Ticks are temporary ectoparasites that attach to a host for a short period of time to take a blood meal. While this feeding usually causes the host few direct problems, ticks are the subject of considerable veterinary and medical significance due to the range of pathogens they can transmit. This article is concerned with hard ticks as these are more important in the spread of disease and are common on pets.
Tick biology
Hard ticks are so called because of a hard scutum or shield on their dorsal surface (Figure 1). The scutum covers the whole of the surface of the male tick but only one third (when unfed) or a small proportion (when fed) of the larva, nymph and adult female tick. The rest of the tick's body is leathery allowing for tremendous expansion when feeding; so they resemble a sac-like bag with anterior mouthparts and three or four pairs of legs depending on their developmental stage.
Tick life cycle and feeding
Hard ticks in the UK have a three-host life cycle (Figure 2) (Arthur, 1963). The eggs hatch producing six-legged larvae. These larvae climb onto grass to wait for (quest) and ambush a passing host that they attach to and take a blood meal. After feeding for a few days they drop off the host, digest the blood and moult (shed their skin) developing into the next growth stage, an eight-legged nymph. The nymph also quests for a host from which it feeds for several days before dropping off to moult into an adult. Mating on or off a host, the female then takes a final and large blood meal over a week or more from a third host. After this she drops off the host to digest the blood and lay her eggs. Ticks feed once at each developmental stage and, as the tick often feeds only once a year in the UK, the whole cycle from egg to adult can take 3 years (Arthur, 1963).
To take a blood meal the tick inserts it mouthparts through the skin. It injects its saliva containing many substances including anti-coagulants and vasodilators that enable it to suck blood. As it feeds it continuously excretes the water from the blood along with its saliva back into the animal but retains the red cells and proteins as food. On initial exposure there is haemorrhage from damage and the anti-coagulants. Non-specific inflammation with polymorphonuclear leukocyte infiltration results in an irritating lesion with necrosis (Figure 3). On repeat exposure the tick's saliva will have sensitized the host so there is an immune inflammatory response of basophils, eosinophils, mononuclear cells and necrosis, enlarging the lesion. Focal reddening and swelling are apparent on the surface of the skin. Pets may rub or scratch the site making the lesion worse.
Tick species and their habitats
The ticks most commonly found on dogs and cats in the UK belong to the genus Ixodes (I. ricinus and I. hexagonus the most common, but also I. canisuga and occasionally I. frontalis and I. trianguliceps). Dermacentor reticulatus and Haemaphysalis punctata and imported Rhipicephalus sanguineus are occasionally found on pets (Ogden et al, 2000; Jameson and Medlock, 2010; Jameson et al, 2010; Smith et al, 2011). The habitat of ticks varies with species from very rural areas, through nests and burrows, to kennels and houses. Ticks are normally inactive in winter, with most ticks becoming active and feeding only in spring and early summer, although, depending on species and habitat, some ticks can be active throughout summer and autumn.
I. ricinus, the castor bean or sheep or deer tick, does have a preferred host species on which to feed (Figure 2) but, despite its name, it will feed on any animal or bird and is the most common tick feeding on dogs and humans. It requires high humidity to prevent dehydration on the ground so it tends to be found in wetter areas, particularly in the West, Northern England and Scotland. Here it occurs in the moist microclimate of the matt of rough pastureland and the litter of moorland, brackenland, heathland and woodland. However, it may be found in woodland even in drier areas such as East Anglia and in some East Anglian and South-Eastern coastal areas (Figure 4) (Arthur, 1963; Scharlemann et al, 2008). I. ricinus activates in spring/early summer (Arthur, 1963; Randolph et al, 2000). In hotter areas of the UK tick activity will almost cease during summer, but ticks remain active in cooler, damp locations. Some ticks become active in the cooler autumn. Pets regularly using these rural habitats during spring and summer are most at risk from ticks. The widespread distribution of I. ricinus coupled with its ability to act as a vector for Borrelia burgdorferi sensu lato (Lyme disease) and Anaplasma phagocytophilum (anaplasmosis) make this species of particular interest. I. ricinus also can be carried by wild animals and dropped off in gardens and parks near its habitats; ticks and tick-borne diseases have been observed even in suburban gardens.
I. hexagonus, the hedgehog tick, is the second most common tick on dogs and can be more common on cats than I. ricinus (Ogden et al, 2000). As hedgehogs abound in parks and gardens I. hexagonus is common throughout the UK, even in urban areas, from very early spring through summer. The agents of Lyme disease and anaplasmosis have been found in I. hexagonus although the epidemiological significance of the tick in transmission is not known.
