Wallenhammar et al.
Revealing new tick-borne encephalitis virus foci by screening antibodies in sheep milk
Parasit Vectors 2020, 13:185
Over the last 15 years, the number of annual TBE cases in Sweden has increased from 174 in 2004 to 369 in 2019. Örebro county is one of the regions in Sweden where new TBE foci have been documented and where the incidence increased from 0.37 per 100,000 inhabitants in 2004 to 3.97 in 2019. In order to detect new TBE foci, milk from goats and sheep has been collected during 2017-2018 and analyzed for TBE virus specific antibodies. Sample collection was preferentially carried out near probable places of infection – where patients knew or suspected to be bitten by ticks. In total, 19/264 (7.2%) of colostrum samples were TBE antibody positive using an ELISA. The specificity of the ELISA results was confirmed by western blot analyses and by neutralization assay.
The stability of TBEV was analyzed by spiking milk and colostrum with 105 TBEV focus forming units and incubated at different temperatures. TBEV was stable at 4 °C for a couple of days, but gradually lost activity when incubated 24 to 72 hours at room temperature or 37 °C. TBEV was completely inactivated by pasteurization treatment (72 °C for 15 s), emphasizing the importance of pasteurization prior to consumption.
The authors concluded that milk from sheep is promising as a sentinel, particularly as sheep graze in small enclosed pasturage areas of limited size. New TBE foci could be identified located in Örebro county.