Imported parasites
Increasing numbers of imported rescue cats and dogs have been seen over the past decade with associated risk of exotic pathogens entering the UK.
The number of Dirofilaria immitis heart-worm cases in imported dogs reported to ESC-CAP UK & Ireland remains high. While mean temperatures in the UK have so far prevented D. immitis establishing, this will become more likely as temperatures rise with global warming. Therefore, vigilance for the parasite is crucial in imported dogs, both for individual prognosis but also to minimise the risk of establishment. 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. Fortunately, the infected dog was diagnosed quickly. Left undetected, this raises the possibility of European mosquitoes being exposed to macrocyclic-lactone resistant D. immitis and local transmission occurring. This includes the UK if temperatures permit transmission.
Brucella canis is a Gram-negative coccobacilli bacterium predominantly infecting domestic dogs, and many infections are clinically mild. Infection is typically associated with reproductive abnormalities including infertility, abortion, endometritis, epididymitis, orchitis and scrotal oedema. Although, a wide range of non-reproductive conditions can also occur including chronic uveitis, endophthalmitis, discospondylitis and lymphadenitis. Increasing numbers of infected dogs associated with importation are being reported year on year, although this is thought to be at least in part because of increased screening and awareness.
The greatest risk of transmission to both dogs and humans is via reproductive fluids but can also be shed in urine, blood and saliva. Once dogs are infected, infection either persists for 2–3 years before elimination by the immune system, or lifelong infection establishes. Antibiotic therapy is not effective at eliminating infection. B. canis is not currently endemic in the UK, with infected imported dogs presenting a risk of UK establishment, particularly if used for breeding or if left entire and exhibiting clinical signs. It is a significant zoonosis with the potential to cause serious disease in humans. There have been two laboratory confirmed cases of B. canis in the UK, both from contact with infected dogs. A recent Human Animal Infections and Risk Surveillance group (HAIRS) risk assessment for B. canis (https://www.gov.uk/government/publications/hairs-risk-assessment-brucella-canis/hairs-risk-as-sessment-brucella-canis) concluded that those individuals at greatest risk of exposure to infection are those who have contact with contaminated materials, especially fluids and tissues associated with breeding and parturition, either in an occupational or domestic setting. Immunocompromised people or those who have underlying health concerns are at greatest risk of significant disease. However, the probability of infection is considered to be very low for the general UK population and low for those brought into contact with infectious material. Zoonotic risks therefore need to be kept in perspective while minimising risk in veterinary practice and to the general public.
Vigilance for relevant clinical signs in practice is therefore vital, alongside screening imported dogs to reduce personal risk and also to help prevent establishment of this pathogen in the UK. 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 limiting contact with other dogs. If these are not achievable, the owner is in a particularly high-risk group because of illness or is highly risk averse, then euthanasia will need to be considered. Infection risk in veterinary practices can be managed by:
- Personal protective equipment (PPE): particularly important in positive dogs and in those with relevant history and reproductive discharge. PPE also helps to protect against a wide range of other potential pathogens including Bartonella from flea infestations, Leptospira and tuberculosis.
- Immediate wound cleaning: if scratched, bitten or if existing wounds come into contact with bodily fluids
- Good hand hygiene
- Care with immune suppressed members of staff: particular care is required when handling clinically affected patients and those with reproductive discharge.
ESCCAP UK & Ireland continues to recommend veterinary professionals follow four key steps (the ‘four pillars’) in all imported dogs. These are:
- Checking for ticks and subsequent identification
- Treating dogs with praziquantel within 30 days of return to the UK in addition to the compulsory treatment and treating for ticks if a tick treatment is not in place
- Recognising clinical signs relevant to diseases in the countries visited or country of origin
- Screening for exotic parasites in imported dogs.
For dogs imported into the UK, the following screening tests are recommended.
- Leishmania: quantitative serology and/or polymerase chain reaction (PCR).
- Heartworm: antigen blood test and, if possible, a Knott's test.
- Ehrlichia canis and Anaplasma spp.: serology and/or PCR
- Hepatozoon canis: option to initially blood smear and then PCR
- Babesia spp.: PCR
- B. canis: antibody serology.