I. canisuga, the British dog tick, cycles in kennels and catteries and is not uncommon in buildings housing cats and dogs; it also is found in fox lairs, on mink, badgers and other animals (Jaenson et al, 1994; Estrada-Peña et al, 1995; Page and Langton, 1996). The female can climb to a considerable height to lay eggs in cracks and crevices of roughly constructed buildings, even in the ceiling of a well-constructed, plastered wall, dog kennel (Arthur, 1963). This tick can be present in large numbers and control requires acaricide treatment of the building (with a pressure hose to penetrate cracks) and an acaricide bath/spray for the dog as large numbers of ticks might be present.
I. frontalis of birds, found in bushes, brambles and hedgerows, and I. trianguliceps, from nests of wild rodents such as voles, very occasionally are found on pets.
D. reticulatus, the ornate tick (Figure 1), is found in the sand dune systems of West Wales and South-West England, particularly North Devon. It has recently been found in coastal Essex perhaps transported by sheep moved from Wales (Jameson and Medlock, 2010). This species transmits Babesia canis canis (an apicomplexan, intraerythrocytic, haemprotozoan piroplasm) in mainland Europe (Irwin, 2009) and potentially could do so in the UK should Babesia-infected dogs from Europe enter a Dermacentor infested area.
H. punctata is usually found in the marshlands of Kent and Essex but now has been reported in West Hampshire (Jameson and Medlock, 2010).
R. sanguineus, the brown dog tick, will utilize a large range of species as hosts but is primarily a tick of dogs and common throughout the tropical and subtropical world between 35S and 50N. It can survive in temperate climates only when protected within domestic environments such as homes and kennels where it can reach high numbers. This tick can act as a vector of B. canis canis and Ehrlichia canis (minute, intracellular, gram-negative bacteria occurring in leukocytes as eliipsoids and cocci that stain well with Geimsa) as well as a range of other pathogens. Although not indigenous to the UK it has been identified on pets and in dwellings after importation from mainland Europe and elsewhere. It is a risk to pets being taken abroad particularly to Southern Europe (Shaw et al, 2001).
Tick identification
Ticks belonging to the genus Ixodes can be identified by the position of the anal groove that surrounds the anus on the ventral side of the tick. In Ixodes species this groove runs forward with its apex anterior to the anus (Figure 5a). The non-Ixodes genera have the apex of the groove posterior to the anus. The main Ixodes species can be identified on the shape of their scutum and the postero-internal angle of coxa 1 (the tick's coxa is equivalent to a hip) attaching leg 1 to the body of the tick. I. ricinus has a rounded scutum (Figure 5a), I. hexagonus a hexagonal scutum (Figure 5b) while I. canisuga's scutum is widest in front of the middle becoming triangular behind this (Figure 5c) (Arthur, 1963). The length of the spine on coxa 1 also varies between the species (Figure 6). Most ticks in the UK have a brown scutum, D. reticulatus has a silvery pattern on its scutum (Figure 1). It is the only ornate tick in Britain. H. punctata is recognized by its extremely short mouthparts. R. sanguineus has festoons. meaning the posterior end of body has a scalloped or blanket-stitch appearance; this is obvious on the male but may not be visible on the fed female. It also has chitinous shields or bulging expansions of cuticle lateral to the anus on the ventral side of the male.
Tick-borne diseases in Britain and Europe
When ticks feed they can transfer pathogens into the animal on which they are feeding. In Britain, the spirochaete, B. burgdorferi, that causes Lyme disease, is perhaps the best known tick-borne disease, named as first identified as a cause of arthritis in children in Lyme, Connecticut. The majority of infected dogs (>95%) remain clinically normal. However, weeks or months after the tick bite, when the spirochaete has disseminated around the body, a small proportion of dogs may show fever, anorexia, polyarthritis, and/or enlarged lymph nodes. A few affected dogs develop kidney problems, ‘Lyme nephropathy’ these dogs do not respond well to treatment (Little et al, 2010). While an important zoonosis, dogs will not transmit Lyme disease to humans.
