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 China and, according to the survey made in 1950, the average prevalence rate was 350 per million. Through mass treatment and sandfly control, the prevalence rate was brought down to 3 per 100,000 in 1958 and the disease 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 evaluation of the control measures, an immunological survey on a relatively 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 people 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 survey, blood samples were also taken from 4232 people for indirect fluorescent 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 epidemiological investigation of KA, for the evaluation of control measurements, the ascertainment of the past and present status of the disease, and detection of subclinical infection.(ABSTRACT TRUNCATED AT 250 WORDS)