Contributors: Eran Dvir, Ian Wright

 Species: Canine   |   Classification: Miscellaneous

Introduction

  • Dogs may harbor nematode (roundworm) and cestode (tapeworm) infections, most inhabiting the intestines. Lungworm (Angiostrongylus vasorum Angiostrongylus vasorum) is now endemic throughout most of the UK and growing in prevalence. Intestinal worms and A.vasorum are the main considerations for worm control regimes in UK dogs, however, worms may be present in other organs, especially in dogs traveling abroad.
  • There is an increased risk of importation of non-endemic species with the increase in the numbers of animals entering the UK under the Pets Travel Scheme (PETs Pet Travel Scheme ) particularly since there has been a recent relaxation in the rules. Dogs traveling abroad will also be at risk of exposure to novel worms such as Dirofilaria immitis Dirofilaria immitis and Spirocerca lupi Canine spirocercosis and Echinococcus multilocularis Echinococcus multilocularis.
  • Some worms carried by dogs have zoonotic potential such as Toxocara canis Toxocara canisEchinococcusspp and Ancylostoma braziliense Ancylostoma braziliense. Worm control programs should identify dogs at high risk of transmitting zoonotic pathogens and risk be minimized accordingly.
  • Worm control centers on suitable anthelmintic regimes and environmental control.
    Print off the owner factsheet on Worm control Worm control to give to your client.

Worms commonly infecting dogs

  •  Toxocara canis: the most common nematode of UK dogs. Four modes of infection are associated with this species include direct transmission, prenatal transmission, paratenic transmission, and trans-mammary transmission. Puppies are infected by the trans-placental and trans-mammary route and may have patent infection by 3 weeks of age. Female worms are prolific egg-layers. Eggs passed in the environment develop into the infectious embryonated stage in 2-4 weeks under optimum conditions. Adult dogs are infected through ingestion of embryonated eggs by eating feces (coprophagia), embryonated eggs in soil (geophagia) and on contaminated objects (pica), hunting, or scavenging carcasses of paratenic hosts or eating uncooked meat containing somatic larvae. Approximately 10% of domestic dogs continue to pass eggs in their feces. Zoonotic risk comes primarily from geophagia and pica. It has been demonstrated that T. canis eggs can embryonate in the fur of dogs making this another possible transmission route. Ingestion can lead to visceral or ocular larval migrans link Visceral larva migrans with neurological and covert forms of the disease also now being recognized.
  •  Toxascaris leonine Toxascaris leonina: infection is acquired through ingestion of paratenic hosts or embryonated eggs. Dogs may acquire infection as soon as they are weaned and may eat non-selectively. Development takes place in the small intestine where the adult worms remain. Infection is much less common than T.caniswith prevalence of 5% or less recorded in UK dog populations.
  • Hookworms Hookworm disease : the 'northern hookworm', Uncinaria stenocephala Uncinaria stenocephala is the most common hookworm found in UK dogs and is most likely to be encountered in dogs in breeding or racing kennels where dogs have access to grass runs. Working dog may also be exposed as foxes act as a significant reservoir of infection with prevalence in foxes having been recorded as high as 68% in England and 90% in Ireland. The life cycle is direct with larvae hatching from eggs passed in the feces and developing into third stage larvae in the environment. Ancylostoma caninum Ancylostoma caninum , a second species associated with warmer temperatures has endemic foci in the UK. This has a similar lifecycle to that of U. stenocephalabut infection can also occur through trans-mammary and percutaneous routes. Ancylostoma brazilienseand A.caninumare more common in the USA, Western and central Europe, Africa and so may be encountered more frequently in traveling or imported dogs. A. brazilienseis a significant zoonosis with the L3 larvae causing the creeping skin eruption known as cutaneous larval migrans.
  • Lungworm AngiostrongylosisAngiostrongylus vasorumand Crenosoma vulpis Crenosoma vulpis are both fox associated infections that dogs acquire through ingestion of infected snails or slugs that act as intermediate hosts. Foxes act as a wildlife reservoir but dogs are susceptible to infection. Canine infection is most commonly reported in the southern part of England and Wales with 'hotspots' that include Cornwall, Swansea and Surrey, however A.vasorumhas spread north through the UK in recent years and can now be considered emerging endemic throughout most of the country. C.vulpisis less common in foxes than A.vasorum and reported cases in dogs are also less frequent. Filaroides hirthi Filaroides hirthi and Oslerus Filaroides osleri Oslerus (Filaroides) osleri are two further species of lungworm that may also occur in dogs in the UK. Oslerus oslerihas been reported particularly in greyhounds where infective larvae can build up in runs.
  •  Dirofilaria immitis: heartworm Canine cardiopulmonary dirofilariasis is not endemic in the UK but dogs traveling abroad may become infected through mosquito bites.
  • Tapeworms: dogs may acquire Taeniaspp Taenia pisiformis tapeworms through hunting and Dipylidium caninum Dipylidium caninum though ingestion of fleas and lice. Exact prevalence data on tapeworm infections is lacking as fecal egg-counts are unreliable for detecting tapeworm infections and post mortem prevalence studies and post mortem studies are scarce but tapeworm infection overall in hunting and flea infested dogs is common. Echinococcus granulosus Echinococcus granulosus is present in the UK with endemic pockets in Herefordshire, Mid Wales and Western isles of Scotland. Sheep act as intermediate hosts with dogs becoming infected by eating carcasses or being fed raw offal. Infected dogs pass infective eggs in the faeces that may cause hydatid disease in people if ingested. Echinococcus multilocularis does not occur in the UK, but is endemic across a large area of central Europe and travelling pet dogs may be exposed. The intermediate hosts are small rodents and the fox acts as a definitive reservoir host. E.multilocularis is the cause of the serious zoonosis alveolar echinococcosis.
  • The whip worm nematode Trichuris vulpis Trichuris vulpis is relatively common in the UK. It has a direct life cycle; however it is difficult to control, due to its resistance of the embryonated eggs within the environment.

