Infectious Enterocolitis

Slide 1 · Infectious Enterocolitis

Mechanisms • morphology • clinicopathologic correlation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Link pathogen localization and virulence strategy to the diarrheal phenotype

Recognize mechanisms of secretory, inflammatory, and malabsorptive injury

Distinguish common bacterial, viral, and parasitic infections

Interpret histology without overcalling an organism-specific diagnosis

Slide 3 · Clinical spectrum: One syndrome, many mechanisms

Diarrhea may coexist with pain, urgency, perianal discomfort, incontinence, or bleeding

Small bowel infection often produces watery diarrhea and malabsorption

Invasive colonic disease more often causes dysentery and systemic inflammation

Clinical phenotype narrows—but does not prove—the causal pathogen

Slide 4 · Etiologic families and dominant patterns

Group

Typical setting

Usual pathological response

Bacterial

Food, water, host-to-host exposure

Secretory injury or inflammatory colitis

Viral

Close-contact outbreaks; Pediatric infection

Enterocyte injury, transient villous dysfunction

Protozoal

Contaminated water; Immune deficiency

Surface adherence or invasive ulceration

Helminthic

Soil / food exposures

Eosinophilia, mucosal injury, obstruction

Slide 5 · Host context changes the causal spectrum

Age and nutrition change susceptibility and consequences

Immune status influences organism clearance and dissemination

Geography, sanitation, and access to clean water modify exposure

Travel, antibiotic exposure, and food history are diagnostically informative

Slide 6 · Read the stool phenotype as a mechanism

Phenotype

Mechanistic clue

Illustrative pathogens

Profuse watery

Active electrolyte secretion

Vibrio cholerae, ETEC

Bloody / exudative

Invasion or toxin-associated mucosal injury

Shigella, Campylobacter, EHEC

Malabsorptive / prolonged

Impaired enterocyte function or lymphatic drainage

Giardia, Whipple disease

Post-antibiotic watery

Dysbiosis and toxin injury

Clostridioides difficile

Slide 7 · Three pathogen–mucosa relationships

Luminal colonization

Secretory signaling

Watery stool

Noninvasive toxins can drive major fluid loss with little histologic injury

Tissue invasion instead recruits neutrophils, causes epithelial injury, and can produce bleeding

Schematic

Slide 8 · Anatomic localization helps interpretation

Predominant site

Examples

Clinical / tissue clue

Small intestine

Cholera, ETEC, EPEC, Giardia

Watery diarrhea or malabsorption

Colon

Campylobacter, Shigella, EHEC, C. Difficile

Inflammation, blood, or pseudomembranes

Ileum / right colon

Yersinia, typhoid, Cryptosporidium

Peyer patch involvement or focal ileitis

Slide 9 · Beyond stool frequency: Major complications

Fluid and electrolyte loss may cause hypotension or shock

Epithelial damage may result in hemorrhage or toxic megacolon

Invasive pathogens can disseminate through lymphatic or blood vessels

Immune-mediated sequelae can persist after intestinal symptoms resolve

Slide 10 · Vibrio cholerae: Exposure and tissue niche

Comma-shaped gram-negative organisms inhabit aquatic reservoirs, including shellfish and plankton

