Data obtained at the Bush Bush Forest field station in the Nariva Swamp, eastern Trinidad, indicated the continuous presence there of three Guamá-group agents—Bimiti, Catu, and Guamá—all apparently dependent on the same rodent host and vector populations. This suggested the possibility that the antigenic relation of these viruses might influence their epidemiology. The question was investigated by examining the effect of cross-immunity on circulating-virus levels in captive-reared Oryzomys laticeps and Zygodontomys brevicauda, two species of rodent that are natural hosts for these viruses.
Bimiti virus was circulated at lower levels in nonimmune Zygodontomys than were the other two viruses, and in cross-immunized Zygodontomys, Bimiti-virus levels were still lower and occasionally undetectable. Catu viremia reached high titers in both nonimmune Oryzomys and Zygodontomys, and even in cross-immunized rodents, titers often reached 2.4 to 3.3 log LD50. Guamá viremia in nonimmune Oryzomys and Zygodontomys was of the same order as that of Catu virus, but in cross-immunized rodents it was often completely suppressed.
These data suggest that when hosts are scarce Catu virus would be affected least and Guamá virus most. The experimental findings are compared with field observations.