Final answer:
Paucibacillary leprosy, or tuberculoid leprosy, is a less severe form of Hansen's disease with few skin lesions and a strong immune response containing the Mycobacterium leprae bacteria.
Step-by-step explanation:
Definition of Paucibacillary Leprosy
Paucibacillary leprosy, also known as tuberculoid leprosy, is a milder form of Hansen's disease characterized by one or few (typically no more than three) skin lesions.
These lesions are flat, blanched on the skin, and show some numbness due to the involvement of peripheral nerves. A significant feature of paucibacillary leprosy is that there are few bacilli present in the lesions.
The immune system plays a critical role in containing the disease, and in paucibacillary leprosy, an effective cell-mediated immune response keeps Mycobacterium leprae, the causative agent, in check.
Without this effective immune response, the disease could progress to the more serious lepromatous (multibacillary) form, which is characterized by numerous lesions filled with the bacteria.
The microorganism responsible for this condition is M. leprae, a gram-positive acid-fast bacillus that primarily affects the peripheral nervous system.
It leads to nerve damage and, consequently, the sensory loss that can result in ulcers, deformities, and potentially the loss of digits.
Hansen's disease is traditionally confirmed via skin biopsies showing the presence of acid-fast bacilli, although M. leprae does not grow in vitro on any known laboratory media.
Diagnosis can also be supported by in vivo culturing methods and PCR analysis of DNA from infected tissue.