Also transmitted in Britain is A. phagocytophilum, a common cause of tick-borne fever in sheep and cattle in the UK and a rare cause of granulocytic anaplasmosis in dogs, equines and humans. There is no evidence for transmission from dogs to humans. Dogs with positive serology are not uncommon in Europe and PCR has identified a 1% infection rate in the UK (Shaw et al, 2005). A. phagocytophilum multiplies in neutrophils. The few reports of disease in dogs describe acute onset fever, anorexia, lethargy, lameness, and sometimes a cough, pale mucous membranes, or other generalized sign, with possible thrombocytopaenia and anaemia and possibly immunemediated disease occurring 1 to 2 weeks after the tick bite (Bexfield et al, 2005; Kohn et al, 2008) (Table 1).
Table 1. Distribution of tick-borne diseases in Europe including the UK and Ireland (ESCCAP Guidelines http://www.esccap.org/3/Guidelines.htm)
| Tick-borne infection | Distribution |
|---|---|
| The more common tick-borne infections: | |
| Borrelia burgdorferi (Lyme disease) | Throughout Europe including UK, Ireland. Different species/genotypes occur in different regions |
| Anaplasma phagocytophilum (granulocytic ehrlichiosis) | Throughout Europe including UK, Ireland |
| Babesia canis canis | The area in which B. canis canis occurs seems to have expanded. Endemic in much of Portugal, Spain, France through into Central and Eastern Europe as far north now as Holland, Germany, Poland, up to the Baltics. The transmitting tick, Dermacentor reticulatus, does occur further north |
| Ehrlichia canis (monocytic ehrliciosis) | Southern Europe where the transmitting tick, Rhipicephalus sanguineus is common. Much of Portugal, Spain, Italy, southern France, southern Hungary and Romania down to Greece |
| Less common tick-borne infections: | |
| Babesia canis vogeli | Southern Europe where the transmitting tick, R. sanguineus is common |
| Babesia gibsoni | Essentially an Asian parasite. Sporadic in Europe seen in fighting breeds among which it seems not to be tick-borne, spread instead by fighting and wounds |
| Theileria (Babesia) annae | Northwest Spain |
| Hepatozoon canis | Southern Europe, where the tick, R. sanguineus is common. |
| Anaplasma platys | Southern Europe where the transmitting tick, R. sanguineus is common, mainly Spain, France, Italy, Greece |
| Tick-borne encephalitis virus (European) | Eastern France, northern Italy, Switzerland, Austria, Germany, Czech Republic, Slovakia, Norway, Sweden (in only limited areas in these countries) |
| Louping ill virus | UK, Ireland, occurs rarely in gundogs and working dogs |
In cats, while there is occasional serological and PCR evidence for both B. burgdorferi and A. phagocytophilum, disease is rarely documented. Cats have been infected experimentally with both organisms with relatively similar signs to dogs.
Tick control
Limiting exposure of dogs to tick infested areas, particularly during spring and early summer, will help to prevent infection. Regular use of acaricides also will help prevent infection although their efficacy is not absolute. In a tick area owners should be advised to examine dogs carefully for ticks daily and to remove them. The larger more visible adult ticks often infect dogs although the smaller nymphs (a couple of mm in length) also can inject infection so examinations must be meticulous. Regular removal of ticks helps prevent tick-borne disease as many pathogens are not injected until >8–24 hrs after attachment (Mahoney and Mirre, 1974; Schein et al, 1979; Kahl et al, 1998; Hodzic et al. 1998; des Vignes et al. 2001; Crippa et al, 2002). The tick must be examined with a magnifying glass to ensure the mouthparts have been entirely removed; if left in the skin the tick's salivary glands are able to pump in pathogens even after the tick's body has gone. Further, while resolution of the initial bite lesion can leave a small, fibrotic scar, in other cases, a chronic granuloma can ensue. Dense infiltration of histiocytes and macrophages with some eosinophils, mast cells and neutrophils and fibrosis produce a fairly demarcated, palpable nodule. There can be depigmentation and loss of hair on the nodule. The likelihood of progression from the acute inflammation to a chronic granuloma increases if the tick's mouthparts are not removed as these induce a foreign-body reaction. Zenner et al (2006) compared the efficiency of tick-removal devices (with a slit that slides around the mouthparts of the tick) and conventional forceps. The tick-removal devices were found easier and faster to use by both veterinarians and pet owners.
Tick removal
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Wear rubber gloves and avoid handling ticks with bare hands.
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Use a pair of fine-tipped tweezers (Figure 7) or a tick-removal tool.
Figure 7. Tick removal using forceps. -
Try not to crush, puncture or damage the body of the tick as this may cause its stomach contents, which could include infective organisms, to be spilt or squeezed into the host.
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After removal disinfect the bite site with chlorhexiene or other skin disinfectant. Place the tick in a sealed plastic container and keep refrigerated for 1 month in case tick-borne disease develops and further identification is needed.