Fecally contaminated water is a major route of epidemic spread

Loss of sewage infrastructure increases risk of large outbreaks

Disease targets the small intestine without direct mucosal invasion

Slide 11 · Cholera colonization precedes toxigenic diarrhea

Fecal–oral inoculation

Small bowel colonization

Enterotoxin release

Epithelial ion transport

Organism motility and adherence support intestinal colonization

Bacterial detachment and shedding help onward transmission

Schematic

Slide 12 · Cholera toxin is an A–B5 complex

Five B subunits engage GM1 ganglioside on enterocytes

A subunit is responsible for intracellular enzymatic signaling

The toxin is encoded by a bacterial virulence phage

Severe diarrhea reflects disrupted host ion transport—not deep invasion

Slide 13 · Cholera toxin entry pathway

B-subunit binding

Retrograde ER transport

A fragment enters cytosol

Gsα modification

Protein disulfide isomerase processes the A subunit in the ER

Host machinery returns the catalytically active fragment into the cytosol

Schematic

Slide 14 · Cholera: From Gsα to luminal water

Gsα activation

Adenylate cyclase

CAMP elevation

CFTR Cl⁻ secretion

Water loss

Toxin-mediated ADP ribosylation locks Gsα in its active state

CAMP also suppresses absorptive ion transport, amplifying net secretion

Schematic

Slide 15 · Severe fluid loss with subtle histology

Preserved mucosal architecture

Schematic — not a histologic specimen

Massive secretory diarrhea can coexist with minimally altered villi and crypts

A near-normal biopsy cannot exclude cholera

Clinical dehydration severity does not track the degree of mucosal destruction

Slide 16 · Cholera clinical syndrome

Severe cases begin abruptly with vomiting and voluminous watery stool

“Rice-water” stools reflect profound fluid-rich output

Hypotension, cramps, oliguria or anuria, and shock follow rapid fluid depletion

Dehydration is the immediate life-threatening pathophysiology

Slide 17 · Fluid depletion explains systemic manifestations

Excess luminal fluid

Extracellular volume loss

Reduced perfusion

Shock / renal injury

Electrolyte imbalances and muscular cramping accompany volume depletion

Time-critical fluid replacement reverses the principal physiological defect

Schematic

Slide 18 · Secretory diarrhea: Key distinctions

Finding

Cholera

Invasive bacterial colitis

Bacterial location

Luminal, noninvasive

Mucosal epithelial / lamina propria invasion

Typical stool

High-volume watery

Often inflammatory or bloody

Biopsy

Usually minimal change

Cryptitis, erosions, neutrophils

Major threat

Hypovolemia

Mucosal damage ± systemic consequences

Slide 19 · Campylobacter: Food and animal exposure

C. Jejuni is a prominent enteric pathogen in high-resource settings

Undercooked poultry, unpasteurized milk, and contaminated water are major exposures

Farm animals and pets can transmit infection

Direct person-to-person spread is relatively uncommon

Slide 20 · Campylobacter virulence is multifactorial

Motility

Mucosal adherence

Toxin / invasion

Epithelial inflammation

Flagella enhance intestinal colonization

Some strains cause direct epithelial injury; Invasive strains can produce dysentery

Schematic

Slide 21 · Campylobacter: Acute self-limited colitis

Schematic — not a histologic specimen

Neutrophils infiltrate superficial epithelium and crypts

Crypt abscesses may form from intra-crypt neutrophils

Overall crypt architecture often remains preserved

This pattern is not specific for Campylobacter

Slide 22 · Campylobacter clinical and immune sequelae

Manifestation

Biological connection

Watery diarrhea

Inflammatory or enterotoxic epithelial dysfunction

Dysentery

Invasive bacterial phenotype

Reactive arthritis

Postinfectious immune complication; HLA-B27 association

Guillain–Barré syndrome

Ganglioside-directed cross-reactivity after infection

Slide 23 · Campylobacter: Symptoms and diagnosis

A prodrome may precede abdominal pain and watery diarrhea

Some patients develop bloody stools, especially children

Culture-based stool testing establishes the organism

Biopsy demonstrates acute colitis but usually cannot identify the pathogen

Slide 24 · Shigella: Efficient fecal–oral spread

Humans are the recognized reservoir

Acid resistance and a low infective dose facilitate transmission

Crowded settings and inadequate sanitation increase exposure

Shigellosis frequently produces dysentery

Slide 25 · Shigella traverses the mucosal barrier

M-cell uptake

Macrophage injury

Basolateral entry

Epithelial cell invasion

The inflammatory response disrupts surface integrity

Type III secretion machinery assists delivery of bacterial effectors into host cells

