JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
Tickborne Viral Infections
James Diaz, MD
Ticks are versatile arthropod vectors of zoonotic diseases that are not afflicted by the many pathogens they can transmit. Ticks transmit the broadest range of pathogens, including bacteria, viruses, and parasites. As a result, the objectives of this review were to identify tickborne viral pathogens in the U.S., to describe the evolving epidemiology of tick-transmitted viral diseases, to identify the most common tick vectors of viral pathogens and their zoonotic reservoirs and ranges of distribution, to compare U.S. experiences with tick- transmitted viruses with worldwide experiences, and to recommend effective strategies for the control and personal prevention of tickborne viral diseases. Internet search engines were queried with the key words to identify peer-reviewed scientific articles on tick-transmitted viral infectious diseases in theU.S. The tickborne viral infections are causedprimarily by flaviviruses (Family Flaviviridae) and divided into two separate clinical presentations, eachwithpreferred tick vectors and zoonotic reservoirs: (1) the viral encephalitides and (2) the viral hemorrhagic fevers.With very few exceptions, the tickborne viral infections are transmitted by ixodid or hard ticks (Family Ixodidae). The tickborne viral infections share several common clinical and epidemiologic characteristics including incubationperiods of about oneweek; biphasic illnesses separatedby asymptomatic periods; serodiagnosis by enzyme-linked immunosorbent assay (ELISA); and antigen nucleic acid detection in blood or cerebrospinal fluid (CSF) by reverse-transcriptase (RT)-PCR; no specific treatments other than supportive therapy; and high case fatality rates. Avoidance of tick bites is key to prevention.
INTRODUCTION
Ticks are highly versatile arthropod vectors of zoonotic diseases that are not afflicted by the pathogens they can transmit during blood-feeding. Unlike mosquitoes, ticks transmit the broadest range of pathogens, including bacteria, viruses, and parasites. Ticks have capitalized on competitive advantages afforded them by current changes in climate and human lifestyle. The most significant advantages benefitting tickborne diseases include (1) wider geographic distributions at higher elevations; (2) longer active breeding and blood-feeding seasons as a result of increases in global mean temperatures; (3) greater abundance of wild animal reservoir hosts no longer controlled, especially deer and rodents; (4) more residential living in recently cleared woodlands adjacent to pastures and yards frequented by wildlife, domestic animals, and humans; and (5) more vacation and leisure-time activities enjoyed by humans and their pets duringprolonged tick host-questing andblood-feeding seasons. As a result, the objectives of this reviewwere to identify the newly emerging and re-emerging tickborne viral pathogens in the U.S., to describe the evolving epidemiology of tick-transmitted viral diseases, to identify the most common tick vectors of viral pathogens and their zoonotic reservoirs and ranges of distribution, to compare US experiences with tick-transmitted viruses with worldwide experiences, and to recommend effective strategies for the control and personal prevention of tickborne viral diseases.
METHODS
To meet the objectives of this review, Internet search engines including PubMed, Medline, Ovid, Google®, Google Scholar® and Cochrane were queried with the key words as medical subject headings to identify peer-reviewed scientific articles on newly emerging tick-transmitted viral infectious diseases in the U.S. and worldwide. The key words included ticks, tick-transmitted or tickborne viral infectious diseases, new and emerging tick- transmitted or tickborne viral infectious diseases. Data sources reviewed included case reports, case series, observational and longitudinal studies, active and passive surveillance investigations, entomological studies, and meta-analyses. As an analysis of prior published publications, institutional review board approval was not indicated for this review.
RESULTS
The Descriptive Epidemiology of Tickborne Viral Infectious Diseases in the U.S.
Tickborne viral infectious diseases are an increasing public health burden in the U.S. today for several reasons that include human risk factors and the ecology of tick-transmitted diseases. The greatest human risk factors for tickborne infectious
46 J La State Med Soc VOL 170 MARCH/APRIL 2018
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