Risks to animals travelling outside the UK
The pet travel scheme (PETS) is designed to prevent the importation of rabies and other pests and diseases into the UK. Pre-importation treatment with an acaricide is important in preventing importation of exotic tick species and has, to date, prevented any significant population of R. sanguineus from establishing in the UK (Jameson et al, 2010).
Pet travel scheme (PETS)
This scheme allows pet dogs, cats and ferrets from mainland Europe and 52 other countries and islands (Defra, 2010) to enter the UK, travel to other Euro pean Union (EU) countries, and return to the UK, all without entering quarantine. In order to travel under the scheme the animal must meet certain conditions:
- Have been microchipped
- Be vaccinated against rabies
- Have received a satisfactory blood test result displaying sufficient antibodies to the rabies virus
- Be issued with an EU pet passport or a third country official veterinary certificate
- Be treated against ticks and tapeworms before embarkation to the UK and the treatments recorded correctly in the passport.
In order to comply with PETS tick treatment must be carried out no less than 24 hours and no more than 48 hours before embarkation. The treatment must be a veterinary product that has marketing authorization in the country of use and is licensed for use against ticks (tick collars are not acceptable). Each treatment must be signed and stamped in the passport by a veterinarian and clearly show the date and time the treatment was given (Defra, 2010).
As PETS only requires a tick treatment to be administered before re-entry to the UK, adherence to the scheme does not protect animals from becoming infected with tick-borne disease while abroad.
Risk of tick-borne diseases for pets travelling outside the UK
The risk posed to travelling pets from tick-borne disease will depend on the country they are travelling to and the amount of exposure they are likely to have to tick habitats. If acquired, some of the diseases have severe consequences for the pet while abroad, but also may manifest on return to the UK (Table 1). In addition to R. sanguineus, several of these diseases now have been recorded in the UK in travelled dogs. There is potential for transfer of some exotic ticks and diseases in the UK and there is now record of this (Holm et al, 2006; Shaw et al, 2009; Jameson et al, 2010).
Several species of protozoa in the genus Babesia are important. The more common B. canis canis, a large parasite inhabiting red cells, can cause an acute, severe haemolytic disease that also may show multi-organ involvement with hypotensive shock and intra-vascular coagulation. It can be rapidly fatal (Irwin, 2010). Babesia canis vogeli can be acute or more chronic. The very pathogenic, small B. gibsoni is less common; other less characterized Babesia species also occur. The bacterium, E. canis, inhabiting monocytes, can cause severe bleeding with thrombocytopeania, petecchial haemorrhages, nose bleeding, intra-ocular haemorrhage, among others. It is particularly severe in German Shepherd dogs. It can cause disease in cats. Co-infection with B. canis canis and E. canis is not uncommon. Anaplasma platys in platelets, while usually mild, might cause unexpected bleeding at surgery. Hepatozoon canis has an unusual life cycle as it is not injected, instead the infected tick is eaten by the dog, and also cat. It is mainly asymptomatic but may cause variable systemic signs. While most important in humans, dogs also can suffer from fever and encephalitis due to tick-borne encephalitis virus. This disease is transmitted by I. ricinus but only in limited geographic areas in Europe due to its mechanism of transmission (Randolph et al, 2002). These diseases and their distribution are described in detail by Shaw et al (2001).
To reduce tick-borne diseases, a complete parasite control programme should be designed for travelling pets with particular attention paid to the duration of action of various products. Hendricks and Perrins (2007) provide a summary of tick control products currently licensed for use in the UK and their efficacy against different species of tick (Table 2). As travelling pets will need to be treated for ticks again before reentry into the UK, care must be taken to avoid overdosing and possible drug interactions.
