Location: Poisonous Plant ResearchTitle: Poisonous plants affecting the central nervous system of horses in Brazil Author
Submitted to: Poisoning by Plants, Mycotoxins, and Related Toxins
Publication Type: Book / Chapter
Publication Acceptance Date: 8/11/2010
Publication Date: 5/1/2011
Citation: Lima, E.F., Riet-Correa, B., Riet-Correa, F., Medeiros, R.M.T., Gardner, D.R., Riet-Correa, G. 2011. Poisonous plants affecting the central nervous system of horses in Brazil. In: Riet-Correa, F., Pfister, J., Schild, A.L., Wierenga, T., editors. Poisoning by Plants, Mycotoxins, and Related Toxins. Cambridge, MA: CAB International. p. 290-4. Interpretive Summary: The well known diseases of the nervous system in horses in Brazil are rabies, equine eastern, Venezuelan, western virus encephalomyelitis and leukoencephalomalacia. However, there are also a number of poisonous plants found in Brazil that specifically affect the nervous system of horses. Those of most interest include Indigogera pascuori, Turbina cordata, Sida capinifolia, Equisetum spp, Bambusa vulgaris, Hypochaeris radicata, Crotalaria retusa and Senecio spp. The geographical regions of Brazil most affected by these species, the individual clinical signs observed and the toxic compounds found in the plants are described and discussed. It is important to know that poisonous plants may cause nervous signs in equines, what those plants are and the resulting clinical signs that are critical for a differential diagnosis with rabies, equine enecephalomyelitis and other diseases of the nervous system of horses.
Technical Abstract: Poisoning by Indigofera pascuori was recently reported in horses in the state of Roraima. It causes chronic signs of sleepiness, unsteady gait, severe ataxia, and progressive weight loss. Some animals are blind. Young horses are more affected than adults. After the end of plant consumption the animals can recover. In an experimental case the first clinical signs appeared 59 days after the start of ingestion. The only histologic lesion observed was Wallerian degeneration in some brain stem tracts. Turbina cordata in Northeastern Brazil and Sida carpinifolia in Southern Brazil contain swainsonine, and cause induced mannosidosis in horses. Poisoning by Equisetum spp. was reported in the 1940's in Minas Gerais, but new outbreaks have not been reported since. Clinical signs are characterized by weight loss, lethargy, staggers, unsteady gait, and ataxis; and are observed 3-6 weeks after the start of ingestion. The plant contains a thiaminase. The horses recovered if treated with daily administration of 100mg of thiamine, but when the animal is emaciated and recumbent, treatment can be ineffective. Poisoning by Bambusa valgaris f. vulgaris was reported from the state of Para, Northern Brazil. Clinical signs are somnolence, steady gait, ataxia and signs of impairment of cranial nerves. The clinical course is subacute or chronic and most horses recover after being removed from the pastures. Hypochaeris radicata causes stringhalt (high stepping with hyperflexion of the hind limb) in horses in the states of Rio Grande do Sul and Parana. Clinical signs are abnormal gait with involuntary flexing of the hocks of one or both hind legs. The disease is due to axonal degeneration of the peripheral nerves, and most horses recovered after they stopped eating the plant. The disease was experimentally reproduced by the administration of H. radicata. Crotalaria retusa and Senecio spp. cause hepatic encephalopathy in equines. Poisoning by C. retusa is the most important disease of the nervous system in equines in Northern Brazil. Knowing that some toxic plants cause nervous signs in equines is important for the differential diagnosis with rabies, equine encephalomyelitis and other diseases of the nervous system of horses.