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Which wormer should you use – and when?

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01 March 2016, at 12:00am

Michelle Greaves of Virbac provides an insight into the most important nematodes and cestodes affecting dogs in the UK, covering key risk factors and treatment suggestions.

ALL SIGNIFICANT HELMINTH species of dogs in the UK can be transmitted by eggs or larvae in faeces, so hygiene is fundamentally important when preventing transmission. 

Cleaning up faeces reduces environmental contamination, particularly around children’s play areas where there is a zoonotic risk. Several parasites can be transmitted in the faeces of wild canids and most environmental cestode and nematode stages are highly resistant to environmental degradation, resulting in a persistent reservoir of parasites. Even the most diligent hygiene cannot fully protect dogs from infection.

Roundworms

Toxocara canis, the most common zoonotic roundworm, is transmitted both via the placenta in utero and via the milk to pups up to five weeks of age. An appropriate treatment plan with fenbendazole during pregnancy (25mg/kg from day 40 of pregnancy until two days post-whelping) can reduce peri-natal infections.

In puppies, oral pyrantel embonate/ febantel can be given twice weekly from two weeks of age until two weeks post-weaning; milbemycin oxime (combined with praziquantel) monthly from two weeks of age or fenbendazole courses at two, five, eight and 12 weeks of age.

The pre-patent period for Toxocara canis is three to four weeks so, after the initial course of puppy worming, monthly treatments until six months of age are recommended (see www. esccapuk.org for more information).

Infections in adult dogs cause few clinical signs but are significant where zoonotic risk is high, for example where dogs have contact with young children. For the average adult dog a quarterly worming programme should be adequate but monthly treatment is recommended in high-risk situations.

Hookworms

Ancylostoma caninum and Uncinaria stenocephala are the key European hookworm species. A. caninum is not endemic in the UK but is zoonotic and responsible for cutaneous larval migrans.

U. stenocephala is prevalent in the UK, usually acquired by ingestion of eggs, often within a rodent. Parasites migrate to the intestines, feeding on blood and plasma, with potential to cause ill thrift and anaemia in young animals. Age- related immunity develops but subclinical or patent infections commonly occur. Most endoparasiticides treat hookworm infestation – check the relevant data sheets for more information. Hookworms can have shorter pre-patent periods than other parasites so may require two-weekly treatment to clear infection alongside strict hygiene protocols such as clearing faeces from a dog’s environment.

Angiostrongylus vasorum

There are a wide variety of non- speci c clinical signs associated with A. vasorum (“lungworm”). In the UK, sylvatic reservoirs maintain infection of mollusc and amphibian intermediate and paratenic hosts. Macrocyclic lactones, i.e. oral milbemycin oxime (combined with praziquantel) weekly, or topical moxidectin (combined with imidacloprid) monthly, are effective to treat infection.

Off-licence, fenbendazole has been used daily for five to 21 days. Several products authorised in the UK have claims for both treatment and prevention. Monthly doses are required to prevent infection as the pre-patent period is variable but as short as 28 days.

Tapeworms

Tapeworms of importance include Echinococcus, Taenia and Diplydium species. Tapeworms are zoonotic but have variable clinical consequence in dogs, with “scooting” being the primary complaint noted by owners as gravid segments are passed.

E. multiocularis is not endemic in the UK: compulsory tapeworm treatments on entering the UK are enforced to protect against human alveolar echinococcosis. E. granulosus and Taenia spp are also rarely clinically significant in dogs but the environmental resilience of their eggs has public health implications as they can contaminate fur, leading to accidental ingestion by owners and the rare development of hydatid disease.

Canine transmission occurs via ingestion of cysts found in the carcases of intermediate hosts such as sheep. Feeding of raw offal or access to carcases in endemic areas allows infections to persist.

Dipylidum caninum is rarely associated with clinical signs in dogs. Fleas and chewing lice act as intermediate hosts – dogs carrying fleas should be assumed infected with D. caninum and treated accordingly. The pre-patent period is three weeks so re-infection can occur before the next treatment is given if the flea or louse infestation is not controlled.

The pre-patent period of tapeworms is three to 10 weeks, depending on species. Treatment is with praziquantel for all tapeworms, with dogs at high risk of Echinococcus infection treated every four to six weeks. Where Echinococcus is confirmed, dogs should be treated on two consecutive days and shampooed to remove eggs on the coat. Gloves and a mask should be worn when bathing the dog and handling faeces to prevent zoonosis.

Comprehensive information about appropriate anthelmintics, and the less common helminth species can be found at www.esccapuk.org.