Final answer:
Leprosy susceptibility is determined by multiple genes, numerous environmental factors, and exposure to Mycobacterium leprae. Prolonged contact with infected skin or inhalation into nasal mucosa are common modes of transmission. Option 3) Both multiple genes and numerous environmental factors is the correct answer.
Step-by-step explanation:
Leprosy, also known as Hansen's disease, is determined by both multiple genes and numerous environmental factors. The primary causative agent of leprosy is a bacterium called Mycobacterium leprae. While the bacterium itself plays a significant role in determining susceptibility to leprosy, genetic factors and environmental factors also contribute to an individual's susceptibility.
M. leprae primarily transmits from person to person through prolonged and repeated contact with infected skin or inhalation into nasal mucosa. Approximately 95% of the human population has natural immunity to M. leprae and cannot be easily infected. Armadillos, one of the few susceptible mammals, have also been implicated in the transmission of some cases.
It is difficult to reconstruct all the factors that determine an individual's exposure to leprosy and the progression of the disease. Beyond basic epidemiological variables, individual capacities to generate an appropriate immune response against the bacterium may also play a role in differential susceptibility.