Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Description: The unfed adult is reddish brown turning slate blue when fed. The female is about 8 mm in length and the male about 5 mm (Fig. 11.1). The margin of the body appears to be composed of irregular quadrangular plates or cells, and no scutum is present. Unlike hard ticks, the four segments of the pedipalps are equal in length. The stigmata are situated on the sides of the body above the third and fourth pairs of legs. The integument is granulated, leathery and wrinkled. The hypostome is notched at the tip, and the mouthparts are not visible when the tick is viewed from above.

Hosts: Chicken, turkey and wild birds

Life cycle: Argas persicus is nocturnal and breeds and shelters in cracks and crevices in the structure of poultry houses. Females deposit batches of 25–100 eggs in these cracks and crevices. Up to 700 eggs may be produced by a single female at intervals, each oviposition preceded by a blood-meal. After hatching, larvae locate a host and remain attached and feed for several days. After feeding they detach, leave the host and shelter in the poultry house structure. Several days later they moult to become first-stage nymphs. They then proceed through two or three nymphal stages, interspersed with frequent nightly feeds, before moulting to the adult stage. Adult males and females feed about once a month, but can survive for long periods without a blood-meal. Females can become completely engorged within 30–45 minutes. Under favourable conditions the life cycle can be completed in about 30 days. All stages of these ticks remain around the roosting area of poultry, quiescent in the day and actively feeding at night. Argas persicus can survive in empty poultry housing for years, and may travel long distances to find their hosts. This tick can undergo rapid increases in abundance, passing through one to ten generations per year, particularly in areas where birds are present all year round.

Geographical distribution: Worldwide, especially in the tropics

Pathogenesis: Though common pests of chickens and turkeys, they are not usually a significant veterinary problem, except in small, housed flocks. It will bite humans, particularly if living in proximity to an infested flock. Infestation may cause irritation, sleeplessness, loss of egg productivity and anaemia, which can prove fatal. Each tick requires a considerable quantity of blood for engorgement, and therefore heavy infestations can take enough blood to bring about the death of their host. Most species are nocturnal and are parasites of birds, bats, reptiles or, occasionally, small insectivorous mammals and seldom attack humans.

These ticks may transmit Borrelia anserina, the cause of fowl spirochaetosis, and Aegyptianella pullorum, a rickettsial infection. It is a vector of Borrelia anserina and Aegyptianella pullorum among poultry, as well as avian spirochaetosis. The spirochaetes may be passed from one generation of ticks to the next through the egg, and transmitted to the host by biting or by faecal contamination.

Argas reflexus

Common name: Pigeon tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Description: The adult Argas reflexus is between 6 and 11 mm in length and may be distinguished from the fowl tick, Argas persicus, by its body margin, which is composed of irregular grooves, and the hypostome, which is not notched apically (Fig. 11.1). It is reddish brown in colour with paler legs.

Distribution: It is abundant in the Middle and Near East, from where it has spread into Europe and most of Asia.

Hosts: Pigeon

Life cycle: The life cycle is similar to that of A. persicus. The number of nymphal stadia ranges from two to four, with the fewest occuring in cooler temperatures. The egg to adult life cycle can take up to 11 years to complete. It is nocturnal and during the day lives in crevices in the pigeon house or nest material. It can withstand prolonged periods of starvation. Engorged females diapause during the summer months.

If oviposition has already commenced, egg-laying stops and resumes the following year without the need for another blood meal.

Pathogenesis: Heavy infestations may cause death from anaemia. It may also transmit fowl spirochaetosis. This tick occasionally bites humans, causing allergy. Its northern distribution through Europe is limited by the temperature requirement of its eggs and oviposition in summer months, since A. reflexus eggs show low levels of cold tolerance. Typical winter temperatures of 3°C cause approximately 50% mortality in A. reflexus eggs.

Epidemiology: This species lives in close association with its host, Columba livia.

Argas walkerae

Common name: Chicken tick

Predilection site: Skin, commonly beneath the wings

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Life cycle: Like most species of this genus: egg, larva, three nymphal stages and adult. It lives in crevices in the poultry house or nest material moving on to the host to feed.

Hosts: Chicken

Ditsribution: Southern Africa

Pathogenesis: It causes considerable economic losses, especially where it transmits Aegyptianella pullorum and Borrelia anserina. In addition, it may secrete a neurotoxin during feeding, frequently resulting in fatal paralysis.

Epidemiology: This species lives in close association with its poultry hosts and no wild hosts are known.

ORNITHODOROS

This genus includes about 90 species, almost all of which are found in tropical and subtropical habitats in both the Old and New World. Most Ornithodoros species are found in Africa, commonly in the burrows of warthogs and bush pigs, though other species may be found in Central and South America and the Rocky Mountain states of the USA. They are nocturnal and the mouthparts are well developed. The integument has a wrinkled pattern, which runs continuously over the dorsal and ventral surfaces (Fig. 11.2). There is no distinct lateral margin to the body, which appears sac- like. Species of this genus are found largely in habitats such as dens, caves, nests and burrows, and so are not normally a problem for most domestic animals. Only the nymphs and adults are parasitic and may be responsible for considerable irritation; heavy infections can cause mortality of stock from blood loss.

Fig. 11.2 Ornithodoros dorsal view.

Several species of Ornithodoros inflict painful bites and may be major vectors of relapsing fever. Detailed description of only the major species of veterinary importance will be presented here.

