Scrapie is the ovine form of the transmissible spongiform encephalopathies. The understanding of scrapie as a slow viral disease was developed through an international scientific dialogue during the first half of the twentieth century. British investigators used epidemiological and experimental observations to define its very long incubation period before the appearance of symptoms. This enabled French researchers to prove scrapie could be transmitted from sick to healthy animals and allowed them to define the etiological agent as an ultramicroscopic, filterable virus. Following this, an Icelandic scientist, Bjorn Sigurdsson, investigated two other ovine diseases characterized by unusually long periods between contracting the agent and actually developing symptoms of the illness. Because he was able to show the disease was actually present during this time, he reimagined the incubation period as one of latency with subclinical manifestations: the disease was simply progressing very slowly without obvious signs. Thus, Sigurdsson first articulated the concept of the slow viral infection to explain this new understanding of certain transmissible diseases. During the 1950s and 60s, researchers in New Guinea investigated the nature of an entirely new disease, kuru. They ultimately conceptualized it as a slow viral disease transmissible from one host to another. All of this research, taken together, illustrates the way twentieth century scientists worked to conceptualize the etiology of poorly understood diseases. Moreover, this decades-long scientific dialogue nicely illustrates how our understanding of, and appreciation for, the scientific construction of biomedical knowledge complements the more commonly portrayed social construction of scientific knowledge.
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