Ascaris lumbricoides

Slide 1 · Ascaris lumbricoides

Pathology of ascariasis

Life cycle · Tissue response · Clinicopathologic consequences · Diagnosis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Trace the intestinal–pulmonary–intestinal life cycle and explain its diagnostic consequences.

Connect larval migration with eosinophilic pneumonitis and adult worms with luminal obstruction.

Recognize the major intestinal, appendiceal and hepatobiliary complications.

Distinguish ascariasis from other intestinal nematode infections using pathogenesis and tests.

Slide 3 · Parasitic enterocolitis: The relevant context

Enteric parasite groups

Nematodes: Ascaris, Strongyloides, hookworms, pinworms

Cestodes and trematodes also affect the bowel

Protozoa constitute another major group

Ascariasis focus

Large intestinal nematode infection

Distinctive obligatory larval lung migration

Disease from migrating larvae and adult worm burden

Slide 4 · Ascariasis is a nematode infection

Ascaris species colonize the human intestinal lumen as adults.

A. Lumbricoides causes most human ascariasis.

A. Suum also causes a smaller proportion of cases.

The larval phase traverses tissues before intestinal maturation.

Slide 5 · Human and pig-associated Ascaris

A. Lumbricoides

Eggs passed by infected humans

Human fecal contamination seeds exposure

Predominant named cause

A. Suum

Eggs passed by pigs

An additional zoonotic source of infection

Less common human infection

Slide 6 · Global distribution and burden

Approximately one billion infections worldwide.

Most infections occur in Asia, Africa and South America.

The estimate describes disease burden in the source; It is not a live surveillance statistic.

Unequal environmental sanitation sustains exposure.

Slide 7 · Soil-transmitted helminths share an exposure ecology

1

Eggs or larvae enter soil

Fecal contamination

2

Environmental exposure

Contaminated soil or food

3

Human infection

Stage-specific entry

4

Reproduction

New environmental contamination

Slide 8 · Entry route distinguishes nematode groups

Ingestion of eggs

Ascaris: Swallowed eggs

Trichuris: Soil-transmitted whipworm

Enterobius: Egg ingestion, especially from contaminated hands

Larval skin penetration

Strongyloides: Infective larvae penetrate intact skin

Hookworms: Entry begins through skin

All do not share the same intestinal behavior

Slide 9 · Fecal–oral acquisition of Ascaris

1

Infected host

Eggs shed in stool

2

Contaminated surroundings

Soil and produce exposed

3

Ingestion

Eggs enter the gut

4

New host

Larval development begins

Slide 10 · Contaminated produce provides an exposure route

Poorly cleaned or peeled produce may carry eggs from contaminated soil.

The parasite is not acquired from eating adult worms.

The exposure route links sanitation, soil and ingestion.

Environmental contamination precedes infection in a new host.

Slide 11 · Infective stage develops outside the host

1

Eggs are passed

Fresh stool

2

Eggs develop in soil

Warm, moist conditions

3

Embryonated egg

Infective stage

4

Ingestion

Human acquisition

Slide 12 · Eggs passed ≠ immediate infectiousness

At excretion

Eggs leave the intestine with feces

Developmental maturation remains necessary

Direct handling of fresh stool is not the canonical infective stage

After environmental development

Fertilized eggs become embryonated

Ingestion of infective eggs starts a new cycle

Environmental sanitation interrupts maturation and exposure

Slide 13 · Entire life cycle at a glance

1 Eggs in feces

2 Egg development in soil

3 Ingestion of infective eggs

4 Larvae cross intestinal wall

5 Lung maturation

6 Cough → swallow → adults in gut

Schematic: Sequence is conceptual, not a time-scaled or anatomic diagram

Slide 14 · Hatching follows ingestion

1

Infective egg

Swallowed with food or contaminants

2

Larva released

Hatching in small intestine

3

Mucosal crossing

Larva invades gut wall

4

Dissemination

Vascular or lymphatic transit

Slide 15 · Intestinal entry is a transient larval event

Larvae cross the intestinal mucosa before entering the circulation.

Chapter 8 specifically describes proximal colon and cecum penetration.

Chapter 17 summarizes the event as intestinal mucosal penetration.

The early tissue phase is not the same as adult intestinal residence.

Slide 16 · Larval migration connects gut to lung

1

Gut wall

Barrier penetration

2

Vascular / lymphatic route

Systemic transit

3

Pulmonary microvasculature

Delivery to lung

4

Alveolar compartment

Further development

Slide 17 · The larval and adult compartments differ

Early larva

Mucosa → circulation → alveoli

Adult worm

Intestinal lumen (predominantly jejunum)

Slide 18 · Pulmonary maturation precedes return to the gut

Larvae develop in the lungs for approximately 10–14 days.

They reach the alveolar compartment.

