PCR-based diagnosis of surra in equines targeting RoTat 1.2 VSG gene

Trypanosomosis caused by Trypanosoma evansi is an important disease affecting equines. Low parasitaemia often prevents the conventional microscopic and serological techniques from detecting carrier status of T. evansi infections. Polymerase chain reaction (PCR)-based diagnostic tool targeting the VSG gene is highly specific and sensitive for diagnosis of surra in all the stages of infection. A PCR based assay was therefore laboratory standardized and field tested for rapid and accurate detection of T. evansi in equines. Oligonucleotide primers (RoTat VSG F/R) were custom designed and used for PCR amplification of a 681-bp amplicons. Amplification products were not detected when the PCR-based assay was applied to DNA from other blood parasites including Theileria annulata and Babesia bigemina. The PCR assay was field-tested on 86 random cases of equines and compared with the gold standard test, thin blood smear examination. Results revealed PCR was able to detect trypanosomosis even in those cases which blood smear examination failed to detect parasites. A 100 percent sensitivity and high level of specificity (93.98%) was recorded in the PCR assay. The PCR assay described provides a valuable tool to study the epidemiology of T. evansi infection in equines and other susceptible animal populations.