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Are we underestimating tick-borne diseases in cats?

The potential consequences of ticks and tick-borne diseases in cats are often overlooked; what is best practice for tick prevention and removal?

Ian Wright
15 November 2017, at 4:35pm

Ticks and tick-borne diseases in dogs have received a lot of publicity in the veterinary press and wider media over the last 18 months. The Big Tick Project, the outbreak of babesiosis in Essex (sometimes reported sensationally and confusingly in the press – Figure 1) and high-profile human Lyme disease cases all led to increased public awareness and concern regarding canine tick-borne disease potential zoonotic risk. What has been largely overlooked, however, is the number of cats that are also exposed to ticks and the role they might play in spreading tick-borne diseases. 

FIGURE 1 Don’t let the facts get in the way of a good tick headline
FIGURE 1 Don’t let the facts get in the way of a good tick headline

As well as gathering data on dogs, the Big Tick Project (Abdullah et al., 2016; Davies et al., 2017) asked vets to check cats coming into practices, record if any ticks were present and submit any they found: 1,855 cats were examined for ticks across 278 practices and 6.6% of cats were found to have ticks.

This is not as high a number as dogs (approximately one in three), but purely indoor cats are at very low risk of tick infection so prevalence in cats with outdoor access is likely to be much higher.

Male cats, those four to six years of age, those living in rural areas and those not neutered were found to be at greatest risk of infestation. This demonstrates that lifestyle factors (young, male entire cats are more likely to roam) and geographic factors (rural areas are likely to have higher number of ticks) influence the likelihood of cats being exposed. 

The observation that cats with outdoor access are vulnerable to tick infection is also supported by real-time data such as that recently published by Liverpool University (Tulloch et al., 2017). This study confirmed that ticks were being found on cats throughout the year in most parts of the country, but with marked seasonal peaks through the summer.

Cats also experienced a second marked seasonal peak in the autumn. Infection rates in cats were found to be very comparable to dogs. The ticks in both studies were identified as Ixodes spp (predominantly I. ricinus, 57.1% – Figure 2 – and I. hexagonus, 41.4% – Figure 3) capable of transmitting Lyme disease and Borrelia spp were found in 1.8% of ticks examined. Small Babesias such as B. microti and B. vulpis capable of causing disease in pets were also found in 1.1% of the ticks (Davies et al., 2017). 

FIGURE 2 Ixodes ricinus
FIGURE 2 Ixodes ricinus

© Wikimedia Commons

Exposure of cats to ticks, therefore, has a number of potential consequences: 

1. Owner revulsion Ticks are ugly! If they caused no other disease, this would be reason enough for many owners to want to avoid infestation in their pets or have them removed. A strong human-animal bond between pets and their owners has been demonstrated to have numerous psychological and physical bene ts and this bond is eroded by the presence of visible infestations.

2. Local skin reactions Tick attachment can lead to skin reactions at the bite site and subsequent bacterial infection.

3. Anaemia Large numbers of ticks can induce anaemia, especially in small cats and in co-infestations with fleas.

4. Tick-borne disease infection Cats have been demonstrated to be competent hosts for Anaplasma phagocytophilum, which is endemic in the UK. Infection can lead to lethargy, lymphadenopathy and fever and is likely responsible for some pyrexias of unknown origin in cats.

Data concerning the current incidence of Lyme disease and prevalence of Borrelia spp in UK cats is lacking. A small study of cats with clinical signs possibly associated with Lyme disease was carried out by Shaw et al. (2005). PCR analysis was used to determine the prevalence of tick- transmitted infections in 60 systemically unwell cats and B. burgdorferi was detected in two of them. 

There were no statistically significant associations, however, between the infections and the clinical signs shown.

Cats appear to have some natural resistance to developing the clinical signs of Lyme disease if infected, but show similar histological changes to dogs and humans, suggesting that some pathology as a result of infection can occur. Avoiding exposure to infection is therefore desirable.

Although not present in the UK, Cytauxzoon spp found in North America and Africa and Babesia felis found in Africa are highly pathogenic in cats and a concern for cats travelling abroad or that have been imported from these countries.

5. Spread of endemic tick-borne infections Although the prevalence of many tick-borne diseases in cats is unknown and the prevalence of Borrelia spp in cats across Europe is thought to be low, cats have the potential to act as transport hosts, visiting wildlife guilds maintaining Lyme disease and being exposed to ticks there.

Although unlikely to carry the numbers of ticks carried by deer, or transport them similar distances, cats may bring ticks back from wildlife guilds to more peri-urban establish in much closer proximity to human-populated areas.

6. The introduction of ticks and tick-borne diseases from abroad Ixodes spp are the predominant tick on cats and widely distributed across Europe. I. ricinus is the primary vector for tick-borne encephalitis, which has spread rapidly across Europe and carries a 1-2% mortality in infected people. 

FIGURE 3 Ixodes hexagonus
FIGURE 3 Ixodes hexagonus

© Wikimedia Commons

The risk of introduction to the UK of infection through travelled and imported pets is high and infected Ixodes ticks may be brought into the UK on infested cats. Cats may also be infested with Rhipicephalus sanguineus ticks, which carry a range of tick-borne diseases and can establish infestations in centrally-heated homes.

It is important that ticks found on imported pets are identified to establish if house infestation is a risk and which tick-borne pathogens they may be carrying. This can be done by veterinary professionals in practice using the University of Bristol tick identification key or sent to the Public Health England Tick Surveillance Scheme.

Tick-prevention products should therefore be used in cats with a history of tick exposure or those at high risk of infection. This includes young cats, those with prolonged and regular outdoor access and those living in rural areas.

It should be clearly explained to clients that not all flea-preventive products also provide tick protection as 29% of owners surveyed in the Big Tick Project said their cats were protected but the products they were using had no label claim against ticks (Davies et al., 2017). 

It is also important to discuss compliance. Some owners may only be able to apply a spot-on, tablet or collar and some may prefer to come into the practice to have the product applied. Use of products that rapidly kill or repel ticks will significantly reduce disease transmission.

The isoxazolines (Bravecto, Stronghold plus) or an imidacloprid/umethrin collar (Seresto) are all useful for this purpose, but none are 100% effective so if possible, it is also important that owners regularly check their cats for ticks and remove any found.

Ticks should be removed with a tick-removal device or fine pointed tweezers. If tweezers are used, the tick should be removed with a smooth upward pulling action. If a tick hook is used, then a simple ‘twist and pull’ action is employed.

It is important that owners are instructed how to remove ticks without stressing them and without leaving the head and mouthparts in situ

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 disease transmission.

Traditional techniques to loosen the tick such as the application of petroleum jellies, freezing or burning will also increase this likelihood and are contra-indicated. There will also be a very limited window of opportunity with most cats to remove the tick, so delay should be avoided!

The increased awareness surrounding dogs is vital if tick-borne disease control for pets and humans is to be achieved, but to overlook and underestimate the role of cats in the distributing of ticks and tick-borne disease would be a fundamental error.

The importance of their control in relation to the health of cats is only just beginning to be fully explored in the UK, but their potential to expand the range of tick-borne diseases and their vectors should also not be underestimated.

As veterinary professionals, there is now a range of safe and effective tick-preventive products for cats, which should be employed in high-risk cats to help keep them, their owners and the wider public safe.