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Pet travel and relative risk

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THINGS have moved on since the UK introduced the Pet Travel Scheme (PETS) in February 2000 and they could soon move further. At present, a derogation from EU law allows the UK and a few other European countries to apply stricter requirements to pets being brought into the country than most other member states. Having already been extended, that derogation is due to expire in July next year, as the European Commission seeks to harmonise requirements across the EU. As discussed at a seminar entitled ‘PETS or pests?’ at last week’s BSAVA Congress, this raises concerns about whether the controls left in place will prove adequate in protecting the UK not just against rabies, but also other diseases which may be imported.

As the seminar heard, it all boils down to relative risk, evidence-based decision making and applying controls that are proportionate. The problem is that, in many instances, data are lacking, which makes quantitative risk assessment difficult.

This is true for rabies as well as for other diseases of concern, most notably, perhaps, hydatid disease caused by Echinococcus multilocularis. Both Defra and the European Food Safety Authority (EFSA) undertook risk assessments in relation to rabies in 2007 which, while agreeing about the efficacy and importance of vaccination, coupled with animal identification, in preventing the disease, placed different emphases on the value of serological testing. Defra’s risk assessment argued that the test provides confidence that an animal has been successfully vaccinated and that there has been good compliance with the pet movement rules in the country of origin. The EFSA’s assessment, meanwhile, suggested that a second vaccination can provide assurance that sufficient immunity has been achieved and that such assurance is necessary only in the case of movements involving countries with a non-negligible risk of rabies (defined as one or more cases per million pets per year).

One consequence of changes to the pet travel rules could be that it might no longer be possible to require serological testing for animals entering the UK from other EU countries. This is worrying, not least because in some EU countries the risk of rabies is non-negligible by the EFSA’s definition. In a presentation at last week’s seminar, Professor Bill Ollier, of the University of Manchester, explained how genetic variation could contribute to the response to vaccination and argued that rabies vaccination without some measure of response could inevitably misclassify the immune status of some dogs (see p 447 of this issue).

The requirement for animals to be treated against ticks and tapeworms just before entering or re-entering the UK could also go if the rules are changed. This requirement has proved irksome to pet owners, but it does serve a purpose. As predicted, and as reported at the symposium, various diseases other than rabies have found their way into the UK since the introduction of PETS, and the number of cases can be expected to rise, and the diseases perhaps become better established, as the rules are relaxed and it becomes easier to bring animals into the country.

The UK is currently free of E multilocularis, but will this continue to be the case if the requirement for treatment against tapeworms is removed? This is of concern not just to the UK, but also to other EU countries currently free of this parasite – with good reason, because of the public health implications and because, once established in the animal population, it is extremely difficult to eradicate. From a (necessarily) qualitative risk assessment on the consequences of abandoning national rules undertaken in 2007, the EFSA concluded that the risk of dogs and cats becoming infected with E multilocularis as final hosts in endemic areas is ‘greater than negligible’, and that abandoning the additional controls would increase the risk of introducing the parasite into areas considered free of it. A separate risk assessment commissioned by Defra was similarly hampered by a lack of data but advocated extending the window for tick and tapeworm treatment to one to 10 days. It further recommended that pet owners should be given clear advice on avoidance and control of animal disease problems during the time spent abroad and be strongly advised to repeat tick and tapeworm treatments on return to the UK. It also argued that more detailed data are needed on the movements of animals before entry to the UK and called for more active disease surveillance of livestock, companion animals and wildlife.

The question arises whether it is wise to remove certain controls when the information available is limited. As Defra’s risk assessment on rabies remarked, ‘even a small risk of importation of rabies is of serious concern’ and the consequences of its introduction ‘though variable, are all severe’. Similar arguments could be applied in relation to E multilocularis.

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