The isolation of a Hanta-like virus from rats in Hawaii

Abstract

Earlier studies in Hawaii by Diwan et al. (1985) detected antibody to Hantaan virus in rats and people although attempts to isolate an etiological agent were unsuccessful at that time. The purpose of this study was to confirm the serological evidence for a Hantaan related virus in Hawaii, to isolate the etiologic agent, characterize it, and determine its relationship to other hantaviruses. In this study 364/1272 (29%) feral rats, 163/420 (39%) laboratory rats, and 33/227 (14%) feral cats were found to have antibody to Hantaan virus (76-118) by indirect immunofluorescent antibody test (IFAT) at a titer of 1:32 or greater. Attempts to isolate virus from the lungs and spleen of seropositive rats were successful, and the virus was named Manoa virus. This study has demonstrated a widespread prevalence of antibody to Hantaan virus by IFAT among peridomestic and laboratory Rattus species and feral cats in Hawaii. The antibody is not typical of antibody to other rat-associated hantaviruses and has a unique cross reactive pattern to other known hantaviruses by IFAT. By western blot analysis, the antibody was non-reactive to the major Hantaan virus proteins but was weakly reactive to some minor proteins. Manoa virus is between 100 and 220 nm in size, it is deoxycholate sensitive, supernatant from infected monolayers contain 106 TCID/ml, and it causes mild cytopathic effect in Vero E-6 cells. Fine fluorescent cytoplasmic granules are detectable by IFAT early after inoculation, and they eventually fill the cytoplasm. Ultrastructurally there are numerous electron dense intracytoplasmic inclusions characteristic of the hantaviruses as well as numerous viral particles in thin section of infected Vero E-6 cells. Manoa virus, isolated from Hawaiian peridomestic and laboratory rats with antibody to Hantaan virus, is Hantavirus-like but has unique characteristics that differ from those of other known hantaviruses. The known rat associated hantaviruses are all very similar and are strains of Seoul virus. The basic characteristics of Manoa virus suggest that it is a bunyavirus and possibly a Hantavirus although it does not appear to fit in the Seoul virus subgroup of rat hantaviruses. Current investigations suggest that Manoa virus may be a new and unique Hantavirus.