The anatomical distribution of single leprosy lesions in an African population, and its implications for the pathogenesis of leprosy.

Data on the anatomical sites of single leprosy lesions found in 635 newly diagnosed and biopsy-confirmed leprosy patients are presented. These patients were found during total population surveys carried out by the Lepra Evaluation Project, a prospective longitudinal study of the epidemiology of leprosy in Karonga District, Northern Malawi. There was a striking excess of single lesions on the face and the back of the arms, compared to the distribution of skin surface area, and a deficit on the legs, regardless of age. There is some evidence for a sex difference in lesion distribution among adults, with facial and arm lesions being relatively more common in females and back lesions being more common in males. The excess of lesions on the face compared to the lower limbs is similar to data from Uganda, but very unlike data from Burma and elsewhere in Asia. Overall, the distribution of lesions does not suggest a pattern reflecting entry of Mycobacterium leprae, nor does it suggest an association with anatomical distribution of the nervous or vascular system. It is argued that the distribution reflects the influence of some 'local' environmental or behavioural factors.

Failure of Mycobacterium leprae soluble antigens to suppress delayed-type hypersensitivity reaction to tuberculin.

In order to test a published claim that the inclusion of Mycobacterium leprae antigens with a tuberculin skin test reagent can suppress delayed-type hypersensitivity (DTH) to tuberculin in both paucibacillary and multibacillary leprosy cases, 109 leprosy cases and 104 non-leprosy controls were skin-tested simultaneously with tuberculin with and without M. leprae soluble antigens. Tests were randomized between arms and carried out double-blind. There was a clear tendency for larger DTH responses with the combined tuberculin plus M. leprae antigen than with tuberculin alone in paucibacillary leprosy cases and in non-leprosy controls. No evidence for M. leprae antigen-mediated suppression of DTH was observed in any group. It is unclear whether the difference between the results reported here, which were obtained in Malawi, and those in the published literature which were obtained in India, is attributable to geographic differences in important biological variables or to differences in the experimental protocols. The need for methodological rigour in skin-test studies is stressed.

The distribution and implications of BCG scars in northern Malawi.

Reported are data on the BCG scar status of more than 112,000 individuals who were surveyed in Karonga District, northern Malawi, between 1979 and 1984. The age and sex patterns of apparent BCG scars reflect the history of BCG vaccination activities in the district. Repeated independent examinations of large numbers of people revealed that the proportions remaining with the same observed scar status among those initially classified as being scar "positive" or scar "negative" were each approximately 90%. The repeatability of positive scar reading was lower among children and older adults than among young adults aged 15-24 years, and blind follow-up of children known to have been vaccinated as infants in child health clinics indicated that less than 60% had a detectable scar 3 years after receiving the vaccine. "Negative" repeatability increased consistently with age. The implications of these findings for estimating BCG vaccine uptake and for assessing its efficacy in case-control and cohort studies are discussed. The finding that BCG scars may be difficult to read suggests there is a danger of observer bias that could lead to distortion--in particular, to overestimates of vaccine efficacy.

PIP: In the Karonga district of northern Malawi, a study was made of the resultant scars from BCG vaccinations. BCG vaccines, while highly popular, are also highly controversial because they do not always protect against the tuberculosis and leprosy they are designed for, varying in effectiveness with the group being vaccinated. After an intradermal injection of live BCG vaccine, an ulcer and a subsequent scar develop. Research discovered age and sex patterns among those with BCG scars in northern Malawi from which conclusions on vaccination activities could be drawn. Because of a program which emphasized the vaccination of schoolchildren from 1979-1984, there is a higher prevalence of scars among young men aged 20-24 than among young women or adults. A definite connection was found between school status and vaccination. Socioeconomic background also contributed to scar finding with the better educated, financially secure, choosing to be vaccinated more often. Problems in research were also identified: The misclassification of repeatability and sensitivity data was recognized. This misclassification may have an effect on the determination of vaccine efficacy. Further, the relationship between scars and vaccine efficacy is discussed.

Protective efficacy of BCG against leprosy in Northern Malawi.

The effectiveness of a BCG vaccination programme in protecting against leprosy was assessed by case-control and cohort analyses of data from the Lepra Evaluation Project in Karonga District, Northern Malawi. Results indicate that BCG provides at least 50% protection against leprosy in this population and that protection is independent of age, sex, schooling status, or location within the project area. Agreement between these findings and those from a controlled trial in Uganda indicates that BCG is sufficiently effective against leprosy in East and Central Africa to be considered an important element of leprosy control in that region.