True incidence of
leprosy and its impact on transmission will not be understood until a tool is available to measure pre-symptomatic
infection. Diagnosis of
leprosy disease is currently based on clinical symptoms, which on average take 3-10 years to manifest. The fact that incidence, as defined by new case detection, equates with prevalence, i.e., registered cases, suggests that the cycle of transmission has not been fully intercepted by implementation of multiple
drug therapy. This is supported by a high incidence of childhood
leprosy. Epidemiological screening for pre-symptomatic
leprosy in large endemic populations is required to facilitate targeted chemoprophylactic interventions. Such a test must be sensitive, specific, simple to administer, cost-effective, and easy to interpret. The intradermal skin test method that measures cell-mediated immunity was explored as the best option. Prior knowledge on skin testing of healthy subjects and
leprosy patients with whole or partially fractionated Mycobacterium leprae bacilli, such as
Lepromin or the Rees' or Convit'
antigens, has established an acceptable safety and potency profile of these
antigens. These data, along with immunoreactivity data, laid the foundation for two new
leprosy skin test
antigens, MLSA-
LAM (M. leprae soluble
antigen devoid of mycobacterial
lipoglycans, primarily
lipoarabinomannan) and MLCwA (M. leprae cell wall
antigens). In the absence of commercial interest, the challenge was to develop these
antigens under current good manufacturing practices in an acceptable local pilot facility and submit an
Investigational New Drug to the Food and Drug Administration to allow a first-in-human phase I clinical trial.