Field and laboratory comparative evaluation of ten rapid malaria diagnostic tests

The paper reports on a comparative evaluation of 10 rapid malaria tests available in South Africa in 1998: AccuCheck (AC, developmental), Cape Biotech (CB), ICT Malaria Pf (ICT1) and Pf/Pv (ICT2), Kat Medical (KAT), MakroMal (MM), OptiMAL (OP), ParaSight-F (PS), Quorum (Q), Determine-Malaria (DM). In a laboratory study, designed to test absolute detection limits, Plasmodium falciparum-infected blood was diluted with uninfected blood to known parasite concentrations ranging from 500 to 0.1 parasites per microlitre (P/microL). The 50% detection limits were: ICT1, 3.28; ICT2, 4.86; KAT, 6.36; MM, 9.37; CB, 11.42; DM, 12.40; Q, 16.98; PS, 20; AC, 31.15 and OP, 91.16 P/microL. A field study was carried out to test post-treatment specificity. Blood samples from malaria patients were tested with all products (except AC and DM) on the day of treatment and 3 and 7 days thereafter, against a gold standard of microscopy and polymerase chain reaction (PCR). OP and PS produced fewer false-positive results on day 7 (18 and 19%, respectively) than the other rapid tests (38-56%). However, microscopy, PCR, OP and PS disagreed largely as to which individuals remained positive. The tests were further compared with regard to general specificity, particularly cross-reactivity with rheumatoid factor, speed, simplicity, their ability to detect other species, storage requirements and general presentation.

Assessment of the residual efficacy of lambda-cyhalothrin. 2. A comparison with DDT for the intradomiciliary control of Anopheles arabiensis in South Africa

There are several factors that support the need to assess the efficacy of potential alternative insecticides to DDT for malaria vector control. The objectives of this study were to evaluate the persistence and efficacy against Anopheles arabiensis of lambda-cyhalothrin used as an intradomiciliary insecticide in daub huts and to compare its efficacy in this regard to DDT. Exit trap catches showed the population of An. arabiensis was high during the months of January to March, with a peak in February. During all months, the number caught leaving lambda-cyhalothrin-sprayed huts was markedly less than the number from both control and DDT-sprayed huts. The percentage survival of bloodfed mosquitoes ranged from a low of 55% caught leaving the lambda-cyhalothrin-sprayed huts, to 82% of those caught leaving DDT-sprayed huts. The percentage of bloodfed mosquitoes caught leaving huts was high (> 60%). The survival of unfed mosquitoes was low, even from the control huts (43%).

Detection of Entamoeba histolytica immunoglobulins G and M to plasma membrane antigen by enzyme-linked immunosorbent assay

Sixty-one serum specimens from 22 patients with clinically diagnosed amoebic liver abscess (ALA), 10 hospitalized patients with a variety of diseases other than amoebiasis, 12 normal healthy controls, and 17 subjects from an amoebiasis-endemic area were assayed by enzyme-linked immunosorbent assay (ELISA). The plasma membrane fraction of axenic cultures of Entamoeba histolytica HK9 separated from other subcellular fractions by differential centrifugation was used as the antigen to detect specific immunoglobulin G (IgG) and IgM antibodies. Using a single serum dilution of 1/100 and optical densities at 492 nm of 0.200 and 0.250 as the cutoff values for the IgM and IgG ELISAs, their respective sensitivities in 22 ALA patients were 91% (20 of 22) and 95% (21 of 22). In 22 patients (10 hospitalized and 12 normal healthy controls), the specificities of the IgM and IgG ELISAs were 95% (21 of 22) and 91% (20 of 22), respectively. All five asymptomatic carriers of pathogenic E. histolytica were seropositive by the IgG ELISA and the amoebic gel diffusion test (AGDT). The AGDT was positive for three of six culture-negative controls, while the IgG ELISA was positive for all six. For six asymptomatic carriers of nonpathogenic zymodemes, the AGDT was positive for two, and the IgG ELISA was positive for three. There was an excellent correlation (r = 0.96) between the IgG ELISA and the AGDT. Only one of six culture-negative controls, none of the asymptomatic carriers of pathogenic E. histolytica, and one of six carriers of nonpathogenic E. histolytica were seropositive by the IgM ELISA, thus highlighting the specificity of the IgM ELISA in the diagnosis of ALA. It is believed that the use of plasma membrane fractions has improved the diagnostic potential of the IgM ELISA.

Evaluation of an enzyme-linked immunosorbent assay in the serodiagnosis of amoebic liver abscess

An indirect enzyme-linked immunosorbent assay (ELISA) was evaluated for the detection of anti-amoebic IgG and IgM antibodies to assess its value in distinguishing past from current infection in invasive amoebiasis, particularly in amoebic liver abscess (ALA) patients. Using sera from 295 individuals, the ELISA was also compared with the amoebic gel diffusion (AGD) test. In 100 patients the IgG-ELISA at a single test dilution of 1/6,400 had a sensitivity of 99% for clinically diagnosed ALA. In these same patients the IgM-ELISA at a single dilution of 1/400, had a sensitivity of 64% and a specificity of 97.9%. No cross-reactions were observed in sera from patients with collagen vascular disease. In 121 patients without clinical invasive amoebiasis, 8 were AGD-positive and 12 were IgG-ELISA-positive, giving the latter assay a specificity of 91.7%. This is thought to be due to past infection with Entamoeba histolytica. In symptomless carriers of pathogenic zymodemes, 10/11 were seropositive by the IgG-ELISA and 11/11 by the AGD test. There was an excellent correlation between the IgG-ELISA and the AGD test (r = 0.99). The IgG-ELISA is a sensitive, specific, simple and rapid test. It has the clinical advantage that results are obtainable 2 1/2 hours after receipt of the specimen, compared with the 24-48 hours required for the AGD test. The prompt availability of IgG-ELISA results could prove advantageous for implementation of early therapy. The IgM-ELISA was not found to be sensitive enough to be used as an index of active amoebic infection.

Fetal prostaglandin levels in twin pregnancies

Umbilical venous plasma and amniotic fluid concentrations of prostaglandins E2 (PGE), F2 alpha (PGF) and 13,14 dihydro-15-keto-F2 alpha (PGFM) were measured in 31 twin pregnancies by specific radioimmunoassays. There was no significant difference between twins I and II in the same pregnancy but PGE and PGFM were significantly increased during labour in fetal blood. This rise was not manifest in the latent phase. PG concentration in amniotic fluid rose with advancing gestational age but was more pronounced in the case of PGE than for PGF and PGFM. No significant differences between amniotic sac concentrations of PGs of twin I and II were found during the prelabour period, but in all four patients in labour with intact membranes, the PG levels were increased in twin I. The fetal plasma and amniotic fluid levels of PGE and PGFM were significantly correlated in the prelabour group.