Plague / Epidemic
The "Double Plague", appearing almost simultaneously on 19 widely spaced worlds (on six different plots) was so-called because it affected only adult human males (causing pneumonia-like symptoms) and in utero humans (causing spontaneous stillbirth abortions). It was initially not recognized as a single pathogen, and no apparent vector could be identified.
The Intercolonial Health Council investigation team eventually identified the source of infection as a group of largely asymptomatic carriers who had attended a Trade Fair on Aynelram, departing from there on more than a dozen vessels. The team had great difficulty identifying the pathogen, but a breakthrough came when a Strill medical researcher noted that a number of characteristics of the pathogen resembled those of a pathogen causing a rare syndrome that affected strill of certain hearth lineages. The identification of the sporulated paravirus was the needed breakthrough and the outbreak was controlled within 15 years.