Chlamydial Infections

Slide 1 · Chlamydial Infections

Pathogenesis • morphology • clinical correlation

Elementary body ⇄ Reticulate body

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Explain the elementary-body ⇄ reticulate-body cycle and the role of the inclusion

Associate serovars with anatomic disease patterns

Recognize urethritis and lymphogranuloma venereum morphology

Connect mucosal and ocular inflammation to long-term structural complications

Organism

Pathogenesis

Morphology

Clinical impact

Slide 3 · Chlamydia trachomatis: Defining properties

Small bacterium with a gram-negative cell organization

Obligate intracellular pathogen: Replication occurs inside a host cell

Infection couples specialized entry, protected intracellular growth, and release

Small bacterium

Intracellular growth

Biphasic forms

Slide 4 · What “obligate intracellular” means

A permissive host cell is needed for organism proliferation

The intracellular niche supplies metabolites and protects the growth phase

The infectious form and the replicating form perform different tasks

Outside host cell: Transmission

Inside host cell: Multiplication

Slide 5 · Host cell as a metabolic resource

The pathogen draws nutrients from the intracellular environment

Glucose-6-phosphate and glutamine support differentiation to the replicative form

A membrane-bound inclusion enables an adapted intracellular compartment

Host cell

Inclusion

Host cytoplasm

Original schematic — not a histologic image

Slide 6 · Two forms, two biological functions

Elementary body: Infectious and comparatively metabolically inactive

Reticulate body: Metabolically active, intracellular, replicating

Conversion between forms separates transmission from amplification

Elementary body

Infectivity • reduced metabolism

Reticulate body

Replication • active metabolism

Slide 7 · Elementary body: The infectious stage

Infectious elementary bodies bind susceptible host cells

They initiate entry rather than extensive extracellular replication

Their low metabolic activity contrasts with the reticulate form

Host cell

Inclusion

Elementary body

Original schematic — not a histologic image

Slide 8 · Host cell attachment precedes uptake

Elementary bodies first contact and bind the host-cell surface

Attachment is followed by bacterial manipulation of host actin

Entry culminates in uptake into a membrane-bounded compartment

Attachment

Actin remodeling

Uptake

Slide 9 · Type III secretion during entry

An elementary body injects effector molecules into the host cell using a type III secretion system

The injected effectors alter host-cell processes at the attachment site

This is an active pathogen-driven entry mechanism

Elementary body

Type III effectors

Host-cell response

Slide 10 · Actin remodeling facilitates entry

Secreted effectors trigger local changes in the host actin cytoskeleton

Remodeling occurs where the elementary body enters

The resulting cytoskeletal rearrangement supports phagocytic uptake

Effector delivery

Local actin change

Internalization

Slide 11 · Internalization creates a protected niche

The organism is taken into the cell by a phagocytic process

A membrane-bound inclusion originates from an endosomal compartment

The pathogen subsequently modifies this compartment for survival

Host cell

Inclusion

Surface uptake

Original schematic — not a histologic image

Slide 12 · Elementary-to-reticulate transition

Intracellular host metabolites permit differentiation of the elementary body

The resulting reticulate body becomes metabolically active

This transition precedes intracellular replication

Elementary body

Host metabolites

Reticulate body

Slide 13 · The inclusion is more than a vacuole

Reticulate bodies persist within a membrane-bound inclusion

The inclusion is derived from an endosomal membrane

Its membrane is actively remodeled by bacterial products

Host cell

Inclusion

Inclusion membrane

Original schematic — not a histologic image

Slide 14 · Inclusion membrane proteins: “Incs”

Type III secretion delivers proteins that alter the inclusion membrane

These inclusion membrane proteins are termed Incs

They help create a compartment favorable for chlamydial growth

Type III secretion

Incs at membrane

Modified inclusion

Slide 15 · Escape from phagolysosomal destruction

A conventional endocytic compartment can mature toward a degradative phagolysosome