Ornithodoros erraticus

Synonym: Ornothodoros marocanus

Common name: Sand tampan

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Particularly small mammals, but also domestic livestock and humans

Life cycle: Females lay batches of approximately 100 eggs in the sand of the host den, cave, nest or burrow and remain with them until they hatch to produce larvae several days later. The larvae remain quiescent until they have moulted to the nymphal stage. There are several nymphal stadia. Both nymphs and adults only feed on their hosts for short periods of time.

Geographical distribution: Europe, Africa and the Middle East

Pathogenesis: Ornithodoros erraticus is a vector of the rickettsial parasite Coxiella burnetii, the causative agent of Q fever in cattle, sheep and goats. It also transmits Borrelia hispanica in the Spanish peninsula and adjacent North Africa, and B. crocidurae in Africa, the Near East and central Asia. These are both spirochaetes which cause tick-borne relapsing fever. This species also acts as a reservoir and vector for African swine fever and Babesia.

Ornithodoros hermsi

Common name: Sand tampan

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Description: Ornithodoros hermsi is a pale, sandy coloured soft tick, which appears greyish blue when engorged. The adult female O. hermsi is typically 5–6 mm in length and 3–4 mm wide. The male is morphologically similar, though slightly smaller.

Hosts: Most mammals, particularly rodents

Life cycle: Females lay batches of approximately 100 eggs in the sand of the host den, cave, nest or burrow and remain with them until they hatch to produce larvae several days later. The larvae remain quiescent until they have moulted to the nymphal stage. There are several nymphal stadia. Both nymphs and adults only feed on their hosts for short periods of time, typically 15–30 minutes. This species is able to survive for long periods without feeding; juvenile stages may live as long as 95 days unfed, and the adults more than 7 months.

Geographical distribution: North America (Rocky Mountains and Pacific coast)

Pathogenesis: This species transmits Borrelia hermsi, the agent of tick-borne relapsing fever in America, and may also act as a vector for African swine fever. Rodents, including deer mice, squirrels and chipmunks, are the primary reservoir hosts for B. hermsi.

Epidemiology: Ornithodoros hermsi is found in rural areas that are usually mountainous and forested. They live in dark, cool places where rodents nest, such as woodpiles outside buildings, under houses, between walls or beneath floorboards inside cabins. They are most active during the summer months.

Ornithodoros moubata

Common name: Sand tampan

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Most mammals, birds and some reptiles

Geographical distribution: Africa and the Middle East

Pathogenesis: This species may be a reservoir host for the virus of African swine fever and for the spirochaete, Borrelia duttoni, which causes African relapsing fever in humans. Ornithodoros moubata is also a vector for viruses of Suidae (Phacochoerus, Potamochoerus, Hylochoerus) and for Q fever. It may transmit Borrelia anserina and Aegyptianella pullorum in fowl.

Ornithodoros porcinus porcinus

Synonym: O. moubata porcinus

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Warthogs, bushpigs, porcupines and domestic pigs

Geographical distribution: Africa, Madagascar, southern Europe

Pathogenesis: An important reservoir and vector of African swine fever

Epidemiology: This tick spends the day sheltered in the burrows of its natural hosts (warthogs), or the cracks and crevices of pig housing, emerging to feed at night.

Ornithodoros parkeri

Common name: Sand tampan

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Most mammals, particularly rodents

Geographical distribution: Western states and Pacific coast of North America.

Pathogenesis: The bite of this species can cause a severe toxic or allergic reaction in the host, which may involve skin rashes, fever, nausea, diarrhoea, shock and death. Ornithodoros parkeri transmits Borrelia parkeri, the agent of tick-borne relapsing fever in America, and may also act as a vector for African swine fever.

Ornithodoros savignyi

Common name: Sand tampan

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Most mammals, particularly camels, and poultry

Geographical distribution: Africa, India and the Middle East

Pathogenesis: Toxicosis may occur in response to the tick saliva, characterised by cutaneous oedema, haemorrhage, rapidly progressing weakness and prostration. Toxocosis can suppress the host’s immune system, allowing the reactivation of chronic infections. Such toxicosis with O. savignyi occurs in young calves and lambs, especially when there are large tick populations and multiple bites.

Ornithodoros tholozani

Common name: Sand tampan

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Most mammals, birds and some reptiles

Geographical distribution: Africa and the Middle East

Pathogenesis: This species transmits Borrelia persica, the causative agent of Persian relapsing fever in northeast Africa and Asia.

Ornithodoros turicata

Common name: Sand tampan, relapsing fever tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Most mammals, particularly rodents

Geographical distribution: North America, particularly southern areas between Florida and California and northward to Colorado and Utah

Pathogenesis: The bite of this species can cause a severe toxic or allergic reaction in the host, which may involve skin rashes, fever, nausea, diarrhoea, shock and death. This species transmits Coxiella burnetii, the causative agent of Q fever in America, and Borrelia turicatae, the causative agent of tick-borne relapsing fever. It may also act as a vector for African swine fever.

Ornithodoros rudis

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Most mammals, particularly rodents and humans

Geographical distribution: Central and South America

Pathogenesis: A vector of Borrelia spp, pathogenic agents of relapsing fever.

Epidemiology: This tick spends its life in the burrows of its natural hosts, or cracks and crevices of human or animal housing in dry conditions. It emerges only to feed at night.