The pulmonary phase can induce inflammatory symptoms.

They subsequently ascend the airway before being swallowed.

Slide 19 · Exit from lung depends on airway transit

1

Alveolar larvae

Maturation

2

Airway ascent

Toward trachea and pharynx

3

Coughing and swallowing

Transfer to alimentary tract

4

Small bowel

Final maturation to adult

Slide 20 · Time course of development

1

Ingestion

Infective eggs swallowed

2

Lung phase

Larvae mature over 10–14 days

3

Return to gut

Cough and swallow

4

Egg output

Typically 2–3 months after ingestion

Slide 21 · Adult worms inhabit the intestine

Adults are found throughout the bowel, mainly the jejunum.

Worms return to the gut after pulmonary development.

The mature parasites occupy the intestinal lumen.

Heavy parasite burdens are linked to obstructive complications.

Slide 22 · Adult morphology: Large intestinal roundworm

Intestinal luminal adult — schematic longitudinal outline

Anterior

Posterior

Adult worms measuring approximately 15–35 cm.

CDC differentiates generally larger female and smaller male worms.

Recognition of an expelled adult can establish infection.

Slide 23 · High egg output perpetuates transmission

A female Ascaris may release approximately 200,000 eggs per day.

Eggs are shed in feces, contaminating the environment.

Production occurs once intestinal sexual maturity is reached.

The number is a biological source estimate, not an infection-intensity cut-off.

Slide 24 · Egg shedding completes the environmental cycle

1

Adults in jejunum

Reproduction

2

Eggs into intestinal lumen

Continuous release

3

Feces

Environmental dissemination

4

Soil contamination

Opportunity for another exposure

Slide 25 · Stage determines symptoms and investigations

Larval migration

Transient pulmonary inflammatory phase

Dry cough, dyspnea and fever may occur

Stool eggs may still be absent early

Adult intestinal phase

Frequently clinically silent

Pain or bowel obstruction with heavy burdens

Stool egg detection usually establishes diagnosis

Slide 26 · Clinical manifestations cluster by parasite stage

Stage

Dominant process

Clinical consequences

Migrating larva

Passage through lung

Eosinophilic pneumonitis

Luminal adult

Intestinal worm burden

Abdominal symptoms, obstruction

Migrating adult

Entry into ducts / appendix

Cholangitis, pancreatitis, appendiceal obstruction

Slide 27 · Most infected individuals have no symptoms

Ascariasis is often asymptomatic.

Clinical severity varies with stage and worm burden.

Absence of abdominal complaints does not exclude infection.

Complicated cases arise disproportionately with heavy burdens or aberrant migration.

Slide 28 · Worm burden predicts the intestinal phenotype

Light infection

Often asymptomatic

Nonspecific symptoms may be absent

Detected only when eggs or worms are observed

Heavy infection

Greater likelihood of pain, nausea and vomiting

Malnutrition may occur

Mechanical intestinal obstruction is an important complication

Slide 29 · Eosinophilic inflammation is a key tissue response

Parasite exposure

Tissue antigens and larval passage

Host response

Eosinophil-rich inflammatory infiltrates

Slide 30 · Eosinophilic response is not species-specific

Eosinophil-rich tissue inflammation supports helminthic injury, not Ascaris identification.

Robbins Figure 17.34B demonstrates eosinophilic tissue reaction.

Strongyloides may produce a similar reaction.

Identify the parasite through morphology or appropriate specimen findings.

Slide 31 · Lung migration can cause Loeffler syndrome

1

Larvae enter alveoli

Pulmonary parasitic stage

2

Inflammation develops

Eosinophilic reaction

3

Respiratory symptoms

Dry cough, dyspnea, fever

4

Resolution

Often self-limited pneumonitis

Slide 32 · Loeffler syndrome: Clinical pattern

Transient eosinophilic pneumonitis during pulmonary larval migration.

Symptoms include dry cough, dyspnea and fever.

It may precede evidence of mature intestinal worms.

The initial pulmonary illness as self-limited.

Slide 33 · Pulmonary disease and stool tests may be discordant

Clinical finding

Cough and dyspnea during early infection

Eosinophilic pulmonary inflammation

History of relevant exposure

Laboratory limitation

Intestinal sexual maturity has not occurred

Eggs may not yet be passed in stool

Early negative stool examination does not exclude larval ascariasis

Slide 34 · Uncommon larval complication: Hepatic abscess

Migrating larvae can also produce hepatic abscesses.

This is described in the gastrointestinal chapter.

It represents extraintestinal larval-associated tissue injury.

Avoid conflating it with biliary obstruction by mature worms.

