The past decade has seen increasing numbers of imported rescue cats and dogs into the UK with associated risk of infections with exotic pathogens. These may pose an individual risk of disease to the host, zoonotic risk and risk of UK establishment depending on the parasite concerned.
Echinococcus multilocularis, the cause of cystic echinococcosis, is a severe zoonosis present in many European countries, but currently not present in the UK, Ireland, Malta, Finland or Norway. The adult tapeworm is carried by both foxes and domestic canids, with foxes acting as a reservoir of infection and rodents such as microtine voles as intermediate hosts. Dogs and foxes become infected by predation of these rodents, with infection in dogs bringing the parasite into close proximity to humans. Cats can act as definitive hosts for E. multilocularis, but have a lower worm burden with lower fecundity than canids. The UK currently remains free of the parasite with no untravelled human cases or detection in fox reservoirs or domestic dogs. The compulsory treatment with praziquantel for dogs before entry to the UK has been instrumental in maintaining the UK's E. multilocularis-free status. However, the half-life of praziquantel is short, so infection may occur in the 5-day window between compulsory treatment and entry into the UK. This is demonstrated by the legislation that allows treatment to be given before travel if the duration of the journey is less than 5 days, even though the parasite is not present in the UK. It is important that owners understand that praziquantel will not be protective against the parasite if they take this option. In addition to the compulsory praziquantel treatment, dogs should be treated monthly for tapeworm while abroad in endemic countries and within 30 days after arrival in the UK.
The number of Dirofilaria immitis heartworm cases in imported dogs reported to European Scientific Counsel Companion Animal Parasites (ESCCAP) UK & Ireland continue to remain high, with 19 cases reported in the past 12 months. While mean temperatures in the UK have so far prevented D. immitis establishing in UK mosquito vector populations, the risk of establishment will increase as temperatures climb, particularly in the south of England. Therefore, vigilance for the parasite is crucial in imported dogs. Early detection and treatment improve individual prognosis and reduce the risk of UK establishment by minimising the time that mosquito vectors can feed on infected individuals. This was recently emphasised by the first reported case of macrocylic-resistant heartworm infection in Europe (Traversa et al, 2024). The dog had been imported into Italy from the United States where macrocyclic lactone-resistant D. immitis is focally endemic. The infected dog was diagnosed quickly, but if left undetected this may have allowed resistance to spread. Leishmania cases reported to ESCCAP UK & Ireland also remain high, with 31 cases reported in the past 12 months. An article examining Small Animal Veterinary Surveillance Network (SAVSNET) data on Leishmania testing in UK cats and dogs found Leishmania infantum antibodies detected in 39.7% of tested dog samples and 1.07% of cat samples (Checa et al, 2025). A total of 368 dogs with leishmaniosis were identified from clinical narratives and of these, 189 had either visited, or were rescued or imported from, Spain, Greece, Cyprus and other southern European countries. Risk factors for UK dogs with clinical leishmaniosis were identified. Dogs aged between 3 and 6 years were 4.71 times more likely to have leishmaniosis than those 2 years or younger, and there was increased risk between 2017 and 2022 compared to 2014 (Checa et al, 2025). These figures also suggest an increased trend in UK cases over time associated largely with pet travel and importation. Although the sandfly vector is not present in the UK, transmission is possible via blood transfusion, venereal and congenital routes, as well as possibly dog bites and direct contact with open sores. Early detection of cases is crucial both to minimise the risk of these forms of transmission and to manage individual cases.
Increasing numbers of Brucella canis infected dogs associated with importation continue to be detected. A Human Animal Infections and Risk Surveillance group's risk assessment for B. canis concluded that the risk of human exposure was very low, with individuals at greatest risk of exposure being those who have contact with contaminated materials, especially fluids and tissues associated with breeding and parturition (UK Health Security Agency, 2024). Zoonotic risks need to be kept in perspective for pet owners and the wider public while minimising risk in veterinary practice and to the general public.
Vigilance for relevant clinical signs in high-risk dogs is vital alongside screening imported dogs, both to reduce zoonotic risk and the chances of UK establishment. B. canis is classed as a reportable disease under the Zoonoses Order, and any positive results must be reported to the Animal and Plant Health Agency (APHA). Transmission risks from positive dogs can be managed by neutering, good hygiene and managing contact with other dogs. Once neutered, zoonotic risk to animals who are immune competent is negligible, but if these control measures are not achievable or if the owner is in a particularly high-risk disease group, then euthanasia is an option to be discussed. Infection risk in veterinary practices can be managed by use of personal protective equipment, good wound and hand hygiene, and care regarding immunocompromised and pregnant members of staff.
