Manticore was one of few planets where a virus capable of seriously attacking humans existed. The primary exploration company, Franchot et Fils, had not discovered its presence, and thus the colonists of the colonial expedition to Manticore had no knowledge of it when they arrived.
History of the outbreak
The "Plague" was first discovered on Manticore in 1464 PD, but was not considered a serious health risk in its original form. However, in 1480 PD, after persistently resisting efforts to simply erradicate it and be done with it, the virus suddenly mutated into an extremely lethal form and the death toll soared within months. In 1482 PD, the Plague jumped quarantine from Manticore to the neighboring colony world of Sphinx.
In 1484 PD, an effective vaccine was developed. Soon, new immigration policies to attract the needed replacement population were debated. In the next two years, aided immigration was proposed and the colony transformed itself into the Star Kingdom of Manticore, with a new constitution adopted as a preliminary to aided immigration.
In 1487 PD, the virus mutated a second time, rendering the original vaccine ineffective; the plans for assisted immigration were shelved temporarily, but taken up again two years later as Manticore's manpower needs became critical. A few hardy souls accepted the invitation.
A new effective vaccine against the second mutation was finally developed in 1496 PD, and aided immigration numbers soon soared. The Plague was "thrown back on the defensive", but persisted in isolated pockets and outbursts for several years. The "Plague Years" did not officially end till 1510 PD, when the government announced the eradication of the virus in the Star Kingdom. (SK1, Tech Bu9)
The final outbreak occurred in 1510 PD on Sphinx, but stringent quarantine contained the outbreak to an isolated geographical area on the planet. (SK4)
The social and political consequences of the Plague were enormous: due to the loss of a majority of the population, the surviving Manticorans had to invite new settlers to help rebuild their colony. However, they feared to lose too much influence on the world they had purchased for 5.75 billion EuroDollars if thousands of new colonists arrived.
The solution was re-writing the Manticoran constitution: the original colonists transformed their star nation into a constitutional monarchy under the leadership of Roger Winton, now King Roger I of the Star Kingdom of Manticore. MCT shareholders purchased vast areas of land and established themselves as the Manticoran peerage, thus assuring their continued domination of the planet and its society. (UHH)
The aided immigration policy was officially ended in 1541 PD. (Tech Bu9)