Fernandez reaction
Encyclopedia
The Fernandez reaction is reaction that occurs to signal a positive result in the lepromin
skin test for leprosy
. The reaction occurs in the skin at the site of injection if the body possesses antibodies
to the Dharmendra antigen, one of the antigen
s found in Mycobacterium leprae
, the bacteria that causes leprosy. The reaction occurs via a delayed-type hypersensitivity
mechanism. This reaction occurs within 48 hours of injection of lepromin
and is seen in both lepromatous and tuberculoid forms of leprosy. In contrast, the Mitsuda reaction occurs 5–6 weeks after injection of lepromin
and is only seen in patients with the tuberculoid form of leprosy (not the lepromatous form, in which the body does not mount a strong response against the bacterium). In terms of mechanism of action and appearance, the reaction is similar to the tuberculin
reaction of a positive Mantoux test
for tuberculosis
.
Lepromin
The lepromin skin test is used to determine what type of leprosy a person has. It involves the injection of a standardized extract of the inactivated "leprosy bacillus", under the skin...
skin test for leprosy
Leprosy
Leprosy or Hansen's disease is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Named after physician Gerhard Armauer Hansen, leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions...
. The reaction occurs in the skin at the site of injection if the body possesses antibodies
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
to the Dharmendra antigen, one of the antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
s found in Mycobacterium leprae
Mycobacterium leprae
Mycobacterium leprae, also known as Hansen’s coccus spirilly, mostly found in warm tropical countries, is a bacterium that causes leprosy . It is an intracellular, pleomorphic, acid-fast bacterium. M. leprae is an aerobic bacillus surrounded by the characteristic waxy coating unique to mycobacteria...
, the bacteria that causes leprosy. The reaction occurs via a delayed-type hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...
mechanism. This reaction occurs within 48 hours of injection of lepromin
Lepromin
The lepromin skin test is used to determine what type of leprosy a person has. It involves the injection of a standardized extract of the inactivated "leprosy bacillus", under the skin...
and is seen in both lepromatous and tuberculoid forms of leprosy. In contrast, the Mitsuda reaction occurs 5–6 weeks after injection of lepromin
Lepromin
The lepromin skin test is used to determine what type of leprosy a person has. It involves the injection of a standardized extract of the inactivated "leprosy bacillus", under the skin...
and is only seen in patients with the tuberculoid form of leprosy (not the lepromatous form, in which the body does not mount a strong response against the bacterium). In terms of mechanism of action and appearance, the reaction is similar to the tuberculin
Tuberculin
Tuberculin is the name given to extracts of Mycobacterium tuberculosis, M. bovis, or M. avium that is used in skin testing in animals and humans to identify a tuberculosis infection. Several types of tuberculin have been used for this, of which purified protein derivative is the most important....
reaction of a positive Mantoux test
Mantoux test
The Mantoux test is a diagnostic tool for tuberculosis. It is one of the two major tuberculin skin tests used in the world, largely replacing multiple-puncture tests such as the Tine test...
for tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
.