The introduction of the EU Pet Travel Scheme (PETS) greatly simplified pet travel to and from the UK, while attempting to limit the risk of the introduction of significant zoonosis into the country. While many of the rules associated with the scheme are still in place (compulsory microchipping, rabies antibody titre testing and compulsory tapeworm treatment for Echinococcus multilocularis-free countries), Brexit has meant that animal health certificates (AHCs) are now required for travel to and from the UK unless the pet has an up-to-date pet passport issued in an EU country. The additional expense associated with AHCs and the COVID pandemic severely curtailed international pet travel but now, as COVID restrictions have been lifted and pet owners get used to the new travel rules, pet travel is increasing once again.
Brexit has meant that animal health certificates (AHCs) are now required for travel to and from the UK unless the pet has an up-to-date pet passport issued in an EU country
There are a number of exotic parasites which cats and dogs travelling abroad are likely to be exposed to and vets need to ensure that owners taking their pets abroad receive adequate advice regarding parasite protection while they are away and on their return. In the first part of this miniseries we will review E. multilocularis and tick-borne pathogens, while the second part will review Dirofilaria species and Leishmania.
E. multilocularis, the cause of cystic echinococcosis, is a severe zoonosis. The adult tapeworm is carried by both foxes and domestic canids, with foxes acting as a reservoir of infection and microtine voles as intermediate hosts. Dogs and foxes become infected by predation of these voles, with infection in dogs bringing the parasite into close proximity to people. Cats can act as definitive hosts for E. multilocularis but have a lower worm burden and fecundity than canids.
Zoonotic infection occurs through the ingestion of eggs passed in the faeces of dogs and foxes, which are immediately infective. This can occur through association with infected dogs, through contamination of public spaces through dog fouling, or through eating contaminated fruit and vegetables intended for raw consumption. Zoonotic infection results in the local and metastatic spread of cysts leading to hepatopathy with the potential for multiple organ involvement.
Although E. multilocularis is not currently endemic in the UK, the increase in international pet movement across UK borders, the relaxation in the time period allowed between tapeworm treatment and return to the UK, and the spread of the parasite across Europe potentially threatens this status
Although E. multilocularis is not currently endemic in the UK, the increase in international pet movement across UK borders, the relaxation in the time period allowed between tapeworm treatment and return to the UK, and the spread of the parasite across Europe potentially threatens this status. Currently, only the UK, Ireland, Malta, Finland and Norway have confirmed endemic-free status in Europe. The PETS system currently still requires dogs to be treated with praziquantel between one and five days before entry to the UK. This simple treatment has prevented endemic foci from developing and the treatment remains vital. Statistical modelling has demonstrated that if this compulsory treatment is abandoned altogether then it is almost inevitable that E. multilocularis will be introduced into the UK (Torgerson and Craig, 2009).
Although the current treatment rule has provided protection against endemic spread, it does allow a window of opportunity for infection. If E. multilocularis is allowed entry into the UK, the large scale of the fox and microtine vole population will make the spread of E. multilocularis difficult if not impossible to achieve. It is therefore vital that the opportunity for the parasite to gain entry to the UK is kept to a minimum.
Control and prevention of entry into the UK
Preventative treatment with praziquantel is the mainstay of control. The prepatent period is at least 30 days, so the prevention of patent infection can be achieved by monthly treatment. Treatment is essential for dogs living and travelling in endemic areas to help prevent zoonotic exposure. Cases of infection in cats are uncommon but have been reported, meaning that treatment in cats is still worthwhile. However, the half-life of praziquantel is short so infection may occur in the five-day window between compulsory treatment and entry into the UK. All travelled dogs should therefore receive an additional praziquantel treatment within 30 days of entry into the UK.
Ticks and tick-borne pathogens
UK pets travelling abroad may come into contact with ticks and tick-borne pathogens not thought to be endemic in the UK. Tick-borne pathogens in cats and dogs in Europe are most commonly associated with exposure to Dermacentor reticulatus, Rhipicephalus sanguineus and Ixodes ricinus.
D. reticulatus is the vector of Babesia canis and the parasite can be transmitted to dogs via the saliva of a feeding tick, occurring approximately 48 hours after the start of blood feeding. Transmission has also been reported through blood transfusion.
