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Tric

TRIC agents are Chlamydia trachomatis serotypes A through K, which cause two ophthalmic diseases: trachoma and inclusion conjunctivitis. Chlamydiae are obligate intracellular parasites that infect humans in two forms - the infectious elementary body and reproductive reticulate body. They have a cell wall structure similar to gram-negative bacteria. Trachoma is a chronic eye infection spread through contact and causes scarring that can lead to blindness, while inclusion conjunctivitis is generally milder and does not progress to scarring. Laboratory diagnosis involves examining corneal scrapings for inclusion bodies through microscopy or culturing the agent in eggs or cell lines.

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98 views1 page

Tric

TRIC agents are Chlamydia trachomatis serotypes A through K, which cause two ophthalmic diseases: trachoma and inclusion conjunctivitis. Chlamydiae are obligate intracellular parasites that infect humans in two forms - the infectious elementary body and reproductive reticulate body. They have a cell wall structure similar to gram-negative bacteria. Trachoma is a chronic eye infection spread through contact and causes scarring that can lead to blindness, while inclusion conjunctivitis is generally milder and does not progress to scarring. Laboratory diagnosis involves examining corneal scrapings for inclusion bodies through microscopy or culturing the agent in eggs or cell lines.

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madfrop
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TRIC AGENTS

TRIC is derived from words Trachoma and Inclusion Conjunctivitis. Both of these ophthalmic diseases are produced
by a bacterium Chlamydia trachomatis. Serotypes of C. trachomatis A to K are together called TRIC agents.

Properties:
Chlamydiae are obligate intracellular parasitic organisms that exclusively infect humans. They were once considered
as viruses. Though they can’t be stained well with Gram’s stain, they are considered gram negative on the basis of
cell wall structure. The cell wall is proposed to be gram-negative in that it contains an outer lipopolysaccharide
membrane, but it lacks peptidoglycan in its cell wall. They exist in two forms, namely elementary body and reticulate
body. Elementary body is considered to be the extracellular infective form while reticulate body is the reproductive
form that is seen in infected host cells. Once inside, elementary body reorganizes into reticulate body. Over a 24-hour
period, these reticulate bodies divide and begin to reorganize back into elementary bodies. About 48-72 hours after
infection, the cell is lysed and numerous infectious elementary bodies are released. These can be demonstrated in
infected cells by Iodine stain, Machiavello stain, Gimenez stain, Giemsa stain and immunofluorescence. Chlamydiae
can’t be grown on inanimate culture medium. They can be propagated only on embryonated eggs, mouse or tissue
culture.

Life cycle:

Trachoma: It is a chronic keratoconjunctivitis characterized by follicular hypertrophy, papillary hyperplasia, pannus


formation and cicatrisation (in late stages). Infection is transmitted from eye to eye by fingers or fomites (towels and
washcloths). There is no genital involvement in this disease. Both children and adults can be infected.
Trachoma is an infection of the epithelial cells of the conjunctiva, producing inclusion bodies. Vascularization and
clouding of cornea along with trichiasis (inward growth of eyelashes) can produce scarring that may lead to blindness.
This is the leading cause of blindness in the world.

Inclusion conjunctivitis: It is a milder form that occurs in both children and adults. This form generally heals without
scarring or blindness. During the birth process, when the fetus passes down the birth canal, it can contract an eye
infection from the mother's infected genital tract after an incubation period of 5-12 days.
In the adult, it resembles the early stages of trachoma, but usually does not progress to a chronic disease or
blindness. It was known as ‘swimming pool conjunctivitis’ as infection was associated with bathing in community
swimming pools, which probably got contaminated with chlamydia from the genital secretions.

Laboratory diagnosis:
ƒ Specimen collection: Corneal scrapings
ƒ Microscopy: Demonstration of inclusion bodies (HP bodies) by Giemsa, Castaneda, Machiavello methods,
Iodine or immunofluorescence.
ƒ Culture: Yolk sac of 6-8 day old embryonated egg, McCoy cell lines.

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