Slide 35 · Intestinal symptoms may be nonspecific

Common gastrointestinal complaints

Abdominal discomfort or pain

Loss of appetite, nausea, vomiting

Diarrhea

Interpretive limitation

Symptoms overlap with many other enteric disorders

Clinical pattern alone does not establish the parasite

Find eggs or adult organisms for confirmation when possible

Slide 36 · Mechanical obstruction: The luminal mechanism

1

Numerous adult worms

High intraluminal burden

2

Crowding or aggregation

Impaired intestinal passage

3

Obstructive symptoms

Pain, vomiting, distention

4

Potential intervention

Severe cases may require surgery

Slide 37 · Intestinal obstruction is a major severe outcome

Heavy worm burden can obstruct the bowel.

The process is primarily mechanical rather than invasive mucosal destruction.

The small intestine is the principal adult habitat.

Severe obstruction may require surgery.

Slide 38 · Ileocecal obstruction is a separate anatomic risk

1

Adult worms travel distally

Beyond dominant jejunal location

2

Ileocecal region

Narrow anatomic passage

3

Luminal interference

Valve obstruction

4

Acute presentation

Possible obstructive syndrome

Slide 39 · Appendiceal entry can produce local obstruction

1

Migrating adult

Within intestinal lumen

2

Appendiceal lumen

Entry into blind-ending structure

3

Obstruction

Local blockage

4

Clinical concern

Appendiceal complication

Slide 40 · Adult migration explains hepatobiliary complications

Small intestinal adult

Aberrant migration into biliary tree

Ductal lumen

Obstruction ± secondary inflammation

Slide 41 · Biliary ascariasis may cause cholangitis

1

Adult enters biliary tree

Ectopic migration

2

Bile duct obstructed

Impaired bile drainage

3

Inflammatory / infectious complication

Cholangitis

4

Clinical severity

Potentially urgent biliary disease

Slide 42 · Pancreatitis can follow worm migration

1

Migration toward ampullary region

Adult in ductal system

2

Drainage disturbance

Pancreatic outflow impeded

3

Pancreatic injury

Acute pancreatitis

4

Diagnosis

Consider biliary ascariasis in an exposed patient

Slide 43 · Complications by anatomic location

Compartment

Parasitic process

Recognized consequence

Lung

Larval migration

Loeffler pneumonitis

Small intestine

Large adult worm mass

Bowel obstruction

Ileocecal / appendix

Adult migration

Regional obstruction

Biliary / pancreatic ducts

Aberrant adult migration

Cholangitis, pancreatitis

Liver

Larval tissue complication

Hepatic abscess

Slide 44 · Heavy infection can impair nutrition

Malnutrition is a documented complication of heavy ascariasis.

Malnutrition among intestinal complications.

CDC notes that severe infection in children may contribute to stunted growth.

Do not infer a precise risk magnitude from these qualitative source statements.

Slide 45 · The standard diagnostic specimen is stool

1

Suspected intestinal ascariasis

Clinical / exposure context

2

Stool collection

Specimen for microscopy

3

Ova identification

Characteristic Ascaris eggs

4

Diagnosis

Intestinal ascariasis established

Slide 46 · Fertilized eggs: Conceptual morphology

Schematic fertilized Ascaris egg

Fertilized eggs are rounded and have a thick shell.

An outer mammillated layer is often bile-stained brown.

CDC DPDx describes a length range of 45–75 µm.

Mammillated coat (when present)

Slide 47 · Fertile and infertile eggs differ

Fertilized egg

Relatively rounded / oval

Thicker shell

Common mammillated outer surface

Can develop to infectivity in soil

Unfertilized egg

Often more elongated

Larger and thinner-walled

Variable mammillation; Granular contents

Not infective on ingestion

Slide 48 · Decorticated eggs: An important pitfall

Schematic egg without mammillated coat

Loss of the outer mammillated coating changes egg appearance.

Decorticated eggs can be fertilized or unfertilized.

Missing outer bumps does not alone exclude Ascaris.

Outer coat absent

Slide 49 · Stool microscopy workflow

Step

Rationale

CDC DPDx procedure

Collect and preserve

Maintain diagnostic morphology

Stool specimen with fixative

Concentrate

Increase recovery of ova

Formalin–ethyl acetate sedimentation

Microscopic review

Find characteristic eggs

Wet mount of concentrate

Alternative

Moderate/heavy burden

Direct wet mount if concentration unavailable

Slide 50 · Why a single negative stool result can mislead

Early pulmonary phase

Adult female has not matured

Egg shedding may not have begun

Clinically suspected infection may be stool-negative

Established intestinal phase

Egg shedding is usually demonstrable

Stool microscopy becomes more informative

Adult worms may occasionally be passed

Slide 51 · Adult worm identification is another diagnostic route

Intestinal luminal adult — schematic longitudinal outline

Anterior

Posterior

Large roundworm morphology may be evident after spontaneous passage.

Adult worms passed from the rectum or occasionally coughed up.