ESCCAP UK & Ireland continues to recommend that veterinary surgeons follow four key steps (the ‘four pillars’) in all imported dogs. These are:
For dogs imported into the UK, the following screening tests are recommended:
Leishmania and heartworm testing should be repeated 6–9 months after importation and B. canis 3–6 months after importation. These tests can be run from one blood draw approximately 6 months after UK entry.
A thorough clinical exam is also essential to identify relevant clinical signs and to look for evidence of gross worm infestation, such as Thelazia callipaeda, Dirofilaria repens and Linguatula serrata. ESCCAP UK & Ireland has collaborated with the APHA to provide a free service for the identification and surveillance of these exotic parasites in UK dogs. This is vital to improve prognostic outcomes and minimise the risk of UK establishment. The APHA will carry out morphological identification of suspected cases of these parasites seen in veterinary practices in England and Wales free of charge.
Toxocara spp
Toxocara spp infection continues to be endemic in cats and dogs throughout the UK, with potential for zoonotic exposure via exposure to embryonated eggs in the environment. This can lead to a number of disease syndromes, including visceral larval migrans, ocular larval migrans and neurological larval migrans. Associations have also been made between human seropositivity to Toxocara and increased risk of chronic conditions, such as asthma, epilepsy and cognitive impairment (Overgaauw and Van Knapen, 2013).
The most recent study of environmental contamination in the UK with Toxocara eggs demonstrated Toxocara-type eggs in 86.6% of public parks across the UK, with an average of 2.1 eggs per 50 g of topsoil (Airs et al, 2023). Therefore, measures are required to limit this contamination and reduce human exposure. A multifactorial approach is required as compliance for any single strategy used is also unlikely to be 100% effective. Preventative measures include:
Routine faecal testing at least annually alongside routine treatment is important to confirm that treatment frequencies and owner compliance are adequate as well as detecting any anthelmintic resistance developing.
Angiostrongylus vasorum
A study has been published highlighting the potentially serious consequences of bleeding in Angiostrongylus vasorum cases (Thomsen et al, 2024). A total of 180 infected dogs between 2005 and 2019 were included in the study, including 65 dogs (36.1%) with bleeding diathesis. Cutaneous and mucosal bleeding were the most common clinical findings, with 20 dogs presenting with neurological signs associated with intracranial and intraspinal bleeding. The survival rate of bleeding dogs was lower at hospital discharge (76.9%) and 1 month after diagnosis (66.0%) when compared with dogs that had no signs of bleeding (94.8% and 90.1% at discharge and at 1 month, respectively). Bleeding was identified as an important negative prognostic indicator in A. vasorum-positive dogs (Thomsen et al, 2024).
Veterinary professionals should continue to be vigilant for cases of A. vasorum in their geographic area and advise preventative treatment for high-risk dogs (previously infected dogs, those living in close proximity to other cases, that are coprophagic and that eat slugs, grass and amphibians).
Tapeworms
The incidence of Echinococcus granulosus is much more widespread in Britain than previously thought, with untravelled cases of cystic echinococcosis increasing over time. Data presented at this year's BSAVA congress by Dr Marisol Collins showed evidence of E. granulosus in previously unreported areas of the UK. Of 46 sheep farms sampled, 17% had dogs that were positive for Echinococcus spp coproantigen, and 11% had dogs positive for E. granulosus coproDNA. Positive cases were more likely to be in Wales, but cases were also found in northeast England, Northern Ireland and eastern Scotland. Northern Ireland has previously been thought to be free of the parasite; while these results do not confirm endemicity, the do warrant further investigation. Out of 32 hunting packs, 9% of hunts tested positive for Echinococcus species coproantigen, with cases found in the northwest and southwest of England and the Scottish Borders. Four cases identified in cattle carcasses in abattoirs found in Gloucestershire, Herefordshire, Staffordshire and North Yorkshire had never entered Wales.
Human cases were also discussed at the Congress, with Dr Laura Nabarro describing five UK-acquired human cases that were treated in 2024, compared to just two UK-acquired cases between 2006 and 2016.
Further work is required to establish more accurate prevalence statistics. In the meantime, providing prevention advice to pet owners remains important and should be based on the lifestyle risk of the pet alongside current geographic information.
Potential environmental contamination with ectoparasiticides
There has been further research regarding contamination of UK waterways, with fipronil and imidacloprid as potential sources.
