Red maple leaf toxicosis causes acute hemolytic anemia due to oxidizing agents in the leaves. Exposure occurs in spring, summer, or fall. Horses usually become ill within a week of exposure, with the most common signs being urine discoloration, lethargy, inappetence, and colic. Wilted or dried leaves of Acer rubrum contain gallic acid and tannins that are thought to be responsible, although the mechanism of action is not certain. A diagnosis often requires known ingestion of the leaves. A metabolite, pyrogallol, produced by gastrointestinal bacteria may be the causative agent. The oxidative damage to erythrocytes can result in the formation of Heinz bodies, eccentrocytes, and methemoglobin. Increased destruction of damaged erythrocytes and the decreased oxygen-carrying capacity of methemoglobin can lead to tissue hypoxia, including bone marrow. Horses may present with mild-to-severe anemia and variable amounts of methemoglobin. Systemic inflammation is often present due to hemolysis and tissue damage. Complications include colic, fever, renal insufficiency, and laminitis. Treatment involves general supportive therapy with IV fluids, NSAIDs, whole blood products, and laminitis preventive measures. Despite therapy, this condition has a high mortality rate of more than 50%.
Read more about Clinical Hematology,
Urinalysis,
Hemolytic Anemia, and
Range Plants of Temperate North America in The Manuals.
References
Alward A, Corriher CA, Barton MH, et al. Red maple (Acer rubrum) leaf toxicosis in horses: a retrospective study of 32 cases. J Vet Intern Med. 2006 Sep-Oct;20(5):1197-201. doi: 10.1111/j.1939-1676.2006.tb00722.x
Agrawal K, Ebel JG, Altier C, Bischoff K. Identification of protoxins and a microbial basis for red maple (Acer rubrum) toxicosis in equines. J Vet Diagn Invest. 2013 Jan;25(1):112-9. doi: 10.1177/1040638714550183
Walter KM, Moore CE, Bozorgmanesh R, et al. Oxidant-induced damage to equine erythrocytes from exposure to Pistacia altlantica, Pistacia terebinthus, and Pistacia chinensis. J Vet Diagn Invest. 2014 Nov; 26(6):821-6. doi: 10.1177/1040638714550183
Back