First Detection of Diffuse and Cerebral Theileria equi Infection in Neonatal Filly

Theileria equi is a tick-borne hemoparasite that may cause severe illness in equids. Intrauterine transmission of T. equi can occur and may result in abortion, stillbirth, or neonatal piroplasmosis of foals. Theileria equi and Babesia caballi infection are present in Israel, and subclinical infection with T. equi is highly prevalent. Here, we describe a case of a neonatal piroplasmosis that manifested with diffuse and cerebral T. equi infection. A Quarter Horse filly was born to a mare chronically infected with T. equi. The filly was born weak, could not stand and suckle, and had jaundice, pigmenturia, and died within hours from parturition. High T. equi parasitemia was detected in stained blood smears and imprint smears of different organs, further confirmed by polymerase chain reaction and sequence analysis. Intraerythrocytic parasites were also found in brain capillaries. Theileria equi infection in brain, to our knowledge, has never been reported previously. In vitro culture from the mare's blood enabled isolation of T. equi parasites. Phylogenetic analysis of the T. equi 18S rRNA gene from the dam's isolate and from the filly was identical and showed high similarity to previously reported T. equi sequences from Israel. Further studies should be done to determine whether the cerebral infection observed here was caused by the phenotypic particularities of the T. equi strain involved or resulted from intrinsic/unique characteristics of the immune responses elicited by the parasite in the infected foal.