Incs and other bacterial molecules obstruct that maturation

The protected inclusion permits survival of intracellular reticulate bodies

Unmodified vesicle

Phagolysosomal maturation

Chlamydial inclusion

Maturation prevented

Slide 16 · Protection against autophagy

The intracellular inclusion is also protected from host autophagic clearance

Incs and additional bacterial molecules contribute to this protection

Avoiding degradative pathways favors persistence of the replicative niche

Host autophagic clearance

Bacterial countermeasures

Inclusion protected

Slide 17 · Nutrient acquisition across the inclusion

Reticulate bodies require access to host-cell nutrients

The modified inclusion facilitates nutrient entry

Nutrient use supports bacterial metabolism and reproduction

Host metabolites

Modified inclusion

Bacterial growth

Slide 18 · Reticulate body: Intracellular amplification

Reticulate bodies use host-derived nutrients to replicate

Replication increases the number of organisms within the inclusion

This is the active multiplication stage of the cycle

Host cell

Inclusion

Replicating reticulate bodies

Original schematic — not a histologic image

Slide 19 · Reappearance of infectious elementary bodies

After reticulate-body replication, newly infectious elementary bodies form

Differentiation prepares progeny organisms for transmission to additional cells

An infected inclusion may therefore contain successive developmental stages

Reticulate body expansion

Developmental conversion

Elementary bodies

Slide 20 · Two routes of exit

New infectious organisms are released by lysis of the infected host cell or by extrusion

Either route delivers elementary bodies to the extracellular environment

Released elementary bodies can initiate another host-cell infection

Lysis

Infected cell breaks open

Extrusion

Organisms leave in an extruded compartment

Slide 21 · Life cycle: One integrated sequence

Elementary body → attachment and type III-dependent entry

Inclusion formation → differentiation to reticulate body → replication

Elementary body re-formation → lysis or extrusion

EB entry

Inclusion

RB division

EB formation

Release

Infectious → replicative → infectious

Slide 22 · Why the cycle matters for tissue injury

Intracellular growth permits organism multiplication in epithelial cells

Release enables involvement of additional host cells and sites

The host inflammatory response contributes to mucosal lesions and their sequelae

Epithelial infection

Local inflammatory response

Tissue consequences

Slide 23 · Serovar–syndrome map

Different C. Trachomatis serovars preferentially produce different disease syndromes

A–C: Trachoma; D–K: Genital infection and inclusion conjunctivitis

L1–L3: Lymphogranuloma venereum

A–C

Trachoma

D–K

Genital infection • inclusion conjunctivitis

L1–L3

Lymphogranuloma venereum

Slide 24 · Different sites, one pathogen species

The same species is associated with ocular, urogenital, and lymphatic manifestations

Serovar identity is linked to the characteristic clinical syndrome

Organism identification alone does not specify the full extent of tissue injury

C. Trachomatis

Genital mucosa

Conjunctiva

Regional nodes

Slide 25 · Genital infection: Population relevance

C. Trachomatis as a leading bacterial sexually transmitted infection

Infections may be clinically silent and remain untreated

Silent infection is important because complications may occur beyond the initial mucosal site

Common infection

Often unrecognized

Potential sequelae

Slide 26 · Sexual transmission and silent reservoirs

Chlamydial genital infection is primarily transmitted through sexual contact

Transmission may occur from a person without recognized symptoms

The absence of symptoms does not imply absence of infection

Asymptomatic infection

Sexual exposure

New mucosal infection

Slide 27 · Anatomic spectrum of genital infection

Lower genital tract: Urethritis and cervicitis

Adjacent or ascending involvement: Epididymitis, prostatitis, endometritis, salpingitis

Extragenital mucosa or surfaces: Proctitis, pharyngitis, conjunctivitis

C. Trachomatis

Urethra / cervix

Upper genital tract

Rectum / pharynx / eye

Slide 28 · Chlamydial urethritis: Clinical presentation

Urethral infection may cause local symptoms or remain asymptomatic

Commonly silent chlamydial urethritis with gonococcal urethritis in men

Unrecognized urethritis can delay testing and treatment

Symptomatic

Discharge and local irritation

Asymptomatic

No obvious warning signs

Slide 29 · Urethritis: Predominant exudate

Acute chlamydial urethritis may produce a mucopurulent discharge

Neutrophils predominate in the inflammatory exudate

This inflammatory pattern is not unique to Chlamydia

Mucosal epithelium

Neutrophil-rich inflammatory zone

Simplified inflammation schematic — not microscopy

Slide 30 · Why a Gram stain can mislead

Chlamydial organisms are not visible in routine Gram-stained smears or sections

Neutrophil-rich discharge indicates inflammation rather than a specific cause

A negative organism finding on Gram stain does not exclude chlamydial urethritis

Mucopurulent exudate

No visible organisms

Nucleic-acid test

Morphology is not etiologic confirmation

Slide 31 · Nucleic-acid amplification: Diagnostic principle

Amplified nucleic-acid testing for C. Trachomatis urethritis

Acceptable specimen categories in the text include genital swabs and urine

The diagnostic target is microbial nucleic acid rather than visually detectable bacteria