Ornithodoros lahorensis

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Wild sheep, domestic sheep and goats

Geographical distribution: Eastern Europe, northern India, southern former USSR, Middle East

Pathogenesis: An important vector of the agents of piroplasmosis, brucellosis, Q-fever, and tularaemia. Its feeding activity may also cause paralysis, anemia and toxicosis.

Epidemiology: This species is unusual because of its relatively prolonged contact with its host, to which it remains attached over winter. Large populations may build up on sheep and goats that are housed in infested stables and caves over winter.

OTOBIUS

This small genus contains only two species: Otobius megnini and Otobius lagophilus.

Otobius megnini

Common name: Spinose ear tick

Predilection site: Ears

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Description: The adult body is rounded posteriorly and slightly attenuated anteriorly (Fig. 11.3). Adult females range in size from 5–8 mm in length; males are slightly smaller. They have no lateral sutural line, and no distinct margin to the body. Nymphs have spines. In adults the hypostome is much reduced and the integument is granular. The body has a blue–grey coloration with pale yellow legs and mouthparts. Larvae measure 2–3 mm in length and a fully-grown, engorged nymph measures 7–10 mm.

Hosts: Commonly infests wild and domestic animals, including sheep, cattle, dogs, horses and occasionally humans.

Life cycle: This species is a one-host tick. The larval and nymphal stages are parasites of a wide range of mammals, but the adults are not parasitic. Mating takes place off the host, and batches of eggs are laid in sheltered sites such as in cracks and crevices in the walls of animal shelters, under stones or the bark of trees. The larvae hatch within 3–8 weeks and attach to a host animal. They may survive without food for 2–4 months. The preferred predilection site for larvae is deep within the ear. The larvae moult in the ears and nymphs remain there for 1–7 months. When fully grown and engorged, the nymphs drop off the host and seek dry, sheltered sites, where they moult after a few days to become adults. The adults do not feed, and unmated females can survive in empty shelters and stables for over a year. Females lay 500–600 eggs; oviposition can last for up to 6 months.

Fig. 11.3 Dorsal view of nymphal Otobius megnini and part of the integument showing hairs and spines (reproduced from Arthur, 1962).

Geographical distribution: North and South America, India and southern Africa

Pathogenesis: The larvae and nymphs feed in the external ear canal of the host, producing severe inflammation and a waxy exudate in the ear canals. Secondary bacterial infections can occur, which may extend up the ear canal. Infested hosts may scratch and shake their heads. Scratching can cause local skin trauma and occasionally perforate the eardrum. This can lead to infection, ulceration and in some cases meningitis. In horses, clinical signs may be mistaken for signs of colic.

Otobius lagophilus

Common name: Rabbit ear tick

Predilection site: Ears

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Argasidae

Hosts: Rabbits

Life cycle: This species is a one-host tick. Only larvae and nymphs are parasitic.

Geographical distribution: North America, Canada

Pathogenesis: The larvae and nymphs feed in the external ear canal of the host, producing severe inflammation and a waxy exudate in the ear canals. Infested hosts may scratch and shake their heads. Scratching can cause local skin trauma.

HARD TICKS

Life cycle: The life cycles of ixodid ticks involve four instars: egg, six-legged larva, eight-legged nymph and eight-legged adult. During the passage through these stages ixodid ticks take a number of large blood meals, interspersed by lengthy free-living periods. They are relatively long-lived and each female may produce several thousand eggs.

Most hard ticks are relatively immobile and, rather than actively hunting for their hosts, the majority adopt a strategy known as questing, in which they wait at the tips of vegetation for an appropriate host to brush past. Once contact is made the ticks transfer to the host, and then move over the surface to find their preferred attachment sites, such as the ears. Preferred sites for attachment may be highly specific to the particular species of tick.

Ticks have developed a variety of complex life cycles and feeding strategies, which reflect the nature of the habitat, which the various species of tick inhabit, and the probability of contact with an appropriate host. For most a three-host life cycle has been adopted (Fig. 1.41). Larvae, nymphs and adults all feed on different hosts. Blood-feeding typically takes between 4 and 6 days after which they drop to the ground and either moult to the next life cycle stage or lay eggs. Ticks must then relocate a suitable host to feed and moult again or lay eggs. For a relatively small number of ixodid ticks, about 50 species, which inhabit areas where hosts are scarce and in which lengthy seasonal periods of unfavourable climate occur, two- and one- host feeding strategies have evolved.

In temperate habitats, feeding and generation cycles of hard ticks are closely synchronised with periods of suitable temperature and humidity conditions. Ticks, particularly in the immature stages, are very susceptible to desiccation, particularly when ticks are active. To minimise drying out they start questing when saturated with water and return to the humid ground level when dehydrated. Water may also be imbibed by drinking.

Clinical signs: There are no obvious signs of tick infestation other than the presence of the parasites and the local skin reactions to their bites.

Diagnosis: The adult ticks, particularly the engorged females, are easily seen on the skin, the predilection sites being the face, ears, axilla and inguinal region. Usually small, inflamed nodules are also seen in these areas. Ticks may be collected from the host or directly from the environment and microscopic examination used to identify individual species.

Pathology: The local reaction to tick bites varies considerably; commonly small granulomatous reactions may form at the site of tick bites consisting of a mixed inflammatory cell response with fibrosis.

