Ixodes ricinus and Ixodes persulcatus
The Ixodes ricinus tick is the most common tick in Northern Europe and is held responsible for Lyme disease transmission to both livestock and humans. It was identified as a vector in Lyme disease transmission in 1983. There has been considerable research carried out over nearly a hundred years on the effects of microclimate and diapause phenomena in regards to I. ricinus activity, disease transmission, and, more recently, Lyme disease outbreaks. I. persulcatus is closely related to I. ricinus and is a key vector in tick-borne encephalitis in Eastern Europe and Asia (in temperate areas). The similarities between the two ticks meant that I. persulcatus was quickly established as a Lyme disease vector following identification of I. ricinus as such. This identification of I. persulcatus as a transmitter of Lyme disease led to recognition that the infection could potentially occur right across Asia. There are differences between I. ricinus and I. persulcatus however, with the former thought to transmit Lyme disease bacteria in both the nymphal and adult (female) stage and the latter predominantly in just the adult female stage. I. persulcatus nymphs appear to be reluctant to bite adult humans.
Animal hosts of I. ricinus include birds, reptiles, deer, and small mammals, including rodents. There are a number of other diseases, affecting animals and/or humans, attributed to bacteria and viruses carried by the Ixodes ricinus tick. Lyme disease, Ehrichiosis, tick-borne encephalitis, Louping-ill (also known as Ovine Encephalomyelitis as it can affect sheep), tick pyaemia, Babesiosis, and Rickettsiosis can all be transmitted following a bite from an infected I. ricinus tick. There is also speculation over the ticks’ involvement in transmission of tularaemia and Q-fever.
Ixodes scapularis and Ixodes pacificus
The two most important vectors for Lyme disease in North America are I. scapularis and I. pacificus. These ticks are identifiable by their relatively long mouthparts (compared to the basis capituli or the ‘head-like’ part of the tick) and their inornate dorsal shield amongst other features. Adult ticks are easier to identify although younger ticks may also transmit disease. Ixodes scapularis is known as the blacklegged tick and as the ‘deer tick’ although it has a number of animal hosts other than deer. The blacklegged tick can carry and transmit the organisms that cause anaplasmosis, Babesiosis, and Lyme disease which may require different forms of treatment to successfully eradicate.
Ixodes scapularis is found in the northeastern and upper midwestern United States and commonly feeds on birds and small mammals as larvae and nymphs, before progressing to larger hosts such as deer in the adult stage of the tick lifecycle. Ticks may not be infected with the Borrelia bacteria however as this is dependent on the presence of a host reservoir of infected wild rodents or other small mammals to feed larvae and nymphs.
The western blacklegged tick is the more common name for Ixodes pacificus which is the major vector for Lyme disease in the Pacific Northwest of the US and Canada. These ticks are also carriers of anaplasmosis along with Lyme disease bacteria. The host reservoirs for these infections are wild rodents and small mammals which serve as the source of infection for larval ticks and nymphal ticks along with birds. Adult ticks tend to feed on deer and other mammals, including humans.