The areas most commonly affected by leprosy are the superficial peripheral nerves , skin, mucous membranes of the upper respiratory tract, anterior chamber of the eyes , and testes. These areas tend to be cooler parts of the body .
Tissue damage is caused by the degree to which cell-mediated immunity is expressed, the extent of bacillary spread and multiplication , the immunologic complications (ie, lepra reactions), and the nerve damage and its sequelae
Tissue smear test: An incision is made in the skin, to obtain fluid from a lesion. The fluid is placed on a glass slide and stained by using the Ziehl-Neelson acid-fast method to look for organisms.The bacterial index (BI) is then determined
Skin biopsy : for morphologic features and the presence of acid-fast bacilli.
Sensory testing : Tactile and temperature sensations should be tested.
It indicates host resistance to M leprae. and does not not confirm the diagnosis, but they are useful in determining the type of leprosy.
A positive finding indicates cell-mediated immunity,. A negative finding suggests a lack of resistance to disease.
To perform this test, bacillary suspension is injected into the forearm. When the reaction is assessed at 48 hours , it is called the Fernandez reaction When the reaction is read at 3-4 weeks , it is called the Mitsuda reaction .