- Chlamydiae are obligate intracellular bacteria that cause diseases in humans infecting the eye, genital organs, and lungs. The three main pathogenic species that infect humans are Chlamydia trachomatis, Chlamydophila psittaci, and Chlamydophila pneumoniae. - C. trachomatis causes trachoma (the leading cause of preventable blindness), and other genital infections. C. psittaci causes psittacosis which is transmitted from birds. C. pneumoniae causes atypical pneumonia. - Diagnosis involves microscopy, antigen detection, culture, PCR and serology. Treatment involves antibiotics like azithromycin, doxycycline and

1. Chlamydiae

2. Chlamydiae
• Obligate intracellular bacteria, cause a spectrum of diseases in man
infecting eye, genital organs and lungs.
• Chlamydia trachomatis: 19 serovars, trachoma, genital chlamydiasis,
inclusion conjunctivitis, infant pneumonia (serotype D-K) and LGV
(lymphogranuloma venereum)
• Chlamydophila psittaci: history of exposure to birds; atypical
pneumonia, IE
• Chlamydophila pneumoniae: exclusively human pathogen, causes
atypical pneumonia (CAP), rhinitis, bronchitis

3. • Family Chlamydiaceae comprises of two genera:
1. Chlamydia: It has one pathogenic species, C.trachomatis
2. Chlamydophila: It has two pathogenic species—C. psittaci and C.
pneumoniae. They cause interstitial (atypical) pneumonia
• Chlamydia trachomatis: Most common agent of NGU

4. Life cycle of Chlamydia
EBs are the extracellular and infective form; attach to
the specific receptors on the host cells (e.g. squamous
epithelial cells)
Following entry, they transform into reticulate
bodies; which are the intracellular form
RBs are replicative form; divide by binary fission.
They are also the metabolically active form and can
synthesize their own nucleic acid, lipids and proteins
except ATP; hence, they are called as energy parasites
RBs present inside the vacuole may enlarge to form
inclusion bodies

5. Antigenic Structure
• Genus/group specific antigen: Chlamydial lipopolysaccharide (LPS) is
genus specific. It plays an important role in the pathogenesis, acts by
induction of TNF-α and other proinflammatory cytokines, which leads
to scarring and fibrosis
• Species specific protein Ag: They are present at the envelope surface
• Serovar specific Ags: They are the major outer membrane proteins
(MOMP), encoded by ompA gene
• Other antigens: Such as outer membrane complex proteins and heat
shock proteins, play important role in pathogenesis.

6. • Chlamydia trachomatis is primarily a human pathogen, causing ocular,
urogenital and neonatal infections
• Historically, based on the disease produced, C. trachomatis was subdivided
into two strains or biovars
1. TRIC (Trachoma-inclusion conjunctivitis)
2. Lymphogranuloma venereum (LGV) biovar
• Based on antigenic structure of MOMP (and its gene ompA)
of C. trachomatis, 18 serovars have been identified affecting
humans

7. • Serovars A, B, Ba and C are associated primarily with ocular disease
called trachoma—a form of chronic keratoconjunctivitis
• Serovars D–K are associated with—(1) genital tract infections (2)
infant pneumonia (interstitial pneumonia) and (3) ocular disease,
called inclusion conjunctivitis
• Swimming pool conjunctivitis in adults
• Ophthalmia neonatorum in new born
• Serovars L1–L3 causes a sexually transmitted infection,
lymphogranuloma venereum (LGV), an ulcerative genital disease

8. • Nongonococcal urethritis (NGU): C. trachomatis is the most common
cause of nongonococcal urethritis (NGU), responsible for 30–50% of
cases of NGU
• Postgonococcal urethritis (PGU):C. trachomatis is the most common
cause of PGU
• This occurs when patients with GU are treated with penicillin or
cephalosporin alone without adding any antichlamydial drugs (such
as azithromycin)
• C. trachomatis is the most common cause of epididymitis in males