Leishmania and heartworm testing should be repeated 6–9 months after importation and B. canis 3-6 months after importation.
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 to minimise the risk of UK establishment. APHA will carry out free of charge, morphological identification of suspected cases of these parasites seen in veterinary practices in England and Wales. Samples should be posted to the APHA Carmarthen Veterinary Investigation Centre. Sample submissions must be accompanied by full clinical history to qualify for free testing.
Cat and dog helminth control
Debate continues around the need to treat routinely for Toxocara spp. in cats and dogs as a result of zoonotic risk. It has been proposed that no action needs to be taken because zo-onotic risk is low and cases in the UK rare. Toxocara spp. infection, however, can lead to a number of disease syndromes in people with a wide range of clinical presentations and is therefore likely significantly underdiagnosed. Possible consequences of infection include disease syndromes such as visceral larval migrans, ocular larval migrans and neurological larval migrans. In addition, being seropositive for Toxocara has also been shown to have associations with increased risks of chronic conditions such as asthma, epilepsy and cognitive impairment (Overgaauw and Van Knapen, 2013).
Although people can be infected by eating the undercooked meat of paratenic hosts such as wild game, the most common route of human infection is by the ingestion of embryonated eggs. This can occur through the accidental or deliberate consumption of soil (geophagia) and the transfer of the sticky eggs onto other objects that may be placed in the mouth (pica). One study 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, 2022). Therefore, measures are required to limit this contamination and reduce human exposure. A multifactorial approach is required as eggs can come from stray cats and foxes as well as from domestic cats and dogs. Compliance for any single strategy used is also unlikely to be 100%. Preventative measures include:
- Picking up of dog faeces: responsible disposal of dog waste will potentially limit environmental contamination
- Covering of sandpits: to reduce cat faecal contamination, and covering fruit and vegetables in allotments and gardens.
- Good hand hygiene: washing hands, particularly before preparing and handling food
- Washing of fruit and vegetables intended for raw consumption: produce from gardens and allotments can easily be contaminated with cat faeces and as a result should be washed before consumption
- Feeding dogs cooked diets or pre-frozen raw diets: to kill arrested larval stages in meat and offal
- Preventing fox access to public spaces: foxes have a high prevalence of Toxocara infection but their overall contribution has been demonstrated to be low by modelling due to their low numbers when compared to domestic cats and dogs
- Routine deworming: puppies and kittens are at highest risk of infection. 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. Kittens should be treated in the same way but the first treatment can be given at 3 weeks' old as there is no trans-placental transmission. Adult cats and dogs with outdoor access may shed eggs intermittently throughout their life. ESCCAP recommends treating these pets four times a year or monthly if high risk (those hunting, in contact with young children or immune-suppressed individuals). As an alternative, routine faecal testing can be performed at similar frequencies to treatment as long as pet owners understand that zoonotic egg shedding may take place in between tests.
Routine faecal testing at least annually alongside routine treatment is important to confirm that treatment frequencies are effective, compliance is adequate and as an early warning system for anthelmintic resistance.
For tapeworms and Angiostrongylus vasorum infections, routine monthly preventative treatments are required for high-risk pets. For tapeworms in cats that is those that hunt or have uncontrolled flea infestations. Dogs at high risk of tapeworm infection are those allowed offlead in known Echinococcus granulosus endemic areas, those with access to raw offal or livestock carcasses or with poor flea control. Dogs at high risk for Angiostrongylus vasorum infection include those living in known endemic foci or where local cases have been reported, those that are coprophagic, eat slugs, snails, grass and amphibians.
Potential environmental contamination with ectoparasiticides
There has been further research regarding contamination of UK waterways with fipronil and imidacloprid and potential sources. An online cross-sectional survey of UK cat and dog owners investigated ectoparasiticide usage and the frequency of activities that may result in transfer of the active substance to the environment. The survey found 86.1% of dog and 91.1% of cat owners had administered an ectoparasiticide treatment to their pet in the preceding 12 months, with imidacloprid being the most frequently administered. Encouragingly, 84% of owners who applied topical ectoparasiticides to their dog said they were aware of product warnings regarding swimming and bathing after application. Of these pets however, 36.2% of cats were still reported to swim at least monthly and 54% of dogs were reported to be washed at least monthly (Perkins and Goulson, 2023).
