infectious diseases
Other Arbovirus Infections
Tick borne encephalitis
Tick-borne encephalitis is caused by a flavivirus that has 3 subtypes, European, Siberian, and Far Eastern. Tick-borne encephalitis is transmitted to humans in focal areas extending from eastern France to northern Japan by the bite of infected hard–bodied ticks,Ixodes ricinusin Europe andIxodes persulcatusin Siberia and the Far East. Ticks are both vector and virus reservoir, and small rodents are the primary amplifying host. Tick-borne encephalitis can also be acquired by ingesting unpasteurized dairy products (such as milk and cheese) from infected goats, sheep, or cows. Cases occur from early spring to late summer when ticks are most active. Initially, a mild flu-like illness occurs; the illness usually clears up within a few days, but some patients develop more severe symptoms (eg, Overview of Meningitis , meningoencephalitis). Incidence is highest and severity of disease is greatest in people ≥ 50 years. The case fatality rate and frequency of neurologic sequelae vary by viral subtype (see Centers for Disease Control and Prevention [CDC]: Tick-borne encephalitis is not a nationally notifiable disease in the United States; however, the CDC reports that 5 cases of tick-borne encephalitis occurred among United States travelers to Europe and China from 2000 through 2011 ( Arbovirus references ). Tick-borne encephalitis should be suspected in travelers who have both of the following: A nonspecific febrile illness that progresses to neuroinvasive disease within 4 weeks after arriving from an endemic area Risk of tick exposure The diagnosis of tick-borne encephalitis is usually made serologically by detection of specific IgM antibodies in blood or cerebrospinal fluid, which typically appear only after onset of neurologic manifestations. The virus that causes tick-borne encephalitis can sometimes be detected in serum by virus isolation or reverse transcriptase polymerase chain reaction (RT-PCR) earlier in disease before antibody titers have risen. As with other viral meningoencephalitides, treatment is supportive. Prevention of tick-borne encephalitis involves avoiding tick bites. A vaccine is available in some areas where tick-borne encephalitis is endemic (seeThe European Centre for Disease Prevention and Control [ECDC]: Tick-Borne Encephalitis Recommended Vaccinations). A vaccine is available in the United States for US travelers visiting endemic areas who are at risk of tick exposure (seeCDC: Tick-borne encephalitis vaccine). 