Which tick species specifically transmit Lyme disease?

Tick Species That Transmit Lyme Disease

Lyme disease is transmitted by ticks of the Ixodes genus, specifically Ixodes scapularis (blacklegged or deer tick) in the eastern United States, Ixodes pacificus (western blacklegged tick) in the western United States, and Ixodes ricinus in Europe. 1, 2

Primary Vectors by Geographic Region

North America

• Eastern United States: Ixodes scapularis (blacklegged tick, also called deer tick) is the primary vector 1, 2
• Western United States: Ixodes pacificus (western blacklegged tick) transmits the disease in California and the Pacific coast 1, 2
• The northeastern tick vector (I. scapularis) is far more efficient at disease transmission than the western vector (I. pacificus) 3

Europe and Asia

• Europe: Ixodes ricinus is the primary vector 1, 2
• Asia: Ixodes persulcatus transmits Lyme disease 4
• All Ixodes species belonging to the Borrelia burgdorferi sensu lato complex can transmit the various genospecies 1

Life Cycle and Transmission Dynamics

• Tick larvae and nymphs feed primarily on small rodents (particularly Peromyscus mice) and birds, while adult ticks feed on larger mammals including deer, domestic animals, and wild carnivores 1
• The majority of human Lyme disease cases result from bites by infected nymphs, not adult ticks 1
• In highly endemic areas of the northeastern United States, approximately 15-30% of questing I. scapularis nymphs are infected with B. burgdorferi 1, 3
• In the western United States, up to 14% of I. pacificus nymphs carry the infection 1

Transmission Timeline

• The feeding time of Ixodes ticks is prolonged, lasting several days to more than one week 1
• Transmission of B. burgdorferi typically requires at least 36-48 hours of tick attachment to result in infection 1, 5
• There is no experimental evidence for transmission by single infected I. scapularis nymphs when attached for only 24 hours 5
• The probability of transmission increases to approximately 10% by 48 hours and reaches 70% by 72 hours 5

Common Pitfall: Amblyomma americanum Does NOT Transmit Lyme Disease

• Amblyomma americanum (lone star tick) is NOT a vector of Lyme disease, despite early confusion in the literature 6, 7
• This tick can cause a rash similar to erythema migrans in southern states like Texas, which can lead to misdiagnosis 3, 7
• More than 54 surveys involving over 52,000 A. americanum ticks have revealed extremely low or absent B. burgdorferi prevalence 7
• At least nine transmission experiments have failed to demonstrate vector competency for A. americanum 7
• The spirochetes occasionally found in A. americanum are Borrelia lonestari, a different species of uncertain clinical significance 7

Geographic Risk Variation

• Approximately 90% of U.S. Lyme disease cases occur in roughly 140 counties along the northeastern and mid-Atlantic seaboard 3
• Connecticut has the highest state incidence at 70 cases per 100,000 population 3
• In the southern United States, the prevalence of infection in I. scapularis ticks is generally 0-3%, making Lyme disease rare in these regions 1
• The distribution of I. scapularis has been spreading slowly in the northeastern and upper north-central United States due to white-tailed deer repopulation 1, 3