Serodiagnosis of human gnathostomiasis.

An enzyme-linked immunosorbent assay (ELISA) was evaluated for serodiagnosis of human ocular and visceral gnathostomiasis in comparison to an indirect haemagglutination (IHA) and precipitin (PPT) tests. The ELISA antibody titers were found to range from 1:400 to 1:51,200 against somatic and 1:200 to 1:25,600 against excretory-secretory (ES) antigens. When sera were tested at single dilutions, the ELISA was positive in 7 of 8 gnathostomiasis cases while only 5 and 3 were positive by IHA and PPT respectively. The overall specificity of the ELISA was 96.7% and 97.4% with somatic and ES antigens respectively. Since somatic and ES antigens produced similar ELISA results, either can be used for diagnostic purpose. It was suggested that the ELISA was a reliable serodiagnostic test for human gnathostomiasis.

Evaluation of counterimmunoelectrophoresis for serodiagnosis of human cysticercosis.

Counterimmunoelectrophoresis (CIEP) was evaluated in comparison to the indirect haemagglutination test (IHA) for serodiagnosis of human cysticercosis. It was found that CIEP detected antibodies in 7 of 11 (64%) and IHA detected them in 6 of 11 (55%) confirmed cysticercosis sera. Only 2 of 130 control sera were positive by each technique. Taenia saginata adult worm extract was found to be satisfactory for use in CIEP in place of Taenia solium cysticercus extract, with only little loss of sensitivity. Finally, CIEP in combination with IHA greatly increased the diagnostic sensitivity for human cysticercosis.

Seroepidemiology of malaria in northern Thailand: II. Focal and temporal variations in endemicity.

Four population groups from regions of Northern Thailand were surveyed for the presence of antibodies to Plasmodium falciparum using the indirect immunofluorescent antibody (IFA) test. Each of the four populations was selected from areas known to represent different patterns of malaria transmission. Group 1 was from an area where there had been no malaria transmission for approximately 30 years. Individuals in this group below age 40 showed an extremely low prevalence of malaria antibodies. Group 2 was chosen from an area where low levels of transmission have continued despite more than 30 years of DDT spraying. In this group the age related pattern of malaria antibodies varied from village to village but in all villages there was a sharp increase in the prevalence of IFA positive tests in individuals over 30. The third group has had continuously high levels of transmission. Although there are differences in the age related prevalence of IFA positives when individual villages are compared, there is a greater prevalence at all ages than in the first two groups. The fourth group was selected from an area where transmission had recently resumed after freedom from indigenous cases for approximately six years. There was little difference in the prevalence of IFA positive individuals below the age of 25 but above that there was a steady increase in prevalence with age. The correlation of IFA antibody positives with known patterns of malaria transmission in these four areas demonstrates the usefulness of this serological technique in assessing malaria endemicity and the effectiveness of control measures as well as in the interpretation of other malaria statistics.

Prevalence of Toxoplasma antibodies in Chiang Mai population.

Five hundred sera from blood donors were examined for antibodies to Toxoplasma by the indirect hemagglutination antibody (IHA) and the indirect fluorescent antibody (IFA) techniques. In addition, the IHA test was used to detect Toxoplasma antibodies in 500 pregnant women's sera. It was found that 4.6% of the blood donors were positive by the IHA and only 1.2% by the IFA methods. The seroprevalence, however, was less in pregnant women as only 2.8% were positive. Interestingly, 7.5% of the blood donors and 15.2% of pregnant women showed no detectable antibodies. The frequency distribution curves of IHA titers were unimodal in both groups studied. From the basis of these findings, it was concluded that there was a low degree of Toxoplasma transmission in Chiang Mai.