Tick Threat and Control Methods

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Tick threat and control methods

Author : Hany Elsheikha

Categories : Farm animal, Vets

Date : May 29, 2017

ABSTRACT

Ticks are a complex group of ectoparasites considered the most important vector of pathogens in the northern hemisphere. Control of ticks in companion animals (dogs and cats) is essential – not only to maintain the health and welfare of the animal, but also to protect people from tick infestation and the potential transmission of serious zoonotic infections. A large number of effective acaricides are already available; however, optimal management of ticks is a task that has always been difficult to accomplish. This is due to many variables, including the large number and ecological complexity of tick-borne pathogens, the geographic expansion of the tick vectors, the broad range of reservoir hosts, and limitations associated with diagnosis and treatment of tick-borne pathogens.

Integrated interventions tailored to each animal and engaging pet owner to enhance drug compliance are the way forward if we are to achieve effective tick control. Also, knowledge of the indications and safety of available acaricide drugs is crucial when choosing the appropriate treatment for the individual animal. In this article, the clinical impact of tick infestation is discussed and information regarding the control of ticks is provided.

Ticks are arthropods belonging to the class Arachnida. To date, more than 900 tick species exist worldwide and they are classified as hard ticks (Ixodidae) or soft ticks (Argasidae).

Ticks can cause physical damage to their victims and, in some instances, death. Indeed, companion animals have always suffered from a broad range of tick infestations. Irritation, allergic reactions and fatal illnesses can occur in infested animals.

Ticks are efficient blood suckers and among the most dangerous haematophagous ectoparasites. All stages of ticks feed on blood of their hosts. Therefore, they can transmit many tick-borne pathogens to animals and humans. Ticks vector a broad range of disease-causing pathogens and

1 / 7 are second only to mosquitoes in their capacity to transmit disease agents of importance to human and animal health.

Figure 1. Adult females of the common tick species of dogs and cats in the UK. (A) Ixodes ricinus (the sheep tick, wood tick, deer tick or castor bean tick), (B) Ixodes hexagonus (the hedgehog tick), (C) Ixodes canisuga (the British dog tick), (D) Dermacentor reticulatus (the ornate cow tick or the marsh tick), (E) Haemaphysalis punctate (the red sheep tick) and (F) Rhipicephalus sanguineus (the brown dog tick or kennel tick). Figures A to D show the dorsal view of the tick and Figures E and F show the ventral aspect of the tick. Scale bar = 1mm. IMAGE: University of Bristol tick ID online (http://bristoltickid.blogs.ilrt.org) with permission of Richard Wall.

Therefore, better understanding of the tick epidemiology and available approach to control tick infestation is more important than ever.

Health impacts of tick infestation

Tick infestation can seriously compromise the health of the affected animal through multiple ways. Firstly, severe anaemia or immunosuppression can result from blood-feeding and engorgement of many adult female ticks (Figure 1).

Secondly, bacterial infection of bite sites can lead to dermal pathologies or pyogenic lesions. Thirdly, toxins secreted in the saliva of certain ticks can cause tick paralysis.

More importantly, ticks can transmit many pathogens, which can cause diseases more serious than the damage caused by ticks themselves (Elsheikha, 2016). For example, canine ehrlichiosis due to Ehrlichia canis and canine babesiosis due to Babesia gibsoni and Babesia canis can significantly cause ill health of dogs.

2 / 7 Infections may progress to a chronic disease, resulting in immunosuppression and pancytopenia in cases of ehrlichiosis or haemolysis, and shock due to multi-organ ischaemia during babesiosis. Fortunately, babesiosis is rare in British dogs – most cases are acquired abroad. However, the detection of a cluster of dogs with babesiosis in Harlow in the year 2016, and bearing in mind some of the affected dogs have not travelled abroad, has raised concerns babesiosis might become endemic in the UK.

In nature, risk of exposure to ticks is high. Dogs can be infested with hundreds of ticks and infestation may involve different tick species. Dogs with heavy tick exposure can be infected at a high rate with multiple tick-borne pathogens. Indeed, clear evidence exists for simultaneous acquisition and transmission of various pathogenic species and strains in dogs following tick bites (Diniz et al, 2007; Breitschwerdt et al, 2014).

Ticks are also responsible for the spread of zoonotic diseases to humans. During the past two decades, a dramatic increase has occurred in human infection with tick-borne pathogens such as Borrelia, Anaplasma, Ehrlichia and Rickettsia.

Tick control methods

Given the complexity and diversity of ticks and their life cycles, it is sensible to expect tick control to require an integrated approach combining off-host and on-host treatment.

