Evaluation of immunodiagnostic techniques for the detection of human hydatid cyst carriers in field studies

Asymptomatic Abdominal Hydatidosis Detected by Ultrasonography

Ultrasonography (US) and serology (double diffusion for antigen 5 (dd5)) were used for the screening of hydatid disease in 1418 asymptomatic individuals from two provinces in Argentina. A total of 122 positive subjects were identified and in 120 of them lesions consistent with hydatid disease were observed at US (98.4%) while only 19 had positive dd5 tests (15.8%). Chest radiography was performed in 647 of the subjects and an additional 4 lesions were found. Surgery was performed in 32 patients, confirming in all of them the sonographic diagnosis. It is suggested that US should be used in the screening for hydatidosis in high-risk populations as well as in follow-up programmes.

Treatment of liver hydatidosis: How to treat an asymptomatic carrier?

Liver hydatidosis is the most common clinical presentation of cystic echinococcosis (CE). Ultrasonographic mass surveys have demonstrated the true prevalence, including the asymptomatic characteristic of the majority of cases, providing new insight into the natural history of the disease. This raises the question of whether to treat or not to treat these patients, due to the high and unsuspected prevalence of CE. The high rate of liver/lung frequencies of cyst localization, the autopsy findings, and the involution of cysts demonstrated in long time follow-up of asymptomatic carriers contribute to this discussion. The decision to treat an asymptomatic patient by surgery, albendazole, or puncture aspiration injection and reaspiration or to wait and watch, is based on conflicting reports in the literature, the lack of complications in untreated patients over time, and the spontaneous disappearance and involution of cysts. All these points contribute to difficulties of individual clinical decisions. The patients should be informed of the reasons and the risks of watchful/waiting without treatment, the possibility of complications, and the risks of the other options. As more information on the natural history of liver hydatidosis is acquired, selection of the best treatment will be come easier. Without this knowledge it would be very difficult to establish definitive rules of treatment. At present, it is possible to manage these patients over time and to wait for the best moment for treatment. Follow-up studies must be conducted to achieve this objective.

Diagnostic value of a synthetic peptide derived from Echinococcus granulosus recombinant protein

A specific monoclonal antibody (MAb; EG 02 154/12) directed against a protein epitope of Echinococcus granulosus antigen 5 was used to screen a cDNA library constructed from E. granulosus protoscoleces RNA. One clone designated Eg14 was selected and shown to code for an amino acid sequence partially homologous to that of the clone Eg6 previously identified with the same MAb. Hydrophobic cluster analysis showed that both recombinant antigens may adopt a similar alpha-helical organization and share a common conformational epitope. A synthetic peptide (89-122) mimicking the conformational site of Eg6 and Eg14 was constructed and demonstrated to be able to inhibit binding of the MAb and human hydatid sera to the Eg6 fusion protein (FP6) or to native hydatid antigens. To assess the diagnostic value of the peptide 89-122, we tested sera from patients infected with different parasites for their antibody reactivity with this peptide in ELISA. A high binding sensitivity and specificity of IgG-A-M antibodies were obtained with E. granulosus-infected patient sera. Moreover, the peptide 89-122 was found to be specifically recognized by IgE antibodies from patients with hydatid disease. These results indicate the particular interest of this synthetic peptide as a standardized antigen in diagnosis and treatment surveillance of hydatidosis.

Improvements in the serodiagnosis of helminthic zoonoses

Remarkable progress has been achieved in developing improved serodiagnostic assays for a group of diseases for which other diagnostic methods are often lacking. Toxocariasis, trichinellosis, dirofilariasis, Taenia solium cysticercosis and the cystic and alveolar forms of hydatid disease are occult infections in humans and sometimes in lower animal hosts. Although Strongyloides stercoralis achieves patency in humans, parasitologic diagnosis is often very difficult. Efforts to develop reliable immunodiagnostic methods have spanned several decades but progress had been slow until recently. The complexity and nonspecificity of helminth antigens were major problems which prevented the full realization of the benefits of the highly sensitive assay systems now available. Modern immunologic methods including hybridoma technology, immunoaffinity chromatography and immunoblotting, however, have yielded improved reagents and the means to characterize their nature and function. The outcome of this research has been more sensitive and specific serologic tests based on measurement of both circulating antigens and antibodies as well as improved understanding of the nature of host-parasite interactions. Although much remains to be done, many improved immunodiagnostic procedures are already being applied in clinical diagnosis, epidemiologic studies and control programs directed against the helminthic zoonoses.

