Hemolytic Anemia in Horses Associated with Ingestion of Pistacia Leaves

A 6-year-old Peruvian Paso-Mustang cross mare was presented to the William R. Pritchard Veterinary Medical Teaching Hospital, University of California, Davis during the fall (October) with a 2-day history of lethargy and icterus. The mare was from a herd of 26 mares and 3 foals from which 5 mares had died (leaving 21) during the preceding 7 days. These mares had varying degrees of colic, ataxia, pigmenturia, pale and icteric mucous membranes, lethargy and inappetance; they died within 48 hours of initial signs. Three of the affected mares had been pyrexic with rectal temperatures ranging from 102 to 102.5 °F. Treatment with nonsteroidal anti-inflammatory medications and oral antimicrobials was initiated on the affected mares, with no improvement in clinical signs. The herd had been moved to the current property 6 months previously. It consisted of 40 acres of undulating land comprised of native woodland and a planted Pistacia orchard (containing P. atlantica, P. terebinthus, P. chinensis). Mares with suckling foals were housed in a separate corral and the remaining mares grazed the entire 40 acres and were supplemented with orchard grass hay. All affected horses were part of the latter group. The horses were provided with county irrigation water, which was piped to troughs, and they had access to the irrigation ditch directly. There were no recent changes in herd management or housing, except for felling of the Pistacia orchard shortly before the first horse developed clinical signs; the owner had witnessed the horses eating from trees that had been cut down. The same owner housed 11 stallions on a property 1.5 miles away where they were provided with well water and the same orchard grass hay. None of these horses, or the lactating mares who were housed separately and fed the same hay, exhibited any signs of illness. Physical examination revealed tachycardia (56 beats per minute) and icteric oral, ocular, and vulvar mucous membranes. Pertinent laboratory results are listed in Table 1. Many eccentrocytes were noted on the blood smear. The low hematocrit, presence of nucleated erythrocytes, increased RDW, and indirect hyperbilirubinemia are consistent with hemolytic anemia. The eccentrocytes are indicative of oxidative damage to hemoglobin and erythrocyte membrane proteins. A Coggins test and Babesia caballi and Theileria equi PCR results were negative. Leptospira antibody titers were not indicative of active infection (L. bratislava and L. icterohemorrhagiae titers were positive at 1 : 100, and L. Pomona, canicola, grippothyphosa and hardjo titers were negative). Serum was negative for nitrate, nitrite, monensin and lead, and trace minerals were within acceptable ranges except for an increased iron (3.9 ppm, reference range 0.8–2.5 ppm) consistent with hemolysis, and slightly decreased magnesium (15 ppm, reference range 18–35 ppm) consistent with reduced feed intake. Urinalysis revealed a specific gravity of 1.032, pH = 8, and proteinuria (150 mg/dL, reference range: 0 mg/dL), 6–8 erythrocytes/HPF (reference range 0–2/HPF), and hemoprotein 150 ery/lL (reference range 0 ery/lL) with no other important abnormalities. The urine was negative for the presence of myoglobin, indicating the hemoprotein present was because of From the Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA (Bozorgmanesh, Rhodes); the Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA (Magdesian); the Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA (Walter, Moore, Puschner); the California Animal Health and Food Safety Laboratory System, School of Veterinary Medicine, University of California, Davis, CA (Puschner, Woods); the Animal Medical Center, Auburn, CA (Torrisi); and the Arizona Equine Medical & Surgical Centre, Gilbert,AZ (Voss). The work was carried out at the William R. Pritchard Veterinary Medical Teaching Hospital and the Department of Molecular Biosciences, California Animal Health and Food Safety Laboratory System, School of Veterinary Medicine, University of California, Davis, CA; and Arizona Equine Hospital,1685 South Gilbert Road, Gilbert, AZ. The paper was not presented at any meetings. Corresponding author: K.G. Magdesian, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California–Davis, Davis, CA 95616; e-mail: kgmagdesian@vmth. ucdavis.edu. Submitted July 20, 2014; Revised September 29, 2014; Accepted November 25, 2014. Copyright © 2015 by the American College of Veterinary Internal Medicine DOI: 10.1111/jvim.12532 Abbreviations: