Milk outbreaks of tick-borne encephalitis in Slovakia, 2012-2016.

Objective: Tick-borne encephalitis virus (TBEV) is most commonly transmitted to humans via the bite of an infected tick. Alimentary infection through the consumption of TBEV-contaminated dairy products is also well-documented and is responsible for some diseases in endemic areas. The aim of the study was to emphasize the risk of contracting tick-borne encephalitis (TBE) by consuming raw milk and dairy products and to describe TBE epidemics in Slovakia for the period 2012-2016.

Methods: The data on epidemics were obtained from the Annual Reports for the period 2012-2016 available on the website of the Public Health Authority of the Slovak Republic. Medical records of patients hospitalized during epidemics were provided by the Department of Infectology and Travel Medicine, Faculty of Medicine, Pavol Jozef Šafárik University in Košice, and the Louis Pasteur University Hospital in Košice.

Results: During the period 2012-2016, 13 smaller or larger TBE epidemic outbreaks were recorded in the Slovak Republic. The two outbreaks of TBE reported in 2012 were associated with the consumption of raw goat's milk and dairy products. The first case was an outbreak involving 12 infected people in the Lučenec District. The second case was a family outbreak in the Žilina District, where 3 persons out of 4 family members were infected. In 2013, one epidemic was reported involving 5 persons following the consumption of sheep's cheese from a farm in the Prešov District. One outbreak with 11 cases was reported in 2014. The investigation confirmed its association with the consumption of sheep's cheese in a restaurant located in the Ružomberok District. In 2015, 4 epidemics were described related to the consumption of goat's/sheep's milk and cheese (Žilina District, Krupina District, Kysucké Nové Mesto District, Trenčín District). In 2016, there were 5 TBE epidemics related to the consumption of milk and dairy products. The largest TBE epidemic outbreak in the last 5 years occurred in the Košice District. In this outbreak approximately 500 people were exposed, and 44 contracted the disease. Infected persons confirmed consumption of sheep's cheese from a farm.

Conclusions: Consumption of milk and dairy products made only from pasteurized milk, as well as the immunization of humans and animals are the most effective preventive measures against TBE.