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tick bites

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Ticks are arachnids with a global distribution. Different tick species are found in different habitats

  • commonly found in woodland, heathland, upland or moorland pastures and grassland.
  • ticks are particularly abundant in ecotones, the transition zone between two vegetation communities, such as woodland and meadow or shrub communities, which permit a wider range of potential hosts (1,2). 

Ticks can be classified into two groups

  •  Ixodidae (hard ticks) 
    • contains a shield like scutum on their dorsal side and visible mouthparts that protrude forward
    • have a three stage life cycle
      • larval – about 0.5 mm long (the size of a poppy seed) and have six legs
      • nymph – about 1.5 mm long and  have eight legs
      • adult stages - about 3 mm long (but once fed they can enlarge to 11 mm in length) and  have eight legs
    • can feed for up to one week until engorgement is reached (if left undisturbed) after which they detach and moult to the next lifecycle stage.
  • Argasidae (soft ticks)
    • do not have a scutum and mouthparts are not visible (since they are located on the underside)
    • life cycle is similar to hard tick but have two or more additional nymph stages
    • feed for up to several hours (1)

Ticks are important vectors of disease pathogens and include the following:

  • Lyme borreliosis –
    • most common human tick born disease
    • transmitted by Ixodes ricinus (also known as deer/sheep/castor bean tick)
    • 959 laboratory confirmed cases were reported in UK in 2011 (incidence of 1.73/100 000)
  • tickborne encephalitis
    • a viral disease caused by Flaviviridae virus family
    • around 10 000 cases are seen annually across Europe
  • rickettsioses
    • includes
      • Rocky Mountain spotted fever - Rickettsia rickettsii found in the US
      • Mediterranean spotted fever - R conorii found in the Mediterranean
      • African tick bite fever - R africae found in sub-Saharan Africa and the Caribbean
    • pathogenic rickettsiae is now thought to occur in British ticks according to a new study
  • babesiosis
    • an emerging tick born disease caused by haematotropic parasites that infect red blood cells
    • includes
      • Babesia divergens - responsible for most European cases
      • B microti - most prevalent and is found mainly in the US
      • Borrelia miyamotoi - a new subspecies of Borrelia which has recently emerged in the UK (1).

The length of time that the infected tick has been feeding is proportional to the risk of transmission of infection.

  • in animal experiments 5% of infected ticks feeding for 1 day transmited spirochaetes. This compares with almost 100% transmission of spirochaetes if the tick has been feeding for 4 days.

People who were exposed ticks or have been bitten by a tick should look for symptoms associated with Lyme disease e.g. - erythema migrans, a localised bull’s eye rash unexplained headaches and neck stiffness, flu-like symptoms, facial palsy, arthralgia, within weeks of the tick bite or exposure. It is important to consult a GP if patients develop any of these symptoms (1)

Reference:

Last reviewed 01/2018

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