Rickettsiainfection rate along an altitudinal gradient as influenced by population genetic structure of Ixodid ticks

Abstract

AbstractIxodid ticks, such asIxodes ovatusandHaemaphysalis flava,are important vectors of tick-borne diseases in Japan, such as Japanese spotted fever caused byRickettsia japonica. This study describes the population genetic structure and gene flow ofI. ovatusandH. flavaand theirRickettsiainfection rates along an altitudinal gradient. A total of 346 adultI. ovatusand 243H. flavawere analyzed for the presence ofRickettsiaby nested PCR targeting the 17kDA,gltA, rOmpA,andrOmpBgenes. Population genetic structure was performed using the mitochondrial cytochrome oxidase 1 (cox1) marker. TheRickettsiainfection rates were 13.26% inI. ovatusand 6.17% inH. flava.ForI. ovatus,the globalFSTvalue revealed significant genetic differentiation among the different populations, whereasH. flavashowed non-significant genetic differentiation. Thecox1 I. ovatuscluster dendrogram showed two cluster groups, while the haplotype network and phylogenetic tree showed three genetic groups. The two cluster groups and the three genetic groups found inI. ovatusshowed a significant difference in theirRickettsiainfection rates and mean altitude per group. No significant differences were found in the mean altitude orRickettsiainfection rates ofH. flava. Our results suggest that low gene flow in theI. ovatuspopulations has caused spatially heterogenousRickettsiainfection rates along the altitudinal gradient. This information can be used in understanding the relationship between the tick vector, its pathogen, and environmental factors, such as altitude, and for the control of tick-borne diseases in Japan.