Abstract
In May 2016, two cases of tick-borne encephalitis (TBE) were confirmed by serology (positive IgM and IgG antibodies against TBE virus (TBEV) in serum), with a possible link to raw milk and cheese from a goat farm in a region in Baden-Württemberg, Germany not previously known as TBE-endemic. The outbreak investigation identified 32 consumers of goat dairy products (29 consumers, one farm employee, two owners) of whom none had IgM antibodies against TBEV 3–8 weeks after consumption. Of the 27 notified TBE cases in the State, none reported consumption of raw goat milk or cheese from the suspected farm. Five of 22 cheese samples from 18 different batches were RT-qPCR-positive for TBEV -genome, and two of the five samples were confirmed by virus isolation, indicating viability of TBEV in the cheese. Nine of the 45 goats had neutralising TBEV antibodies, two of them with a high titre indicating recent infection. One of 412 Ixodes ricinus was RT-qPCR-positive, and sequencing of the E gene from nucleic acid extracted from the tick confirmed TBEV. Phylogenetic analyses of tick and cheese isolates showed 100% amino acid homology in the E gene and a close relation to TBEV strains from Switzerland and Austria.
Highlights
Tick-borne encephalitis (TBE) is caused by an RNA virus of the genus Flavivirus, family Flaviviridae [1]
We investigated a cluster of two human tick-borne encephalitis (TBE) cases that occurred in the spring/summer of 2016 in southern Germany in consumers of raw goat milk and cheese from a goat farm
To exclude false positive results caused by cross-reactivity to other flaviviruses, all sera were tested for IgM and IgG antibodies against different flaviviruses (TBEV, West Nile virus, dengue virus, yellow fever virus, Japanese encephalitis virus) using an indirect immunofluorescence assay (Euroimmun, Lübeck, Germany), according to standard procedures
Summary
Tick-borne encephalitis (TBE) is caused by an RNA virus of the genus Flavivirus, family Flaviviridae [1]. There are at least three known subtypes and so far, only the European subtype has been detected in various central European countries (Austria, Czech Republic, France, Germany, Slovak Republic, Switzerland) in ticks, rodents and patients since the 1950s [2]. TBE virus (TBEV) circulates between ticks and natural hosts (small mammals) in geographically strictly limited natural foci. Milk-borne TBE outbreaks have been reported in a number of central and eastern European countries [8,9,10,11,12,13]. One TBE outbreak caused by goat cheese happened in 2008 in a mountainous region in Austria [14]
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