Ixodes ricinus is the main vector (transmitter) of species of the Borrelia burgdorferi complex - the spirochaete that causes Lyme borreliosis (Lyme disease).


Lyme borreliosis is the commonest tick-borne disease of humans in Europe and North America. The various spirochaete species are associated with different types and severity of symptoms – for example, those that occur in the UK are apparently less virulent than those in North America.


The longer a tick feeds, the more opportunity there is for spirochaetes to pass into the host. Therefore, early tick removal can reduce the chances of acquiring the disease.


Ticks also transmit other infectious organisms including those of:

  • louping-ill (an encephalomyelitis of sheep, cattle and occasionally humans)
  • Q-fever (a rickettsial disease of domesticated mammals and humans caused byCoxiella burnetii)
  • bovine and ovine tick-borne fever (rickettsial diseases of livestock and, in the first case, humans)
  • tularemia or rabbit fever (a bacterial disease of cats, sheep, rabbits, rodents and their predators, and humans)
  • tick pyaemia of lambs (caused by the bacterium Staphylococcus aureus)
  • redwater fever of cattle (caused by the protozoan Babesia divergens)