From July 2006 through August 2017, a passive surveillance study of Ixodes ticks 
submitted from California, Oregon, and Washington was conducted by the 
TickReport program at the University of Massachusetts, Amherst. In total, 549 
human-biting Ixodes ticks were submitted comprising both endemic and nonendemic 
species. We found that 430 endemic ticks were from 3 Ixodes species: Ixodes 
pacificus, Ixodes spinipalpis, and Ixodes angustus, whereas Ixodes scapularis 
(n = 111) was the most common species among the 119 nonendemic ticks. The 
submission peak for nymphal I. pacificus and I. spinipalpis was June, while 
submission peak for adult I. pacificus and nymphal I. angustus was April and 
September, respectively. Endemic ticks commonly attached to the lower 
extremities of their victims, and individuals younger than 9 years old were 
frequently bitten. The infection prevalence of Borrelia burgdorferi sensu lato, 
Borrelia miyamotoi, and Anaplasma phagocytophilum in I. pacificus ticks was 
1.31%, 1.05%, and 0.52%, respectively, and the prevalence of B. burgdorferi s. 
l. and A. phagocytophilum in I. spinipalpis ticks was 14.29% and 10.71%, 
respectively. Furthermore, two species within the B. burgdorferi s. l. complex 
were detected in West Coast ticks: B. burgdorferi sensu stricto and Borrelia 
lanei. I. spinipalpis had the highest Borrelia prevalence among endemic ticks, 
and it was caused exclusively by B. lanei. Borrelia mayonii, Babesia microti, 
and Ehrlichia muris-like agent were not detected in these endemic ticks. In this 
study, we show that many nonendemic Ixodes ticks (119/549) are most likely 
acquired from travel to a different geographic region. We report cases of 
conventionally recognized nonhuman feeders (I. spinipalpis and I. angustus) 
parasitizing humans. The highest pathogen prevalence in I. spinipalpis may 
indicate a larger public health threat than previously thought, and the enzootic 
life cycle and pathogenicity of B. lanei warrant further study.