Strongyloidiasis

Slide 1 · Strongyloidiasis

Etiology • autoinfection • intestinal morphology • hyperinfection

Pathology lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Reconstruct skin-to-lung-to-intestine transmission and the two larval fates.

Distinguish limited infection from hyperinfection on clinical and tissue findings.

Explain why immunosuppression amplifies autoinfection and may produce enteric sepsis.

Interpret a simplified intestinal biopsy and select relevant specimen types.

Slide 3 · Strongyloidiasis is a nematode infection

Agent

Strongyloides stercoralis is the named organism.

A parasitic metazoan (helminth).

Anatomic focus

Female worms occupy small-intestinal mucosa.

Larvae migrate through lung and gut.

Key distinction

Larvae may become infective inside the host.

Autoinfection permits persistent disease.

Slide 4 · Metazoal infections involve multicellular parasites

Metazoa are multicellular eukaryotes with organ systems.

Parasitic metazoa may enter by ingestion, skin invasion, or arthropod transmission.

Their tissue distribution may extend beyond the gastrointestinal tract.

Microscopic recovery of larvae or ova is a central diagnostic principle.

Slide 5 · Endemic and sporadic strongyloidiasis

Geographic pattern

Distribution

Tropical / subtropical

Endemic in parts of South America, sub-Saharan Africa, and Southeast Asia.

United States

Sporadic infections are reported, including in Appalachia.

Interpretation

Exposure history is relevant beyond a single geographic region.

Slide 6 · Global burden requires edition-specific context

An estimated 30–100 million people are infected worldwide.

This estimate describes worldwide infection burden—not prevalence within any individual region.

No patient-level risk can be inferred from the worldwide estimate alone.

The range is a global estimate—not a region-specific rate.

Slide 7 · Fecally contaminated soil is an exposure setting

Larvae in soil

Contact with exposed skin

Larval skin entry

The parasite is environmentally associated with soil.

The intestinal-stage offspring leave the host in stool and can contaminate soil.

Soil contaminated by human feces sustains environmental exposure.

Slide 8 · Infective larvae penetrate intact skin

Entry route

Exposure is through skin penetration by larvae.

Skin penetration does not require an obvious break in the skin.

Clinical implication

A skin route distinguishes infection from ingestion of fully developed intestinal adult worms.

Cutaneous entry precedes systemic migration.

Slide 9 · The early host route is a migration sequence

Skin penetration

Circulatory transit

Lung migration

Airway ascent

Larvae enter through skin and travel in the circulation.

They reach the lungs, then ascend the trachea to be swallowed.

Slide 10 · Blood-borne movement precedes lung arrival

Larvae move from skin into the circulation and onward to the lungs.

The circulation is a migration route, not the usual final habitat of adult females.

This sequence links a peripheral skin exposure to pulmonary findings.

Slide 11 · Lung migration can provoke inflammation

Migrating larvae

Pulmonary tissue transit

Inflammatory infiltrates

Migrating larvae can induce inflammatory infiltrates in the lungs.

The pulmonary phase occurs before establishment of adult intestinal infection.

Slide 12 · Airway ascent returns larvae to the gut

Lung phase

Tracheal ascent

Swallowing

Small intestine

Larvae ascend the trachea and are then swallowed.

The airway route provides the connection between lung migration and intestinal residence.

Slide 13 · Female worms reside in small-intestinal mucosa

Habitat

Female worms occupy the small-intestinal mucosa.

In a biopsy, attention is directed to duodenal crypts.

Pathologic importance

Intestinal residence allows egg production and generation of larvae.

The bowel is also the site of host-tissue interaction.

Slide 14 · Parthenogenesis is an intestinal reproductive mechanism

Female worms

Asexual reproduction

Eggs in mucosa

Larval offspring

Female Strongyloides produce eggs by parthenogenesis.

The intestinal offspring may follow different routes rather than necessarily leaving the host.

Slide 15 · Larval development creates two possible fates

Environmental branch

Most larvae are passed in stool.

Larvae may contaminate soil.

Further exposure starts another infection.

Internal branch

Some larvae develop into an infective form within the host.

Internal infective stages drive autoinfection.

