Selenium poisoning in swine in southern Brazil

摘要

> face="verdana" size="2">Two outbreaks of poisoning by selenium in swine in southern Brazil are described. Piglets were affected in the post-weaning period, between 27 and 22 days, with mortality rates ranging from 16% to 15.3% (Outbreak 1 and 2 respectively). The pigs had focal symmetrical poliomielomalacia and hoof lesions, which were initially characterized by a reddish line at the coronary band that evolved in surviving pigs to release of the hooves. Clinical signs were observed after six days (Outbreak 1) and 30h (Outbreak 2) after the introduction of feed with high selenium content. The appearance of the signs was abrupt, characterized by gait and progressing to paralysis of the hind limbs and later to tetraparesis. Macroscopically, in some animals there were yellow circular foci with darker areas restricted to the ventral horn of the gray matter in the cervical and lumbar intumescence. Microscopically, these areas correspond to gray matter malacia, characterized by microcavitation, neuronal loss, chromatolysis, neuronophagia, infiltrating Gitter cells, microgliosis, Alzheimer’s type II astrocytes and proliferation of endothelial cells which were labeled by immunohistochemistry (IHC) as von Willebrand factor. Also in the second outbreak, two pigs showed diffuse vacuolation of the cytoplasm of neurons and in one pig  gemistocytic astrocytes were observed. In IHC for GFAP astrocytosis and astrogliosis was observed. Besides those spinal changes in two pigs symmetrical polioencephalomalacia in the brainstem was found. In feed samples, 3.38ppm (Outbreak 1) and 154ppm (Outbreak 2) of Se/kg were detected, and in liver samples higher dosages than 3.34ppm (range from 3.34 to 10ppm) were found. In Outbreak 2, 44 days after the withdrawal of the diet, the euthanasia of six pigs was performed to monitor liver selenium levels (two controls and four surviving pigs per outbreak); all had normal levels of selenium in the liver.