Clinical occurrence of trypanosomiasis in Arabian horses from Ahvaz

Trypanosoma evansi (T. evansi) is a hemoprotozoan parasite affecting camels and equids, such as horses, mules, and donkeys, and is known to cause surra disease in these animals. Despite the worldwide distribution of T. evansi infections in equids, surra has not been reported in Arabian horses in Khuzestan Province for over 60 years. In September 2018, a 7-year-old Arabian mare was referred from a 10-horse farm in the suburbs of Ahvaz City. The mare presented with a history of weight loss, poor appetite, and proximity to a camel herd. Physical examination revealed a poor body condition score (BCS ≤ 3/9), pale conjunctival and oral mucosal membranes, dehydration, tachycardia, and fever. Other horses in the herd also exhibited gradual weight loss and hyporexia, with two fatalities reported. A hematologic examination of the referred mare showed leukopenia, severe anemia, and thrombocytopenia. Microscopic examination of a whole blood smear confirmed severe infection with Trypanosoma. PCR assessment of a blood sample further confirmed the infection with T. evansi. The referred mare and seven nonreferred patients from the herd received treatment with diminazene diaceturate (5 mg/kg, a single dose) and penicillin for 4 days. Unfortunately, the referred mare died despite the treatment, while the remaining nonreferred horses recovered. This report marks the first molecular diagnosis of surra in an Arabian horse in Khuzestan Province, highlighting the need for further investigation into surra as a re-emerging disease in this significant population of Arabian horses in the region.