Systematic Review and Meta-analysis of Foodborne Tick-Borne Encephalitis, Europe, 1980-2021

Abstract

Tick-borne encephalitis (TBE) is a viral infection of the central nervous system that occurs in many parts of Europe and Asia. Humans mainly acquire TBE through tick bites, but TBE occasionally is contracted through consuming unpasteurized milk products from viremic livestock. We describe cases of TBE acquired through alimentary transmission in Europe during the past 4 decades. We conducted a systematic review and meta-analysis of 410 foodborne TBE cases, mostly from a region in central and eastern Europe. Most cases were reported during the warmer months (April–August) and were associated with ingesting unpasteurized dairy products from goats. The median incubation period was short, 3.5 days, and neuroinvasive disease was common (38.9%). The clinical attack rate was 14% (95% CI 12%–16%), and we noted major heterogeneity. Vaccination programs and public awareness campaigns could reduce the number of persons affected by this potentially severe disease.

Keywords: Europe; Israel; Tick-borne encephalitis; alimentary infection; attack rate; food safety; foodborne diseases; meningitis/encephalitis; unpasteurized milk; vector-borne infections; viruses; zoonoses.

Figure 1

Geographic distribution of reported foodborne tick-borne encephalitis (FB-TBE) cases (blue shading), Europe, 1980–2021. A) The FB-TBE triangle in Europe. Russia had 5 cases in 1991 (not shown). Map created by using MapChart (https://mapchart.net). B) The tick-borne encephalitis belt, spanning from western Europe, across Russia, China, and Mongolia to Japan. Map from the Centers for Disease Control and Prevention (https://www.cdc.gov/tick-borne-encephalitis/geographic-distribution/index.html).

Figure 2

Analysis of clinical attack rate of foodborne tick-borne encephalitis, Europe, 1980–2021. A) Attack rate calculated for 10 outbreaks in which the number of exposed persons was reported. B) Attack rate calculated only for 7 outbreaks with >10 reported persons affected. I², level of heterogeneity.

Figure 3

Rates of FB-TBE per country and year from a systematic review and meta-analysis, Europe, 1980–2021. Rates indicate FB-TBE per all TBE cases reported in the country, per year. Data are based on those reported in Table 1. FB-TBE, foodborne tick-borne encephalitis; TBE, tick-borne encephalitis.