Cystic echinococcosis (CE) is an important helminthic zoonotic disease caused by the Echinococcus granulosus complex. In humans, CE is a chronic disease driven by the growth of echinococcal cysts in different organs. Prognosis of this disease depends on multiple factors, including location, number, size, and stage of the cysts, making CE a disease of complex management. CE is usually asymptomatic for years and attracts limited attention from funding organizations and health authorities. For this reason, only experts' recommendations are available but no evidence-based conclusions have been drawn for CE clinical management. One of those pitfalls refers to the lack of evidence to support the use of serological tools for the diagnosis and follow-up of CE patients. In this respect, crude antigens are used to detect specific antibodies in patients, giving rise to false positive results. The advent of molecular techniques allowing the production of recombinant proteins has provided a number of candidate antigens that could overcome the problems associated with the use of crude parasite extracts in the serological assays. In this review, we present the last advances in this field, proposing the use of serology to support cyst stage-specific diagnosis and follow-up.

A standardized test for the serodiagnosis of human cystic echinococcosis (CE) is still needed, because of the low specificity and sensitivity of the currently available commercial tools and the lack of proper evaluation of the existing recombinant antigens. In a previous work, we defined the new ELISA-B2t diagnostic tool for the detection of specific IgGs in CE patients, which showed high sensitivity and specificity, and was useful in monitoring the clinical evolution of surgically treated CE patients. Nevertheless, this recombinant antigen gave rise to false-negative results in a percentage of CE patients. Therefore, in an attempt to improve its sensitivity, we constructed B2t-derived recombinant antigens with two, four and eight tandem repeat of B2t units, and tested them by ELISA on serum samples of CE patients and patients with related parasites. The best diagnostic values were obtained with the two tandem repeat 2B2t antigen. The influence of several clinical variables on the performance of the tests was also evaluated. Finally, the diagnostic performance of the 2B2t-ELISA was compared with that of an indirect haemagglutination commercial test. The 2B2t recombinant antigen performed better than the HF and B2t antigens, and the IHA commercial kit. Therefore, this new 2B2t-ELISA is a promising candidate test for the serodiagnosis of CE in clinical settings.

Four different recombinant antigens derived from Echinococcus granulosus, designated B1t, B2t, E14t, and C317, were tested with enzyme-linked immunosorbent assays (ELISAs) for the detection of specific immunoglobulin G (IgG) in patients with unilocular hydatid disease (UHD). The results were compared to those obtained with hydatid fluid and were subjected to receiver operator characteristic analysis. The diagnostic performance of the above-listed proteins was defined with respect to their specificity, sensitivity, and predictive values (PV); the influence of cyst location; and usefulness in the follow-up of surgical treatment for UHD and in the determination of whether or not patients have been surgically cured of UHD. The best diagnostic results were obtained with the anti-B2t IgG ELISA, with 91.2% sensitivity, 93% specificity, and high positive and negative PV (89.4 and 94.2, respectively). In addition, this diagnostic tool proved to be useful for the follow-up of surgically treated UHD patients. The anti-B2t IgG ELISA may find an application in the serodiagnosis of UHD in clinical laboratories.Human unilocular hydatid disease (UHD) is caused by the larvae of the tapeworm Echinococcus granulosus. The diagnosis of UHD usually is approached by applying an imaging technique. In 2003, the World Health Organization Informal Working Group on Echinococcosis (28) proposed the use of ultrasonography (US) as the imaging technique of choice in order to promote uniform standards of UHD diagnosis and follow-up. It also was pointed out that US images suspected of showing UHD should be examined by alternative diagnostic methods, such as serological techniques (28). In addition, for pulmonary UHD, US is unhelpful in most cases, unless the cysts are close to the pleural surface (12). Currently, the preferred UHD immunodiagnostic techniques used in clinical practice detect serum immunoglobulin G (IgG) against crude parasite extracts (mainly hydatid fluid [HF]), most commonly by hemagglutination and enzyme-linked immunosorbent assay (ELISA) (26). However, HF cannot be standardized and gives rise to relatively frequent false-positive and false-negative results (3, 15). Moreover, HF is not useful for the follow-up of UHD, since the levels of specific (IgG) antibodies against HF remain high over long periods of time after curing (19). Many authors have attempted to find alternative antigens to improve UHD serodiagnosis and follow-up. Thus, purified, recombinant antigens and synthetic peptides, mainly derived from two parasite molecules (antigen B [AgB] and antigen 5 [Ag5]), have been applied, with various levels of success. Specifically, antigens derived from AgB have been shown to be good candidates for UHD serodiagnosis (3). AgB is formed by several subunits (6), two of which (AgB1 and AgB2) have been produced as recombinant molecules. Both AgB1 and AgB2 have been tested for the detection of specific antibodies, although authors disagree about the diagnostic performance of these two subunits (11,20,27). Thus, the standardization ...