Schematic

Slide 26 · Shiga toxin adds cytotoxic damage

Shigella dysenteriae serotype 1 can produce Shiga toxin

Toxin inhibits eukaryotic protein synthesis and kills host cells

Severe mucosal injury underlies bleeding and ulceration

Shiga toxin may be complicated by hemolytic uremic syndrome

Slide 27 · Shigella: Ulcerative inflammatory colitis

Erosion

Schematic — not a histologic specimen

The left colon is commonly affected; Ileal involvement is possible

Hemorrhage, ulceration, and occasional pseudomembranes may be seen

Aphthous ulcers can resemble Crohn disease

Architecture and disease distribution must be interpreted with clinical context

Slide 28 · Shigellosis: Clinical consequences

Fever, cramps, diarrhea, and bloody stools develop during acute infection

Reactive arthritis may be accompanied by urethritis and conjunctivitis

Severe toxin-associated disease can cause hemolytic uremic syndrome

A subacute presentation may mimic inflammatory bowel disease

Slide 29 · Nontyphoidal Salmonella: Foodborne infection

Raw or undercooked meat, poultry, eggs, and milk are common sources

Young children and older adults are especially affected

Food handling and delayed refrigeration can facilitate outbreaks

The illness is commonly self-limited gastroenteritis

Slide 30 · Salmonella promotes enterocyte uptake

Type III secretion

Rho GTPase activation

Actin rearrangement

Endocytosis

Intracellular bacterial survival enables mucosal infection

Innate sensors TLR4 and TLR5 amplify host inflammation

Schematic

Slide 31 · Recruitment of neutrophils damages mucosa

Epithelial hepoxilin A3

Neutrophil chemotaxis

Crypt / surface injury

Exudative stool

Neutrophils help control infection but intensify epithelial damage

Inflammatory signaling supports the dysenteric phenotype

Schematic

Slide 32 · Nontyphoidal salmonellosis: Clinical range

Symptoms range from loose stool to profuse diarrhea or dysentery

Stool testing distinguishes it from other acute enteric pathogens

Bacterial shedding may persist beyond clinical recovery

Immunocompromised hosts face greater risk of invasive complications

Slide 33 · Host defense determines dissemination risk

Th1 and Th17 responses contribute to bacterial clearance

Impaired cell-mediated immunity increases the risk of systemic infection

Hemolytic anemia, sickle cell disease, and other comorbidities can worsen outcomes

