Canis ISSN: 2398-2942

Ixodes ricinus

Synonym(s): Castor bean tick, Sheep tick, Deer tick

Contributor(s): Dwight Bowman, David Scarff

Introduction

Classification

Taxonomy

  • Class: Arachnida.
  • Family: Ixodidae.
  • Genus: Ixodes.

Active Forms

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Clinical Effects

Epidemiology

Habitat

On the host
  • On the larger domestic hosts I. ricinus attaches primarily to the head, ears, axilla and inguinal regions although they may be found anywhere on the body.
Off the host
  • The tick spends the vast majority of its lifecycle off the host.
  • In Britain it occurs mainly in rough grazing (within the protection of a moisture-retaining mat of dead grass or litter of bracken on rough, high ground land) or in the litter of a woodland or copses.
  • Ticks can also survive to a degree in hedgerows and I. ricinus also are described in parks in cities.
  • The high ground humidity in Ireland means ticks will also survive on wet arable land but again they are most common around woodlands and will be found on grass road verges also.
  • In Europe, I. ricinus is most common in woodlands and fields around woods in association with the deer hosts.

Lifecycle

  • See lifecycle diagram Lifecycle Ixodes ricinus - diagram :
    • Eggs.
    • Larva.
    • Nymph.
    • Adult.
  • Larvae prefer to feed on small rodents (Apodemus mice and Clethrionomys voles) although they will feed on insectivores, birds, reptiles and mammals up to the size of stoats. They are much less common on larger animals.
  • Nymphs prefer to feed on medium-sized animals (hares, rabbits, stoats, etc) and sand lizards but also include rodents and birds. In the absence of these, nymphs will feed on larger animals.
  • Adults prefer to feed on medium-sized, eg hedgehogs, stoats, badgers, etc to large animals, eg deer, sheep, cattle, man, dog, etc.

Transmission

  • Ixodes ricinus actively searches for a host mainly in the spring and autumn (March to June and August to October) although longer springs extend activity and the coolness of woodland in summer can allow activity throughout the year.
  • The ticks move up onto the vegetation and 'quest' for a host. Size is important. Various tactile and olfactory sensory organs detect shadow, movement, CO2, temperature, odor, etc of a preferred host.

Pathological effects

  • A basophil/eosinophil hypersensitivity response occurs around the mouthparts of engorging ticks.
  • On first infection there is a decrease in Langerhans cells in the dermis surrounding the mouthparts as they migrate to, and present antigen in, the draining lymph node. This is followed, 4-5 days after infection, with infiltration into the dermis and degranulation of particularly basophils and eosinophils. By this time the tick may be detaching but the response continues to the injected materials. The response occurs within a few hours on reinfection.
  • This hypersensitivity response has been associated with some, although not marked, protective immunity resulting in reduced weights of fed ticks, fewer eggs produced, etc.
  • A basophilic and eosinophilic granulomatous nodule forms around the mouthparts of the feeding tick.
  • The inflamed nodule may persist for some time after detachment of the tick.
  • The pruritus and itching induced may result in scab formation or secondary infection with pustule formation.

Other Host Effects

  • The adults, nymphs and larvae feed on blood for 2-14 days. The longer periods of 7-14 days are particularly true of some females.
  • The chelicerae of the mouthparts cut into skin and the central hypostome is inserted. Teeth directed backwards on the hypostome assist in anchoring the tick to feed. Saliva flows down the hypostome and contains a cement-like substance that assists anchoring, and enzymes and anticoagulants to aid feeding.
  • The engorging ticks increase greatly in size and weight. A female I. ricinus ingests over 500 mg blood, reaching about 250 mg in weight, excreting excess water mainly via the saliva into the host.
  • Ixodes ricinus is the main European host of the spirochete, Borrelia burgdorferi, that causes Lyme disease.
  • The main reservoir species for B. burgdorferi areApodemus mice and Clethrionomys voles. These develop lifelong infections with B. burgdorferi.
  • Larval I. ricinus become infected with B. burgdorferi in the spring or autumn when feeding on rodents which have been infected by nymphs feeding on them earlier in the spring or on rodents in which the infection has overwintered.
  • The infection is then transmitted stage to stage in the tick, ie the larva acquires the infection and transmits it to humans as a nymph feeding. Or a nymph will acquire the infection and transmit it to a dog as an adult. There is a limited amount of transovarian transmission of the spirochete from the female through the egg to the larva but this seems much less important epidemiologically than is infection overwintering in the nymphs and rodents.
  • As the main reservoir hosts for B. burgdorferi are the rodents (although many other host species including man and dog, sheep, deer, lagomorphs, etc are infected) the highest proportion of infected ticks are larvae transmitting the infection as nymphs. The nymph to adult cycle is less important but as it is the adults that prefer to feed in the larger hosts they must contribute significantly to infection in man and domestic animals.

Control

Control via animal

  • Ixodes ricinus usually are found on dogs only singly or in small numbers.
  • The long mouthparts of I. ricinus penetrate well into the dermis and so make the tick difficult to remove.
  • Remove the tick(s) manually being careful to remove the mouthparts by grasping the tick very close to, or preferably by, the mouthparts with forceps and rocking it back and forth gently while extracting.
  • Various reagents, including acaricides have been sprayed or dabbed onto ticks to relax them and aid removal. There is no real evidence that these are effective within the short time required.
  • The tick should be examined microscopically to ensure removal of the mouthparts.
  • The skin should be examined carefully, visually and manually, to detect any small nymphs or larvae.
  • Spray or wash the dog with acaricide if a large number of ticks are present.

Control via chemotherapies

For treatment and/or prophylaxis in Lyme disease areas
  • Fipronil Fipronil.
  • Phosmet (not licensed for this use in dogs).
  • Fenvalarate (not licensed for this use in dogs).
Longer term protection
  • Fipronil Fipronil.
  • Flumethrin and propoxur collar (not licensed for this use in dogs).
  • Diazinon collar (not licensed for this use in dogs).
  • Permethrin (not licensed for this use in dogs).

Control via environment

  • Avoid known infected areas or use persistent acaricide collars, etc.

Vaccination

  • No vaccine is available for I. ricinus but technology developed for other tick species potentially could be adapted.
  • Recently there have been considerable developments in vaccines against Boophilus microplus in Australia. Protection can be elicited using hidden antigens, ie antigens in the tick not normally exposed to the host. The relevant antigens are gut antigens and one of these protective gut antigens, Bm86, has been cloned and patented for commercial production.

Other countermeasures

  • In tick areas in tick season, important to check dog after walking.
  • Important to remove tick or wash or bath the animal immediately, because B. burgdorferi is not injected immediately the tick starts feeding but is injected from 24-36 hours after the start of feeding.
    If the tick is removed but the mouthparts remain they will continue to elaborate and inject the spirochete.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from VetMedResource and PubMed.
  • Gray J S, Kahl O, Janetzki C & Guy E (1995) The spatial distribution of Borellia burgdorferi infected Ixodes ricinus in the Connemara region of County Galway, Ireland. Experimental and Applied Acarology 19, 163-172 (Reservoir hosts).
  • Opdebeeck J P (1994) Vaccines against blood-sucking arthropods. Veterinary Parasitology 54, 205-222 (Review).

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