Genital swab OR urine

Amplified nucleic-acid test

Organism detected

Morphology is not etiologic confirmation

Slide 32 · Gonorrhea and chlamydia: Overlapping phenotype

Both may cause urethritis and genital mucosal infection

Their urethritis morphology is virtually identical

Clinical symptoms and neutrophils alone cannot reliably separate the two infections

Chlamydial urethritis

Neutrophilic mucosal exudate

Gonococcal urethritis

Similar inflammatory phenotype

Slide 33 · The discriminating value of organism visibility

Gonococci may appear as gram-negative diplococci within neutrophils in exudate

Chlamydiae are not visualized on routine Gram-stained sections or smears

Microbiological testing, rather than appearance alone, determines the etiology

Gonorrhea

Diplococci may be seen

Chlamydia

Organisms not seen by Gram stain

Slide 34 · The broad differential of nongonococcal urethritis

Chlamydia is one important cause of nongonococcal urethritis

Robbins also describes Ureaplasma and noninfectious urethritis

The morphologic label “urethritis” is not a microbiologic diagnosis

Urethritis

Gonococcal

Nongonococcal / noninfectious

Slide 35 · Female genital infection: Cervicitis

The female genital tract chapter describes cervicitis as the predominant presentation

Chlamydial infection in females is frequently asymptomatic

Cervical involvement can be a starting point for ascending infection

Cervix

Uterus

Fallopian tube

Schematic of anatomic relationships / consequences

Slide 36 · Ascending chlamydial infection

In some patients infection ascends from the cervix

Endometritis and salpingitis may develop as infection involves the upper genital tract

This places Chlamydia among recognized causes of pelvic inflammatory disease

Cervicitis

Endometritis

Salpingitis

Schematic of anatomic relationships / consequences

Slide 37 · Pelvic inflammatory disease: Clinical picture

PID is infection and inflammation involving upper female genital structures

The source associates PID with pelvic pain, adnexal tenderness, fever, and discharge

This is a syndrome with multiple possible microbial causes

Upper-tract inflammation

Pelvic pain / tenderness

Fever / discharge

Slide 38 · PID has multiple etiologies

Chlamydia and gonorrhea are both established causes of PID

Other pelvic infections may be polymicrobial, including postprocedural or puerperal disease

A diagnosis of PID does not by itself identify the organism

STI-associated

Chlamydia • gonorrhea

Other contexts

Mixed postprocedural or puerperal infection

Slide 39 · From tubal inflammation to impaired function

Inflammation of the fallopian tubes may lead to healing with scarring

Distortion of the tube and fimbriae can impair oocyte capture or passage

Infertility and ectopic pregnancy are recognized sequelae of PID in the source

Tubal inflammation

Healing and scarring

Transport impairment

Slide 40 · Why infertility can follow PID

Normal tubal architecture matters for transport of the oocyte

PID-related scarring may obstruct the lumen or alter fimbrial function

Structural damage may persist after the active infection has resolved

Patent tube

Scarred tube

Reduced transport

Schematic of anatomic relationships / consequences

Slide 41 · Ectopic pregnancy: The pathological link

Tubal damage can interfere with orderly passage of the conceptus

The female genital tract chapter lists ectopic pregnancy among PID sequelae

The relationship is a complication of tubal injury, not a diagnostic sign of active Chlamydia

Prior salpingitis

Tubal dysfunction

Ectopic risk

Slide 42 · Other sites of chlamydial inflammation

The infectious-diseases chapter lists epididymitis and prostatitis among associated syndromes

Pharyngitis, proctitis, and perihepatic inflammation are also described

Clinical evaluation depends on the affected anatomic site

C. Trachomatis

Genitourinary

Rectal / pharyngeal

Perihepatic

Slide 43 · Perinatal acquisition and conjunctivitis

The general STI section describes perinatal C. Trachomatis as a cause of neonatal conjunctivitis

The maternal genital infection may be clinically silent

Neonatal conjunctivitis is distinct from serovar A–C trachoma

Maternal genital infection

Perinatal exposure

Neonatal conjunctivitis

Slide 44 · Lymphogranuloma venereum: Distinct serovars

L1, L2, and L3 cause lymphogranuloma venereum (LGV)

Unlike uncomplicated mucosal infection, LGV features ulcerative lesions and regional lymph node disease

