Evaluation of a malarial antibody assay for use in the screening of blood and tissue products for clinical use.

BACKGROUND AND OBJECTIVES: A new recombinant Plasmodium antigen enzyme immunoassay (EIA) for the detection of malarial antibodies was evaluated for the screening of 'malaria-risk' blood and tissue donations. MATERIALS AND METHODS: A total of 13,269 donor and patient samples were tested by both the EIA and the standard diagnostic antibody immunofluorescence test (IFAT). RESULTS: A total of 114/138 (82.6%) samples from patients with P. falciparum and 11/13 (84.6%) samples from patients with P. vivax tested positive. A total of 714/13,053 (5.47%) samples from donors identified as 'malaria risk', owing to residency or travel, were reactive in the EIA. CONCLUSIONS: The assay is more sensitive than a previously implemented malarial antibody EIA (73% in acute P. falciparum and 56% in acute P. vivax infections). The sensitivity of this new EIA is comparable to that of the IFAT, and the specificity is sufficient to screen 'malaria-risk' donors.

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

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.

Evaluation of a malaria antibody ELISA and its value in reducing potential wastage of red cell donations from blood donors exposed to malaria, with a note on a case of transfusion-transmitted malaria.

BACKGROUND AND OBJECTIVES: Blood donations are often wasted for lack of a satisfactory procedure to evaluate donors potentially exposed to malaria. MATERIALS AND METHODS: We evaluated a commercial ELISA for the detection of antibodies to malaria and compared it with an immunofluorescent antibody test (IFAT). RESULTS: When 5,311 sera from routine non-exposed donors were tested, 24 (0.45%) were positive by the ELISA, using a Plasmodium falciparum antigen. Seventeen were subjected to confirmatory testing but none were positive by IFAT. Of 1,000 donors potentially exposed in endemic areas 15 (1.5%) were repeatably reactive by ELISA. 10 of these were tested by IFAT and 2 were positive. When 150 patients attending the Hospital for Tropical Diseases in London with acute malaria were tested, 73% of those infected with P. falciparum were repeatably reactive for malarial antibodies by ELISA and 56% with Plasmodium vivax. Of 88 stored clinical sera tested by both IFAT and ELISA 56 were positive by IFAT and of these 52 (93 degrees/0) were positive by ELISA. CONCLUSION: The ELISA is sufficiently sensitive and specific to screen at-risk donors. Its use could safely retrieve 40,000 red cell units currently discarded each year in Great Britain.

Rapid latex agglutination test for extraluminal amoebiasis.

AIMS: To develop a rapid latex agglutination screening test for invasive amoebiasis. METHODS: The performance of an in-house latex agglutination test was compared with three standard serological techniques--the immunofluorescent antibody test (IFAT), the indirect haemagglutination test (IHA), and the cellulose acetate precipitin (CAP) test. Forty six sera were screened; 12 from negative controls; 10 sera from infections other than amoebiasis, and 24 sera from patients with luminal or extraluminal infection with Entamoeba histolytica. RESULTS: Strong positive latex agglutination reactions were observed, with 12 of 12 sera giving combined CAP positive, IFAT positive, and IHA positive results. These results are indicative of invasive amoebiasis. Twelve CAP negative, IFAT positive sera, and 10 of 12 IHA negative gave weak or negative agglutination reactions. One of 12 CAP negative, IFAT positive, and IHA positive sera gave a strong positive latex agglutination result; one with CAP negative, IFAT positive, and IHA positive sera gave a weak latex agglutination reaction. These results correlate with either treated amoebiasis or with the early stages of invasive amoebiasis for which the CAP test is known to have a lower sensitivity than the IFAT, but a higher specificity. No reactions were observed with 12 out of 12 CAP negative, IFAT negative, and IHA negative control sera and all 10 sera from other infections (two giardiasis, three schistosomiasis, three malaria, one filariasis). CONCLUSIONS: The latex agglutination test was a useful indicator test, paralleling the results obtained with standard serological techniques. It could also be a useful screening tool in the field.