Chemotherapeutic treatment and prevention

A number of anti-tick (acaricide) products can be used to reduce the risk of exposure of pets to ticks. However, the selection of acaricide-resistant ticks and environmental impacts due to chemical residues are the only two limitations of using chemical acaricides (Eiden et al, 2015). This was the reason for the increased interest in exploring plant extracts as eco-friendly acaricides or repellents against ticks (Benelli et al, 2016). Regardless, acaricides remain the mainstay to achieve effective tick control.

Choice of acaricide product should be based on animal lifestyle factors, geographical location, previous tick exposure, travel to an endemic region/country, owner affordability, and preference and any other drug needs for the pet. Some products contain pyrethroids, which have a tick- repellent (prevent tick from taking a blood meal), as well as insecticide and acaricide effects. Besides ticks and tick-borne diseases, many other diseases are transmitted by other arthropod vectors. Those should be also take into account when devising chemical control strategy for pets.

It is important to know cats can develop toxicity if a canine permethrin product is applied inappropriately or via secondary contact with a dog treated with a spot-on product containing permethrin. So, it is best to avoid the use of permethrin-containing products on a dog that shares a home with a cat. Cat collars that contain small amounts of permethrin may be appropriate for use

3 / 7 on cats. For more information on ectoparasiticides, Veterinary Prescriber created the parasiticides database to guide practitioners on the available products (www.veterinaryprescriber.org/subscribers-content/2014/7/10/ecto). A tutorial also exists on how to use the parasiticides guide (www.veterinaryprescriber.org/free-articles/2015/4/16/how-to-use-the-ectoparasiticide-guide).

Protective measures and tick removal

Tick control can be effective without the adoption of some protective measures. These include avoidance of tick habitat, avoiding heavily wooded and grassy areas, using repellents, and frequent tick checks (at least one check per day) to pick up and remove ticks, with a tick removal device or fine pointed tweezers, before they can transmit disease.

Although the transmission time for Borrelia (agent of Lyme disease) and Babesia is one to two days, transmission can occur in less than 16 hours and the minimum attachment time for transmission of infection is still unclear. It is also possible Rickettsia and Ehrlichia can be transmitted quickly (within three to four hours). In general, transmission is correlated to duration of tick attachment, hence it is advisable to use products that kill or repel ticks as quickly as possible to reduce the risk of disease transmission.

Ticks can be collected directly from the animals by hand-picking. This method involves manual search for ticks on the body and fur of animals. Pet owners should be advised to check pets for ticks after walks. If a tick is found on the body, it should be removed completely. The body of the tick should be grasped gently and vertical traction applied, using blunt, medium-tipped, angled forceps, until it displaces. Commercially available devices (known as tick twisters) especially designed for tick removal using “twist and pull” action can also be used.

Some tick removal methods should be avoided, such as applying a hot match to the tick body, covering the tick with petroleum jelly, nail polish, alcohol, or gasoline, using lidocaine and passing a needle through the tick. If any of these improper techniques is applied, parts of the mouth may remain in the skin, which can lead to infection or elicit inflammation.

Vaccination has been shown to be a feasible tick control method in cattle and offers a cost- effective, environmentally friendly alternative to chemical control (Jonsson et al, 2000). However, identification of tick-protective antigens remains the limiting step in vaccine development. Tick antigens exposed naturally to the host during tick feeding and those concealed have both shown promise as candidate vaccine antigens.

Development of effective vaccines against multiple tick species infesting dogs and cats may be possible using highly conserved tick-protective antigens that exhibit immune cross-reaction to different tick species or using a combination of key protective antigens.

4 / 7 What to do with collected ticks?

Ticks removed from animals or humans should be effectively disposed of (www.gov.uk/guidance/tick-surveillance-scheme) to prevent contamination of the environment.

The collected ticks should be preserved in glass vials containing 70% ethanol with a few drops of glycerine to maintain the natural colour and prevent them from hardening. Ticks should then be identified using phenotypic identification keys for local tick species (http://bristoltickid.blogs.ilrt.org). Also, animal owners and vet professionals can send ticks to Public Health England’s Tick Recording Scheme or the Big Tick Project (www.bigtickproject.co.uk) for proper identification of the species.

Morphological identification can be difficult in damaged or immature specimens, and because it requires entomological expertise. However, it is still worthwhile because it is important to understand the geographic pattern of tick distribution and for early identification of exotic tick species.

Importantly, revealing the pathogens transmitted by these ticks is essential for obtaining a better understanding of how pathogens emerge and compete under natural vector-borne transmission conditions.

Travelling animals

Veterinary staff often encounter clients preparing to travel to potentially tick-endemic or tick-borne, disease-endemic regions. The risk of acquisition of tick-borne diseases is based mainly on geographic location and travel season. Hence, an individual risk assessment should be performed for every traveller, taking into account the travel destination and the season of travel. Also, travellers to tick-endemic areas should be advised to use proper prophylactic medication before travel and continue its use after return.

