Abstract: Objective  To analyze the characteristics of serum antibody reactivity of cystic echinococcosis （CE） patients with different clinical status towards five native antigens obtained from Echinococcus granulosus （Eg）.  Methods  The protoscolex somatic soluble antigen （EgPS）, crude hydatid cyst fluid antigen （EgHF）, partially purified hydatid fluid antigen （Burstein′s antigen, EgBu）, adult somatic soluble antigen （EgAs） and the native antigen B （EgAgB） were prepared. 369 serum samples from CE patients and 281 sera samples from healthy individuals were examined for the antibodies against 5 native antigens with indirect ELISA. The serologic results were classified according to clinical status, and the statistical analyses were carried out to understand the relationship between the results of different antigen-ELISA and the clinical status of patients.  Results  The results of EgBu, EgAS and EgAgB-ELISA showed that the antibody positive rate in hepatic CE patients [74.1% （212/286）， 73.4% （210/286）, 63.6% （182/286）] was significantly higher than that of other groups （including renal CE and pelvic CE, 1/8, 2/8, 1/8）（P＜0.05）. Except EgAS, the S/N value of other groups examined by the rest four antigen-ELISA （EgPS: 3.10, EgHF: 2.40, EgBu: 1.60, EgAgB: 2.38) was also significantly lower than that of hepatic CE patients （3.73, 3.65, 4.40, and 3.61） （P＜0.05）. EgBu, EgAS and EgAgB-ELISA results showed that the antibody positive rate in sera of recurrent CE patients [82.4% （150/182）, 86.3% （157/182）, 70.9% （129/182）] and the S/N value （5.54, 3.23, 3.75） were significantly higher than that of primary patients [positive rate: 67.4% （126/187）; 63.6% （119/187）; 57.2% （107/187）; S/N value: 4.20, 2.70, 3.75] （P＜0.05）. The S/N value detected by EgPS-ELISA and the positive rate examined by EgAgB-ELISA significantly increased with the increasing of the number of operations （P＜0.05）, reached 4.23 and 91.7% （11/12）, respectively, in the patients with ≥4 times of operations. The positive rate and S/N value of EgAS-ELISA and EgAgB-ELISA increased with the number of hydatid cysts in patients （P＜0.05）, reached 90.5% （19/21）, 76.2% （16/21）, and 3.97, 4.42, respectively, in patients with at least 4 cysts. Among the five antigen-ELISA, the positive rate increased with the cyst diameter （P＞0.05）. The S/N value of EgHF-ELISA and EgAS-ELISA increased significantly with the cyst diameter （P＜0.05）, reached 3.66 and 3.69, respectively, when the cyst diameter was ≥15.1 cm. ROC analysis result showed that among the 5 native antigen-ELISA, the AUCROC was highest in patients with cysts at CE2 stage （EgPS: 0.988±0.009, EgHF: 0.957±0.013, EgBu: 0.969±0.011, EgAs: 0.910±0.024, EgAgB: 0.894±0.021）, EgAgB-ELISA presented the lowest AUCROC of 0.267±0.031 in patients with cysts at CE5 stage. Except EgAgB, the positive rate of another 4 antigen-ELISA in detection of patients with cysts at CE 2 stage [EgPS: 97.2% （69/71）, EgHF: 93.0% （66/71）, EgBu: 88.7% （63/71）, EgAs: 85.9% （61/71）] was slightly higher than that of the patients with cysts at CE1 stage, and then promptly reduced in patients with cysts at CE5 stage （EgPS: 56.3%, EgHF: 43.8%, EgBu: 12.5%, EgAs: 12.5%）. In the patients with cysts at CE5 stage, the S/N value of the five antigen-ELISA was lowest （EgPS: 2.29, EgHF: 1.50, EgBu: 1.11, EgAs: 0.78, and EgAgB: 1.11）.  Conclusion  Compared with the other three antigens, the EgPS and EgAgB antigens have higher antigenicity, sensitivity, and specificity. The sera of hepatic CE patients are more reactive to the five native antigens than the other clinical types.

Key words: Echinococcus granulosus, Native antigen, Enzyme-linked immunosorbent assay, Diagnostic performance, Clinical analysis, Cystic echinococcosis