Epidemiology and pathology of a tetrachlorodibenzodioxin poisoning episode.

We describe epidemiological and laboratory investigation of a poisoning outbreak that involved three riding areas and killed fifty-seven horses, five colts, and numerous other animals. The outbreak was traced to the spraying of the areas with salvage oil contaminated with tetrachlorodibenzodioxin, trichlorophenol, and polychlorinated biphenyls. The contamination of the salvage oil resulted from the improper disposal of toxic industrial waste. In the tissues of the horses available for study, the most prominent lesion was a centrilobular fibrosis of the liver that arose in the wall of the central veins. This lesion resembled the chronic form of veno-occlusive disease of the liver in humans.