Postinfectious arthritis and bowel dysfunction are recognized sequelae

Slide 34 · Enteric fever is not simple salmonellosis

Feature

Nontyphoidal Salmonella

S. Typhi / Paratyphi

Typical pattern

Acute intestinal gastroenteritis

Systemic enteric fever

Distribution

Small bowel and colon

Small bowel with systemic spread

Bacteremia

In selected high-risk hosts

Integral to illness evolution

Tissue response

Neutrophilic enterocolitis

Mononuclear phagocyte / lymphoid response

Slide 35 · Typhoid: Mucosal entry to systemic disease

Ileal M-cell entry

Lymphatic spread

Bacteremia

Reticuloendothelial response

Humans are the principal reservoir for typhoidal Salmonella

Gallbladder colonization can support chronic carriage

Schematic

Slide 36 · Typhoid morphology: The Peyer patch lesion

Terminal ileum

Enlarged Peyer patches

Schematic — not a histologic specimen

Peyer patches enlarge within the terminal ileum

Macrophage-rich inflammation and epithelial loss may create longitudinal ulcers

Ulcers may penetrate the bowel wall and perforate

Regional lymph nodes and spleen show reactive enlargement

Slide 37 · Systemic morphology in enteric fever

The spleen may be enlarged, soft, and rich in phagocytes

Typhoid nodules are macrophage-rich hepatic lesions with focal necrosis

Reticuloendothelial involvement reflects systemic dissemination

Intestinal perforation is a serious consequence of deep ulceration

Slide 38 · Typhoid fever: Changing clinical phases

Gastrointestinal symptoms can precede an interval of systemic fever

Bacteremia produces constitutional illness; Rose spots may occur

Extraintestinal complications include neurologic and cardiac involvement

Blood cultures contribute to microbiologic confirmation during febrile disease

Slide 39 · Yersinia: Right-sided enterocolitis

Y. Enterocolitica and Y. Pseudotuberculosis cause intestinal infection

Exposure is linked to pork, raw milk, and contaminated water

Ileum, appendix, and right colon are favored sites

Lymphoid involvement can simulate acute appendicitis

Slide 40 · Yersinia targets mucosal lymphoid tissue

Adhesin–β1 integrin binding

M-cell invasion

Peyer patch response

Regional adenitis

Lymphoid tissue supports bacterial proliferation and inflammation

Iron acquisition systems can increase virulence and systemic spread

Schematic

Slide 41 · Yersinia: An infectious Crohn mimic

Ileal / appendiceal region

Lymphoid hyperplasia + focal ulcer

Schematic — not a histologic specimen

Focal aphthous ulcers and granulomas can occur

Lymphoid hyperplasia, neutrophils, and bowel-wall thickening may coexist

A right-sided distribution supports but does not establish Yersinia

Culture and exposure history prevent a mistaken chronic IBD diagnosis

Slide 42 · Yersinia clinical presentation

Abdominal pain and tenderness can dominate over diarrhea

Mesenteric lymphadenitis produces pseudoappendicitis

Postinfectious reactive arthritis and erythema nodosum are recognized

Stool culture may require organism-selective conditions

Slide 43 · E. Coli pathotypes are mechanistically distinct

Pathotype

Main interaction

Characteristic syndrome

ETEC

Secreted LT / ST enterotoxins

Watery traveler’s diarrhea

EPEC

Attaching-and-effacing injury

Infant watery diarrhea

EHEC

Shiga-like toxin-associated damage

Hemorrhagic colitis ± HUS

EIEC

Intracellular epithelial invasion

Inflammatory diarrhea

EAEC

Aggregative adherence

Sometimes prolonged nonbloody diarrhea

Slide 44 · ETEC: Two routes to secretory diarrhea

Luminal ETEC

Heat-labile LT / heat-stable ST

CAMP / cGMP

Net ion secretion

ETEC remains noninvasive

Histologic change is often mild despite abundant watery stool

Schematic

Slide 45 · Cyclic nucleotide mechanisms

Toxin

Host signal

Principal consequence

Cholera toxin

Activated Gsα → adenylate cyclase → cAMP

CFTR-associated chloride and water secretion

ETEC heat-labile toxin

Adenylate cyclase → cAMP

Chloride-rich watery output

ETEC heat-stable toxin

Guanylate cyclase → cGMP

Altered epithelial ion transport

Slide 46 · EPEC produces attaching-and-effacing lesions

Apical adherence / microvillus effacement

Schematic — not a histologic specimen

Bacteria adhere intimately to the enterocyte apical surface

Adjacent microvilli are effaced rather than invaded deeply

Loss of brush-border function contributes to watery diarrhea

Bacterial factors responsible for adherence can aid molecular diagnosis

Slide 47 · EHEC: Exposure and toxin-mediated colitis

Cattle are an important reservoir; Undercooked beef and contaminated produce transmit infection