The course can proceed from acute inflammation to fibrosis and strictures

L serovars

Node-centered inflammation

Late obstruction

Slide 45 · The early LGV lesion may be missed

LGV may begin with a small papule on genital mucosa or nearby skin

The initial lesion is often inconspicuous

Subsequent lymphadenopathy may dominate the clinical presentation

Small papule

Stage 1

Often unnoticed

Stage 2

Regional nodes

Stage 3

Slide 46 · The lymph-node phase develops over weeks

A 2–6 week interval after the primary lesion

Bacterial growth and host response develop in draining regional nodes

Nodes become enlarged and tender

Initial papule

Stage 1

2–6 weeks

Stage 2

Tender lymphadenopathy

Stage 3

Slide 47 · Coalescent nodes and rupture in LGV

Regional lymph nodes may coalesce as inflammation progresses

Advanced inflamed nodes may rupture

This clinical progression reflects intense destructive lymphadenitis

Tender nodes

Coalescence

Possible rupture

Slide 48 · Mixed inflammatory pattern in LGV lesions

The source describes both granulomatous and neutrophilic inflammation

The mixture suggests an ongoing inflammatory response with focal tissue destruction

LGV is therefore not appropriately characterized as purely granulomatous

Mucosal epithelium

Neutrophil-rich inflammatory zone

Simplified inflammation schematic — not microscopy

Slide 49 · LGV lymphadenitis: Stellate abscesses

Affected nodes contain irregular foci of necrosis populated by neutrophils

The source names these lesions stellate abscesses

Granulomatous inflammation surrounds or accompanies the necrotic foci

Stellate abscess

Inflammatory nodal tissue

Schematic only; No specimen image supplied

Slide 50 · Intracytoplasmic inclusions may be present

Variable numbers of chlamydial inclusions may be seen in epithelial or inflammatory cells

This finding corresponds to the intracellular phase of the organism

Inclusions are variable: Absence in a particular section is not definitive exclusion

Host cell

Inclusion

Epithelial / inflammatory cell

Original schematic — not a histologic image

Slide 51 · Chronic LGV: Inflammatory remodeling

With time, chronic inflammatory cells and fibrosis predominate

Destructive inflammation can be replaced by scar tissue

Late pathological findings may differ markedly from active suppurative lymphadenitis

Acute mixed reaction

Stage 1

Chronic inflammation

Stage 2

Fibrosis

Stage 3

Slide 52 · Lymphatic obstruction and lymphedema

Fibrosis from chronic LGV can obstruct local lymphatic channels

Impaired lymph drainage can produce lymphedema

The obstructive consequence is explained by tissue remodeling, not merely organism burden

Fibrotic remodeling

Lymphatic obstruction

Lymphedema

Slide 53 · Anogenital strictures: Late complications

Anogenital fibrosis can narrow luminal structures

The source particularly emphasizes rectal strictures in females

Stricture represents a chronic structural endpoint of untreated infection

Chronic injury

Collagenous fibrosis

Stricture

Slide 54 · LGV proctitis: An important syndrome

Robbins records LGV as a cause of proctitis in men who have sex with men

It describes sporadic cases in the United States and Western Europe

The anatomic presentation can draw attention to lymphatic and rectal complications

C. Trachomatis

Anorectal mucosa

Draining nodes

Fibrotic changes

Slide 55 · Active versus chronic LGV diagnosis

Detection of organisms in biopsy or exudate during active disease

For chronic cases, it discusses antibodies directed at the relevant serovars

These statements report the supplied textbook, not an independently updated diagnostic guideline

Active lesion

Organism demonstration

Chronic lesion

Serotype antibody approach in textbook

Slide 56 · Non-LGV and LGV: Pathological contrast

D–K genital infection: Often silent mucosal disease with neutrophilic urethral discharge

L serovars: Ulcerative disease, regional lymphadenitis, stellate abscesses

Late LGV may progress to lymphatic obstruction, lymphedema, and strictures

D–K infection

Mucosal-centered inflammation

L1–L3 infection

Ulcerative • nodal • fibrosing disease

Slide 57 · Trachoma: The ocular serovar group

Serovars A, B, and C produce trachoma, particularly an ocular infection of children

The eye chapter identifies trachoma as an important preventable cause of blindness

Chronic injury involves the conjunctival surface and tear-producing apparatus

A–C serovars

Repeated ocular inflammation

Scarring and vision loss

Slide 58 · How trachoma spreads

The eye chapter describes contact transmission involving hands, clothing, bedding, and surfaces

Flies contaminated by ocular or nasal discharge can contribute to spread

This differs from the primary sexual-transmission context of genital serovars

C. Trachomatis

Contact materials

Ocular/nasal discharge

Flies

Slide 59 · Conjunctival scarring is the critical lesion

Untreated trachoma and conjunctivitis may cause progressive conjunctival scarring