Epidemiology: The distribution of ticks in a temperate climate with frequent and non-seasonal rainfall is closely linked with the availability of a microenvironment with a high relative humidity, such as occurs in the mat which forms under the surface of rough grazing. In contrast, in tropical grazing areas the grass cover on pastures is discontinuous and often interspersed with bare or eroded patches. Where suitable grass cover does exist it has been generally accepted, since temperatures are suitable for development throughout a large part of the year, that the distribution of ticks is mainly governed by rainfall, and with the exception of Hyalomma spp, a mean annual rainfall of more than 60 cm is required for survival.

However, recent studies have shown that the factors underlying the maintenance of the necessary microclimate with a high relative humidity are rather more complex, and depend on the transpiration of plant leaves. As long as this continues, adequate humidity is maintained in the microclimate despite the dryness of the general environment. However, when the rate of evaporation increases beyond a certain level, the stomata on the leaves close, transpiration ceases and the low humidity created in the microclimate rapidly becomes lethal to the ticks.

In the field, the stability of the microclimate is dependent on factors such as the quantity of herbage or plant debris and the grass species. The various genera of ticks have different thresholds of temperature and humidity within which they are active and feed, and these thresholds govern their distribution. Generally, ticks are most active during the warm season provided there is sufficient rainfall, but in some species the larval and nymphal stages are also active in milder weather. This affects the duration and timing of control programmes.

Treatment: The control of ixodid ticks is largely based on the use of chemical acaricides applied either by total immersion in a dipping bath or in the form of a spray, shower, spot-on or slow-release ear tags. A wide variety of formulations of organophosphate (e.g. malathion, chlorpyrifos, fenthion, dichlorvos, cythoate, diazinon, propetamphos, phosmet) and pyrethroid insecticides (e.g. permethrin, deltamethrin) are available for application as sprays, dips, spot-on or showers. Macrocyclic lactones or closantel given by the parenteral route have also been shown to be a useful aid in control of ticks. Where severely parasitised animals require individual treatment, special formulations of acaricides suspended in a greasy base may be applied to affected areas.

In companion animals, topical acaricidal compounds, such as fipronil (phenylpyrazole), imidacloprid (chloronicotinyl), selamectin (macrocyclic lactone), amitraz (formamidine) and the organophosphates (e.g. malathion, ronnel, chlorpyrifos, fenthion, dichlorvos, cythoate, diazinon, propetamphos, phosmet) and carbamates can be used to kill ticks on the host. Pyrethroids (e.g. permethrin, deltamethrin) should not be used in cats.

Control: The long-term control of three-host ticks is geared to the period required for the adult female stage to become fully engorged, which varies from 4–10 days according to the species. If an animal is treated with an acaricide which has a residual effect of, say, 3 days, it will be at least 7 days before any fully engorged female reappears following treatment (i.e. 3 days’ residual effect plus a minimum of 4 days for engorgement). Weekly treatment during the tick season should therefore kill the adult female ticks before they are engorged, except in cases of very severe challenge when the treatment interval has to be reduced to 4 or 5 days.

Theoretically, weekly treatment should also control the larvae and nymphs, but in several areas the peak infestations of larvae and nymphs occur at different seasons to the adult females and the duration of the treatment season has to be extended.

Since many ticks occur on less accessible parts of the body, such as the anus, vulva, groin, scrotum, udder and ear, care must be exercised to ensure that the acaricide is properly applied.

Traditional control methods such as burning of cattle pastures are still used in some areas and are generally practised during a dry period before rains, when ticks are inactive. This technique is still a most useful one in extensive range conditions, and provided it is used after seeding of the grasses has taken place, regeneration of the pastures will rapidly occur following the onset of rains. Cultivation of land and, in some areas, improved drainage help to reduce the prevalence of tick populations and can be used where more intensive systems of agriculture prevail. Pasture ‘spelling’ in which domestic livestock are removed from pastures for a period of time has been used in semi-extensive or extensive areas, but often has the disadvantage that ticks can still obtain blood from a wide variety of other hosts.

Fig. 11.4 Diagrammatic dorsal view of the gnathosoma of seven genera of ixodid ticks (from Smart, 1943). (a) Ixodes. (b) Hyalomma. (c) Dermacentor. (d) Amblyomma. (e) Boophilus. (f) Rhipicephalus. (g) Haemaphysalis.

IXODES

Ixodes is the largest genus in the family Ixodidae, with about 250 species. They are small, inornate ticks, which do not have eyes or festoons. The mouthparts are long and are longer in the female than male. The fourth segment of the palps is greatly reduced and bears chemoreceptor sensilla. The second segment of the palps may be restricted at the base, creating a gap between the palp and chelicerae (Fig. 11.4). Males have several ventral plates, which almost cover the ventral surface. Ixodes can be distinguished from other ixodid ticks by the anterior position of the anal groove. In other genera of the Ixodidae the anal groove is either absent or is posterior to the anus (see Fig. 11.8a).

Ixodes ricinus

Common name: Sheep tick; castor bean tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: The engorged adult female is light grey, up to 1.0 cm in length and bean shaped (Figs 11.5, 11.6). However, when engorged the legs are not visible when viewed from above. Adult male Ixodes ricinus are only 2.0–3.0 mm long, and because they take smaller blood meals than females, the four pairs of legs are readily visible from above. Nymphs resemble the adults but are less than 2.0 mm in length. The larvae, often described as ‘seed ticks’ or ‘pepper ticks’, are less than 1.0 mm in length and usually yellowish in colour.

