Consistent patterns in the contact of domestic animals with tick-borne encephalitis virus in the eastern part of the Russian plain.

Hemagglutination inhibition test (HIT), neutralization test (NT) and complement fixation test (CFT) were used to serologically examine goats and cows in the southern area of the Kirov region and in the Udmurt ASSR. A total of 1641 sera of goats and 1414 sera of cows were examined for the presence on antibodies against tick-borne encephalitis virus. The tests showed a relatively intensive contact of goats and cows with TBE virus in the forests of the eastern part of the Russian Plain: HIT was positive in 27% of goat sera and 17% of cow sera, virus-neutralizing antibodies were detected in 25% of sera of goats and the positivity of CFT was recorded in 32% of goat sera and 29% of cow sera. The relative number of immune animals differed considerably from locality to locality. The localities with great numbers of immune animals were characterized by a distinct increase in the incidence of adult ticks Ixodes persulcatus. The immunization of domestic animals in the natural foci of infection was found to be season-dependent: the highest immunity rates were observed at the end of summer and in the autumn. The seasonal variations in animal immunity are demonstrated in detail on adult goats. Towards the spring time some serum antibodies, namely virus neutralizing antibodies and antihemagglutinins, tended to disappear in a certain number of animals. A similar, but somewhat different pattern of immunization could be observed in cows. In contrast to goats, cows appeared to be less susceptible to the tick-borne encephalitis virus infection, which was substantiated by both serologic data obtain in this study and the data reported in the literature. In the natural foci of TBE virus infection grazing goats and cows had the most intensive contact with the pathogenic agent in the first year of their lives.