Two Chinese companies and an American importer have been indicted on charges of intentionally defrauding and misleading American manufacturers about poisonous ingredients used in pet food last year.

Tainted wheat gluten, used as an ingredient in moist pet food, killed at least 16 dogs and cats, sickened thousands of others and led to one of the biggest pet food recalls in U.S. history, involving companies like Procter & Gamble and Menu Foods. It was a prelude to scores of other recalls of Chinese-made products last year, including tires, fish, children's jewelry and toys.

The U.S. federal indictment on Wednesday, citing e-mail traffic between the Chinese manufacturer and the American importer, says the importer of the tainted ingredient knew it was being mislabeled to avoid inspection.

The case resulted from a long investigation by the U.S. Food and Drug Administration and was filed by the U.S. federal prosecutor's office in Kansas City, Missouri, which was the port of entry for the tainted wheat gluten.

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