In I. ricinus, as compared with I. canisuga and I. hexagonus, the tarsi are tapered (Fig. 11.7) and not humped and the posterior internal angle of the first coxa bears a spur, which overlaps the second coxa (Fig. 11.8).

Hosts: Sheep, cattle, goat, but can feed on all mammals and birds; juvenile stages may also feed on lizards.

Life cycle: I. ricinus is a three-host tick and the life cycle requires 3 years. The tick feeds for only a few days each year, as a larva in the first year, a nymph in the second and an adult in the third.

Mating takes place on the host. After attachment the female is inseminated once and subsequently completes a single large blood meal; in contrast, the males feed intermittently and mate repeatedly. During mating, the male crawls under the female and, after manipulating the female genital opening with its mouth-parts, transfers the spermatophore, a sac containing the spermatozoa, into the opening, with the aid of his front legs. Once fertilised, the female subsequently feeds for about 14 days and then drops to the ground to lay several thousand eggs in the soil in sheltered spots, over a period of about 30 days, after which it dies.

Fig. 11.5 Adult Ixodes ricinus in dorsal view. (a) Male. (b) Female (reproduced from Arthur, 1962).

Fig. 11.6 Unfed female Ixodes ricinus. Note the relatively long mouth-parts.

The eggs hatch to produce larvae. Larvae begin to quest several days to several weeks after hatching, the precise time depending on temperature and humidity. The larvae climb up the stems of vegetation ready to attach to a passing host. Once a host is located, larvae feed for 3–5 days, increasing their body weight by 10–20 times, then drop back on to the vegetation where they digest their blood meal and moult to become nymphs. The following year the nymphs begin to seek a new host, again feeding for 3–5 days, before dropping off the host and moulting into the adult stage.

The host on which nymphs feed is usually larger than that of the larvae, typically a bird, rabbit or squirrel. Twelve months later adults begin to quest for a host, on which they feed and mate. Adults feed on larger mammals, such as sheep, cattle or deer and achieve this selection by climbing to different levels in the vegetation while questing.

Although the life cycle takes 3 years to complete, the larvae, nymphs and adults feed for a total of only 26–28 days and I. ricinus is therefore a temporary parasite. Unfed larvae can survive for approximately 13–19 months, unfed nymphs for 24 months and unfed adults for 21–31 months, but the precise period over which they can survive depends on temperature and humidity.

Geographical distribution: Temperate areas of Europe, Australia, South Africa, Tunisia, Algeria and Asia. It is more common in areas of rough grazing moorland and woodland.

Fig. 11.7 The tarsi of adult male (a) Ixodes ricinus, (b) Ixodes hexagonus and (c) Ixodes canisuga (reproduced from Arthur, 1962).

Fig. 11.8 Ventral view of the coxae of adult male (a) Ixodes ricinus, (b) Ixodes hexagonus and (c) Ixodes canisuga (reproduced from Arthur, 1962).

Although recorded, this species has never become established in North America.

Pathogenesis: Ixodes ticks ingest blood and, occasionally, heavy infestations can cause anaemia. Tick bites may damage the host at the site of attachment caus ing local injury, which may predispose to secondary bacterial infection. The lesions caused during feeding may predispose to myiasis. Also at slaughter the value of the hide or fleece may be reduced.

Most significant of all, this tick transmits a range of pathogens. In western Europe, in cattle it transmits Babesia divergens and B. bovis, the causes of red-water fever and Anaplasma marginale, the cause of anaplasmosis in cattle. In sheep and cattle, it transmits the virus that causes louping-ill and the rickettsia responsible for tick-borne fever. It is also associated with tick pyaemia, caused by Staphylococcus aureus, in lambs in Britain and Norway.

Ixodid ticks also transmit Borrelia burgdorferi, the spirochaete responsible for Lyme disease in humans. Ixodes ricinus has been reported to cause tick paralysis and act as a vector for Czechoslovakian encephalitis, Russian spring–summer encephalitis and Coxiella burnetii. This tick may also transmit Bukhovinian haemorrhagic fever.

Ixodes canisuga

Common name: Dog tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: Ixodes canisuga is an inornate tick, without festoons or eyes. The palps are long and the ventral surface of the male is almost entirely covered with a series of plates. An anal groove is present anterior to the anus. The engorged female is light grey, up to 10 mm in length and bean-shaped, with four pairs of legs. The males are only 2.0–3.0 mm long, and the four pairs of legs are readily visible. I. canisuga can be differentiated from I. ricinus by the presence of humped tarsi (Fig. 11.7) and the absence of a spur on the posterior internal angle of the first coxa (Fig. 11.8). Nymphs resemble the adults and also have four pairs of legs, but are less than 2.0 mm in size. The larvae (‘pepper ticks’) are less than 1.0 mm, usually yellowish in colour and have only three pairs of legs.

Hosts: Mammals including dogs, foxes, sheep, horses and mules

Life cycle: Ixodes canisuga is a three-host tick and the life cycle requires approximately 3 years to complete. The tick feeds for only a few days each year; as a larva in the first year, a nymph in the second and an adult in the third. The life cycle is adapted to life in a lair or den. Mating takes place in the den and adult males are only rarely found on the host. Adult females lay relatively small numbers of eggs, probably about 400.