This mechanism can repeat without a new soil exposure.

The fork in larval fate is the central pathogenetic feature.

Slide 16 · Stool excretion completes the environmental branch

Intestinal larval production

Larvae passed in stool

Soil contamination

New skin exposure

Most intestinal larvae are passed in stool.

A further environmental exposure can continue the infection cycle.

Slide 17 · Autoinfection is development inside the host

Eggs hatch in intestine

Larvae mature internally

Larvae enter mucosa

Repeat infection

Strongyloides eggs can hatch within the intestine.

The resulting larvae may penetrate intestinal mucosa without an obligatory external stage.

Slide 18 · Autoinfection makes long-term persistence possible

Persistence

Internal recycling can maintain infection.

Infection can persist for the lifetime of the host.

Consequences

A remote exposure may remain biologically relevant.

Host immune status may later change the course of infection.

Slide 19 · The life cycle branches to external exit or autoinfection

Soil-associated

Infective larvae

Skin penetration

And migration

Lungs → airway

→ swallowing

Intestinal females

And offspring

Larvae passed in stool

→ environmental continuation

Larvae infectious inside host

→ autoinfection

Two branches arise from intestinal larval development

Slide 20 · Strongyloides differs from many intestinal worms

Feature

Strongyloides

Other intestinal helminths

Infective development

May occur within the host

Other intestinal worms often require an outside stage

Chronicity

Autoinfection permits lifelong persistence

Persistent internal cycling is not the general model

Clinical hazard

Uncontrolled autoinfection in immunosuppression

This particular hazard is emphasized for Strongyloides

Slide 21 · Contrast: Acquisition differs from ascariasis

Strongyloides stercoralis

Larvae penetrate the skin.

Autoinfection can follow internal larval maturation.

Biopsy may reveal larvae and adult females.

Ascaris lumbricoides

Infection follows ingestion of eggs.

Eggs from stool contaminate the environment.

Intestinal infection may be established by identifying eggs in stool.

Entry stage and autoinfection distinguish these two nematodes.

Slide 22 · Anatomy connects entry, migration, and disease

Skin entry

Blood transit

Lungs / airway

Intestinal mucosa

Different anatomic sites reflect different stages of one infection.

Mucosal residency establishes a site for chronicity; Deeper invasion characterizes severe disease.

Slide 23 · Many immunocompetent infections are silent

In an immunocompetent host, infection is frequently asymptomatic.

Clinical silence does not demonstrate absence of intestinal parasites.

The parasite may nevertheless persist by autoinfection.

Clinical severity and infection persistence are separate dimensions.

Slide 24 · Uncomplicated disease may cause gastrointestinal symptoms

Diarrhea

A listed intestinal symptom.

Interpret in the context of potential helminth exposure.

Bloating

Another possible manifestation.

Not specific by itself.

Malabsorption

Malabsorption occurs occasionally.

Can indicate intestinal functional involvement.

Slide 25 · Mucosal disease explains gastrointestinal involvement

Parasites in intestinal crypts

Mucosal reaction / edema

Possible GI disturbance

Intestinal infection combines crypt parasites, lamina-propria inflammation, and edema.

Linking structural changes to symptoms is a clinicopathologic interpretation, not a measured causal estimate.

Slide 26 · Pulmonary manifestations track the larval phase

Larval passage through the lungs can induce inflammatory infiltrates.

The lung is part of the ordinary migratory trajectory.

Pulmonary parasites during severe infection may also reflect a high organism burden.

Slide 27 · Eosinophils signal a tissue response

Intestinal tissue

Mild infection features eosinophil-rich lamina-propria inflammation.

Peripheral blood

Peripheral eosinophilia may occur.

Interpretation

Eosinophils are a response to infection—not a stand-alone parasite identification.

Slide 28 · Mild infection has a crypt-centered pattern

Simplified intestinal wall

Epithelium / crypts

Lamina propria

Submucosa / deeper tissue

No tissue-invasive larvae shown in mild infection

Larvae predominate among visible worms.

Parasites are located in duodenal crypts.

The underlying tissue does not show invasion in mild infection.

