<P> Several genes have been associated with a susceptibility to leprosy . Often, the immune system is able to eliminate leprosy during the early infection stage before severe symptoms develop . A defect in cell - mediated immunity may cause susceptibility to leprosy . The region of DNA responsible for this variability is also involved in Parkinson's disease, giving rise to current speculation that the two disorders may be linked in some way at the biochemical level . Some evidence indicates not all people who are infected with M. leprae develop leprosy, and genetic factors have long been thought to play a role, due to the observation of clustering of leprosy around certain families, and the failure to understand why certain individuals develop lepromatous leprosy while others develop other types of leprosy . </P> <P> How the infection produces the symptoms of the disease is not known . </P> <P> According to the World Health Organization, diagnosis in areas where people are frequently infected is based on one of these main signs: </P> <Ul> <Li> Skin lesion consistent with leprosy and with definite sensory loss </Li> <Li> Positive skin smears </Li> </Ul>

Why is there no leprosy in north america