O157:H7 and other serotypes produce Shiga-like toxins

EHEC may cause hemorrhagic diarrhea and systemic toxicity

Recognition matters because toxin-associated HUS is a major complication

Slide 48 · EHEC: Mucosal toxin to microangiopathy

Shiga-like toxin

Cellular injury

Hemorrhagic colitis

HUS risk

The mechanism can resemble ischemic injury in colonic biopsies

Source text warns that antibiotics may enhance toxin release and HUS risk

Schematic

Slide 49 · EHEC may mimic ischemic injury

Surface epithelial attenuation

Schematic — not a histologic specimen

Surface epithelial atrophy and erosion can predominate

Ischemia-like morphology does not prove primary vascular insufficiency

Correlate with bloody diarrhea and epidemiologic exposure

Stool microbiology and toxin detection resolve etiologic uncertainty

Slide 50 · EIEC: Inflammation without chronic distortion

Schematic — not a histologic specimen

EIEC invades the intestinal epithelium much like Shigella

Acute self-limited colitis includes cryptitis and intraepithelial neutrophils

Preserved crypt spacing helps differentiate acute from chronic injury

Inflammatory histology is not pathotype-specific

Slide 51 · EAEC: Adherence with limited tissue damage

Aggregative fimbriae support epithelial attachment

Dispersin reduces electrostatic repulsion at the bacterial surface

Nonbloody diarrhea may persist, particularly with immune dysfunction

Biopsy changes may be minimal

Slide 52 · C. Difficile follows loss of microbial resistance

Antibiotics disrupt normal colonic microbial communities

C. Difficile can overgrow and elaborate toxins

Hospital exposure, older age, and impaired immunity increase susceptibility

Colonization without symptomatic disease must be distinguished from colitis

Slide 53 · C. Difficile toxins break epithelial integrity

Toxin exposure

Rho-family GTPase disruption

Cytoskeletal failure

Junction loss + cell death

Proinflammatory cytokines and neutrophils amplify injury

Barrier disruption enables inflammatory exudate to reach the surface

Schematic

Slide 54 · The pseudomembrane “volcano” pattern

Surface exudate

Schematic — not a histologic specimen

Damaged, dilated crypts release a column of mucopurulent material

Neutrophils, fibrin, and necrotic epithelial debris accumulate on the surface

Coalescent exudates form pale adherent pseudomembranes

Schematic illustrates morphology; It is not a histologic specimen

Slide 55 · Pseudomembranes are a pattern, not a microbiologic test

Observation

Interpretation

Surface exudate of fibrin and neutrophils

Suggests severe superficial epithelial injury

Crypt-associated “volcano” lesion

Strongly favors C. Difficile in appropriate context

Similar membranes in ischemia or necrotizing infections

Morphology is not universally organism-specific

Positive organism detection without symptoms

May indicate colonization rather than active toxin disease

Slide 56 · C. Difficile: Clinical and dangerous variants

Watery diarrhea, cramps, fever, and leukocytosis are typical

Hypoalbuminemia may result from protein-losing mucosal injury

Extensive colonic damage can cause toxic megacolon

Recurrent symptomatic episodes are an important clinical problem

Slide 57 · Correlate toxin tests with the syndrome

The supplied textbook emphasizes stool toxin detection over culture alone

Interpretation requires compatible diarrhea and risk factors

A characteristic biopsy can support but should not substitute for infection testing

Histologic pseudomembranes have a differential diagnosis

Slide 58 · Whipple disease: Intracellular organisms and malabsorption

Tropheryma whipplei is associated with chronic, multisystem infection

Macrophages accumulate in small-intestinal lamina propria and mesenteric nodes

Lymphatic outflow obstruction contributes to malabsorptive diarrhea

Weight loss and arthralgia may accompany digestive symptoms

Slide 59 · Whipple pathogenesis: Lymphatic obstruction

Bacterial infection

Macrophage accumulation

Intestinal lymphatic obstruction

Malabsorption

Foamy histiocytes expand villi and replace normal lamina propria

Extraintestinal macrophage accumulation explains multisystem manifestations

Schematic

Slide 60 · Whipple histology: PAS-positive macrophages

Lamina propria macrophage expansion

Schematic — not a histologic specimen

The lamina propria becomes crowded with distended foamy macrophages

Intracellular granules stain PAS-positive and resist diastase

Expansion of villi creates a broad, shaggy mucosal appearance

Authentic micrographs are required for definitive morphologic recognition

Slide 61 · Whipple versus intestinal mycobacterial infection

Finding

T. Whipplei

Intestinal mycobacteria

Lamina propria

Foamy macrophages

Foamy macrophages possible

PAS stain

Granules positive

May also be positive

Acid-fast stain

Negative

Positive in acid-fast organisms

Interpretation

Tissue stain + context

Microbial confirmation needed

Slide 62 · Whipple: Recognize systemic involvement

Arthritis or arthralgia may precede intestinal symptoms

Lymphadenopathy, fever, and weight loss may occur

Central nervous system, cardiac valves, and other sites can be involved

Consider the disease in otherwise unexplained malabsorption with systemic findings