9. • Reactive arthritis (Reiter’s syndrome): It consists of conjunctivitis,
urethritis (or, in females-cervicitis), arthritis, and characteristic
mucocutaneous lesions
• It occurs in 1–2% of cases of NGU, develops after 1–4 weeks after
genital infection
• It is the most common cause of peripheral inflammatory arthritis in
young men
• Knee, ankle, small joints of feet and sacroiliac joints are commonly
affected
• Most of the patients possess HLA-B27 haplotype

10. • Mucopurulent cervicitis is the most common manifestation in females
• may progress to endometritis, salpingitis (fallopian tube), PID (pelvic
inflammatory disease) and finally pelvic peritonitis
• Perihepatitis (Fitz–Hugh–Curtis syndrome)

11. • Lymphogranuloma venereum (LGV) is an invasive systemic sexually
transmitted infection, caused by Chlamydia trachomatis serovars L1,
L2, and L3.
• The clinical course in three stages- First stage: Painless ulcer develops
on the penis or vulva after an incubation period of 3 days to 6 weeks
• Second stage: Inguinal lymph nodes in the groin become enlarged,
tender and soft (called bubo)
• Fistulae: Buboes may breakdown and discharge may spread externally
as chronic fistulae
• Groove sign (unilateral) may be present, as a result of enlargement of
nodes below the inguinal ligament

12. LGV
• Third stage: Occurs in untreated cases, especially in women and
homosexual men- Rectal stricture or rectovaginal and rectal fistulae
• Esthiomene—the vulva, scrotum or penis may undergo edematous
granulomatous hypertrophy
• Elephantiasis of the vulva or scrotum
• Lab Diagnosis of LGV is usually based on serology; Biopsy is
contraindicated as there is a risk of sinus tract formation

13. • C. pneumoniae is an exclusively human pathogen. It is transmitted from
person to person by inhalational route.
• Atypical pneumonia: C. pneumoniae is a common cause of atypical
(interstitial) pneumonia accounting for 10% of cases of community-
acquired pneumonia
• Upper respiratory tract involvement is frequent, such as pharyngitis and
sinusitis
• Atherosclerosis: There is a strong evidence of association between C.
pneumoniae and atherosclerosis of coronary and other arteries
• Asthma and COPD: C. pneumoniae may cause exacerbations of bronchial
asthma and COPD (chronic obstructive pulmonary disease)

14. • Interstitial or atypical pneumonia: It refers to infection of interstitial
space of lungs
• Cough is characteristically non-productive. Radiologically, it presents
as patchy reticulonodular opacities (chest X-ray) and ground glass
opacities (CT scan)

15. • C. psittaci is a pathogen of parrots and other psittacine birds causing
psittacosis
• Reservoirs: Pet birds (parrots, parakeets, macaws, and cockatiels) and
poultry (turkeys and ducks) act as natural reservoir of infection
• Mode of transmission: C. psittaci can be transmitted to humans by
inhalation of aerosols from avian nasal discharges and from infectious
avian fecal or feather dust
• Clinical manifestations: Incubation period ranges from 5–19 days. It can
present as—(1) Respiratory manifestation (most common form), varies
from a mild influenza-like syndrome to an interstitial pneumonia, (2) rarely
septicemia and typhoid-like syndrome

16. • Treatment: Tetracycline is the drug of choice, given 250 mg four times
a day for at least 3 weeks to avoid relapse.
• Erythromycin (500 mg four times a day, per oral) is given alternatively.