Slide 29 · Duodenal crypts are the first histologic search zone

The typical mild-infection location is within the crypt compartment.

A crypt-limited organism distribution is different from stromal or vascular invasion.

Correlate any candidate organism with the accompanying mucosal response.

Slide 30 · Lamina propria shows eosinophil-rich inflammation

Simplified intestinal wall

Epithelium / crypts

Lamina propria

Submucosa / deeper tissue

No tissue-invasive larvae shown in mild infection

An eosinophil-rich cellular infiltrate is described in mild infection.

The infiltrate involves the lamina propria.

Organism localization and inflammatory pattern should be documented separately.

Slide 31 · Mucosal edema accompanies mild intestinal disease

Mucosal edema may accompany crypt-centered intestinal infection.

It accompanies the lamina-propria eosinophil-rich reaction.

Edema is a tissue response; It is not itself proof of strongyloidiasis.

Slide 32 · A negative deep-tissue finding has meaning

Mild infection

Worms are in crypts.

Underlying tissue is not invaded in the described mild pattern.

Eosinophil-rich mucosa and edema may be present.

Hyperinfection

Larvae enter submucosa.

Lymphatics and vessels can contain invading parasites.

Invasion is accompanied by a mononuclear infiltrate.

Slide 33 · Morphologic interpretation requires compartment mapping

Simplified intestinal wall

Epithelium / crypts

Lamina propria

Submucosa / deeper tissue

Vascular / lymphatic compartment

First define crypt, lamina propria, and submucosal compartments.

Then ask whether larvae remain luminal/crypt-associated or enter deeper tissues.

Vessel involvement supports the invasive hyperinfection pattern.

Slide 34 · Normal host defenses limit autoinfection

Immunocompetent hosts frequently have limited or asymptomatic disease; Immunosuppression permits severe infection.

Suppression of eosinophils and other responding immune cells weakens host control.

A change in host defenses can convert persistent infection into high-burden disease.

Slide 35 · Immunosuppression changes the clinical phenotype

Persistent infection

Weakened host control

Uncontrolled autoinfection

Hyperinfection

Uncontrolled internal reinfection underlies extreme organism burdens.

Severe hyperinfection can be fatal.

Slide 36 · Prolonged corticosteroid therapy is a major risk

Prolonged corticosteroid treatment is a prominent hyperinfection risk.

Corticosteroids inhibit functions of eosinophils and other host immune cells.

Corticosteroids also stimulate increased infective larval production by female worms.

Corticosteroids affect host defense and infective larval production.

Slide 37 · Corticosteroids suppress responding immune cells

Corticosteroid exposure

Impaired eosinophil / immune-cell functions

Reduced control of infection

Eosinophils accumulate in tissues in response to Strongyloides.

Suppression of immune-cell function is one mechanism linked to hyperinfection.

Slide 38 · Corticosteroids may increase infective larval production

Corticosteroid exposure

Stimulated female Strongyloides

More infective larvae

Female worms produce more infective larvae in response to corticosteroids.

This parasite-directed effect complements suppression of host immunity.

Slide 39 · HTLV-1 infection is associated with severe infection

Human T-lymphotropic virus type I is named as a risk context.

The association reflects perturbed immune control mechanisms.

The HTLV-1 association does not specify individual risk or exact mechanism.

Slide 40 · Transplantation and lymphoma are additional risks

Organ transplantation

A listed condition associated with increased hyperinfection risk.

Immune control can be perturbed.

Lymphoma

Also named among associated disease states.

Risk should be interpreted in the clinical context.

Slide 41 · Hyperinfection amplifies a pre-existing pathway

Autoinfection

Internal larval multiplication

High tissue organism burden

Organ injury

The cycle becomes uncontrolled in susceptible hosts.

Severity derives from repeated internal infection and tissue invasion.

Slide 42 · Hyperinfection yields numerous intestinal parasites

Simplified intestinal wall

Epithelium / crypts

Lamina propria

Submucosa / deeper tissue

Vascular / lymphatic compartment

Adults, larvae, and eggs become numerous in intestinal crypts.

Hyperinfection can involve both duodenal and ileal crypts.

Parasite stages should not be conflated when reading the section.

