Paulsen et al.
Experimental evidence for milk-borne transmission of tick-borne encephalitis virus to suckling lambs Doi/10.2139/ssm.543722, posted September 4, 2025
TBE virus is primarily transmitted to humans and animals through the bite of ticks. In addition, infection can occur by consumption of non-pasteurized milk and milk products from cows, sheep and goats. Milk-borne human infections are well documented (see e.g., Newsletter October 2022, Newsletter May 2022). However, experimental evidence for natural mother-to-offspring transmission in livestock remains scarce. An experimental study has been carried out to investigate the potential for TBE virus transmission from infected ewes to their suckling lambs via milk.
Eight ewes were subcutaneously infected with TBE virus strain Hochosterwitz (European subtype), when the lambs were one month old. In ewes, virus-specific RNA could be detected by RT-PCR in 3/8 serum samples on day 1 post-infection and 6/8 milk samples. In milk, TBE virus could be detected to day 18.
In lambs, TBE virus RNA was first detected in 1/16 serum samples on day 5, peaking at 9/16 on day 7, providing evidence of maternal virus transmission by milk.
TBE virus neutralizing antibodies were first detected in1/8 ewes on day 4 and in all ewes by day 7. In lambs, 11/16 were seropositive on day 13. The delay in antibody detection in lambs compared to their mothers indicates an active immune response following maternal transmission of TBE virus.
These findings provide direct experimental evidence that TBE virus can be transmitted via milk from ewes to their suckling lambs throughout the lactation period and highlight the relevance of milk-borne transmission for animal and human health in TBE-endemic regions.