Domain species and large number of mammalian species. Severity

Domain – Bacteria, Phylum – Chlamydiae, Order –
Chlamydiales, Family – Chlamydiaceae, Genus – Chlamydia,
Species – C.trachomatis, C.psittaci, C.pneumoniae, C.abortus, C.felis, C.suis,

Chlamydia organisms are obligatory intracellular parasite.
Chlamydia lacks several metabolic and biosynthetic pathways and they depend upon
host cell machinery for their replication. Earlier days, Chlamydiae
were originally thought to be a virus but due to the presence of cell wall,
DNA, RNA & ribosomes they classified as Bacteria

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Chlamydiae are the small group of non – motile coccoid bacteria. Their
Cell wall is similar to Gram – negative bacterium (but it lacks
muramic acid). Chlamydia is consider to be an obligatory
intracellular parasites it require high
energy compound like ATP and it depends the host cell machinery for their
replication Known as “Energy
parasites”. Chlamydia has unique developmental cycle. It is
a dimorphic
bacterium with a two phase life cycle can exist either in the
form of Elementory body / Reticulate body.

Elementary Body (EB) – size is around 200 to 300 nm in diameter. EBs is small
and infectious form which represents the extracellular form of the organism.
Elementary bodies are metabolically inert and osmotically stable. They
into the host cell by receptor mediated endocytosis

Reticulate Body (RB) – Larger, intracellular form and size is around 1
µm. it promote metabolic activity. Reproduction occurs by binary fission

Elementary bodies are relatively resistant and
remain viable for several days under suitable environmental conditions. Chlamydial infections are considered to be persistent
are the rule in both birds &
mammals. C.psittaci often present in G.I tract. Organism shed in faeces
for prolonged period.

Chlamydiae do not show strict host specificity. They infect
more than 150 avian species and large number of mammalian species. Severity
of the infection is depends up on the strain and virulence of the agent, age, sex, physiological state and
species of the host, route of infection,
degree of exposure to Chlamydiae,
environment and management