A second study 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 bets and washing of bedding) were found to be equivalent to 20–40% of the daily per capita load in wastewater of fipronil and imiadacloprid (Perkins et al, 2024).
These and previous studies suggest that companion animal parasiticides may be responsible for a significant proportion of fipronil and imidacloprid contamination in UK waterways but also that a significant proportion of this contamination may be coming from other sources. It also demonstrates the potential for owner education regarding reducing contamination from the application of product and avoiding bathing/washing/swimming/bed washing with treated animals.
As the climate changes, the trend towards milder winter temperatures seen in the UK increases the opportunity for outdoor flea life stages to survive and continue to develop. These factors mean that in the UK, flea populations are unlikely to show marked seasonal variations. Even where seasonal fluctuations in exposure do occur, they would have to be significant enough to prevent infestations establishing over time for year-round flea treatment not to be required. There is also an absence of data regarding lifestyle risk factors that would be significant enough to prevent household flea infestations over time. 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. In a similar fashion, cats visiting multiple households may be infested by newly emerged adults outdoors and then bring them indoors.
Year-round prevention is required as without it there is a high risk of flea infestations establishing (Coles and Dryden, 2014) and cat fleas are present across the UK (Abdullah et al, 2019). 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 when putting effective flea prevention in place.
Ticks
A range of tick-borne pathogens are present in the UK and/or present in travelled dogs. One study looked 76 dogs diagnosed with tickborne diseases in the UK between 2005 and 2019 (Silvestrini et al, 2023). In total, 25 were diagnosed with ehrlichiosis, 23 with babesiosis, eight with Lyme borreliosis and six with anaplasmosis. Fourteen dogs had co-infections with two or three pathogens. Except for those dogs with anaplasmosis and Lyme borreliosis, most dogs with tick-borne diseases had a history of travel to or from endemic countries. However, three dogs with ehrlichiosis, and one dog each infected with Babesia canis and Babesia vulpes did not have any history of travel. Babesia vulpes is thought to be endemic in the UK, likely carried by foxes. Foci of Dermacentor reticulatus ticks capable of transmitting Babesia canis 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. Sands et al (2022) found another infected tick in Devon, demonstrating the potential for further endemic foci to occur.
Louping ill virus (LIV) and tick-borne encephalitis virus (TBEV) are tick-borne flaviviruses transmitted by Ixodes spp. ticks. They are both capable of causing severe neurological disease in humans and, less commonly, dogs. Both are now endemic in the UK. Six cases of suspected tick-borne flavivirus meningoencephalomyelitis in dogs from the UK in 2021 resulted in three dogs surviving with neurological sequelae and three dogs having to be euthanased (Gonzalo-Nadal et al, 2024). This demonstrates the potential severity of disease in dogs. A paper published this year also demonstrated an increase in incidence of fatal infection from presumed LIV infection (Dagleish et al, 2024).
Preventative strategies are therefore important for pets at high risk of tick exposure. These include:
- Preventative tick treatments: the use of licensed preventative products that rapidly kill or repel ticks are useful in reducing tick feeding and therefore transmission of infection. Products containing an isoxazoline or pyrethroid fulfil these criteria. It should be remembered that no product is 100% effective and owners should therefore still be advised to check their pet for ticks after outdoor activity if possible
- Checking for ticks after outdoor activity: tick surveillance scheme data suggest that the majority of ticks are located and found around the head, face, legs and ventrum (Wright et al, 2018). Nymphs are extremely small and are easily missed so tick removal alone should not be relied upon for high-risk cats and dogs. Ticks should be removed with a tick removal device
- Sticking to paths where possible will greatly reduce the risk of tick exposure.
What is the rest of 2024 likely to hold?
Risk assessment is likely to be a major focus through 2024 alongside continuing concerns about the importation of exotic parasites. More data are required to accurately assess both the risks of pet parasite exposure and contamination of the environment and further data are likely to emerge through the remainder of this year and beyond. Vigilance is also required to combat the threat of novel pathogens entering the UK.