Persistence of Tick-Borne Encephalitis Virus in Goat and Cow Milks Under Different Storage Conditions and Following Thermal Inactivation

Tick-borne encephalitis virus (TBEV) is a neuroinvasive arbovirus that is primarily transmitted to humans through the bites of Ixodes ricinus ticks. Consumption of unpasteurised milk and dairy products from infected ruminants can also cause infection in humans. In the majority of food-borne TBE (FB-TBE) cases, goat milk and/or cheese has been identified as the source of infection. The aim of the present study was to analyse the persistence of the infectious strain TBEV_Ain_2020 virus in spiked goat and cow raw milks under different storage conditions, and following pasteurisations performed at 63 °C/30 min or 72 °C/15 s. The total genome of TBEV was stable up to 48 h in goat and cow's milks at 4 °C and 21 °C. In contrast, the viral titre was significantly lower in goat milk from T + 2 h post-contamination up to 17 h compared to culture cell medium and cow milk at 4 °C. At 21 °C, viral titres were lower than in DMEM in both milks up to T + 12 h. Thermal inactivations were effective in goat milk, but were not sufficient to eliminate all infective virus particles in cow milk. These unexpected findings highlighted that pasteurisation processes should be adapted to the species of origin of the milk and to the initial viral load to ensure food safety.