EPIZOOTIOLOGICAL STUDIES OF HANTAVIRUS INFECTION AMONG URBAN RATS IN HOKKAIDO, JAPAN - EVIDENCES FOR THE PERSISTENT INFECTION FROM THE SERO-EPIZOOTIOLOGICAL SURVEYS AND ANTIGENIC CHARACTERIZATIONS OF HANTAVIRUS ISOLATES

Epizootiological studies of hantavirus infection among urban rats were carried out through the surveys repeated 11 times at the same dumping ground area in 1983 to 1988. A total of 279 rats (Rattus norvegicus) were captured during the surveys. Sero-positive animals to hantavirus strain SR-11 were detected in all the surveys. Overall positive rate o f rats 6 months old or more (94/128, 73.4%) was significantly higher t han that of younger rats (23/151, 15.2%, x2 = 96.4, P<0.001). Therefor e, age dependent acquisition of hantavirus infection among rats was co nfirmed. Seven hantavirus strains, KI-83-262 (August, in 1983, designa ted as strain KI-262 in our previous report (2)), KI-85-1 and 85-2 (Ju ly in 1985), KI-88-4, 88-11, 88-15 and 88-24 (October, 1988) were isol ated from lung tissues of adult rats which have high titers of neutral izing antibody. Although the serum specimens of virus carrier rats neu tralized the infectivity of all the KI isolates, no apparent antigenic change in the isolates was detected by indirect immunofluorescent ant ibody (IFA) assay using polyclonal and monoclonal antibodies (MAbs) re gardless of isolation years. However, neutralization test showed sligh t difference of antigenicity among KI strains. These results epizootio logically confirmed that hantavirus infected persistently among urban rats in a presence of neutralizing antibody.