Evaluation of an in-house enzyme linked immuonosorbent assay (ELISA) for detection of anti-Oestrus ovis antibodies in sheep

Oestrus ovis is a fly with cosmopolitan dispersion. Its zoonotic larvae are one of the important causes of myiasis in both humans and sheep. This study was conducted in first time in Iran to evaluate the efficiency of ELISA for diagnosis of Oestrus ovis infection in sheep. The assay was evaluated by testing somatic (S) and excretory-secretory (ES) antigens derived from the second and third stage larvae of the parasite (L2, L3) collected of the study area. Somatic/excretory-secretory antigens of the larvae were prepared by ultrasonic homogenization of the larvae and culturing of them in RRMI-1640 respectively. After determining the appropriate dilutions of antigens, conjugate and serum, a total of 71 samples of positive serum and 61 negative sera (from indoor lambs) were evaluated by ELISA method and then the results were compared with the results of abattoir study. The results of this study revealed that proper dilutions of SL2, SL3, conjugate and serums for the ELISA were (1:46), (1:30), (1:8000) and (1:10) while also of ESL2, ESL3, conjugate and sera were 1:9, 1:6, 1:4000, 1:5, respectively. The sensitivity and specificity rates of the assay with the SL2 and SL3 were 90.1 %, 89.1 %; 54.9 %, 96.9 % and with ESL2 and ESL3, 74.6 %, 93.8 %; and 74.6 %, 73.4 %, respectively. Positive / negative predictive values of the test with the SL2 and SL3 were 90.1 %, 95.1 % and 89.1 %, 66.0 % while with the ESL2 and ESL3 were 93.0 %, 75.7 % and 76.9 %, 72.3 %, respectively. The results showed that L2 was more sensitive to ELISA test than that of L3, furthermore, L2 somatic antigens were more efficient than that of its secretory excretory antigens, and therefore, its antigens can be used in serological diagnosis and epidemiological studies of oestrosis in sheep.