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 the U.S. The tickborne viral infections are caused primarily by flaviviruses (Family Flaviviridae) and divided into two separate clinical presentations, each with preferred 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 incubation periods of about one week; biphasic illnesses separated by 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.

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