CHLAMYDIA intracellular form and size is around 1 µm.


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

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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

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 enter
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

Development Cycle: –

Elementary body (EB) is entering into the host
cell by using receptor mediated endocytosis. After enter into the host cell EB
is transformed into active reticulate body. Reticulate body (RB) is multiplied
by binary fission. At 20 hours, reticulate body will be mature and condense to
form EB. At 40 hours of infection EB are released from the host cell by lysis

Natural Habitat: –

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




Suitable samples for isolation of Chlamydia: –

Abortion: –

Smears from the affected Cotyledons / Chorion
of Smears from vaginal swab (if placenta not available) within 1 to 2 days
of abortion
Piece of affected cotyledon, vaginal
swab, foetal lung and foetal liver should be placed in the Chlamydial
Transport Medium and held at 4?C

conditions: –

– aspirated synovial fluid
– Conjunctival swab
infection – Spleen, Lung & Liver
– Paired serum sample (both affected & normal animals)



Microscopy: –

q  Elementary
body in smear / tissue section can be detected by the use of either chemical
stains / immunological staining techniques

Ziehl – Neelsen Stain: –

v  Elementary
bodies are  clumps together and  stain red against a blue background (Methylene
Blue) / green background (Malachite green)


Enzyme Linked Immunosorbent assay (ELISA), Complement Fixation
Test (CFT), Indirect immunofluorescence antibody test (IFA) – used to detect antibodies directed against the common genus –
specific antigen (LPS)


To identify Chlamydia organism three laboratory systems
can be used

1. Mouse inoculation was used on older days

2. Inoculation of 6 to 7 days old embryonated eggs via Yolk sac
route used to detect all Chlamydiae organism (but the main disadvantage of this
method – laborious & more prone for bacterial contamination)

3. Cell Culture – Number of continues cell lines are susceptible to
Chlamydial infections (McCoy, BHK – 21, L929, Vero). Chemical treatment of the
cells with Cycloheximide (1 –
2 µg/ml), 5-iodo-2-deoxyuridine (80 µg/ml), Cytochalasin B (I µg/ml) or Diethyl- aminoethyl – dextran (30 µg/ml). Centrifuge the sample onto the monolayer – greatly enhances the
sensitivity of the isolation procedure. Use of antibiotics in the tissue culture medium to which Chlamydiae
are sensitive (oxytetracycline, erythromycin penicillin / tylosin) should be


Enzootic Abortion of ewes caused by C.abortus.
It is the major cause of economic loss in intensively
managed sheep flocks. It should be a serious problem in many sheep rearing areas of
the world. This condition is very rare in Australia and Iyreland.


Infection is mainly occurs by ingestion of contaminate materials

Spread of infection is occur at the time of lambing

Clean flocks usually
become infected through the introduction of replacement breeding females which
contaminate the flock during parturition. The following year can bring a
serious outbreak with up to 30% of ewes aborting. Ewes have solid immunity
post-abortion and thereafter, only younger females will pick up the infection
and an annual incidence of 10-20% can
be expected if no control measures are put in place

Disease is mainly characterized by abortion (last 2 to 3 weeks of pregnancy),
of premature weak lambs,
diffuse and necrotic placentitis

Prevention and Control: –

Three vaccines available in UK that
provide protection against EAE. Two live-attenuated vaccines can only be used
in non – pregnant females but
the inactivated vaccine can be used during pregnancy.

The inactivated
vaccine has been shown to reduce
the number of abortions in a flock of already infected sheep and it
can be used during an outbreak to
control the number of abortions.

Whole – flock
treatment with long acting Oxytetracycline can
be used 3 to 6 weeks before lambing to increase the number of viable lambs born
to ewes known to be infected with EAE. Repeat injections might be necessary and
ewes still excrete the organism if the lambs are born alive.

In the face of an
EAE outbreak, it is best to mark
and isolate the aborting ewes, disposes of the bedding and aborted products and disinfects the pen thoroughly.

Ewes that have
aborted should not be used as foster ewes



Sporadic Bovine Encephalomyelitis is caused by C.pecorum (biotype 2)


Disease reported from the USA, Japan and Israel. It is characterized
by Inflammation of vascular
endothelium throughout the body and nervous signs tend to
predominate. Subclinical intestinal infections in cattle and other animals
may be the source of infection in SBE. The disease is most often seen in calves
<6 month old and rarely in older cattle. Morbidity rates are usually low but can reach 50%. Many sick calves die if not treated at an early stage Clinical signs: - High fever, in coordination, depression, excessive salivation, diarrhea, weight loss, stiffness / knuckling at the fetlock, nasal discharge, finally recumbent & animal may develop opisthotonus (Neck bend with the eye looking upward) Chlamydia may also cause abortion in Cattle is known as  Epizootic Bovine abortion (EBA) / foothill abortion Treatment: - Antibiotics which are effective against C.pecorum (tetracyclines, oxytetracyclines, and tylosin) Oxytetracyclines, the drug of choice is given at 10 – 20 mg/kg/day for 10 - 14 days. High doses appear to be more effective (if treatment is effective, the fever should drop significantly within 24 hr). No vaccines are available