Slide 43 · Duodenum and ileum may contain every parasite stage

Hyperinfection increases the number of adult worms, larvae, and eggs visible in crypts.

Both the duodenum and ileum are named in the hyperinfection description.

This is a qualitative histopathologic distinction; No count threshold is supplied.

Slide 44 · Hyperinfection invades colonic submucosa

Simplified intestinal wall

Epithelium / crypts

Lamina propria

Submucosa / deeper tissue

Vascular / lymphatic compartment

Larvae can invade the colonic submucosa.

Deeper location indicates departure from the mild crypt-only pattern.

Submucosal larvae should be reported as tissue-invasive organisms.

Slide 45 · Lymphatic and vascular invasion marks severity

Intestinal invasion

Lymphatic entry

Blood-vessel entry

Potential extraintestinal spread

Larvae can enter lymphatics and blood vessels in hyperinfection.

Filariform larvae can enter blood vessels and the muscularis mucosa.

Slide 46 · The cellular reaction may become mononuclear

Limited intestinal infection

Eosinophil-rich lamina propria.

Mucosal edema.

Crypt-associated larvae.

Hyperinfection

A mononuclear infiltrate accompanies tissue invasion.

Submucosal / vascular larvae may be seen.

Markedly increased parasites across intestinal sites.

Slide 47 · Crypt and vessel involvement in hyperinfection

Simplified intestinal wall

Epithelium / crypts

Lamina propria

Submucosa / deeper tissue

Vascular / lymphatic compartment

Female worm, eggs, and rhabditoid larvae occur within duodenal crypts.

Filariform larvae are entering vessels and muscularis mucosa.

The described severe case occurred after high-dose cortisone exposure.

Slide 48 · Hyperinfection can involve organs beyond bowel

Skin

Parasites of multiple stages may be found.

Evidence of disease outside the intestinal crypts.

Lung

Parasites can be found in lung tissue.

Respiratory specimens may carry many larvae.

Other organs

Different parasite stages may occur outside the gastrointestinal tract.

No exhaustive organ list is supplied.

Slide 49 · Large larval burdens may be visible in sputum

Numerous parasites may occur in sputum during hyperinfection.

Sputum is therefore a possible direct source of parasite detection.

This finding illustrates extraintestinal parasite burden, not merely a nonspecific lung infiltrate.

Slide 50 · Intestinal wall invasion can compromise the barrier

Invading larvae

Intestinal wall damage

Bacterial passage into blood

Invading larvae can damage the intestinal wall.

This damage provides a route for enteric bacteria to enter circulation.

Slide 51 · Enteric bacterial sepsis is a serious complication

Tissue-invasive larvae

Bowel-wall injury

Intestinal bacteria in blood

Sepsis

Sepsis originates from intestinal bacteria in the stated mechanism.

The microbial complication is secondary to parasitic intestinal injury.

Slide 52 · Limited infection and hyperinfection are distinct

Feature

Limited / mild infection

Hyperinfection

Parasite burden

Usually fewer; mainly crypt larvae

Many adults, larvae, eggs

Tissue site

Duodenal crypts

Crypts plus submucosa / vessels

Inflammation

Eosinophil-rich lamina propria

Mononuclear infiltrate with invasion

Beyond intestine

Often little clinical illness

Other organs and possibly sputum

Clinical concern

GI symptoms or asymptomatic

Severe disease and bacterial sepsis

Slide 53 · Case: Eosinophils and crypt-associated larvae

CLINICAL / HISTOPATHOLOGY VIGNETTE

A duodenal biopsy shows larvae restricted to crypts, lamina-propria eosinophils, and mucosal edema. No submucosal invasion is described.

Which disease pattern best fits the supplied morphology?

Mild intestinal strongyloidiasis; The organisms are crypt-limited rather than deeply invasive.

Slide 54 · Case: Steroid exposure and systemic larvae

CLINICAL / HISTOPATHOLOGY VIGNETTE

A person treated with prolonged corticosteroids has numerous intestinal parasite stages; Larvae are identified in vessel-like channels and sputum.

What unifies the organ distribution and predisposing factor?

