[Porperties of a strain of Herpesvirus suis isolated in cases with various epizootologic and clinical courses of the disease].

A varying epizootologic, clinical and morphologic picture was established in studying the course of the disease on six pig-breeding farms. The isolated strains showed differences in their virulence, cultural properties and physicochemical behaviour. Two of them had lowered virulence, and one showed affinity to the respiratory organs which corresponded to the peculiarities and course of the disease. It is concluded that the interaction between the virulence of the strains and the herd immunity results in the varying epizootologic course of the disease.