Rónai, Z. and Egyed, L.
Survival of tick-borne encephalitis virus in goat cheese and milk.
Food Environ. Virol. 2020, doi: 10.1007/s12560-020-09427-z
Humans usually acquire TBE through a tick bite, but infection through the consumption of raw milk and raw milk products occasionally occur. A recent TBE outbreak by the alimentary route of infection has been discussed in Snapshot week 26/2020.
Inactivation of TBE virus and alimentary infections can effectively be avoided by pasteurization of milk. This has clearly been documented by a Hungarian team. The authors used naturally infected raw goat milk samples (with either 1107.8 pfu/ml or more than 1900000 pfu/ml) from two milk-borne TBE virus epidemics for inoculation of 5 l goat milk. Samples of fresh raw goat milk was incubated at either 63°C for 10 min or at 72°C for 15 s, immediately cooled on ice and then, 25 µg samples were used to inoculate suckling mice. The rest was kept at 4°C and 25 µg samples were taken out every 5 days and used to inoculate mice.
Both pasteurization procedures eliminated all infective virus particles from the milk samples. A lower amount of virus survived in unpasteurized milk for 5 to 10 days, while a higher amount of virus for 20 to 25 days.
Cheese was made from three types of goat milk, i) control, not infected with TBE virus, ii) infected with TBE virus titer similar to milk shed by naturally infected goats, iii) infected with 180 times higher titer. Four types of cheese were made, i), natural (not salty), ii) natural spicy, iii) salty, iv) spiced salty. Salt treatment (25wt%) inactivated the TBE virus in cheese, while spices did not inactivate the virus.
To avoid milk-borne TBE virus infections, only pasteurized milk should be consumed.