Bacterial communities in ticks and blood from rodent hosts

Background/Question/Methods

Ticks are the most common disease vector in North America. Ticks take blood meals from one or more hosts throughout their life cycle, and conversely hosts can be bitten by many ticks over their lifetime. This provides ticks with many opportunities to become infected with bacteria from infected hosts, and for hosts to become infected with bacteria from ticks. We conducted a field survey and next-generation pyroseqencing of ticks and rodent hosts from two sites during peak tick season in 2011 to compare bacterial community composition between ticks and their hosts. Most previous research has focused on single bacterial taxa, such as Borrelia burgdorferi, but because microbial interactions can influence infection and transmission, investigating the whole bacterial community may provide additional insights.  We used next-generation pyroseqencing to analyze the bacterial communities in ticks taken off rodents and in rodent blood samples. A total of 134 tick samples and 95 blood samples were sequenced and OTU clusters were created at 97% identity and assigned to taxonomic groups using a BLAST comparison to the SILVA SSU non-redundant database. 

Results/Conclusions

Peromyscus leucopus was the most common rodent host and two tick species were found (Dermacentor variabilis and Ixodes scapularis). The two most abundant OTUs from tick samples most closely corresponded to the Francisella endosymbiont of Dermacentor ticks (56% of tick sequences) and Rickettsia massiliae (23%). Many of these Rickettsia sequences are likely from the Rickettsia endosymbiont of Ixodes ticks. However, there were some co-occurrences of Rickettsia and Francisella, suggesting non-endosymbiont Rickettsia infection in Dermacentor. The most common OTU from rodent blood samples was associated with three Bartonella species (45% of sequences), which have been identified as flea-borne pathogens of mammals. Two taxa were found in both tick and blood samples, Afipia broomeae (0.67% tick sequences, 4.5% blood sequences) and Bartonella (3% of tick sequences), suggesting ticks may also be infected by flea-borne bacteria. Mycoplasma, a directly-transmitted bacterial pathogen, was also found in rodent blood samples. Arsenephonus and Wolbachia sequences were infrequently detected in tick samples. Species in these genera have been found to infect ticks and other arthropods. These results suggest that the dominant bacteria in ticks and host blood samples are different, but that the common flea-borne pathogens, Bartonella and Afipia co-occur in rodent blood and in ticks.