Powassan/Deer Tick Virus and Borrelia Burgdorferi Infection in Wisconsin Tick Populations
Knox Konstance K., Thomm Angela M., Harrington Yvette A., Ketter Ellen, Patitucci Jacob M., and Carrigan Donald R. Vector-Borne and Zoonotic Diseases. May 2017 Online Ahead of Print
Powassan/Deer Tick Virus (POWV/DTV) is an emerging cause of arboviral neuroinvasive disease in the upper Midwest. These studies describe the prevalence and geographic distribution of Wisconsin ticks carrying POWV/DTV as well as the high frequency of Ixodes scapularis ticks coinfected with both POWV/DTV and Borrelia burgdorferi, the causative agent of Lyme disease. These findings suggest that concurrent transmission of POWV/DTV and B. Burgdorferi from coinfected ticks is likely to occur in humans.
Results (see link for maps and graphs of locations and results)
The distribution of I. scapularis and D. variabilis tick collection sites are categorized by geographic quadrant (QNW, QNE, QSW, & QSE) of the state (Fig. 1, Table 1). Nearly 80% of adult female I. scapularis ticks analyzed were collected from the northern half of the state (QNW and QNE) and accounted for 85% of POWV-positive ticks. While only 90 I. scapularis ticks were collected from the southern two quadrants, POWV-positive ticks were identified in both QSE and QSW. QNW I. scapularis ticks revealed the highest MLE of infection for both POWV and B. burgdorferi (4.67% and 23.42%, respectively). A separate analysis of I. scapularis collections from Harvest One endemic zone (Spooner/Hayward) QNW demonstrated a frequency of infection for both POWV (4.65%) and B. burgdorferi (27.91%) that is comparable to the total QNW (Fisher’s exact, p = 1.00 and p = 0.35, respectively). QSE contained the lowest MLE for POWV (1.53%), but B. burgdorferi-infected ticks were high with a MLE of 15.69%. Of the 295 D. variabilis ticks analyzed from both harvests, none (0%) had evidence of POWV infection; however, B. burgdorferi infection in D. variabilis ticks was seen in both QNW (3.1%) and QSW (2.86%), consistent with the high B. burgdorferi infection rate observed in I. scapularis ticks in these same quadrants.
Powassan Virus: An Emerging Arbovirus of Public Health Concern in North America
Hermance Meghan E. and Thangamani Saravanan. Vector-Borne and Zoonotic Diseases. May 2017 Online Ahead of Print
Powassan virus (POWV, Flaviviridae) is the only North American member of the tick-borne encephalitis serogroup of flaviviruses. It is transmitted to small- and medium-sized mammals by Ixodes scapularis, Ixodes cookei, and several other Ixodes tick species. Humans become infected with POWV during spillover transmission from the natural transmission cycles. In humans, POWV is the causative agent of a severe neuroinvasive illness with 50% of survivors displaying long-term neurological sequelae. POWV was recognized as a human pathogen in 1958 when a young boy died of severe encephalitis in Powassan, Ontario, and POWV was isolated from the brain autopsy of this case. Two distinct genetic lineages of POWV are now recognized: POWV (lineage I) and deer tick virus (lineage II). Since the index case in 1958, over 100 human cases of POWV have been reported, with an apparent rise in disease incidence in the past 16 years. This recent increase in cases may represent a true emergence of POWV in regions where the tick vector species are prevalent, or it could represent an increase in POWV surveillance and diagnosis. In the past 5 years, both basic and applied research for POWV disease has intensified, including phylogenetic studies, field surveillance, case studies, and animal model development. This review provides an overview of POWV, including the epidemiology, transmission, clinical disease, and diagnosis of POWV infection. Recent research developments and future priorities with regard to the disease are emphasized.
Early timeline of POWV transmission
The duration of I. scapularis attachment required for successful transmission of DTV to a host was found to be as little as 15 min (Ebel and Kramer 2004). This finding was particularly striking because unlike other tick-borne pathogens (Borrelia burgdorferi, Babesia microti, and Anaplasma phagocytophilum), very little time between tick attachment and virus transmission is needed for POWV. The reactivation period required for some nonviral tick-borne pathogens provides a grace period of approximately 24 h, where a minimal risk of transmission occurs if humans remove the attached tick within this timeline; however, there is no such grace period for POWV due to its very short timeline of transmission. These differences underscore why the timeline of POWV transmission must be carefully considered when analyzing the early immunomodulatory events that occur at the feeding site of the tick.
The idea of a “grace period” is ludicrous. Ticks do not understand grace, trust me. For accurate information about transmission times of Lyme see:
https://madisonarealymesupportgroup.com/2017/04/14/transmission-time-for-lymemsids-infection/. In short, it can happen in hours for sure – not requiring the oft repeated dogma of 24-48 or more hours. Ticks often feed partially and then drop off. These partially fed ticks have spirochetes in their saliva and can transmit much more quickly.
Every single tick bite should be taken seriously!