The immunological characteristics of 26 strains of Japanese encephalitis virus (JEV) isolated in Japan and Malaya between 1935 and 1966 have been investigated mainly by the antibody-absorption variant of the haemagglutination-inhibition test, and to a certain extent also by conventional haemagglutination-inhibition and complement-fixation tests. The antibody-absorption technique shows promise as a routine method for the immunotyping of JEV.At present, two immunotypes can be distinguished. One comprises 2 strains, Nakayama-NIH and I-58, and is designated as the I-58 immunotype. The other immunotype, JaGAr 01, comprises 17 strains which share the characteristics of the JaGAr 01 strain, including one subline of the Nakayama strain, Nakayama-Yakken. The Nakayama-RFVL strain was found to have the characteristics of both immunotypes. The I-58 immunotype differs more markedly from related arboviruses, such as the Murray Valley encephalitis virus and the West Nile Eg101 strain, than does the JaGAr 01 immunotype.Evidence is presented which suggests that a given JEV strain can change immunotype on repeated passage through mice.
Epidemiological studies of human leptospirosis have generally been limited to countries with specialized laboratories employing the microscopic-agglutination (MA) test. The sensitized-erythrocyte-lysis (SEL) test is much simpler for routine hospital laboratories to carry out and it has been found valuable in the diagnosis of human leptospirosis. This paper reports the results of studies of the SEL test as an epidemiological tool in serological surveys.The results showed that the significant SEL titre was 1:80 and that the sensitivity of the test depended possibly on the antigen preparation and the amount of complement used. Most of the SEL antibodies were found to persist at significant titres for about 1 year after active infection, but less than half persisted longer than that. The SEL test is therefore useful for detecting recent infections and for indicating that stability of leptospirosis in an area.The endemicity of leptospirosis in West Malaysia was confirmed by the SEL test, based on the employment of 1:80 as the significant titre.
The sensitivity and specificity of each of five screening tests were estimated in each of three to ten countries by testing subjects drawn from the general populations of adults over thirty-four years of age. This permitted comparisons among countries and among the different tests (fasting, postprandial, and postglucose urine tests, and fasting and postprandial blood glucose values). Sensitivity and specificity of each test varied widely among populations. For example, the sensitivity of the two-hour urine glucose ranged from 17 per cent in Nicaragua to 100 per cent in East Pakistan. Apparently specificity and sensitivity of such tests are influenced by many factors including both the circumstances under which the tests are performed and the characteristics of the population tested. It is, therefore, not possible to predict prevalence rates reliably by extrapolating from the results of screening tests. However, we believe the data for specific populations on the sensitivity and specificity of various tests will provide a rough guide in predicting the cost-effectiveness of alternative approaches to case detection in those particular countries. For instance, these results suggest that roughly 56 per cent of the occult diabetics in Costa Rica in this age group would be detected by a two-hour urine glucose, but only about 41 per cent of those in whom this test was positive would prove to have diabetes. Even modest changes of criteria in defining either "diabetes" or "abnormality" of the screening results produced marked changes in rates of sensitivity and specificity. With few exceptions, tests which were more sensitive were, comparably, less specific, and the reverse was also true. Rates of "diabetes" were markedly influenced by modest changes in diagnostic criteria.