Table 2. Products available for the treatment and/or prevention of tick infestation so reducing the incidence of tick-borne disease (NOAH Data Sheet Compendium)
| Product name Acaricide (other drugs) | Suitable for | Safe for pregnant/lactating bitches | Do not use if under | Active against and duration of activity | Contraindications and warnings. Consult the data sheet and footnotes |
|---|---|---|---|---|---|
| Advantix spot on permethrin (imidacloprid) | Dogs only | Yes | 7 wks/1.5 kg | R. sanguineus | Very toxic for cats (remove cats until product is dry and cats should not lick the application area). Toxic orally. Rare hypersensitivity or behavioural changes may be seen in dogs or humans. |
| I. ricinus | |||||
| 4 weeks | |||||
| D. reticulatus | |||||
| 3 wks | Not to be used more than once weekly | ||||
| Frontline spray fipronil | Dogs and Cats | Yes | 2 days | Rhipicephalus spp. | Very toxic for rabbits. Keep from fires/heat for >30 min and dry. Pets should not lick wet coat (induces salivation). Rare hypersensitivity may be seen in pets or humans. |
| Ixodes spp. | |||||
| 4 wks | |||||
| Not to be applied more than 4 weekly | |||||
| Effipro spray fipronil | Dogs and Cats | Not established, risk assess | 2 days | R. sanguineus | As above |
| I. ricinus | |||||
| 4 wks | |||||
| Frontline Combo spot on fipronil (methoprene) | Dogs or Cats, specific for each | Yes | Kittens 8 wks/1 kg Puppies 8 wks/2 kg | R. sanguineus | As above |
| I. ricinus | |||||
| D. variabilis | |||||
| Cats 2 wks | |||||
| Dogs 4 wks | |||||
| Frontline spot on fipronil | As above | Yes | As above | Rhipicephalus spp. | As above |
| Ixodes spp. | |||||
| Dermacentor spp. | |||||
| Cats/dogs 1 mo | |||||
| Effipro spot on fipronil | As above | Not established, risk assess | Kittens 2 mo/1 kg Puppies 2 mo/2 kg | R. sanguineus | As above |
| I. ricinus | |||||
| D. reticulatus | |||||
| Cats 2 wks | |||||
| Dogs 4 wks | |||||
| Prac-Tic pyriprole | Dogs only | Not established, risk assess | 8 wks/2 kg | R. sanguineus | As above except not to be used on cats |
| I. scapularis | |||||
| Dermacentor spp. | |||||
| 4 wks | |||||
| Promeris Duo amitraz (metaflumizone) | Dogs only | No | 8 wks | R. sanguineus | Not to be used on cats. Pets should not lick wet coat (induces salivation). Can have sedative and other effects on dogs. Can have adverse neurological effects on humans, should not be used by persons taking mono-oxygenase containing medication. Rare hypersensitivity may be seen. |
| Ixodes spp. | |||||
| Dermacentor spp. | |||||
| 4 wks | Not to be applied more than 2 weekly | ||||
| Scalibor Protectorband deltamethrin | Dogs only | Yes | 7 wks | R. sanguineus | Not to be used on cats. Children <2 years should not touch collar, children should not have prolonged contact sleeping with treated dog. Rare cases of hypersensitivity, dermatitis, neurological signs. Withstands wetting but remove collar before pet bathing or swimming for environmental effects. Not to be used for the PETS treatment required 24–28 hrs before travel to Britain |
| I. ricinus | |||||
| 5–6 mo. One wk to full efficacy. |
Consult the data sheets. None of these products will be 100% affective. Ticks on the animals will not be killed immediately and ticks may attach and could remain long enough to transmit disease although incidence of tick-borne disease can be reduced. Shampoos should not be used for a few days before and days to 2 wks after application of most products. Efficacy of most products will not be affected if the dog becomes wet, but prolonged wetting will reduce efficacy; in the latter case or in the case of heavy exposure, some products may be given more frequently. Some products are licensed for ticks found elsewhere in the world and may be active against other ticks in the UK. Care and veterinary advice is necessary when treating sick/debilitated animals. Do not handle pet until coat is dry, recently treated animals should not sleep with owners. Avoid inhaling and contact with mouth, eyes, skin.
Conclusions
The tick species indigenous to Britain may cause irritation and skin lesions on pets. Correct removal is required to reduce potential permanent damage. Species identification on removal is important as I. ricinus can transmit autochthonous disease in Britain. D. reticulatus potentially could acquire and transmit B. canis canis from an imported dog. When travelling in continental Europe, tick control by acaricide treatments of pets and regular removal of ticks before the tick-borne disease can be injected will reduce the likelihood of disease. Strict adherence to the conditions of PETS by tick treatment 24–48 hours before embarkation to Britain is essential. This to reduce the likelihood of import of these exotic infections.
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Key Points
- Ticks are commonly found on pets in the UK.
- Tick biology and identification is dependent on the species.
- When ticks feed they can transfer pathogens into the animal on which they are feeding.
- The pet travel scheme (PETS) allows pet dogs, cats and ferrets from mainland Europe and 52 other countries and islands to enter the UK.
- There is potential for transfer of some exotic ticks and tick-borne diseases in the UK.
- Tick control helps to reduce tick-borne disease.