Immuno-epidemiological studies on subclinical infection in leprosy. I. Clinical and immunological findings in schoolchildren and adults in Okinawa.

For the purpose of understanding subclinical infection with Mycobacterium leprae among the inhabitants in an endemic area, 3,547 schoolchildren and 1,487 adults in several regions of Okinawa were surveyed by using clinical examinations and immunological tests, i.e. the fluorescent leprosy antibody absorption (FLA-ABS) test and the lepromin test using Dharmendra's antigen, during a period from 1978 to 1984. The enlargement of peripheral nerves, especially that of lateral or bilateral auricular and/or ulnar nerves, without loss of sensation was found in 8.4% of the schoolchildren and in 9% of the adults. A frequency of these signs and symptoms was significantly higher in male than in female and tended to increase with age. The percentage of positive reactions in FLA-ABS tests for schoolchildren and adults was 21.8 and 22.5, respectively, the values suggesting a minimum frequency of subclinical infection with M. leprae among these inhabitants. The percentage of positive FLA-ABS tests was significantly higher in those with neural signs and symptoms than in those without. Such a correlation was not found in the lepromin test. Ill-defined depigmentation of the skin without loss of sensation was found in a few percentage of both schoolchildren and adults. However, this sings and symptoms did not correlate with the FLA-ABS test nor with the lepromin test. A history of tuberculin test and BCG vaccination in the schoolchildren seemed to influence the lepromin-reactivity. Among 770 schoolchildren tested with both FLA-ABS and lepromin, 70 (9.1%) were the FLA-ABS positive but lepromin non-positive responders. Neural signs and symptoms were found in 31 of these children.