Eastern fence lizards clean the agent of Lyme borreliosis from blacklegged ticks

Background/Question/Methods

It has been known for a decade that western blacklegged ticks (Ixodes pacificus) are cleaned of Lyme disease-causing spirochetes, Borrelia burgdorferi, after feeding on western fence lizards (Sceloporus occidentalis). This observation has been proposed as a partial explanation for the relative scarcity of Lyme borreliosis in the western U.S., where S. occidentalis commonly serves as a host for larval and nymphal ticks. There has been interest in the role that the sister lizard taxon, the eastern fence lizard (S. undulatus) may play in B. burgdorferi persistence in the Northeast, where the majority of Lyme borreliosis cases occur. Recent work has detected B. burgdorferi in S. undulatus, but the viability and infectivity of the pathogen were undetermined. Another recent study found, in one instance, the natural transmission of B. burgdorferi from S. undulatus to a naturally feeding larval I. scapularis. Our objective was to directly test the hypothesis that S. undulatus, like its western congener, actively clears B. burgdorferi infection from infected ticks. We collected lizards in southern New Jersey, where I. scapularis and B. burgdorferi are common. In the field, we found little naturally-occurring parasitism of I. scapularis on S. undulatus, during a time of year when nymphal I. scapularis were actively host-seeking in the Northeast. In the lab, we first fed B. burgdorferi-infected nymphal ticks on S. undulatus and then checked the molted ticks for infection. 

Results/Conclusions
We found that S. undulatus cleaned I. scapularis of the Lyme pathogen. We subsequently fed uninfected larval ticks on challenged lizards to assay for transmission of B. burgdorferi, and while transmission to larvae was not completely blocked, it was extremely low. Our data strongly suggest that S. undulatus is not a highly competent reservoir for B. burgdorferi, at least not for the B. burgdorferi strain (Vallhalla, Westchester County, N.Y.) we used. It remains to be seen whether S. undulatus is more permissive to other B. burgdorferi strains. In sum, we found that while S. undulatus can clear B. burgdorferi infection from feeding ticks, they most likely do not serve the same role in reducing Lyme borreliosis risk as do western fence lizards, because eastern fence lizards are far less important as hosts for I. scapularis in the northeast than are S. occidentalis in the western U.S.