Differential diagnosis of theileriosis through blood smear examination and polymerase chain reaction in small ruminants from Pakistan

Abstract

Background: Ovine and caprine theileriosis is a tick-borne hemoprotozoan disease, caused by Theileria spp., responsible  for heavy economic losses in terms of high mortality and morbidity rates. Diagnosis of ovine theileriosis is  primarily based on clinical symptoms, microscopic screening of stained blood smears, and lymph node biopsy smears,  but the limitations of these detection methods against Theileria spp. infection limits their specificity.

Aim: To overcome  these limitations, the current study reports the differential diagnosis of theileriosis through a blood smear examination  and polymerase chain reaction (PCR) in small ruminants from Pakistan.

Methods: The study was conducted on 1,200  apparently healthy small ruminants (737 sheep and 463 goats). First, blood smears were screened for the presence of  Theileria piroplasms in red blood cells. Second, PCR amplification based on 18S rRNA gene was performed by using  primers specific to Theileria spp.

Results: Out of the 1,200 samples of examined blood smears, 100 animals (8.33%) were  found positive for Theileria species, which showed intra-erythrocytic bodies in the form of dot and comma shapes.  Amplification of the isolated DNA from randomly collected blood samples of 737 sheep and 463 goats showed  that an amplicon size of 1,098 bp was positive for Theileria spp. In total, 315 out of the 1,200 small ruminants examined  in this study were found positive for Theileria spp. DNA through PCR amplification. Notably, out of the 885 blood  samples negative by PCR amplification, only 15 blood samples were found positive by the blood smear test. Conversely,  230 blood samples that tested negative in the smear technique produced a specific band through PCR amplification.  Overall, the sensitivity and specificity rates were 26.98% and 98.31% for the blood smear method and 73.01% and 100%  for the PCR assay, respectively.

Conclusion: Our finding suggests that PCR is the gold standard method compared to the  conventional method of smear examination for the diagnosis of ovine and caprine theileriosis in Pakistan.