Ličková et al.
Alimentary infections by tick-borne encephalitis virus
Viruses. 2022; 14(1):56. doi: 10.3390/v14010056
TBE virus infections of humans mostly occur by tick bites and more than 22 tick species have been described which can be infected by this virus. Occasionally, additional transmission routes of the virus can occur like aerosol infections among laboratory workers, blood transfusion, organ transplantation, slaughtering of a viraemic goat, and transmission from a viraemic mother to her baby by breast milk. A Slovakian team has now reviewed what is known about the alimentary route of TBE virus infection.
Alimentary TBE virus infections, historically called biphasic milk fever, were described for the first time in the European part of Russia between 1947 and 1951. This form of disease was associated with the consumption of non-pasteurized milk from goats. Later, in 1951, one of the greatest outbreaks has been documented in Roznava (southern Slovakia) with at least 660 individuals infected of which 271 patients were hospitalized with meningoencephalitis.
Alimentary infections have been reported from 10 European countries: Slovakia, Croatia, Hungary, Czech Republic, Slovenia, Austria, Poland, Estonia, Germany, and Romania.
TBE virus can be inactivated by heat – 50% of infectivity are lost at 50°C within 10 min; however, in milk, conditions for complete inactivation may vary. Pasteurization of milk is usually carried out at 72°C for 15 s or at 63°C for 30 min. TBE virus remains infectious in gastric juice (pH 1.5 – 1.8) for up to two hours, and the virus is transmitted by the intestinal M cells of Peyer’s patches into the intestinal lymphoid tissue where primary replication occurs.
There are some differences in the clinical course of tick- vs. milk-borne TBE:
- With 3–4 days, the incubation time of an alimentary infection is shorter compared to 4–28 days after a tick bite.
- The biphasic form is more often seen in milk-borne TBE cases compared to tick-borne TBE.
- Milk-borne infections mostly are milder than tick-born infections.
- After an alimentary infection, the probability of recovery without neurological sequelae is higher.