The advent of new, safe and long-lasting acaracide products that can repel and kill ticks makes the prevention of tick-borne diseases an important priority for veterinary professionals and pet owners. Veterinary staff should provide travellers with resources (for example, www.esccap.org/travelling- pets-advice/) that provide advice and discuss risk factors for tick-borne infection transmission (http://bit.ly/2pOybf5).

Tick treatment of pets entering the UK is not obligatory, but compelling evidence still exists for the need for treating dogs before entering the UK to protect travelling and resident pets. It is important to treat pets for ticks while abroad and continue treatment on return, as some tick-borne diseases are already endemic in the UK. A Lyme disease vaccine is also available and can be discussed with pet owners based on the individual risk of the animal.

5 / 7 Minimising zoonotic transmission

Veterinary professionals routinely deal with diagnostic biological samples that may contain tick- borne pathogens, such as Bartonella organisms, that have been isolated from dog, cat or human blood and body fluids. Any contact with infected body fluids constitutes potential zoonotic risks.

Hence, staff should be aware of proper use of personal protective equipment, regularly wash their hands and avoid cuts and needle sticks.

Veterinary staff can also be at risk of tick bites while handling infested animals. Ixodes ricinus, for example, can transmit a large number of pathogens of medical and veterinary importance, including Borrelia burgdorferi (causative agent of Lyme borreliosis), tick-borne encephalitis virus, Anaplasma phagocytophilum (causative agent of human granulocytic ehrlichiosis), Francisella tularensis (causative agent of tularaemia), Rickettsia helvetica and Rickettsia monacensis, and Babesia divergens and Babesia microti (causative agent of babesiosis), and louping ill virus, among other pathogens.

Bearing in mind these concerns, it is essential veterinary staff exercise increased precautions to avoid not only direct contact with body fluids from animals infested with ticks, but also to avoid tick bites, animal bites or scratches (Maggi et al, 2013; Breitschwerdt et al, 2014).

Conclusions

Tick distribution and abundance is growing in the UK. Ticks are not only a nuisance, but can also be a significant source of diseases and a substantial public health challenge. In particular, ticks of the genus Ixodes can transmit numerous pathogens that affect human and animal health.

Chemical acaricides and tick repellents are the main tools to control ticks. The author also imagines the future of tick control as one that continues to rely heavily on chemotherapeutic drugs. However, prevention of tick and tick-borne diseases should also consider increasing the awareness of vets, physicians and the public to the risks imposed by these diseases.

The potential for the development of new acaricides has yet to be fully realised, but it will require more and better understanding of the tick biology and its interaction with hosts.

Bearing in mind the considerable effort and cost of developing new acaricides and the potential side effects of some of these drugs, perhaps now is the time to consider complementary and more supportive strategies. As future biotechnology tools and novel approaches for vaccine formulation and delivery are knocking on our doors, the prospect for research directed toward development of tick vaccines is exciting. We have to be ready to welcome them to maintain animal health and safety.

6 / 7 The author declares this article was written in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

Benelli G, Pavela R, Canale A and Mehlhorn H (2016). Tick repellents and acaricides of botanical origin: a green roadmap to control tick-borne diseases? Parasitol Res 115(7): 2,545-2,560. Breitschwerdt EB, Hegarty BC, Qurollo BA et al (2014). Intravascular persistence of Anaplasma platys, Ehrlichia chaffeensis, and Ehrlichia ewingii DNA in the blood of a dog and two family members, Parasit Vectors 7: 298. Diniz PPVP, Maggi RG, Schwartz DS et al (2007). Canine bartonellosis: serological and molecular prevalence in Brazil and evidence of co-infection with Bartonella henselae and Bartonella vinsonii subspecies berkhoffii, Vet Res 38(5): 697–710. Eiden AL, Kaufman PE, Oi FM et al (2015). Detection of permethrin resistance and fipronil tolerance in Rhipicephalus sanguineus (Acari:Ixodidae) in the United States, J Med Entomol 52(3): 429–436. Elsheikha H (2016). Tick-borne diseases in dogs, The Veterinary Nurse 7(8): 440-449. Jonsson NN, Matschoss AL, Pepper P et al (2000). Evaluation of tickGARD(PLUS), a novel vaccine against Boophilus microplus, in lactating Holstein-Friesian cows, Vet Parasitol 88(3-4): 275– 285. Maggi RG, Compton SM, Trull CL et al (2013). Infection with hemotropic Mycoplasma species in people with and without extensive arthropod and animal contact, J Clin Microbiol 51(10): 3,237– 3,241.

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