Serological speciation of human schistosome infections by ELISA with a panel of three antigens

Abstract

Aims: To find out whether serology can reliably speciate human schistosomiasis using a simple enzyme linked immunosorbent assay (ELISA) technique. Methods: Stored sera from 66 patients with microscopically confirmed schistosomiasis were subjected to ELISA using a panel of three antigens, namely: unfractionated Schistosoma mansoni soluble egg antigen (SEA); CEF6, a cationic fraction of SEA; and crude S margrebowiei egg antigen, prepared from an animal schistosome closely related to S haematobium. Results: The optical densities (ODs) obtained using CEF6 as antigen were significantly higher in sera from S mansoni infected patients than in sera from S haematobium infected patients (median OD, 0.810 v 0.595). Using S margrebowiei egg antigen, the optical densities were significantly higher in S haematobium sera than in S mansoni sera (median OD, 0.794 v 0.544). There was no significant difference in optical densities between S mansoni and S haematobium sera using SEA (median OD, 0.725 v 0.737). The ratio of ODs (CEF6 to S margrebowiei egg antigen) was calculated: a ratio of .1 indicated S mansoni infection (sensitivity, 88%) and a ratio of ,1 indicated S haematobium infection (sensitivity, 84%). The odds ratio for S haematobium having an OD ratio of ,1 was 36.8 (95% confidence interval, 7.0 to 194). Conclusions:The identity of the infecting species of schistosome can be determined using the panel of antigens described. SEA should be used to screen serum samples, and the CEF6 : S margrebowiei egg antigen ELISA optical density ratio can be used where serological speciation is required. The laboratory diagnosis of schistosomiasis can be achieved by both microscopic and serological methods. 2Schistosome ova may be seen in membrane filtered terminal urine, formol/ether concentrated stools, and biopsy specimens. Microscopy has a specificity of 100% in expert hands, but variable sensitivity. Ova were found in only 45% of 1107 patients from Africa diagnosed serologically with schistosomiasis in the UK.3 There are a variety of serological methods available for the diagnosis of schistosomiasis. The Hospital for Tropical Diseases in London (HTD) uses an enzyme linked immunosorbent assay (ELISA) with crude Schistosoma mansoni soluble egg antigen (SEA), which has a published specificity of 97% and sensitivities of 96% (S mansoni) and 92% (S haematobium).4 The SEA ELISA is a good serological screening test for schistosomiasis, but gives no indication of the infecting species of schistosome. The Centers for Disease Control in the USA screen sera by falcon assay screening test (FAST)-ELISA using S mansoni adult worm microsomal antigen and subsequently confirm the results with a species specific immunoblot.5 They report excellent sensitivity and specificity for both the ELISA and the immunoblot.A cationic fraction of S mansoni egg homogenate, known as CEF6, contains the antigens v-1 and a-1.6 In several studies, CEF6 has been found to be potentially useful for the serodiagnosis of S mansoni infections. [7][8][9][10] In a large colla...

Use of recombinant calreticulin and cercarial transformation fluid (CTF) in the serodiagnosis of Schistosoma mansoni

“…Un-fractionated SEA cannot distinguish between S. mansoni and S. haematobium infection, however S. margrebowiei egg antigen and CEF6 (a cationic fraction of SEA) give distinctly different results for the two infections, so that a combination of S. margrebowiei egg antigen and CEF6 antibody detection assays can be used for serological speciation (Turner et al, 2004). The species specificity of CTF still needs to be determined.…”

New Approaches with Different Types of Circulating Cathodic Antigen for the Diagnosis of Patients with Low Schistosoma mansoni Load

“…However, fluctuation in egg output and the chance of missing light infections necessitate repeated examinations [9]. Serologic testing has been used to enhance our ability to detect the disease in order to be more sensitive in demonstrating light infections [10]–[12], [38]. This study applied a multievaluation approach, combining specific antibody detection for four different antigens with an investigation performed on parasitological data in efforts to produce a more field-applicable assay format.…”

“…Immunodiagnostic techniques are rapid, sensitive, convenient, and easy to apply, and hence they have been used to estimate infection rates with the goal of improving diagnosis in epidemiological surveys and identifying individuals to target for treatment [10]–[13]. Nonetheless, low specificity is frequently seen in immunodiagnostic assays, largely due to the use of crude antigens that contain many antigens that might be shared with unrelated pathogens.…”

Clinical Diagnosis of Schistosoma japonicum Infection Complicating Infective Endocarditis and Liver Cirrhosis

“…Hepatic fibrosis by examined US is a sound marker for chronic S. japonica (6). Although cross-reactions between schistosoma species sometimes occur in serology tests (10)(11)(12), because the patient was an immigrant from the Philippines, and it was mostly the liver that had been affected, involvement by S. japonicum seemed certain based on where the patient lived and the clinical picture. We administered praziquantel because the serological test still revealed a strong response that might cause inflammatory immune reactions in the patient's body.…”