On the morning of April 12, the farmworker woke up struggling to breathe and delirious with fever. Jiaai Zeng had spent the past month working nonstop at a marijuana farm in Oklahoma run by fellow Chinese immigrants. The job was brutal, the 57-year-old had told relatives in New York. He said his bosses made him labor up to 15 hours a day in the blast-furnace heat of a greenhouse.