Abstract
Ixodes scapularis ticks harbor a variety of microorganisms, including eukaryotes, bacteria and viruses. Some of these can be transmitted to and cause disease in humans and other vertebrates. Others are not pathogenic, but may impact the ability of the tick to harbor and transmit pathogens. A growing number of studies have examined the influence of bacteria on tick vector competence but the influence of the tick virome remains less clear, despite a surge in the discovery of tick-associated viruses. In this study, we performed shotgun RNA sequencing on 112 individual adult I. scapularis collected in Wisconsin, USA. We characterized the abundance, prevalence and co-infection rates of viruses, bacteria and eukaryotic microorganisms. We identified pairs of tick-infecting microorganisms whose observed co-infection rates were higher or lower than would be expected, or whose RNA levels were positively correlated in co-infected ticks. Many of these co-occurrence and correlation relationships involved two bunyaviruses, South Bay virus and blacklegged tick phlebovirus-1. These viruses were also the most prevalent microorganisms in the ticks we sampled, and had the highest average RNA levels. Evidence of associations between microbes included a positive correlation between RNA levels of South Bay virus and Borrelia burgdorferi, the Lyme disease agent. These findings contribute to the rationale for experimental studies on the impact of viruses on tick biology and vector competence.
Highlights
Ixodes scapularis, the blacklegged or deer tick, is the main North American vector for Borrelia burgdorferi, the causative agent of Lyme disease
Primers were created for viral sequences, while existing primers were used for Borrelia burgdorferi, Anaplasma phagocytophilum, Babesia microti, Borrelia miyamotoi [48], and the positive control I. scapularis glycerol-3-phosphate dehydrogenase (GPDH) primers [49]
These 18 taxa included South Bay virus, Suffolk virus, Blacklegged tick phleboviruses 1–3, Powassan virus, Ixodes scapularis associated viruses 1 and 2, B. burgdorferi sensu stricto, B. mayonii, We focused our analyses on 18 taxa that accounted for 89% of the assigned non-tick reads in our datasets
Summary
The blacklegged or deer tick, is the main North American vector for Borrelia burgdorferi, the causative agent of Lyme disease. To understand the possible influence of nonpathogenic viral components of the microbiota of I. scapularis, we simultaneously measured RNA levels of eukaryotic, bacterial and viral microbes in or on 112 individual adult ticks collected from Wisconsin, USA This is an area of high Lyme disease risk, and the microbiome of I. scapularis from this region has not been evaluated in this manner [34]. As in other I. scapularis populations, South Bay virus and blacklegged tick phleboviruses were common in these ticks [24,27,30] These viruses were involved in the majority of statistically significant associations with other microbes, including with B. burgdorferi
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