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The risk of Lyme disease exposure to UK dogs

With an increasing number of dogs at risk of Lyme disease, prevention is key

11 November 2018, at 10:28am
FIGURE 1 Ixodes ticks are still the most common ticks found on dogs in the UK
FIGURE 1 Ixodes ticks are still the most common ticks found on dogs in the UK

© John McGarry, University of Liverpool

Tick-borne disease represents an ongoing and growing risk to UK dogs and their owners. This comes from both increasing numbers of endemic ticks and increased outdoor activity and creation of green spaces bringing people and their pets into closer proximity with them. The most common ticks found on UK dogs continue to be Ixodes spp. ticks (Figure 1), the vectors of Lyme disease (Abdullah et al., 2016). Lyme disease is caused by spirochaete bacteria of the Borrelia burgdorferi complex and has been reported in a wide variety of mammals. Canines and humans, however, appear to be relatively more susceptible to disease.

Clinical signs in dogs and people are immune mediated. Most infections with B. burgdorferi are subclinical with 5 to 10 percent of infected dogs developing clinical signs. Dogs that do develop Lyme disease can be severely affected with acute arthritis in one or more joints with associated lameness, joint swelling and heat. Other acute signs may follow, including fever, anorexia, lethargy and lymphadenopathy. The acute form is often transient with relapses occurring.

FIGURE 2 The erythema migrans rash is a common presentation in humans, but does not occur in dogs
FIGURE 2 The erythema migrans rash is a common presentation in humans, but does not occur in dogs

Response to treatment with four weeks of doxycycline or amoxycillin is good if recognised early but if missed, then chronic disease can develop. This can potentially lead to non-erosive polyarthritis and protein losing nephropathy. Rarely, heart disease, seizures and behavioural changes may also occur. The common primary human clinical presentation of a circular skin rash known as erythema migrans, which can act as an early sign of infection (Figure 2), is absent in dogs and the lack of a pathognomonic sign in canines means that infection can easily be missed.

Prevention is therefore infinitely preferable to treating existing disease and preventative measures for dogs at high risk will also reduce transmission of other tick-borne pathogens present in the UK such as Anaplasma and Babesia spp. While the reported incidence of Lyme disease in people is increasing year on year, there is no similar prevalence or disease incidence data for dogs. It has been suggested that dog owners might be at greater risk of infection from Lyme disease than people without dogs, but studies have found no correlation between dog ownership and risk of infection, and infected dogs pose little or no direct risk to humans. On dogs, however, 2.37 percent of Ixodes ticks have been found to be infected with Borrelia burgdorferi complex bacteria, demonstrating that dogs are being exposed to infection. This prevalence of infection has not increased over the past 10 years but the number of ticks that dogs have been exposed to has. This increase in tick exposure is likely to be driven by two significant changes over the past decade: increases in tick activity and increases in outdoor activity and green space.

Increases in tick activity

Ticks in the UK demonstrate increased activity and questing behaviour for hosts in the spring and autumn, but real-time data from the Liverpool University SAVSNET scheme and the Public Health England Tick Surveillance Scheme (TSS) (Wright, 2018) have demonstrated that this increase in exposure now occurs in dogs throughout the summer months as well, with the potential to be exposed to tick bites at any time of year. It is uncertain what has driven this increase in activity, but it is likely that a milder, wetter climate, promotion of green spaces and corridors into urban areas and increasing numbers of deer and wildlife reservoirs are all factors.

Increases in outdoor activity and green space

Outdoor recreational activity is becoming more popular and many dog owners are now travelling with their pets to rural green locations to exercise and enjoy outdoor holiday activities. This will inevitably lead to increased tick exposure, particularly where this land is shared by deer and livestock. In addition to this, there is a trend known as the “crossroads phenomenon”.

High numbers of ticks will thrive in pristine wilderness, but few domestic pets or humans will ever encounter them. Increased housing development on rural land, green corridors for wildlife and overall urban encroachment by wildlife, however, will bring ticks increasingly into closer contact with people and their pets.

These trends are unlikely to be reversed over the coming years and forestation across the whole of Europe is steadily increasing. Increased green space and outdoor recreational activity carries many benefits but means that protection from ticks and tick-borne transmission in dogs requires preventative treatments and physical removal of ticks.

Use of tick preventative products

The use of routine preventative products that rapidly kill or repel ticks is useful in reducing tick feeding and therefore transmission of infection. Products containing an isoxazoline (eg Bravecto, Credelio, Nexgard, Nexgard Spectra and Simparica), permethrin (Activyl plus, Advantix and Vectra 3D), deltamethrin (Scalibor collar) and flumethrin (Seresto collar) all fulfil these criteria. These should be recommended for dogs walking in tall grass, bracken, pasture or woodland and environments shared by ruminants or deer. Any dog with a history of tick exposure should be routinely treated as it is likely that lifestyle will re-expose them.

It is important to consider compliance when discussing which product to use, as well as lifestyle. Whether a client prefers or is able to administer a tablet, collar or spot-on, and whether the dog has had reactions to products in the past, should be established. Frequent swimming or bathing of dogs may make some topical products unsuitable. No product is 100 percent effective, so owners should still be advised to check their dog for ticks at least every 24 hours.

FIGURE 3 Ticks should be removed carefully using a tick hook
FIGURE 3 Ticks should be removed carefully using a tick hook

Daily monitoring for ticks

As the bulk of Borrelia spp. infection is thought to be transmitted at least 24 hours after attachment, clients should be advised to check their pets every 24 hours and carefully remove any ticks found (Figure 3) with a tick hook, using a simple “twist and pull” action. It is important that owners are instructed how to remove ticks without stressing them and without leaving the mouthparts in situ. Removal can also be performed with tweezers with a “straight pull” technique. They should be fine pointed and not blunt, as crushing will stress the tick, causing it to release stomach and salivary gland contents, increasing the risk of disease transmission. The application of petroleum jellies or burning will also increase this likelihood and are contraindicated.

Vaccination

A licensed vaccine is available for Lyme disease prevention (Merilym3) in high-risk dogs. The vaccine prevents migration of the spirochaete to the salivary glands, reducing the risk of infection as a result.

Conclusions

Lyme disease is a significant threat to dogs exposed to ticks in the UK. Although early treatment can carry a favourable prognosis, prevention is desirable in pets that are at significant risk of exposure. Environmental, climate and lifestyle trends are putting dogs at increased risk of infection, so it is vital that veterinary professionals give appropriate risk-based prevention advice to help keep dogs safe.

A full reference list is available on request

Ian Wright, BVMS, MSc, MRCVS, is a veterinary surgeon and co-owner of the Mount Veterinary Practice in Fleetwood. He has a master’s degree in veterinary parasitology, is head of the European Scientific Counsel of Companion Animal Parasites (ESCCAP) UK and Ireland and guideline director for ESCCAP Europe.

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