm eggs
  • Cover sandpits when not in use

Feed pets with commercial diets or cooked food to prevent raw meat-transmitted parasite infection. Hunting should be deterred where possible and dogs and cats should not be allowed to access carcasses or placentae. Fresh, drinking water should also always be provided


There may also be a risk of infection to indoor house cats, as pet owners can bring contaminated soil and worm eggs into the home without realising. This means that cats can then become infected in what may be perceived as a safe environment.