# Emergence of tick borne encephalitis in North America

> **NIH NIH R01** · TUFTS UNIVERSITY BOSTON · 2020 · $499,584

## Abstract

Lyme disease was once restricted to coastal North Atlantic and selected Upper Midwest communities,
but the distribution and prevalence of this zoonosis has greatly expanded in the last two decades. The
aggressively human biting deer tick vector of the agent of Lyme disease was first recognized to
maintain a distinct lineage of Powassan virus (POW) in 1997, but human encephalitis cases
attributable to “deer tick virus” was recognized only in 2006. Severe neurologic disease, a hallmark
of classical Powassan fever, remained rare in residents of Lyme-endemic sites until recently.
Encephalitis cases attributed to Powassan virus are now being increasingly reported from New
England and the upper Midwest. The biological basis for the recent zoonotic emergence of POW
requires analysis. The Eurasian tick borne encephalitis virus complex (TBEV) comprises diverse
species (including POW), subtypes and geographic isolates that vary in their capacity to cause human
disease, and there is a rich literature concerning variation in the genetic, phenotypic and clinical
characteristics of Eurasian TBEV that should guide our analysis of the potential public health burden
of POW in North America. Our overaraching hypothesis is that Powassan virus, like
TBEV, also comprises lineages, genotypes, or populations that differ in capacity to
cause human disease. We propose to test this hypothesis using our existing geographic isolates of
POW as well as additional isolates that we shall collect for their capacity to cause neurologic disease
using a published mouse model for TBEV neurotropism. In addition, it may be that certain lineages,
genotypes, or populations of POW are more efficiently transmitted by the human biting deer tick
vector of Lyme disease, and this helps to explain the emerging epidemiological situation. Accordingly,
we shall also determine whether geographic isolates may differ in their capacity to infect and be
transmitted by ticks. Finally, we shall apply the powerful tools of whole genome sequencing to
analyze the population structure of Powassan virus as well as identify any genetic correlates of
neurotropic capacity. Taken together, these observations may help explain the changing
epidemiology of an arbovirus that has been silently enzootic for over 2 decades in Lyme disease
endemic sites, but is now apparently an emerging zoonosis. Ultimately, by describing the
pathobiological correlates of Powassan genetic diversity, we can better define the potential for tick
borne encephalitis to continue to emerge as a public health burden in North America.

## Key facts

- **NIH application ID:** 9837415
- **Project number:** 5R01AI137424-02
- **Recipient organization:** TUFTS UNIVERSITY BOSTON
- **Principal Investigator:** Gregory David Ebel
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $499,584
- **Award type:** 5
- **Project period:** 2018-12-12 → 2023-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9837415

## Citation

> US National Institutes of Health, RePORTER application 9837415, Emergence of tick borne encephalitis in North America (5R01AI137424-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9837415. Licensed CC0.

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