Immunoassay for Human Cystic Echinococcosis Evaluated

The early phase of infection is generally asymptomatic. Small, well encapsulated, viable cysts or old cysts with pseudosolid content typically do not induce major pathology, and patients may remain asymptomatic for years or even permanently. At present, no marker of cyst viability and therapy efficacy exists, and serology may remain positive for years even after successful therapy. As a consequence, long-term follow-up with imaging is required for the clinical management of patients.

A team of scientists led by those at Porto Conte Ricerche (Tramariglio, Italy) examined a total of 327 sera from CE patients with heterogeneous conditions for cyst stage, cyst number, organ localization, drug therapy, and surgical intervention, together with 253 sera from healthy controls. The sera were first analyzed by an enzyme-linked immunosorbent assay (ELISA) based on the antigen 5 (Ag5) preparation in two different setups and, in parallel, by a commercial ELISA routinely used in clinical laboratories for CE serodiagnosis.

Sera were tested in duplicate in the parasitology diagnostic laboratory by laboratory personnel with long standing experience in diagnostic parasitology, using a commercial ELISA test (RIDASCREEN Echinococcus immunoglobulin G (IgG), (R-Biopharm, Darmstadt, Germany) for the detection of Echinococcus specific total IgG. Tests were read at 450 nm in a spectrophotometer, and a Sample Index (SI) was calculated and interpreted for each serum. ELISA was considered positive for SI greater than 1.1, negative for SI less than 0.9, and border line for 0.9 ≤SI ≤1.1. Sera were tested with the Ag5 ELISAs based on their Ag5 enriched preparation following two alternative setups. The absorbance was read at 620 nm after one-hour incubation using a Tecan Sunrise microplate reader (Tecan Group, Ltd.; Männedorf, Switzerland).

The Ag5 ELISAs revealed different sensitivity, 88.3% versus 95.3%, without significant differences in specificity, 94.1% versus 92.5%, for the two setups, respectively. Moreover, possible relationships between the Ag5 ELISA absorbance results and clinical variables were investigated. Chi squared test, bivariate logistic regression and multiple regression analyses highlighted differences in the serology reactivity according to pharmacological treatment, cyst activity, and cyst number.

The authors concluded that the good diagnostic sensitivity and the high reliability of the Ag5 preparation method make this antigen a promising candidate for the serodiagnosis of CE. Further studies will be needed to evaluate the ability of our test to provide useful information on specific CE clinical traits. The study was published on March, 29, 2016, in the journal Public Library of Science Neglected Tropical Diseases.

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Porto Conte Ricerche
R-Biopharm 
Tecan Group, Ltd.