A transcript corresponding to a predicted secreted protein affects flavivirus infection of Ixodes scapularis salivary gland cultures

Ixodes scapularis transmits a number of pathogens, including the agent of Lyme disease and tick-borne flaviviruses (TBFVs). TBFV infections cause thousands of human encephalitis cases worldwide each year. In the US, confirmed human infections with TBFV Powassan virus (POWV) are increasing and have a fatality rate of 10-15%. In addition, Langat virus (LGTV) is often used as an experimental model TBFV of low neurovirulence. Elucidation of tick-virus interactions may inform countermeasures to reduce TBFV transmission. Understanding the functional effect of tick salivary gland transcripts in TBFV infection within tick organs is limited. Organ cultures are an excellent system for studying virus infection in individual tick organs, and RNAi methodology in tick organ cultures can identify selected tick transcripts as possible countermeasure targets. Through dsRNA-mediated RNAi transcript knockdown studies, a transcript corresponding to a predicted I. scapularis secreted protein (SecP) limited LGTV and POWV infection in salivary gland (SG) cultures from unfed female ticks. Because transfection of dsRNA corresponding to a SecP transcript reduced infectious LGTV and POWV replication, SecP is considered to be proviral. Additionally, in situ hybridization-localized SecP transcripts were observed in SG granular acini of unfed female ticks. Further investigation into the role of SecP in TBFV infection is currently underway. Complementary studies with TBFV-infected I. scapularis are being planned. This research approach defines a translational pipeline by which tick transcripts/proteins can be assayed as targets for TBFV countermeasures. This research was supported by the Intramural Research Program of the NIH, NIAID.