17. • Microscopy: Detects chlamydial inclusion bodies
• Gram staining, Lugol’s iodine and other stains such as Castaneda,
Machiavello or Gimenez stains
• Direct IF: Used for direct detection of inclusion bodies.
• Antigen detection (LPS antigens): By enzyme immunoassays
• Culture: was the gold standard method
• Egg (yolk sac), mice inoculation and cell line culture
• Cell lines of choice-
• McCoy, HeLa for C. trachomatis
• HEp2 for C.pneumoniae

18. • ELISA, MIF, uses the species and serovar specific MOMP (major outer
membrane protein) antigen
• Direct detection of inclusion bodies by direct IF
• Frei test: It is a skin test, used in the past to demonstrate type IV
hypersensitivity reaction in LGV

19. • Inclusion bodies: given various names such as
• Halberstaedter–Prowazek (H–P) body in trachoma
• Miyagawa corpuscle in LGV
• LCL body (Levinthal-Cole-Lillie) body in psittacosis

20. Anti-Chlamydia microimmunofluorescence test (MIF).
Chlamydia trachomatis inclusion bodies (brown) in
McCoy cell culture

21. • For obligate intracellular organisms, CMI remains the only effective
immune response
• CFT was widely used for detection of complement fixing antibodies in
Rickettsia, Chlamydia, Mycoplasma Infections
• A fourfold rise in specific IgM antibody titer between acute- and
convalescent-phase serum samples
• NAATs are currently the diagnostic assays of choice for chlamydial
infection as recommended by the CDC, replacing the so called gold
standard culture methods; opacity protein gene or 16S or 23S rRNA

22. Rx:
• For uncomplicated genital infection or trachoma or adult
conjunctivitis:
• Azithromycin is the drug of choice given as single dose of 1 gram
tablet, per oral
• Alternatively doxycycline, tetracycline, erythromycin or ofloxacin can
be given for at least a duration of 7 days
• Both the sex partners should be treated
• Ceftriaxone should be added to the regimen as co-infec. with
gonococcus may be present in most

23. • For complicated genital infection: Doxycycline (100 mg twice daily), or
erythromycin (500 mg four times daily) are the drugs of choice, given
for:
• 2 weeks for pelvic inflammatory disease and epididymitis
• 3 weeks for LGV- Longer treatment course is necessary; doxycycline
for 21 days is drug of choice. Azithromycin (weekly once for 3 weeks)
can be given alternatively

24. • Trachoma is a chronic keratoconjunctivitis, caused by C. trachomatis
serovars A, B, Ba and C
• Mode of transmission: Trachoma is transmitted through direct contact
(fingers and fomites) with discharges from the eyes of the infected patients
or indirect contact through contaminated clothes or flies
• Acute infection: It presents as follicular conjunctivitis (inflammation of
conjunctival lymphoid follicles) and papillary hyperplasia
• Late stage: Recurrent infection leads to conjunctival scarring or
cicatrization, concretions (whitish deposits), trichiasis (eyelashes falling on
eyeball) and corneal ulcers progressing to opacity and blindness

25. • Worldwide, the hyperendemic areas of trachoma include sub-Saharan
Africa, Middle East, and Southeast Asia including India
• Prevention: WHO has initiated an action plan called SAFE strategy, aiming
towards global elimination of trachoma, and prevention of blindness-
• Surgery: Needed in advanced stage to prevent corneal blindness
• Antibiotic (azithromycin single dose): Mass administration is given; the
target population chosen depends upon the prevalence of trachoma in
children in the area
• Facial hygiene such as frequent face wash and avoidance of use of common
towel, handkerchief
• Environmental sanitation to reduce transmission

26. • Topical therapy such as tetracycline or erythromycin eye ointment, given 4
times a day for 6 weeks
• Systemic therapy: Azithromycin is the drug of choice, given for 4 days.
Alternatives include tetracycline or doxycycline.
• Systemic antibiotic is indicated if the ocular infection is severe or when
there is associated genital infection
• The incidence of ophthalmia neonatorum (both gonococcal and
chlamydial) has been reduced dramatically after institution of appropriate
preventive measures during delivery
• Rx:topical ointment (erythromycin or tetracycline) plus oral erythromycin
given for 21 days.