Immunological detection of human and camel cystic echinococcosis using different antigens of hydatid cyst fluid, protoscoleces, and germinal layers

BACKGROUND AND AIM

Cystic echinococcosis (CE)/hydatidosis is one of the most prevalent neglected zoonotic diseases. It is initially asymptomatic and does not produce any clinical signs until the cyst becomes enlarged, causing localized pressure on internal organs and tissues. Therefore, the detection of Echinococcus granulosus antibodies is highly essential. This study evaluated the antigens of hydatid cyst fluid, protoscoleces, and germinal layers for efficient immunological diagnosis of CE in humans and camels.

MATERIALS AND METHODS

Hydatid cyst fluid (FLc), protoscoleces (Psc), and the germinal layer (GLc) antigens were prepared from camel-lung hydatid cysts. In the same way, hydatid cyst fluid (FLh) and protoscoleces (Psh) antigens from human-liver cyst aspirate were produced. The comparative immunodiagnostic efficacy of the prepared antigens was verified using indirect enzyme-linked immunosorbent assay (ELISA), SDS-PAGE, and immunoblotting.

RESULTS

ELISA proves that FLc and GLc antigens were higher than FLh and Psh antigens. This shows that binding reactivity in naturally infected human sera, camel sera, and Psc is the most potent, exhibiting 100% sensitivity with 78.26% and 76.47% specificity in camel and human sera, respectively. The CE prevalence using diagnostic Psc was 54.79% and 61.32% in tested human and camel sera, respectively. The electrophoretic profiles of all shared antigens showed similarities at 52, 41, and 22 kDa. Immunoblotting demonstrated common immune-reactive bands in all antigen types at 52 and 41 kDa against positive human and camel sera.

CONCLUSION

This immunological study introduces camel hydatid cyst Psc as a potent diagnostic antigen and new immune-reactive fractions of 52 and 41 kDa for diagnosing hydatidosis in humans and camels.

Using specific synthetic peptide (p176) derived AgB 8/1-kDa accompanied by modified patient's sera: a novel hypothesis to follow-up of Cystic echinococcosis after surgery

Cystic echinococcosis (CE) is caused by the larval stage of the tapeworm Echinococcus granulosus. Until now, CE does not have an effective follow-up after surgery. To date, CE follow-up is conducted based on either antibody or antigen detection assays by double antibody sandwich ELISA. Unlike antigen detection, antibodies to imply exposure to an Echinococcus infection while their titration could remain for a longer period (1-10years) after surgery. Likewise, antibody respond may be related to the location of a mature hydatid cyst. Antigen detection shows presence of CE infection, it is extremely important and necessary in follow-up of CE after surgery. The circulating antigen (CAg) titration decrease faster than circulating antibody (during 1-3weeks) after operation. Location of hydatid cyst in detecting antigen is affected less than antibody also. Regarding this subject, antigen detection has several limitations that lead to be used less in CE follow-up. Although, AgB 8/1-kDa subunit is considered as a principle and immunogenic CAg but sensitivity of CAg detection compared to with antibody has variable range, between 33% and 85% which owing to formation of circulating immune complexes (CICs) in result of antigen - antibody complex. The another problem is non using specific CAg (AgB 8/1-kDa subunit) for production of specific paratopes (rabbit hyper immune antiserum) against AgB 8/1-kDa which is used as capture (primary) antibody in double antibody sandwich ELISA assay. The designation of synthetic peptides from conserved regions of AgB 8/1-kDa can help to this problem. These regions (motifs) should be selected for allelic, dominant, immunogenic and conserved without any genetic variation. The first part of this hypothesis suggests which patient's sera should be treated with acidic buffers such as boric acid, acetic acid, glycine/HCl, polyethylene glycol (PEG) or combination of each of them accompanied by boiling patient's sera which causes breaking Ag-Ab complexes and in result of releasing AgB 8/1. These modifications are effective to releasing CAg from CIC. To date, the synthetic peptides have been widely used in CE serodiagnosis based on circulating antibody detection only. In second part of this hypothesis suggests the using synthetic peptide of p176 derived AgB 8/1-kDa subunit containing conserved specific epitopes for preparation of specific paratopes (rabbit hyper immune antiserum) based on CAg detection. So, there is no need any native antigens for preparation of non-specific rabbit hyper immune antiserum. These novel improvements can help to decrease the cross-reactivity with other parasitic diseases (specificity). Increasing antigen detection could make a chance in sensitivity of patient's sera and in result of the best and suitable tool for CE follow-up.

