The report by Dr. Mackenzie suggests that hemorrhagic fever in San Joaquín was firmly established in the town by early 1963, that the great majority of humans were susceptible to infection, and that movement of the virus through the population was slow but inexorable. The significance of the rodent, Calomys callosus, demonstrated by the experimental control study, has been indicated by Dr. Kuns. The gathering impression is that the human disease pattern was the result of a mechanism with the following attributes: (1) sustained virus infection in some form of fauna, be it human, vertebrate or arthropod, and (2) relative inefficiency of transmission to susceptible humans. Using the techniques for detection of Machupo virus infection outlined by Dr. Webb, we have now obtained some information that implies, if it does not prove, what this mechanism may be.
It has been suggested that direct human-to-human transmission, though possible, was probably not the principal method of disease dissemination.