Slide 63 · Viruses injure enterocytes without classic dysentery

Norovirus, rotavirus, and enteric adenovirus are major causes of gastroenteritis

Watery stool and vomiting are common clinical features

Epithelial dysfunction or loss impairs nutrient absorption

Viral biopsies are frequently nonspecific

Slide 64 · Norovirus: Rapid transmission and outbreaks

Fecal–oral transmission and contaminated surfaces facilitate spread

Institutional outbreaks occur in schools, hospitals, care facilities, and ships

A very small infectious inoculum contributes to transmission

Virus can be shed before symptoms and after clinical recovery

Slide 65 · Norovirus: Acute syndrome and persistence

Acute vomiting, cramps, and watery diarrhea typically resolve rapidly

Immunosuppressed patients may develop prolonged diarrhea and shedding

Extensive strain diversity makes durable cross-protective immunity difficult

Clinical resolution does not necessarily mark immediate virologic clearance

Slide 66 · Norovirus and host mucosal susceptibility

FUT2 activity

Fucosylated epithelial glycans

Viral binding

Mucosal infection

Some FUT2 loss-of-function nonsecretors resist selected norovirus strains

Viral antigenic diversity also influences population susceptibility

Schematic

Slide 67 · Norovirus: Modest, nonspecific small-bowel changes

Shortened villi / functional enterocyte loss

Schematic — not a histologic specimen

Mild villous shortening and epithelial vacuolization may be present

Crypt enlargement and mixed lamina propria inflammation can occur

Brush-border enzyme reduction adds transient malabsorption

Tissue morphology is supportive, not diagnostic of norovirus

Slide 68 · Rotavirus damages mature villous enterocytes

Viral infection

Mature enterocyte loss

Immature replacement

Malabsorption + fluid secretion

NSP4 may contribute to epithelial apoptosis

Loss of enzymes and absorption creates an osmotic component to watery diarrhea

Schematic

Slide 69 · Rotavirus: Age and clinical disease

Young children are a vulnerable group

Spread in daycare and inpatient settings is efficient

Vomiting and watery diarrhea follow a short incubation period

The source describes vaccination as an important prevention strategy

Slide 70 · Enteric adenovirus: Pathology and course

In children and immunocompromised adults, adenovirus can cause diarrhea

Villous atrophy and reactive crypt hyperplasia are relatively nonspecific

Epithelial degeneration is variable, and viral inclusions are uncommon

Symptoms may include vomiting, pain, fever, and weight loss

Slide 71 · SARS-CoV-2 may involve intestinal epithelium

Gastrointestinal symptoms can accompany respiratory infection

ACE2 and TMPRSS2 expression provides a potential route for epithelial infection

Epithelial cytotoxicity and immune injury may both contribute

GI symptoms should not be equated with a distinct histologic diagnostic pattern

Slide 72 · Common viral enteritides: Focused comparison

Pathogen

Mechanism / site

Histologic clue

Norovirus

Small bowel epithelial dysfunction

Mild villous change; Nonspecific

Rotavirus

Loss of mature villous enterocytes

Functional malabsorption and epithelial repair

Adenovirus

Enterocyte degeneration

Villous atrophy, crypt hyperplasia

SARS-CoV-2

Possible epithelial infection + inflammation

No defining routine pattern in cited text

Slide 73 · Major enteric parasites and injury patterns

Category

Examples

Dominant tissue effect

Nematodes

Ascaris, Strongyloides, hookworm

Eosinophilic injury, bleeding, obstruction

Tapeworms

Taenia, Diphyllobothrium

Usually intraluminal; Nutritional competition

Amoebae

Entamoeba histolytica

Invasion and deep ulceration

Flagellates / coccidia

Giardia, Cryptosporidium

Brush-border dysfunction and watery stool

Slide 74 · Ascaris undergoes lung–gut migration

Egg ingestion

Intestinal hatching

Lung migration

Swallowing

Adult small-bowel worm

Adult worms can cause eosinophil-rich inflammation and bowel or biliary obstruction