Uncontrolled autoinfection with hyperinfection; Corticosteroids reduce immune control and can stimulate infective larval production.

Slide 55 · Case: HTLV-1 and an initially silent infection

CLINICAL / HISTOPATHOLOGY VIGNETTE

An adult with a history of soil exposure and no earlier gastrointestinal complaints subsequently develops severe infection in the context of HTLV-1.

Why does an earlier asymptomatic period not exclude disease?

Strongyloides may persist through autoinfection, and HTLV-1 is a listed risk context for hyperinfection.

Slide 56 · Direct identification remains the diagnostic principle

Excretions

Metazoal infection can be diagnosed by larvae or ova recovered in excretions.

For Strongyloides, larvae may pass in stool.

Tissues

Histologic sections may show worms / larvae and a tissue response.

Site and stage distinguish disease severity.

Serology

The metazoal overview lists serology as a diagnostic modality.

No Strongyloides-specific assay characteristics are supplied.

Slide 57 · The specimen should match the disease compartment

Specimen or site

Expected finding

Interpretive role

Stool

Most larvae exit in stool

Shows environmental exit and an excretion-based detection opportunity

Duodenal tissue

Larvae; in severe disease adults and eggs

Identifies crypt-level infection and reaction

Colon submucosa / vessels

Invasive larvae

Supports tissue-invasive severe infection

Sputum

Numerous larvae in hyperinfection

Can demonstrate respiratory involvement

Slide 58 · Identification requires more than eosinophilia

Supportive reaction

Lamina-propria eosinophils.

Peripheral eosinophilia may occur.

Mucosal edema can accompany infection.

Direct parasitic evidence

Parasites seen in crypts or tissue.

Larvae passed in stool.

Larvae may be recovered from sputum in severe disease.

An inflammatory pattern suggests context; An organism establishes its presence.

Slide 59 · Do not conflate Strongyloides with Ascaris

Question

Strongyloides

Ascaris

Entry

Skin penetration by larvae

Ingestion of environmental eggs

Characteristic recycling

Host autoinfection possible

No parallel mechanism described

Reported stool stage

Larvae commonly passed

Egg detection is diagnostic

Major severe pattern in excerpts

Autoinfection hyperinfection

Obstruction / biliary complications with heavy burden

Slide 60 · A pathologist should report depth of invasion

Organisms

What stages are visible?

Larvae only, or adults / eggs too?

Location

Crypts or deeper submucosa?

Lymphatic / vascular involvement?

Host response

Eosinophil-rich edema?

Mononuclear infiltrate associated with invasion?

These are reporting prompts derived from the described morphology.

Slide 61 · Host context changes interpretation of the biopsy

CLINICAL / HISTOPATHOLOGY VIGNETTE

Two biopsies show duodenal Strongyloides larvae. One patient is clinically well; The other is receiving high-dose corticosteroid therapy.

Which additional histologic and clinical findings require attention?

In the steroid-exposed patient, investigate higher worm burden, eggs/adults, deep or vascular invasion, extraintestinal parasites, and enteric sepsis.

Slide 62 · Synthesis: The central causal pathway

Soil-derived skin entry

Intestinal colonization

Autoinfection

Host-dependent burden

Limited infection: Crypt larvae, eosinophil-rich lamina propria, edema.

Hyperinfection: Invasive larvae, widespread parasites, and possible bacterial sepsis.

Slide 63 · Four histopathologic conclusions

In mild disease, duodenal crypt parasites accompany eosinophil-rich mucosal inflammation.

Autoinfection permits lifelong persistence without an obligatory new exposure.

Immunosuppression—especially corticosteroids or HTLV-1—can lead to hyperinfection.

Deep invasion, extraintestinal larvae, and enteric sepsis define major severity concerns.

Slide 64 · Source references and figure limitations

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026). Chapter 8, Strongyloidiasis, pp. 361–362.

Same textbook, Chapter 17, Parasitic Enterocolitis—Strongyloides, p. 725.

Original Fig. 8.57 was described in the supplied text, but the figure image itself was not available in the provided files.

All diagrams in this deck are editable explanatory schematics, not original microscopy or reproduced textbook figures.