Vector competence and transcriptome response of the western black-legged tick, Ixodes pacificus, to different blood meal hosts

Vector blood meal hosts often vary in their reservoir competency and as a result, the transmission and risk of vector-borne zoonotic diseases are modulated by the availability and composition of hosts. Lyme disease is a bacterial disease (Borrelia burgdorferi) that is maintained enzootically by Ixodes spp. ticks and their vertebrate blood meal hosts. The presence of more competent reservoir hosts can increase disease prevalence. However, in the western United States, the most common tick host is the western fence lizard, Sceloporus occidentalis, a species that is refractory to B. burgdorferi. Thus, lizards serve opposing roles in Lyme disease transmission by feeding a large proportion of the vector but do not transmit the pathogen and, in fact, actively clear the pathogen from infected ticks. To further clarify the role of lizards in Lyme disease ecology, we conducted a pathogen transmission experiment on Ixodes pacificus ticks that fed on either mice or lizards as larvae and paired this experiment with RNAseq transcriptome analysis. We found that a prior lizard blood meal increased pathogen acquisition in the following life stage. Transcriptome analysis revealed that lizard-fed ticks increased expression of an antioxidant protein and antimicrobial proteins that together may create a more favorable environment for B. burgdorferi to establish in the tick midgut. These results indicate a complex and multifaceted role of lizards in the transmission and maintenance of Lyme disease in the western United States.