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Ticks transmit more pathogens to humans and animals than any other arthropod. We describe the 2.1 Gbp nuclear genome of the tick, Ixodes scapularis (Say), which vectors pathogens that cause Lyme disease, human granulocytic anaplasmosis, babesiosis and other diseases. The large genome reflects accumulation of repetitive DNA, new lineages of retro-transposons, and gene architecture patterns resembling ancient metazoans rather than pancrustaceans. Annotation of scaffolds representing ∼57% of the genome, reveals 20,486 protein-coding genes and expansions of gene families associated with tick-host interactions. We report insights from genome analyses into parasitic processes unique to ticks, including host 'questing', prolonged feeding, cuticle synthesis, blood meal concentration, novel methods of haemoglobin digestion, haem detoxification, vitellogenesis and prolonged off-host survival. We identify proteins associated with the agent of human granulocytic anaplasmosis, an emerging disease, and the encephalitis-causing Langat virus, and a population structure correlated to life-history traits and transmission of the Lyme disease agent.

Infected Ixodes scapularis (black-legged tick) transmit a host of serious pathogens via their bites, including Borrelia burgdorferi, Babesia microti, and tick-borne flaviviruses (TBFVs), such as Powassan virus (POWV). Although the role of female I. scapularis ticks in disease transmission is well characterized, the role of male ticks is poorly understood. Because the pathogens are delivered in tick saliva, we studied the capacity of male salivary glands (SGs) to support virus replication. Ex vivo cultures of SGs from unfed male I. scapularis were viable for more than a week and maintained the characteristic tissue architecture of lobular ducts and acini. When SG cultures were infected with the TBFVs Langat virus (LGTV) or POWV lineage II (deer tick virus), the production of infectious virus was demonstrated. Using a green fluorescent protein-tagged LGTV and confocal microscopy, we demonstrated LGTV infection within SG acinus types II and III. The presence of LGTV in the acini and lobular ducts of the cultures was also shown via immunohistochemistry. Furthermore, the identification by in situ hybridization of both positive and negative strand LGTV RNA confirmed that the virus was indeed replicating. Finally, transmission electron microscopy of infected SGs revealed virus particles packaged in vesicles or vacuoles adjacent to acinar lumina. These studies support the concept that SGs of male I. scapularis ticks support replication of TBFVs and may play a role in virus transmission, and further refine a useful model system for developing countermeasures against this important group of pathogens. Author summary: Powassan disease has greatly increased in frequency since its discovery in Powassan, Ontario in 1958. Powassan virus (lineage I; POWV) and Powassan virus lineage II (deer tick virus; DTV) are endemic to North America and there were 133 reported cases between 2009 and 2018, the majority since 2016. Nymphal and adult Ixodes scapularis ticks are thought to be the primary vectors of POWV/DTV to humans. However, little is known regarding DTV infection of male Ixodes ticks or their potential as vectors. In this study we characterized LGTV, a model tick-borne flavivirus, and DTV infection and propagation in male I. scapularis salivary gland cultures using an ex vivo organ culture system. This work provides insight into potential flavivirus transmission by the male I. scapularis tick. [ABSTRACT FROM AUTHOR]

The global incidence of tick-borne infectious diseases has increased since the beginning of the 21st century. The expansion of tick populations into new geographic locations and a variety of anthropogenic and natural factors are all drivers of the increase. In addition to the establishment of known tick-borne pathogens in new areas, several novel agents, including many viruses, have also emerged. At present in North America, there are five tick-borne viruses that are known to cause human disease: deer tick virus, Powassan virus, Colorado tick fever virus, Heartland virus, and Bourbon virus. Although uncommon causes of disease, these viruses pose formidable threats to the health of individuals residing in regions of endemicity, especially since there are currently no medical countermeasures available to combat them. This review focuses on the basic biology, ecology, epidemiology, transmission, clinical presentation, diagnosis, treatment, and prevention of these North American tick-borne arboviruses. [ABSTRACT FROM AUTHOR]