Tick bites

• 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 ticks 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-borne disease
  • transmitted by Ixodes ricinus (also known as deer/sheep/castor bean tick); studies in Europe have found that simultaneous human infection with more than one tick-borne pathogen from I. ricinus is very rare (3)
  • 959 laboratory-confirmed cases were reported in the UK in 2011 (incidence of 1.73/100,000)
• tick-borne encephalitis:
  • a viral disease caused by the 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 are now thought to occur in British ticks according to a new study
• babesiosis:
  • an emerging tick-borne 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)
• anaplasmosis (human granulocytic anaplasmosis, HGA) (3):
  • caused by Anaplasma phagocytophilum and transmitted by Ixodes ticks (I. ricinus in Europe and the UK; I. scapularis and I. pacificus in North America)
  • while highly endemic in UK livestock (causing tick-borne fever in sheep and pasture fever in cattle), human cases are predominantly seen in North America and are rarely reported in Europe (only one documented human case has been acquired in the UK, in Scotland)
  • usually mild or asymptomatic, presenting with fever, chills, and muscle or joint aches, though severe complications (respiratory distress, renal failure) can occur
• ehrlichiosis (3):
  • caused by Ehrlichia species (E. chaffeensis causing human monocytic ehrlichiosis, and E. ewingii causing human ewingii ehrlichiosis)
  • transmitted primarily by the Lone Star tick (Amblyomma americanum) in North America (where co-infection with Lyme disease or babesiosis is relatively frequent); imported cases can present in the UK in travellers returning from risk areas
  • can progress rapidly to severe, life-threatening sepsis and multi-organ failure if untreated

Transmission risk and post-bite monitoring

• 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 transmitted spirochaetes; this compares with almost 100% transmission of spirochaetes if the tick has been feeding for 4 days
• people who were exposed to ticks or have been bitten by a tick should look for symptoms associated with tick-borne infections (such as Lyme disease, or anaplasmosis and ehrlichiosis following travel to endemic regions) including erythema migrans (a localised bull's eye rash), unexplained headaches and neck stiffness, flu-like illness, fever, muscle aches, gastrointestinal upset, facial palsy, or arthralgia within weeks of exposure. It is important to consult a GP if patients develop any of these symptoms

References:

• Aktas M. A survey of ixodid tick species and molecular identification of tick-borne pathogens. Vet Parasitol. 2014 Mar 01;200(3-4):276-83.
• Roupakias S, Mitsakou P, Nimer AA. Tick removal. J Prev Med Hyg. 2011 Mar;52(1):40-4.
• UK Health Security Agency (UKHSA). Guidance: Anaplasmosis and Ehrlichiosis. Published 9 November 2026.