Geographical distribution: Throughout Europe, as far east as Russia

Pathogenesis: Infestation may cause dermatitis, pruritus, alopecia and anaemia, but it is not an important vector of disease. It may be a particular problem in packs of dogs in kennels.

Epidemiology: This species, sometimes called the British dog tick, has been found in a variety of hosts. It is particularly recognised as a problem in kennels, where the tick is capable of survival in crevices and cracks in the floors and walls.

Ixodes hexagonus

Common name: Hedgehog tick

Predilection site: Head, ears

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: Adults are red–brown, with legs that appear somewhat banded in colour. The scutum is broadly hexagonal (hence the name hexagonus) and, like I. ricinus, the coxae of the first pair of legs bear a spur. However, the spur is smaller than in I. ricinus and does not overlap the coxa of the second pair of legs (Fig. 11.8). When engorged the female may be up to 8 mm in length. Males are about 3.5–4 mm in length. The tarsi are long (0.8 mm in the female and 0.5 mm in the male) and sharply humped apically (Fig. 11.7).

Hosts: Hedgehog; other mammals, including dogs, cats, foxes, sheep, horse, moles

Life cycle: Ixodes hexagonus is a three-host tick adapted to live with hosts which use burrows or nests. It is primarily a parasite of hedgehogs but may also be found on dogs and other small mammals. The life cycle is similar to that of I. ricinus: egg, hexapod larva, octopod nymph and adult, occurring over 3 years. All life cycle stages feed on the same host for periods of about 8 days. After dropping to the ground adult females produce 1000–1500 eggs over a period of 19–25 days, before they die. The ticks may be active from early spring to late autumn, but are probably most active during April and May. This species inhabits sheltered habitats such as burrows and kennels and may infest pets in large numbers when they are exposed.

Geographical distribution: Europe and northwest Africa

Pathogenesis: On dogs and cats, adult females usually attach themselves behind the ears, on the jaws, neck and groin, causing localised dermatitis and the risk of wound infection. These ticks are often found to be responsible when dogs become repeatedly infested with ticks, particularly around the head area. It may also become a more significant pest in places where I. ricinus is absent. Ixodes hexagonus is a biological vector of Borrelia spp and tick-borne encephalitis.

Epidemiology: The main host is the European hedgehog, and the movement of this host to urbanised areas may increase the risk of both people and their animals being exposed to infectious diseases carried by I. hexagonus.

Ixodes holocyclus

Common name: Paralysis tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: The engorged adult female is light grey, up to 1.0 cm in length, bean shaped and has four pairs of legs. The males are only 2.0–3.0 mm long, and the four pairs of legs are readily visible. The palps are long and the ventral surface of the adult male is almost entirely covered with a series of plates. An anal groove is present anterior to the anus. Nymphs resemble the adults but are less than 2.0 mm in size while the larvae are less than 1.0 mm in length, and usually are yellowish in colour.

Hosts: Cattle, sheep, goat, dog, cat. All mammals and birds

Life cycle: This species is a three-host tick. The tick feeds for only a few days each year, as a larva in the first year, a nymph in the second and an adult in the third. Mating takes place on the host. After attachment the female is inseminated once and subsequently completes her single large blood meal; in contrast, the males feed intermittently and mate repeatedly. Once fertilised, the female subsequently feeds for about 14 days and then drops to the ground to lay several thousand eggs in sheltered spots, after which she dies. The larvae, which hatch from the eggs, will feed for about 6 days in the following year, then drop to the ground and moult to the nymphal stage. In the third year this stage feeds, drops off and becomes adult. Although the life cycle takes 3 years to complete, the larvae, nymphs and adults feed for a total of only 26–28 days.

Geographical distribution: Australia

Pathogenesis: Ixodes holocyclus is the main cause of tick paralysis in Australia. Its paralysing toxin has been reported to affect at least 20 000 domestic animals annually. Although infestations usually consist of relatively few individual ticks, I. holocyclus infestations can kill cattle, particularly calves, and small domestic animals. Fifty larvae or five nymphs will kill a 40 g rat, and larger numbers of either can cause paralysis in dogs and cats.

Generally only the adult stage infests cattle, with the worst outbreaks in late winter, spring and summer. Ixodes holocyclus is also a vector for Coxiella burnetii (Q fever) and Rickettsia australis (Queensland tick typhus).

Epidemiology: This species is most commonly found amongst low, leafy vegetation since this protects it against sun and wind exposure and maintains the high humidity required for development.

Ixodes persulcatus

Common name: Taiga tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: The taiga tick, Ixodes persulcatus, is morphologically very similar to I. ricinus; it is an inornate, red–brown coloured tick, without festoons or eyes. The palps are long and the ventral surface of the male is almost entirely covered with a series of plates. The engorged adult female is light grey and up to 10 mm in length. The major difference is that the female adult I. persulcatus has a straight or wavy genital opening rather than arched as in I. ricinus.

Hosts: Sheep, cattle, goat, horse, dog, other mammals, birds and man

Life cycle: The taiga tick has a similar life cycle to Ixodes ricinus although adults are rarely active during autumn.

Geographical distribution: It has a more easterly distribution than Ixodes ricinus, being widespread throughout eastern Europe, Russia and as far east as Japan.

Pathogenesis: Ixodes persulcatus is a major vector of the human diseases Russian spring–summer encephalitis virus and Lyme borreliosis.

Epidemiology: Taiga ticks may be dispersed by migrating birds.

