Europe: Just When You Thought It Was Safe!

abstracts & commentary

Synopsis: Tick-borne encephalitis, a vaccine-preventable disease, remains a summertime danger in Europe.

Sources: Logar M, et al. Infection 2000;28:74-77; Kaiser R, Holzmann H. Infection 2000;28:78-84; Ruef C. Infection 2000; 28:65-67.

During the summer of 1997, 80 (37.6%) of 213 patients with aseptic meningitis in Ljubljana, Slovenia, had serum IgM antibody to tick-borne encephalitis (TBE) virus in the absence of antibody to Borrelia burgdorferi sensu lato and of PCR evidence of enterovirus infection in CSF. None of the 60 adults and 20 children had received TBE vaccination. Sixty-five (81.3%) had a history of tick bite. Adults were almost twice as likely as children to have peripheral blood leukocytosis and one-sixth of the adults had thrombocytopenia compared to none of the children. CSF demonstrated findings typical of aseptic meningitis, with lymphocyte predominance in 68.8%; there was no significant difference among important parameters between adults and children. A total of 64 (80%) had a biphasic illness. Fever duration was longer in adults.

Separately, laboratory findings of 100 consecutive adults with TBE admitted to the University of Freiburg hospital between 1990 and 1997 were retrospectively evaluated by Kaiser and Holzmann. Three (3%) had previously received TBE vaccine, but in each case vaccination had been incomplete. All but three of the 100 patients had serum IgM antibody to TBE virus at the time of admission. Findings compatible with intrathecal synthesis of TBE virus-specific IgM or IgG antibodies were detected by the 15th day after the onset of neurological symptoms in all patients studied. In contrast to the Slovenian experience, CSF granulocyte predominance was seen in approximately one-half of patients.

Comment by stan deresinski, md, facp

The TBE pathogen is a flavivirus whose principal vector within central Europe, southern Scandinavia, and European Russia is the hard tick, Ixodes ricinus, which is also the vector for B. burgdorferi in this region. TBE virus may also be acquired by ingestion of infected dairy products, especially unpasteurized goat milk.

Neurological disease develops during the second phase of infection but occurs in only 5-30% of symptomatic patients (and only 1 in 250 infected individuals ever develop symptoms). However, some patients present with neurological disease in the absence of a febrile prodrome.

In a typical symptomatic case, a flu-like illness develops 7-14 days after infection. Symptoms resolve within a week, but in a minority of cases, a second phase of illness occurs after a 2- to 8-day period of remission. It is during this phase that neurological involvement is likely to be observed. Residual abnormalities, including paralysis, are reported to occur in 30-60% of patients. There is evidence that the disease is more severe in adults than in children. TBE in the Far East, caused by other strains of the virus, is more severe and has significantly greater mortality.

A TBE-inactivated vaccine is available in Europe and appears to be safe and immunogenic, although a metaanalysis has concluded that its protective efficacy is, as yet, unproven.1,2 It is administered twice within three months and once more 6-18 months after the second injection; an accelerated schedule has also been described. Protection is believed to last for three years after the last administration. Postexposure TBE virus hyperimmune globulin is also used in Europe, but its value is unproven.

References

1. Demicheli V, et al. Vaccines for preventing tick-borne encephalitis (Cochrane Review). In: The Cochrane Library, Issue 2, 2000. Oxford: Update Software.

2. Must be purchased from the manufacturer. The U.S. Military utilizes the vaccine manufactured by Immuno AG, Industria Strasse 67, 1220 Vienna, Austria.