Co-Infection Patterns in Individual Ixodes scapularis Ticks Reveal Associations between Viral, Eukaryotic and Bacterial Microorganisms

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.

Sharing the Ride: Ixodes scapularis Symbionts and Their Interactions

“…However, we have excluded common environmental microbes demonstrated to be artifacts from contaminated reagents, such as Delftia, Comamonas, Acidovorax, and others (Salter et al, 2014). Sequence-based studies indicate a larger variety of bacterial residents may temporarily survive in this tick species (Benson et al, 2004;Narasimhan et al, 2014;Rynkiewicz et al, 2015;Van Treuren et al, 2015;Zolnik et al, 2016Zolnik et al, , 2018Abraham et al, 2017;Cross et al, 2018;Landesman et al, 2019;Tokarz et al, 2019), but other reports suggest that many of the detectable bacteria from such studies may have been of environmental origin or introduced from contaminated reagents (Martin and Schmidtmann, 1998;Salter et al, 2014;Ross et al, 2018;Zolnik et al, 2018).…”

“…Anaplasma phagocytophilum i, p 1.9-18% (N, A) Adelson et al, 2004;Aliota et al, 2014;Cross et al, 2018;Tokarz et al, 2019 Bartonella spp. p 13-90% (L, N) Adelson et al, 2004;Rynkiewicz et al, 2015 Ehrlichia spp.…”

“…i, p 1.3-3.6% (N, A) Aliota et al, 2014;Cross et al, 2018;Johnson et al, 2018 Rickettsia Adelson et al, 2004;Narasimhan et al, 2014Narasimhan et al, , 2017Kurtti et al, 2015;Rynkiewicz et al, 2015;Zolnik et al, 2016;Cross et al, 2018;Tokarz et al, 2019 Wolbachia spp. Steiner et al, 2008;Tokarz et al, 2010Tokarz et al, , 2019Aliota et al, 2014;Cross et al, 2018Steiner et al, 2008Hamer et al, 2014;Tokarz et al, 2019 *i, isolation from I. scapularis;v, microscopic visualization;d, FISH, IFA or female (Zolnik et al, 2016;Thapa et al, 2019). Its abundance in I. scapularis may relate to the ability of this prokaryote to provide folate (vitamin B9) to the tick, as animals are unable to synthesize this essential vitamin (Hunter et al, 2015).…”

“…Less clear than the diversity of organisms, is the extent, if any, to which some of these microbes may interact with each other, either directly or indirectly. The published studies in this area are largely limited to predicted interactions based on cooccurrences of two or more organisms in the same tick (Cross et al, 2018;Ross et al, 2018). This review will focus on both the composition of the I. scapularis microbiome and the potential microbial interactions occurring within this tick species.…”

Characterization of a Monanema nematode in Ixodes scapularis

“…In 2014, 12S rRNA gene sequences homologous to sequences from larial nematodes were detected in I. scapularis ticks in Connecticut [3]. Subsequent metagenomic analyses of I. scapularis from Wisconsin and our study from New York and Connecticut also reported Filarioidea sequences [4,5]. Because larial nematodes are implicated in veterinary and human disease and there is a high degree of human contact with I. scapularis, we sought to genetically characterize this nematode (tentatively named Ixodes scapularis-associated nematode, or ISN) and determine the level of human exposure.…”