One study has investigated possible routes by which pesticides may enter wastewater and subsequently rivers. Wash-off studies, combined with modelling to account for the frequency of emitting activities, found handwashing post application to be the most significant source. All household routes investigated (hand washing, bathing of pets and washing of bedding) were found to be equivalent to 20–40% of the daily per capita load in wastewater of fipronil and imidacloprid (Perkins et al, 2024). A separate study also investigated dog swimming as a possible source of contamination (Yoder et al, 2024). In this study, the occurrence of fipronil and imidacloprid in Hampstead Heath in London was compared in three ponds with dog swimming and three without. A strong positive correlation was identified between dog swimming activities and concentrations of imidacloprid (R2=0.91) and fipronil (R2=0.79) (Yoder et al, 2024).
These studies suggest that companion animal parasiticides are likely to be responsible for a significant proportion of fipronil and imidacloprid contamination in UK waterways. They also demonstrate the potential for owner education regarding reducing contamination from the application of product and avoiding bathing, washing, swimming or bed-washing with treated animals. Many fipronil and imidacloprid products are sold through non-veterinary channels and advice regarding the correct application and avoidance of swimming or shampooing is likely to be highly variable. The potential impacts of fipronil and imidacloprid in the environment is uncertain and subject to ongoing research. A recent study investigating birds nests suggested an adverse impact and while this is a small pilot study, this area warrants further research (Tassin de Montaigu et al, 2025).
There continues to be an absence of data in the UK regarding lifestyle risk factors for cats and dogs that would be significant enough to prevent household flea infestations over time. Cat fleas are present across the UK (Abdullah et al, 2019); even households with purely indoor cats may be infested by owners triggering outdoor pupal emergence through their heat and movement, and then bringing newly emerged adults inside on clothing. Similarly, cats visiting multiple households may be infested by newly-emerged adults outdoors, which they then bring indoors. Year-round preventative treatment is required to prevent flea infestations, as without it, there is a high risk of flea infestations establishing (Coles and Dryden, 2014). Avoiding household flea infestations has a number of benefits, including reduction of flea bite irritation, flea-allergic dermatitis and zoonotic flea-borne pathogens, such as Bartonella spp. Taking lifestyle factors such as shampooing and swimming into consideration alongside maximising owner compliance is vital to prevent unnecessary environmental contamination. Owners may opt to regularly check for fleas and only treat if fleas are found, but if this approach is taken, it is likely that household infestations will have established by the time fleas are identified on the pet.
Ticks
A range of tick-borne pathogens are present in the UK and/or in travelled dogs. Ixodes spp continue to be present throughout the UK and are capable of transmitting a variety of pathogens, including Borrelia spp, Anaplasma phagocytophilum, small babesias, louping ill virus and tick-borne encephalitis virus (TBEV). Dermacentor reticulatus continues to be present in small endemic foci in Wales, and the southwest and southeast of England. These largely remain unchanged with the exception of southeast England, where there is some evidence of local expansion (Biddlecombe et al, 2025).
Research has suggested an increasing distribution of TBEV in England and increasing exposure to TBEV and louping ill virus in both humans and dogs (Callaby et al, 2025). Both are capable of causing severe neurological disease in humans, and less commonly, in dogs. Between 2015 and 2023, 21 cases of tick-borne encephalitis with a clinical disease were diagnosed in the UK, with 12 of these being diagnosed between 2022 and 2023. Three cases acquired the infection in the UK (Callaby et al, 2025). This is currently a small number, but demonstrates the importance of ongoing surveillance programmes, especially as up to 60% of encephalitis cases in the UK have unknown causes so this may well be an underestimate (Kennedy et al, 2017). Another study demonstrated an increase in incidence of fatal infection from presumed loupin ill virus infection in dogs (Dagleish et al, 2024).
Preventative strategies are important for pets at high risk of tick exposure. These include:
What is the rest of 2025 likely to hold?
Surveillance is crucial in assessing parasite exposure risk and preventing the spread of novel pathogens. In May 2025, ESCCAP will be launching interactive parasite infection maps to show what parasites are being diagnosed in cats and dogs across Europe and the UK. This will help veterinary professionals identify which parasites are being diagnosed in their specific region and use the maps to raise awareness with pet owners. As the emerging risk of TBEV and other tick-borne diseases develop, mapping is also being used to predict future risk. Using wildlife surveillance data and spatial modelling, scientists from the UK Centre for Ecology and hydrology, the UK Health Security Agency, University of Liverpool and University of Glasgow, have mapped suitability for TBEV in Britain and identified key drivers linked to exposure. They have created risk maps which will help to guide future surveillance and prevention strategies (Hassall et al, 2025). Mapping will continue to be an exciting development as plans are made to mitigate parasite risk in the future.