From Halopedia, the Halo wiki
In 2538, there was an outbreak of disease at the Barugi Preparatory Academy. The illness was caused by a protozoal lifeform discovered on the planet termed asteroidea merozoite. It took only thirty hours for ten thousand people at the school to be infected. All but nine died shortly after. These nine were all partially resistant to being infected thanks to mutations they had that resulted in variants of thalassemia. Six with delta-beta thalassemia survived for years before finally succumbing to the asteroidea but those with gamma-thalessemia from a novel mutation did not suffer any adverse consequences whatsoever. These three survivors were Kerbasi Tuwa, the medical officer of the academy, and his two children, Catalin and Yuso. The devastation wrought by the infection caused the academy to be shut down and by 2541, the entire planet was placed under biohazard quarantine (BQ). This entailed encircling Barugi with a net of thermonuclear Hornet mines and blockade beacons that would alert any vessels that showed an intention to approach. The Barugi Incident was first made a matter of public record around a year after it occurred but in late 2553 it was mysteriously classified and compartmentalized.
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