Ixodes rubicundus

Common name: Karoo paralysis tick

Predilection site: Skin, neck, chest and belly

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Hosts: Domestic livestock and wild ungulates

Life cycle: This is a three-host tick species. The tick feeds for only a few days as a larva, a nymph and an adult. The life cycle of this species takes about 2 years. Mating takes place on the host. After attachment the female is inseminated once and subsequently completes her single large blood meal; in contrast, the males feed intermittently and mate repeatedly. Once fertilised, the female subsequently feeds for about 14 days and then drops to the ground to lay several thousand eggs in sheltered spots, after which she dies.

Geographical distribution: Southern Africa, particularly the Karrooveld

Pathogenesis: Ixodes rubicundus, the Karoo paralysis tick, parasitises domestic stock and wild ungulates in South Africa and may lead to serious losses. Ticks may cause damage at the site of attachment causing local injury, which may predispose to secondary bacterial infection. The adult tick produces a toxin that causes paralysis in sheep and goats. Affected animals become paralysed and some may show signs of incoordination and stumbling. Unless ticks are removed, the animal will remain paralysed and die within days. Most affected animals recover within 24 to 48 hours once the ticks have been removed or animals have been dipped.

Ixodes scapularis

Synonym: Ixodes dammini

Common name: Shoulder tick, black-legged tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Hosts: Deer. All mammals and birds

Life cycle: This is a three-host tick species. It feeds for only a few days each year, as a larva in the first year, a nymph in the second and an adult in the third. Mating usually takes place on the host. After attachment the female is inseminated and subsequently completes her single large blood meal. In contrast, the adult males feed intermittently and mate repeatedly. Once fertilised, the female subsequently feeds for about 14 days and then drops to the ground to lay several thousand eggs in sheltered spots, after which she dies. The following year, peak larval activity occurs in August, when larvae attach and feed on a wide variety of mammals and birds, particularly on white-footed mice (Peromyscus leucopus). After feeding for 3–5 days, engorged larvae drop from the host to the ground where they overwinter before moulting to become a nymph. In May of the following year, larvae moult to become nymphs, which feed on a variety of hosts for 3–4 days. Engorged nymphs then detach and drop to the forest floor where they moult into the adult stage, which becomes active in October. Adult ticks remain active through the winter on days when the ground and ambient temperatures are above freezing. The adult ticks feed on large mammals, primarily upon whitetailed deer, Odocoileus virginianus. Although the life cycle takes 3 years to complete, the larvae, nymphs and adults feed for a total of only 26–28 days.

Geographical distribution: North America, particularly in and around wooded areas

Pathogenesis: Ixodes scapularis inflicts a very painful bite. Nymphal and adult stages of this tick are the most common vector for Lyme disease in North America. They are also implicated in the transmission of Francisella tularensis. These ticks are major vectors for the transmission of human babesiosis and human granulocytic ehrlichiosis (HGE) and are responsible for the transmission of anaplasmosis and piroplasmosis.

Epidemiology: Ixodes scapularis requires a relative high humidity to survive, and its patterns of feeding activity reflect this requirement. With feeding restricted to times of year when conditions of temperature and humidity are appropriate, distinct restricted seasonal periods of activity result, usually in spring and autumn. As a result of its requirement for high humidity, in general, it is associated with areas of deciduous woodland containing small mammals and deer.

Ixodes pacificus

Common name: Western black-legged tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodidia (Metastigmata)

Family: Ixodidae

Description: A very similar species to Ixodes scapularis. Adult ticks are red–brown in colour and about 3 mm in size. Larvae and nymphs are smaller and paler in colour.

Hosts: Rodents, lizards and large mammals, such as horses, deer and dogs

Life cycle: This is a three-host tick species.

Geographical distribution: Commonly found in the Western USA and British Columbia

Pathogenesis: It is known to be a vector of Lyme disease and the rickettsia responsible for equine granulocytic ehrliciosis.

Epidemiology: It is found in habitats with forest, north coastal scrub, high brush and open grasslands

Ixodes pilosus

Common name: Russet tick, bush tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Hosts: Cattle, sheep, goats, horses, dogs, cats and wild ungulates

Life cycle: This is a three-host tick species.

Geographical distribution: Most areas of South Africa

Pathogenesis: The feeding activity of this will cause bood loss, local dermatitis and may result in tick paralysis.

Several other species of Ixodes have been reported in North America and have been found mainly on dogs.

AMBLYOMMA

Members of this genus are large, often highly ornate ticks with long, often banded, legs. Unfed females may be up to 8 mm in length and when engorged may reach 20 mm in length. Eyes and festoons are present. Males lack ventral plates. They have long mouthparts (Fig. 11.4) with which they can inflict a deep, painful bite which may become secondarily infected. There are about 100 species of Amblyomma, largely distributed in tropical and subtropical areas of Africa. However, one important species is found in temperate North America. The identification of more than the major species is beyond the scope of this book and interested readers will need to consult a relevant taxonomic specialist.

