Decline of maternal antibodies to plague in Norway rats.

The decline of maternal antibodies to the fraciton I antigen of Yersinia pestis was investigated in newly weaned Rattus norvegicus obtained from dams vaccinated with strain EV76(51F) of Y. pestis. IHA titre decreased by 50% each 7-3 days and CF titre declined 50% each 10-0 days in young rats. An analysis of available data indicated that maternal IHA and CF antibodies could persist to 3 months of age. Therefore, positive serologic reactions in young R. norvegicus, detected in the course of serological surveys, could be the result either of active immunization after exposure to the plague bacillus or of transient passive immunization (i.e. maternal antibody).