Eggs in stool often establish the diagnosis

Schematic

Slide 75 · Strongyloides autoinfection enables persistence

Skin penetration

Pulmonary migration

Intestinal adulthood

Mucosal larval reinvasion

Internal autoinfection allows infection to persist long term

Immune suppression can produce overwhelming disseminated infection

Schematic

Slide 76 · Hookworms produce chronic intestinal blood loss

Larvae enter through intact skin and migrate via the lungs

Adult worms attach to duodenal mucosa and feed on blood

Erosions and repeated bleeding can cause iron-deficiency anemia

Fecal eggs support diagnosis

Slide 77 · Intestinal nematodes: Focused clinical clues

Worm

Location / behavior

Distinguishing manifestation

Trichuris trichiura

Colonic whipworm; Heavy burden

Bloody diarrhea, possible prolapse

Enterobius species

Intraluminal; Nocturnal perianal eggs

Pruritus ani and repeat household transmission

Ascaris lumbricoides

Small intestinal adult worms

Obstruction / biliary migration

Strongyloides

Autoinfection across mucosa

Hyperinfection with immune suppression

Slide 78 · Schistosomiasis: Eggs, not worms, drive bowel injury

Adult worms reside in mesenteric veins

Eggs retained in mucosa and submucosa trigger inflammation

Granulomatous reaction may cause bleeding and obstruction

Parasitic granulomas require appropriate exposure and organism evidence

Slide 79 · Intestinal cestodes are largely luminal

Fish, pork, and other tapeworms attach by a scolex

Most do not invade host intestinal tissues

Eggs and proglottids shed in stool allow identification

Diphyllobothrium may consume dietary vitamin B12 and cause deficiency

Slide 80 · Entamoeba histolytica creates flask-shaped ulcers

Cyst ingestion

Colonic trophozoites

Epithelial death

Submucosal lateral spread

The deep ulcer base can be wider than the surface opening

Inflammation, hemorrhage, and dysentery follow tissue invasion

Schematic

Slide 81 · Amebiasis: Recognize the ulcer topology

Narrow neck

Broad submucosal ulcer

Schematic — not a histologic specimen

Narrow mucosal opening overlies broader submucosal destruction

Trophozoites can resemble macrophages on routine microscopy

Ingested erythrocytes within trophozoites provide a useful morphologic clue

Cecal and right-colonic involvement is common

Slide 82 · Amebiasis can disseminate to the liver

Colonic tissue invasion

Splanchnic vessel access

Hepatic seeding

Liver abscess

A hepatic abscess can persist after intestinal symptoms subside

Spread beyond the liver is uncommon but documented

Schematic

Slide 83 · Giardia: Surface adherence, not deep invasion

Fecally contaminated water transmits resistant cysts

Trophozoites adhere to the small-bowel brush border

Brush-border enzyme loss, epithelial injury, and malabsorption occur

Severe or persistent infection is more likely with antibody deficiency

Slide 84 · Giardia: Organisms can overlay normal villi

Luminal trophozoites along brush border

Schematic — not a histologic specimen

Pear-shaped trophozoites have two similarly sized nuclei

Numerous luminal organisms may accompany nearly normal mucosa

Heavy infection can cause mild blunting and intraepithelial lymphocytosis

Lack of tissue invasion distinguishes it from amebiasis

Slide 85 · Cryptosporidium occupies an apical intracellular niche

Oocyst ingestion

Sporozoite release

Apical uptake

Ion transport / barrier dysfunction

Parasites sit within an epithelial-derived vacuole near the brush border

Malabsorption, chloride secretion, and junction leak produce watery diarrhea

Schematic

Slide 86 · Cryptosporidium: Deceptively surface-associated

Apical parasite-associated vacuoles

Schematic — not a histologic specimen

Tiny organisms appear to sit on the luminal surface

They are actually enveloped by a thin layer of host cytoplasm

Heavy infection can cause villous atrophy and crypt hyperplasia

The terminal ileum and proximal colon are commonly involved

Slide 87 · Three protozoa: Morphology versus mechanism