Severe scarring can obliterate the conjunctival fornix

Loss of normal ocular surface structures contributes to functional impairment

Conjunctival fornix

Scarring

Surface dysfunction

Ocular-surface function

Scarring can produce dryness, irritation, and visual loss

Slide 60 · Loss of goblet cells reduces mucin

The normal fornix contains goblet cells

Scarring and fornix obliteration can remove these mucin-producing cells

Reduced mucin compromises the protective tear-film surface

Goblet cells

Mucin

Tear-film function

Ocular-surface function

Scarring can produce dryness, irritation, and visual loss

Slide 61 · Lacrimal ductule injury reduces tears

Ocular scarring can damage or obliterate lacrimal ductules

Less tear delivery aggravates dryness of the ocular surface

Mucin loss and tear insufficiency act together in the severe end-stage eye

Ductule destruction

Reduced tears

Dry ocular surface

Slide 62 · Trichiasis adds mechanical corneal injury

Trachoma-associated scarring can misdirect eyelashes toward the cornea

This condition is termed trichiasis

Mechanical irritation compounds the damage from chronic dryness

Scarred lid

Misdirected lashes

Corneal irritation

Ocular-surface function

Scarring can produce dryness, irritation, and visual loss

Slide 63 · The pathway to painful blindness

Severe conjunctival scarring leads to mucin and tear deficiency

Trichiasis adds persistent corneal irritation

The combination may culminate in a very dry, painful eye with blindness

Conjunctival scarring

Dryness + trichiasis

Painful visual loss

Slide 64 · Case: Inflammatory discharge without visible bacteria

A patient has urethral discharge rich in neutrophils, but no organisms are identifiable by Gram stain

The result is compatible with chlamydial urethritis but is not organism-specific

The supported next diagnostic principle is an amplified nucleic-acid test on an appropriate sample

1

Neutrophil-rich

2

Gram stain negative for organisms

3

NAAT needed

Slide 65 · Case: New tender nodes after a small papule

A small genital papule was barely noticed several weeks earlier

Tender, enlarging regional nodes now dominate the presentation

This temporal pattern supports consideration of LGV caused by L serovars

1

Unnoticed papule

2

2–6 weeks

3

Tender lymphadenopathy

Slide 66 · Case: An unusual nodal abscess pattern

A lymph-node specimen contains granulomatous inflammation and irregular neutrophil-rich necrotic foci

The combination resembles the stellate-abscess morphology described in LGV

Clinical history and organism-specific investigation remain necessary

1

Granulomatous nodes

2

Stellate abscesses

3

Correlate with infection

Slide 67 · Case: Infertility following pelvic infection

A prior episode of pelvic inflammatory disease is followed by infertility

Tubal scarring can disrupt passage of an oocyte or conceptus

This is a downstream PID complication and does not alone establish a particular pathogen

1

Prior PID

2

Possible tubal scar

3

Infertility

Slide 68 · Case: Ocular dryness and inward lashes

Longstanding conjunctival inflammation is followed by scarring, dryness, and eyelashes directed toward the cornea

Loss of mucin and tear delivery plus trichiasis provide a coherent mechanism

This pattern is consistent with advanced trachomatous damage

1

Scarred fornix

2

Reduced tears

3

Trichiasis

Slide 69 · Integrative pathology map

Intracellular survival depends on inclusion remodeling, nutrient acquisition, and cycle switching

Mucosal infection may be silent yet ascend or produce extragenital manifestations

LGV and trachoma illustrate long-term consequences of chronic inflammation and fibrosis

C. Trachomatis

Intracellular growth

Mucosal inflammation

Fibrotic sequelae

Slide 70 · Three distinctions that prevent diagnostic error

Elementary bodies transmit infection; Reticulate bodies multiply inside cells

A neutrophil-rich smear cannot establish chlamydial etiology by morphology alone

LGV nodal abscesses and trachomatous ocular scarring have different anatomic consequences

Question

Correct distinction

Infectious form?

Elementary body

Gram-stained organism?

Usually not visible

LGV lesion?

Stellate abscess + fibrosis

Trachoma endpoint?

Conjunctival scar + painful blindness

Slide 71 · Source readings

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th ed. (2026)

Source sections: chlamydial infections, sexually transmitted infections, and Neisseria for differential comparison

Related pathology: urethral inflammation, female genital infections, and pelvic inflammatory disease

Related eye pathology: trachoma and ocular-surface scarring

Disease mechanism

Genital pathology

Ocular pathology