Deworming frequency

  • Disease in intestinal worm burdens is a function of numbers present and deworming every 3 months is normally sufficient to prevent significant disease. This frequency may need to increase to monthly regimes in working/rural dogs.
  • Deworming every 3 months reduces Toxocaraspp ova shedding and is therefore a minimum requirement in dogs, especially those scavenging or in contact with children or immune suppressed adults. Where these activities are common or where dogs are communing with very young children whose hand hygiene may not be adequate then frequency should be increased to monthly deworming. This will decrease ova production by over 90%.
  • Treatment of puppies should start at 2 weeks of age, repeated at 2 weekly intervals until 2 weeks post weaning and then monthly until 6 months old. This is to eliminate Toxocara egg shedding from Trans-placental and trans-mammary infection and significant populations establishing in the intestine.
  • Avermectins (Moxidectin Moxidectin, eprinomectin), tetrahydropyrimidines (eg oxantel, febantel Febantel ), emodepside and benzimidazoles such as fenbendazole Fenbendazole are all effective in treatment of T.canis. Praziquantel Praziquantel is and effective and broad spectrum tapeworm treatment.
  • Dogs at risk of A.vasorum infection should be treated monthly with a licensed preventative product. 2 licensed preparations are available, one containing moxidectin and one containing milbemycin oxime Milbemycin oxime. Risk factors include known consumption of slugs, snails and amphibians, previous exposure to the parasite, other known cases in the locale indicating local reservoir of infection and being in a known endemic foci.
  • Dogs in areas endemic for E.granulosus should be treated with praziquantel every 4-6 weeks to prevent patent infection.
  • Dogs traveling abroad to heartworm endemic areas should be treated with a licensed macro cyclic lactone such as selamectin Selamectin, milbemycin oxime or moxidectin a week before travel and then monthly until a month after return to the UK. Monthly praziquantel should also be administered to dogs spending more than a month abroad to prevent patent Echinococcus multilocularis infection.

Environmental management

  • Flea Flea: control/louse/fly control : to prevent D.caninum transmission and to prevent mechanical transmission of eggs.
  • Picking up of dog feces:to reduce environmental contamination with ova and larvae. As most ova take few weeks to be transformed into an infectious stage regular frequent picking is utmost important and should be beneficial.
  • Good hand hygiene: to prevent zoonotic transmission of T.canisand Echinococcusspp eggs.
  • Thorough cleaning/disinfection of kennels and runs: to prevent build-up of infectious environmental stages. However, once an infection in the soil has been established many of the eggs are highly resistance and toping the floor with fresh gravel might be required.
  • Preventing or reducing hunting and scavenging behavior: if practical.