IgG4 detection of Echinococcus granulosus paramyosin is a useful diagnostic test for human hydatidosis

Hydatidosis is a public health problem in many parts of the world, and improvement in diagnosis of the disease is still being pursued. Protoscoleces of Echinococcus granulosus were isolated from hydatid cysts collected from naturally infected sheep slaughtered in abattoirs in Iran. Sonicated extract of protoscolex was subjected to two-dimensional gel electrophoresis and Western blot analysis. Primary antibodies were from serum samples from 130 hydatidosis patients, 38 individuals infected with other parasitic infections, and 30 healthy people, whereas peroxidase (HRP)-conjugated anti-human IgG and IgG4 were used as secondary antibodies. The recombinant form of the identified protein was produced and tested for its sensitivity and specificity for the detection of human hydatidosis. An antigenic band of ∼60 kDa was found to be sensitive (82%) and specific (100%) for the detection of hydatidosis when probed with anti-human IgG4-HRP, while the sensitivity and specificity were 33 and 100%, respectively, with anti-human IgG-HRP. By mass spectrometry, the band was identified as protoscolex tegument paramyosin. The sensitivity and specificity of full-length paramyosin-recombinant protein in IgG4 blots were found to be 86 and 98%, respectively. In conclusion, IgG4 detection of Echinococcus granulosus paramyosin was found to be useful for the diagnosis of human hydatidosis.

Immunology and immunodiagnosis of cystic echinococcosis: an update

Cystic echinococcosis (CE) is a cosmopolitan zoonosis caused by the larval cystic stage of the dog tapeworm Echinococcus granulosus. This complex multicellular pathogen produces various antigens which modulate the host immune response and promote parasite survival and development. The recent application of modern molecular and immunological approaches has revealed novel insights on the nature of the immune responses generated during the course of a hydatid infection, although many aspects of the Echinococcus-host interplay remain unexplored. This paper summarizes recent developments in our understanding of the immunology and diagnosis of echinococcosis, indicates areas where information is lacking, and suggests possible new strategies to improve serodiagnosis for practical application.

Usefulness of four different Echinococcus granulosus recombinant antigens for serodiagnosis of unilocular hydatid disease (UHD) and postsurgical follow-up of patients treated for UHD

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.

Development of a dipstick dye immunoassay for diagnosing hydatidosis

We have developed a kit to diagnose hydatidosis, based on the detection of specific antibodies. This disease, caused by larvae of the cestode Echinococcus granulosus, is a zoonosis commonly found throughout the world. The diagnostic kit discriminates between positive and negative cases in a way that is easily interpreted, i.e., positive cases form a colored band on an inert substrate. The results show test sensitivity to be some 94.87% and specificity 85.71%, which is comparable to those of the ELISA technique. The high sensitivity and specificity of this test affords the great advantage of speed in diagnosing this parasitosis. No other equipment or procedure is required.

Pre- and postsurgical detection of IgG, IgM, and IgA specific to hydatidosis by ELISA with purified antigen enriched with the 5/B antigen complex

An enzyme-linked immunoassay (ELISA) using purified 5/B Echinococcus enriched antigen was used to follow IgG, IgM, and IgA antibody levels pre- and posttreatment or surgical removal of hydatid cysts. The sensitivity was 97%, 37.5%, and 54.5%, respectively, and the specificity was 95.7%, 100%, and 98.9%, respectively. All isotypes could be detected 3 years after surgical removal of cysts in patients showing no remaining cyst evidence. This was especially true for IgG, which persisted in 85.2% of the patients. The data indicate that antigen purification improves specificity without affecting sensitivity, although this new antigen offers no advantages in the postsurgical monitoring of the patients.

Western blot applied to the diagnosis and post-treatment monitoring of human hydatidosis

The serologic diagnosis of hydatidosis (caused by Echinococcus granulosus) can be made by different techniques, although the lack of standardization of the antigens affects the sensitivity, specificity and concordance among the different tests. We have applied the Western-Blot (WB) technique, associated with a purified antigen from sheep hydatid fluid, at 60 samples of serum from 14 patients suffering echinococcosis in different bodily locations, monitored for 3 years. The WB test enabled the detection of antibodies in the pre-surgical samples for proteins of 12-14, 16, 20, 24-26, 34, 39 and 42 kDa in molecular weight in 15-96% of the patients. The combination involving 2 of the 3 proteins of 20, 39 and 42 kDa has made it possible to diagnose 100% of the cases. The antibodies specific to proteins 39 and 42 kDa disappeared in less than one year in the patients cured after surgery, while in patients with persistent or recurrent parasitism the bands present before surgery persisted or other new ones appeared. The WB with purified antigens proved to be highly useful in the diagnosis and post-surgical monitoring of hydatidosis patients. The antigen used is proposed as a standard antigen for the diagnosis and follow-up of pre- and postsurgical hydatidosis.