The tick species which can transmit Lyme disease

In the UK the primary vector of the bacteria that causes Lyme disease is Ixodes ricinus tick (7).

Ixodes ricinus is an ixodid tick and researchers believe that only this group of ticks can transmit the bacteria that cause Lyme disease.

In Europe, three tick species have been described as being vectors of Borrelia burgdorferi s.l.: I. ricinus, I. hexagonus and I. uriae. However, the fact that I. ricinus is a generalist feeder and waits on vegetation for a host, while the other two species are specialists living in the nests of their host species, means that contact between I. ricinus and humans are more frequent than between humans and the other two species (23). I. ricinus is the most abundant species, the one with the highest biting rate and is most frequently found on humans.

Only ixodid ticks satisfy the complex transmission requirements imposed by the agent of Lyme disease (contrary to the soft ticks or mosquitoes), and of these, only members of the genus Ixodes appear to serve satisfactorily as vector hosts.

For the transmission of the bacteria that causes Lyme disease (Borrelia burgdorferi s.l.) from a tick to a host, the tick needs to:

• ingest many Lyme disease spirochetes (the spirally twisted bacteria) from an infected host,
• permit the spirochetes to develop to a stage that is adapted to the tick’s haemocoelic (blood flowing in an open cavity) environment,
• have their salivary glands invaded by spirochetes before the tick finishes feeding and drops off the host and
• successfully implant these spirochete bacteria into the blood of a vertebrate host.
• For further information read (22).

In the UK the following ticks from the genus Ixodes are present: Ixodes apronophorus, I. arboricola, I. canisuga, I. frontalis, I. hexagonus, I. ricinus, I. trianguliceps and I. ventalloi.