A FURTHER STUDY OF LDT AND IFAT TESTS IN EVALUATING THE CONTROL OF KALA-AZAR IN CHINA

Kala-azar (KA) used to be highly prevalent in Shandong Province in Chi na and, according to the survey made in 1950, the average prevalence r ate was 350 per million. Through mass treatment and sandfly control, t he prevalence rate was brought down to 3 per 100 000 in 1958 and the d isease was basically eliminated. Since 1972, only 18 residual patients have been detected and no newly infected cases have appeared. In the meantime, the vector density had been reduced to such a low level that sandflies could not be found in 85% of the villages. For further eval uation of the control measures, an immunological survey on a relativel y large scale was conducted in 78 townships located in 24: counties of 13 prefectures and cities in 1990. A total of 10 239 rural residents of different ages had the Leishmanin dermal test (LDT). None of the pe ople under 30 years of age was positive (0/8020), while in those aged above 30, the average positive rate was 4.4% (98/2219). During the sur vey, blood samples were also taken from 4232 people for indirect fluor escent antibody test (IFAT); results were all negative. This indicates that the transmission of KA had been completely interrupted since the early 1960s and the province is now a non-endemic area of KA. Further analyses of the data showed that LDT is of great value in epidemiolog ical investigation of KA, for the evaluation of control measurements, the ascertainment of the past and present status of the disease, and d etection of subclinical infection. In addition, 138 previous KA patien ts cured 2-51 years ago were visited at home and examined by both LDT and IFAT. We found that fluorescent antibody positivity persists after cure for about 12 years, but cannot be detected in any cured cases fo r longer than 15 years. In contrast, most of these people give a posit ive reaction to LDT and the test was still positive in a man who had b een cured of KA 51 years previously.