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: