Seneciosis is the main cause of livestock mortality due to poisonous plants in the State of Rio Grande do Sul, Brazil. This paper presents epidemiological data of 24 outbreaks in cattle and one in horses, diagnosed by the Regional Diagnostic Laboratory at Pelotas University in southern Rio Grande do Sul, from 1998 to 2000. Additionally, data of 54 outbreaks which occurred in 1978-1997 were analyzed. The farms where outbreaks occurred in 1998-2000 were visited to obtain clinical and epidemiological data and to verify the presence of Senecio spp. Eleven outbreaks (45.83%) affected cattle up to 3 years of age, and 13 (54.16%) cattle over 3 years. Nine (37.5%) outbreaks affected females and 15 (62.5%) males. Ten (41.66%) outbreaks occurred in spring, 4 (16.66%) in summer, 5 (20.83%) in autumn, and 5 (20.83%) in winter. Morbidity rate was estimated with 4.92% and case fatality with 95.59%. The predomionating Senecio species were S. brasiliensis on 12 farms (57.14%), S. selloi on 10 (47.61%), S. oxyphyllus on 6 (28.57%), S. heterotrichius on 3 (14.28%), and S. leptolobus on 1 farm (4.76%). The main clinical signs were progressive emaciation, incoordination, diarrhea, tenesmus, rectal prolapse and aggressiveness. The clinical manifestation periods of affected cattle observed during the farm visits, or of cattle sent for post-mortem examination,were 24-96 hours in 4 outbreaks (16.66%), 4-7 days in 7 (29.16%), 1-2 weeks in 4 (16.66%), 2-3 weeks in 2 (8.33%), 1-2 months in 2 (8.33%), and 2-3 months in 1 outbreak (4.16%). In 4 outbreaks (16.66%) the clinical manifestation period was not established. In outbreaks with longer clinical manifestation periods some animals showed photosensitization. The main necropsy findings were a hard and enlarged liver, distended gall bladder, edema of the mesenterium and abomasum, and increased amount of liquid in the cavities. Histopathological findings were fibroplasia, megalocytosis and biliary ductal proliferation of the liver, and spongy degeneration of the cerebral white matter. Samples of different Senecio species, in different seasons, were analyzed for detection of pyrrolizidine alkaloids (PAs) by thin layer chromatography. Retrorsine was found in Senecio brasiliensis, S. heterotrichius, S. selloi and S. oxyphyllus. In S. brasiliensis and S. heterotrichius one and two more non-identified PAs were detected, respectively. The total PAs concentration by spectrophotometric method was 0.25% for S. brasiliensis, 0.19% for S. heterotrichius, 0.03% for S. oxyphyllus, and 0.03% for S. selloi. The highest PAs concentration occurred in winter (June/July). No alkaloids were found in samples of S. leptolobus. These results show that S. brasiliensis is the most important cause of seneciosis in southern Rio Grande do Sul. Additional data obtained dealt with 54 outbreaks of PAs poisoning in 1978-1997. During this period, 7 outbreaks (12.96%) affected cattle up to 3 years of age, 39 (72.22%) cattle over 3 years, and 3 outbreaks (5.55%) affected cattle of different ages. In 5 outbreaks (9.25%) the age was not informed. Seven outbreaks (12.96%) affected males, 39 (72.22%) females, 3 (5.55%) both sexes, and in 5 outbreaks (9.25%) the sex was not informed. Twenty-three outbreaks (42.59%) occurred in spring, 9 (16.66%) in summer, 9 (16.66%) in autumn, and 13 (24.07%) in winter. The greater number of outbreaks during 1998-2000 (24 outbreaks in 3 years) in regard to 1978-1997 (54 outbreaks in 20 years) is probably due to a decrease of more than 50% in the number of sheep in the region.
Seneciosis; epidemiology; poisonous plants; Senecio spp; Asteraceae; pyrrolizidine alkaloids; cattle