The distribution of B. canis in Europe is closely linked with its main vector, D. reticulatus (Figure 1). While B. canis has spread both northwards and southwards across Europe, D. reticulatus has long been established in Britain in west Wales, Devon, Essex and London (Medlock et al., 2017), presenting an opportunity for B. canis to establish endemic foci if introduced via infected dogs or ticks. This occurred in the winter of 2014/2015 when an endemic foci of B. canis infection was established in Harlow, Essex. The parasite was confirmed in both local Dermacentor ticks and in untravelled dogs (Phipps et al., 2016). Recent studies have failed to find the parasite persisting in Essex but found another infected tick in Devon, demonstrating the potential for further endemic foci to occur (Sands et al., 2022).
[B. canis] infection can lead to immune-mediated haemolytic anaemia and/or thrombocytopenia with associated icterus, lymphadenopathy, pyrexia, secondary renal and hepatic disease, and in severe cases, death
Infection can lead to immune-mediated haemolytic anaemia and/or thrombocytopenia with associated icterus, lymphadenopathy, pyrexia, secondary renal and hepatic disease, and in severe cases, death. Prognosis is dependent on the severity of disease and speed of diagnosis, so it is important that UK vets are familiar with the clinical signs in travelled dogs.
The tick R. sanguineus has been restricted by climate to southern and eastern Europe and although it is unlikely that R. sanguineus would currently establish outdoor endemic populations in the UK, it can complete its life cycle in centrally heated homes, with larvae, nymphs and adults all able to feed on pets and humans (Hansford et al., 2017). This is a concern, as these ticks may carry zoonotic pathogens such as Rickettsia conorii, and are also capable of transmitting a range of pathogens of dogs including Ehrlichia canis, Anaplasma platys and Hepatozoon canis. These should all be considered as differentials in travelled dogs presenting with lymphadenopathy, pyrexia, neurological signs or thrombocytopenia.
Although Ixodes spp ticks are already widespread in the UK, pets travelling abroad may be exposed to these ticks carrying tick-borne encephalitis virus (TBEV). TBEV may infect a variety of mammalian hosts including dogs, foxes and ruminants. It is a potentially severe zoonosis with infections most commonly resulting in a transient fever, but sometimes progressing to meningoencephalitis, CNS signs and death. The European virus has spread rapidly and is endemic in Scandinavia and western, central and eastern Europe. UK surveillance has found strong evidence that it is present in both the New Forest and Thetford Forest in the UK (Holding et al., 2020). Preventing exposure of travelling pets to infected ticks will help to protect them as individuals and limit the risk of fresh foci developing in the UK.
Control and prevention of entry into the UK
It is essential that pets are treated with an effective tick product before, during and after travel. These can be products containing isoxazolines or pyrethroids. A wide range of products are available in spot-on, tablet and collar formulations for cats and dogs, and owner preference should be considered to maximise compliance. Lifestyle should also be considered as pyrethroid spot-on preparations and collars will have their duration of action reduced when shampooing and swimming. Further, if travelling to Leishmania-endemic countries, the product chosen should be a licensed pyrethroid repellent as this will provide some prevention. Most pyrethroids are toxic to cats and only a flumethrin collar (Seresto) is safe for use. Other pyrethroids in cats must be avoided.
While isoxazoline and pyrethroid products are highly efficacious, they are not 100 percent effective so monitoring for ticks after outdoor activity and careful removal with a tick removal device should be performed. Squashing or crushing ticks in situ with blunt tweezers or fingers will stress the tick leading to regurgitation and emptying of the salivary glands, potentially leading to increased pathogen transmission. Application of petroleum jellies or burning will also increase this likelihood and are contraindicated. Ticks found on return to the UK can be sent to the Public Health England Tick Surveillance Scheme for identification and will help to establish which tick-borne pathogens the pet may have been exposed to and whether R. sanguineus ticks may have infested properties.
The increased movement of pets, fluid vectors and parasite distributions in Europe make protecting UK pets and owners from exotic diseases increasingly challenging. Veterinary professionals are on the front line of UK biosecurity and must be prepared to give accurate travel advice to clients. In doing so, pet and human health will benefit and the entry of novel parasites into the UK can be delayed or avoided.