Organism

Mode of injury

Diagnostic clue

Entamoeba

Invasion; Deep ulcers

Flask ulcer; RBC-ingesting trophozoites

Giardia

Small-bowel surface adherence

Paired nuclei; Luminal pear-shaped organisms

Cryptosporidium

Apical vacuolar infection

Small surface-associated bodies; Stool oocysts

Slide 88 · Biopsy pattern: Use it to constrain the differential

Pattern

Likely mechanisms

Potential causes

Intact villi / minimal injury

Secretory toxin, surface adherence

Cholera, ETEC, Giardia

Acute cryptitis; Preserved spacing

Acute invasive infection

Campylobacter, Shigella, EIEC

Pseudomembranes / crypt eruptions

Severe epithelial toxin injury

C. Difficile; Ischemia in differential

Foamy lamina propria cells

Macrophage-rich infection

Whipple; Mycobacterial mimic

Slide 89 · Acute colitis does not equal chronic IBD

Schematic — not a histologic specimen

Neutrophilic cryptitis and crypt abscesses are shared by many infections

Preserved crypt architecture supports an acute self-limited process

Infection can produce aphthous ulcers or granulomas and mimic Crohn disease

Biopsy timing, distribution, and microbiology remain essential

Slide 90 · A pseudomembrane is not organism proof

Classic crypt-associated eruptions strongly suggest C. Difficile

Ischemic injury and other necrotizing disorders may also produce membranes

Tissue morphology should be correlated with toxin testing

Avoid labeling C. Difficile solely from an isolated membrane

Slide 91 · Stool testing is pathogen- and context-dependent

Bacterial stool cultures help identify organisms with overlapping colitis patterns

Stool toxin testing is central to C. Difficile assessment in the source

Eggs and parasites, cysts, or oocysts may be sought in helminthic / protozoal disease

Blood cultures are informative in suspected systemic enteric fever

Slide 92 · Case: Acute febrile bloody diarrhea

Question: Which mechanisms and organisms best fit neutrophilic cryptitis with preserved crypt spacing?

A patient develops fever, abdominal cramping, and bloody diarrhea after a food exposure

Colon biopsy shows cryptitis and focal crypt abscesses without chronic distortion

Consider invasive bacterial colitis before diagnosing inflammatory bowel disease

Slide 93 · Case interpretation: Acute inflammatory colitis

Campylobacter, Shigella, Salmonella, and EIEC are plausible mechanisms

Histology alone cannot separate most acute bacterial colitides

Exposure history and appropriate stool testing determine etiology

EHEC also needs consideration when hemorrhagic disease predominates

Slide 94 · Case: Watery diarrhea with little tissue injury

Question: Why can a near-normal intestinal biopsy accompany severe dehydration?

A patient develops sudden copious watery stools following contaminated-water exposure

Mucosa shows little structural destruction

Enterotoxin-driven electrolyte secretion is more plausible than an invasive ulcerative process

Slide 95 · Case interpretation: Dissociation of function and form

Cholera toxin activates Gsα and cAMP-dependent chloride secretion

ETEC produces related enterotoxin-mediated ion transport defects

Massive luminal water flow need not produce prominent neutrophilic injury

Rapid fluid loss is the immediate clinical danger

Slide 96 · Six integrative principles

Watery versus bloody diarrhea reflects distinct dominant injury mechanisms

Organism tropism and exposure history are diagnostically informative

Histology is a pattern, not usually a species-level diagnosis

Some microbes cause systemic infection, HUS, or immune sequelae

Immune status changes severity and persistence

Test interpretation must distinguish infection from colonization

Slide 97 · The final diagnostic distinction

Clinical syndrome directs the initial pathogen differential

Exposure history and immune status refine pretest probability

Histologic pattern helps identify mechanisms and dangerous mimics

Microbiologic tests establish the causative organism when morphology is nonspecific