Amblyomma americanum

Common name: Lone star tick

Predilection site: Ears, flanks, head and belly

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description, adults: The lone star tick, Amblyomma americanum, is so called because of a single white spot on the scutum of the female (Fig. 11.9). These are large, usually ornate, ticks whose legs have bands of colour. Eyes and festoons are present. The palps and hypostome are long, and ventral plates are absent in the males. The engorged female is up to 10 mm in length, bean-shaped, and has four pairs of legs. The female is reddish-brown in colour, becoming light grey when engorged. On the scutum are two deep parallel cervical grooves and a large, pale spot at its posterior margin. The male is small with two pale symmetrical spots near the hind margin of the body, a pale stripe at each side, and a short oblique pale stripe behind each eye. The males are only 2–3 mm in length, and because of the small idiosoma the four pairs of legs are readily visible. In both sexes, coxa I has a long external spur and a short internal spur, and the mouthparts are much longer than the basis capituli.

Nymphs and larvae: Nymphs resemble the adults and also have four pairs of legs but are less than 2 mm in size, while the larvae (‘pepper ticks’) are less than 1 mm in length, usually yellowish in colour and have only three pairs of legs.

Hosts: Wild and domestic animals, particularly cattle; birds; larvae are most frequently found on wild small mammals.

Fig. 11.9 Dorsal view of the gnathosoma and scutum of adult (a)female and (b) male Amblyomma americanum (from Arthur, 1963).

Life cycle: The life cycle is typical of a three-host tick. Adult females attach to a host and take a single large blood-meal over a period of 3–4 weeks, taking 0.5–2.0 ml of blood, during the course of which they mate once. In contrast, the males feed intermittently and mate repeatedly. Once fertilised, the female drops to the ground to lay several thousand eggs in sheltered spots, after which she dies. The larvae, which hatch from the eggs will feed for about 6 days in the following year, then drop to the ground and moult to the nymphal stage. In the third year this stage feeds, drops off and becomes adult. Although the life cycle takes 3 years to complete, the larvae, nymphs and adults feed for a total of only 26–28 days. Larvae and nymphs feed on rodents, rabbits and ground-inhabiting birds. Adults feed on larger mammals such as deer, cattle, horses and sheep.

Geographical distribution: Widely distributed throughout central and eastern USA

Pathogenesis: This tick is most commonly found on the ears, flanks, head and belly. Tick infestation is irritating and painful, and infestation has been shown to reduce weight gain in cattle. Each female ingests 0.5–2.0 ml of host blood, so large numbers can cause anaemia. Bites may cause tick paralysis. Amblyomma americanum is an important vector of Rickettsia rickettsii (Rocky Mountain spotted fever) and Francisella tularensis (tularaemia). It has also been implicated as a vector of Borrelia burgdorferi (Lyme disease), Q fever, canine ehrlichiosis and human monocytic ehrlichiosis.

Epidemiology: Feeding larvae, nymphs and adults are active between early spring and late summer in distinct periods corresponding with the feeding activity of each stage. There is usually a single generation per year. This species is particularly common in wooded areas, where hosts become infected as they brush against vegetation harbouring ticks.

Amblyomma variegatum

Common name: Bont ticks, variegated or tropical bont tick

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: Female A. variegatum are brown with a large pale patch on the posterior scutum while males are brightly ornamented with orange coloration and a dark brown border to the idiosoma (Fig. 11.10). Both sexes of A. variegatum have hemispherical eyes. A. variegatum and A. hebraeum can be distinguished from A. americanum and A. cajennese by the shorter external spur on coxa I, which is closely associated with the internal spur.

Hosts: Mammals, particularly cattle

Geographical distribution: Africa

Pathogenesis: Amblyomma variegatum transmit the important disease, heartwater, in cattle, caused by the rickettsia, Ehrlichia ruminantium. It also transmits the viral Nairobi sheep disease and Q fever, caused by Coxiella burnetii.

Fig. 11.10 Male Amblyomma variagatum (dorsal view).

Amblyomma cajennense

Common name: Cayenne tick

Predilection site: Skin, lower body surface, especially between the legs

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: In adults the scutum is usually very ornate, lattice patterned often with bright, multicoloured iridescent patterns. There may be pale central patches on the festoons.

Hosts: All mammals but most commonly equines

Geographical distribution: South and Central America, southern USA and the Caribbean

Pathogenesis: Amblyomma cajennense is an important tick in South America, the bites caused by this genus being particularly painful, probably due to the long mouthparts. In severe cases in South America this species has been reported to cause fever and weakness in cattle. The wounds created by this tick may create a suitable site for screwworm myiasis associated with Cochliomyia spp. This species transmits spotted fever in South America and Leptospira pomona.

Amblyomma hebraeum

Common name: Bont ticks

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Description: A. variegatum and A. hebraeum can be distinguished from A. americanum and A. cajennese by the shorter external spur on coxa I, which is closely associated with the internal spur.

Hosts: All mammals and birds

Geographical distribution: Mainly Africa

Pathogenesis: ‘Bont ticks’ transmit the important disease, heartwater, in cattle, sheep and goats; it is caused by the rickettsia, Ehrlichia ruminantium. This species also transmits Rickettsia conorii, the causative agent of Boutonneuse fever.

Amblyomma gemma

Predilection site: Skin

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Hosts: Mammals, particularly cattle, sheep and goats

Geographical distribution: Africa, particularly Kenya

Pathogenesis: Amblyomma gemma may be a vector for the transmission of heartwater in cattle, sheep and goats.

Amblyomma maculatum

Common name: Gulf coast tick

Predilection site: Skin, particularly the ears

Parasite class: Arachnida

Sub-class: Acari

Order: Parasitiformes

Sub-order: Ixodida (Metastigmata)

Family: Ixodidae

Table 11.1 Other Amblyomma tick species.

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