Hydatid disease in the Western Isles

An investigation into the incidence of hydatid disease was carried out in the Hebridean islands of Lewis and Skye. The results showed that 20% of the sheep were infected and 10% of the dogs harboured Echinococcus granulosus. Sporadic human cases continue to occur but using serological tests we were unable to show evidence of subclinical infection in the population sampled.

Comparison of three immunological tests for seroepidemiological purposes in human echinococcosis

The comparative sensitivity and specificity of three immunodiagnostic tests for hydatid disease--the latex agglutination (LA) test, the indirect haemagglutination (IHA) test and the counterimmunoelectrophoresis (CIEP) test--were studied. The results of the IHA test were evaluated using three positivity criteria. Antigen from the same source--hydatid cyst fluid pool of ovine origin--was utilized for the three tests. A total of 123 sera were studied; 30 preoperative sera from patients with other parasitic and infectious diseases, 30 sera from patients with non-parasitic diseases and 30 sera from normal blood donors. The results of the three tests were correlated to the immunoelectrophoresis (IEP) test based on the presence of arc 5. The same sensitivity (86.7%) and specificity (99%) was obtained in LA, CIEP and IHA tests when the minimum cross-reactivity titre criterion was employed for the latter. Non-specificity was relatively high (13%) in the IHA test when only serological reactivity was considered. The sensitivity of the IHA test decreased (83.3%) using the diagnostic titre criterion and non-specific reactions were eliminated. All three tests correlated well with the IEP test.

'Arc 5' antibodies in sera of sheep infected with Echinococcus granulosus, Taenia hydatigena and Taenia ovis

The 'arc 5' precipitin band, formed when test human serum is reacted against immunoelectophoresed hydatid cyst fluid antigen, has provided a positive diagnosis of Echinococcus granulosus infection. These antibodies to 'arc 5' antigen have now been found in the sera of sheep. They appear 2 weeks after infection with Taenia ovis, after 3 weeks with T. hydatigena and after 16 weeks with E. granulosus. An antigen similar to the 'arc 5' antigen of E. granulosus cyst fluid was also demonstrated in cyst fluid from T. hydatigena, but it would not be positively identified in T. ovis cyst fluid. The presence of 'arc 5' in immunoelectrophoresis tests is not suitable for specific immunodiagnosis of E. granulosus infections in sheep in New Zealand. 'Arc 5' antibodies were only associated with living E. granulosus cysts and were not present if cysts were dead. The location of the cysts in either liver or lungs and the onset of brood capsule production did not influence the presence of 'arc 5' antibodies.

Detection of antibodies against Echinococcus granulosus arc 5 antigens by double diffusion test

This report deals with an evaluation of a double diffusion (DD5) test which employs a control antiserum against Echinococcus granulosus arc 5 antigens to recognize arc 5-positive sera by a reaction of identity. The DD5 test was more sensitive than the immuno-electrophoresis (IEP5) test based on the same positivity criterion and was equally specific for the immunodiagnosis of human hydatidosis. Its greater simplicity suggest its application as a substitute for the IEP5 test in diagnosis, particularly areas. The application of both DD5 and latex agglutination tests is recommended for hydatid immunodiagnosis on the basis of the present findings.

Serological and clinical investigations of human hydatid case in Libya

Fifty surgically confirmed cases of hydatid disease in Eastern Libya were investigated. Of these, 30 had cysts of the liver, five had extra-hepatic abdominal cysts and 15 had cysts in the chest, including the lungs. Ten cases of malignancy of the liver and five cases of malignancy of the lung were used as controls. Differential diagnosis of cancer was made by measuring the ESR and glycoprotein levels (elevated x 4 and x 3 respectively, in cancer cases). Serum bilirubin, SGOT, SGPT and serum alkaline phosphatase levels were also significantly raised in malignancy, while the total protein levels and eosinophilia were the same in both diseases. The intradermal test was positive in 88%, the haemagglutination test in 86% and the complement fixation test in 70% of cases. In the post-operative follow-up, complement-fixing antibodies disappeared somewhat faster than did the haemagglutinins. The positive skin test cases, however, remained positive throughout the 12-month follow-up period.

The immunological diagnosis of human hydatid disease

There is evidence that the yearly incidence rate of hydatid disease may be increasing in endemic areas and in regions of the world hitherto free of the infection. The availability of an accurate method of detection in both man and other animals would facilitate understanding of the global epidemiology. The diagnostic procedures in use in human hydatidosis have often given inconclusive results in animal infections. The following tests are discussed and their usefulness appraised: intradermal, complement fixation, haemagglutination, latex agglutination, indirect fluorescent antibody, immunoelectrophoresis, counter immunoelectrophoresis, enzyme linked immunosorbent assay, radio-immuno assay and lymphocyte transformation.