Isolation of deer tick virus (Powassan virus, lineage II) from Ixodes scapularis and detection of antibody in vertebrate hosts sampled in the Hudson Valley, New York State

Abstract

BackgroundDeer tick virus, DTV, is a genetically and ecologically distinct lineage of Powassan virus (POWV) also known as lineage II POWV. Human incidence of POW encephalitis has increased in the last 15 years potentially due to the emergence of DTV, particularly in the Hudson Valley of New York State. We initiated an extensive sampling campaign to determine whether POWV was extant throughout the Hudson Valley in tick vectors and/or vertebrate hosts.MethodsMore than 13,000 ticks were collected from hosts or vegetation and tested for the presence of DTV using molecular and virus isolation techniques. Vertebrate hosts of Ixodes scapularis (black-legged tick) were trapped (mammals) or netted (birds) and blood samples analyzed for the presence of neutralizing antibodies to POWV. Maximum likelihood estimates (MLE) were calculated to determine infection rates in ticks at each study site.ResultsEvidence of DTV was identified each year from 2007 to 2012, in nymphal and adult I. scapularis collected from the Hudson Valley. 58 tick pools were positive for virus and/or RNA. Infection rates were higher in adult ticks collected from areas east of the Hudson River. MLE limits ranged from 0.2-6.0 infected adults per 100 at sites where DTV was detected. Virginia opossums, striped skunks and raccoons were the source of infected nymphal ticks collected as replete larvae. Serologic evidence of POWV infection was detected in woodchucks (4/6), an opossum (1/6), and birds (4/727). Lineage I, prototype POWV, was not detected.ConclusionsThese data demonstrate widespread enzootic transmission of DTV throughout the Hudson Valley, in particular areas east of the river. High infection rates were detected in counties where recent POW encephalitis cases have been identified, supporting the hypothesis that lineage II POWV, DTV, is responsible for these human infections.

Flavivirus Infection ofIxodes scapularis(Black-Legged Tick)Ex VivoOrganotypic Cultures and Applications for Disease Control

“…Also, POWV infections in this study were carried out with POWV lineage I, which may replicate differently than POWV lineage II (DTV) in I. scapularis organs. The latter virus has been isolated from naturally infected populations of I. scapularis (21,22). Detailed growth comparisons between both POWV lineages in tick organ cultures may provide further insight.…”

The Prevalence of Zoonotic Tick-Borne Pathogens inIxodes ScapularisCollected in the Hudson Valley, New York State

“…POWV has been considered to be a minor public health concern due to the relative host specificity of its tick vector, Ixodes cookei and/or Ixodes marxi (Ebel et al 2000). Whereas, DTV is thought to be a greater public health threat, because it mainly has been associated with I. scapularis and therefore has a more likely opportunity to come into contact with humans (Hinten et al 2008, Tavakoli et al 2009, Dupuis et al 2013. DTV was only detected in adult samples (5% of adult samples; 27/561) ( Table 2).…”

“…I. scapularis also has been implicated as a vector for one of two lineages of POWV, deer tick virus (DTV) (for review, see Ebel 2010, Dupuis et al 2013). All of these agents can coexist in I. scapularis, and often they are found in the same geographic locale.…”

Changing epidemiology of Powassan encephalitis in North America suggests the emergence of the deer tick virus subtype

“…Powassan virus prototype has been isolated from three tick species: Ixodes cookei, I. marxi and I. spinipalpus, whereas DTV has been exclusively detected in I. scapularis ticks [5], except once when it was recovered from Dermacentor andersoni ticks [3]. Powassan virus prototype is maintained in an enzootic cycle that involves mainly I. cookei as the tick vector and the groundhog (Marmota momax) or striped skunk (Mephitis mephitis) as the principal reservoir hosts [6].…”