A community ecology perspective on the role of hosts in vector-borne disease transmission

Background/Question/Methods

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 in an enzootic cycle involving 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 remove the pathogen in feeding ticks through immune pathways. A prior study suggested that the experimental removal of lizards led to a decline in tick abundance as well as a decline in infected ticks. This unexpected result suggested that the high lizard abundance may increase disease risk but has not been explicitly tested. In new analyses, we evaluated host diversity and disease risk from a gradient of habitat patches to test the relationship between lizard abundance on entomological risk of Lyme disease.

Results/Conclusions

We found that lizard abundance is positively correlated with entomological disease risk. While the exact mechanism of this pattern is not clear, recent vector competence studies suggest that high lizard abundance may increase I. pacificus vector competence for B. burgdorferi. These results indicate a complex and multifaceted role of lizards in the transmission and maintenance of Lyme disease in the western United States.