Clinical Theileriosis in an Endangered Malayan Tapir Diagnosed Using a Molecular Technique with Successful Treatment and Recovery.

A 12-year-old female captive Malayan tapir (Tapirus indicus) in Thailand presented with clinical signs including depression, anorexia, pale mucous membrane, dark-brown urine, dry feces, and tick infestation. Hematological analysis revealed severe anemia (packed cell volume, PCV = 9%), and blood smear examination suggested blood parasite infection, which was subsequently confirmed as Theileria orientalis using PCR targeting the 18S rRNA gene and sequencing. Treatment consisted of the administration of diminazene aceturate (2.5 mg/kg, IM, q14days for three doses), whole-blood transfusion, fluid therapy, and other supportive care. Clinical improvement was observed within three days post-treatment, including normalization of urine color and a progressive increase in PCV. By Day 42, the PCV had returned to normal (33%), with no observed complications from the medication or blood transfusion. Further screening using PCR targeting the 18S rRNA gene of piroplasmid parasites revealed an 80% apparent prevalence of Theileria infection among sampled tapirs in the same facility, although only one individual exhibited clinical signs. These findings indicate that asymptomatic carriage of T. orientalis can be observed in tapirs and that clinical disease could emerge under stress or immunocompromised conditions. Given the presence of ticks and potential contact with other susceptible species in zoo settings, routine surveillance and preventive tick control are essential for mitigating transmission risks.