Experimental infection of goats with tick-borne encephalitis virus and the possibilities to prevent virus transmission by raw goat milk.

OBJECTIVES The aim of this work was to study the tick-borne encephalitis virus (TBEV) infection of goats and the possibilities to prevent human milk-borne infections either by immunizing animals or the heat treatment of milk. METHODS An experiment was conducted with 20 milking goats. Ten goats (half of them immunized) were challenged with live TBEV and 10 were left uninfected. Clinical signs and body temperatures of the animals were recorded and milk samples were collected daily. The presence of viral RNA and infectious virions in milk were detected by RT-PCR and intracerebral inoculation of suckling mice, respectively. Milk samples containing infectious virions were subjected to various heat treatment conditions and retested afterwards to assess the effect on infectivity. RESULTS The infected goats did not show any clinical signs or fever compared to uninfected ones. Infectious virions were detected for 8-19 days from the milk samples (genome for 3-18 days by PCR) of infected goats. Immunized goats did not shed the virus. After heat treatment of the milk, the inoculated mice survived. CONCLUSIONS Goats shed the virus with their milk without showing any symptoms. Human milk-borne infections can be avoided both by immunizing goats and boiling/pasteurizing infected milk.