CDC DPDx describes three lips at the anterior end and sex-related tail differences.

Slide 52 · Pulmonary-phase specimens are different

Larvae may be demonstrated in sputum during pulmonary migration.

CDC DPDx also discusses gastric aspirates in this phase.

Specimen choice should match the parasite stage.

A stool-based strategy alone is imperfect before egg production.

Slide 53 · Routine tissue reaction is supportive, not definitive

Eosinophils indicate a host response; Morphology determines parasite identity.

An eosinophil-rich lesion in ascariasis.

Similar inflammatory patterns occur in other helminth infections.

A diagnosed parasite should not be named solely from eosinophil predominance.

Slide 54 · Comparing intestinal nematode mechanisms

Organism

Acquisition

Distinctive mechanism

Ascaris

Egg ingestion

Lung transit; Adult luminal obstruction

Strongyloides

Skin penetration

Autoinfection possible

Hookworms

Skin penetration

Duodenal blood feeding, anemia

Trichuris

Soil-transmitted infection

Severe burden: Colitis / prolapse

Slide 55 · Ascaris versus Strongyloides

Ascaris

Infective egg is swallowed

Mature worm occupies bowel lumen

Pulmonary transit during larval phase

High burden may obstruct intestine or biliary tract

Strongyloides

Larvae penetrate intact skin

Autoinfection occurs within host

Immunosuppression may permit hyperinfection

Larvae and adults provoke tissue response

Slide 56 · Ascaris versus hookworm

Ascaris

Ingestion of environmentally developed eggs

Large intestinal luminal adults

Mechanical obstruction is key severe bowel complication

Hookworms

Larvae enter through skin

Adults attach to duodenal mucosa

Blood loss and iron deficiency anemia characterize chronic infection

Slide 57 · Ascaris versus whipworm and pinworm

Trichuris trichiura

Predominantly pediatric burden

Heavy infection can cause bloody diarrhea

Rectal prolapse is a severe complication

Enterobius vermicularis

Perianal deposition of eggs

Nocturnal pruritus ani

Adhesive tape test rather than relying on routine stool eggs

Slide 58 · Clinicopathologic localization exercise

Patient feature

Parasite phase to consider

Reason

Dry cough + eosinophilic pneumonitis

Larval lung phase

Migration through alveoli

Colicky abdominal pain + obstruction

Adult intestinal phase

Crowded luminal worms

Cholangitis + intestinal worm exposure

Migrating adult

Possible biliary duct entry

Early infection + negative stool ova

Prepatent phase

No egg output yet

Slide 59 · Case 1 — cough before stool positivity

Clinical presentation

A patient from an endemic setting presents with dry cough, fever and dyspnea after a plausible soil/food exposure. An early stool examination is negative.

How can ascariasis still explain this presentation?

Reasoning prompts

Identify the life-cycle stage.

Explain the eosinophilic lung response.

Explain the diagnostic timing problem.

Slide 60 · Case 1 — clinicopathologic interpretation

1

Pulmonary larval migration can cause self-limited Loeffler pneumonitis.

2

Egg output requires intestinal adult maturation; Early stool microscopy may be negative.

3

Interpret the negative examination according to the temporal phase.

Slide 61 · Case 2 — an obstructed intestine

Clinical presentation

A child with a heavy intestinal helminth burden develops worsening abdominal pain, vomiting and features of mechanical bowel obstruction.

What pathophysiologic mechanism best links Ascaris to this illness?

Reasoning prompts

Localize the mature worms.

Consider burden-dependent effects.

Identify the potentially severe complication.

Slide 62 · Case 2 — mechanistic interpretation

1

Adult worms occupy the bowel lumen, especially the jejunum.

2

Large parasite numbers can crowd the lumen and obstruct intestinal transit.

3

Severe obstruction may require surgical management.

Slide 63 · Case 3 — pancreatobiliary symptoms

Clinical presentation

A patient with suspected intestinal ascariasis develops a clinical syndrome of acute pancreatitis or cholangitis.

Why does a predominantly intestinal nematode produce ductal disease?

Reasoning prompts

Track where an adult worm might move.

Consider the effect on ductal drainage.

Distinguish adult migration from larval pneumonitis.

Slide 64 · Case 3 — ductal migration

1

Mature worms may migrate from the intestine into the biliary tree.

2

Mechanical interference with biliary/pancreatic drainage can lead to cholangitis or pancreatitis.

3

This is a different complication pathway from pulmonary larval migration.

Slide 65 · Transmission interruption follows life-cycle logic

Environmental control

Sanitation limits dispersal of fecal eggs.

Preventing contamination reduces egg development opportunities.

Produce hygiene reduces ingestion of environmental eggs.

Clinical identification

Stool egg detection identifies intestinal infection.

Recognizing early pulmonary disease prevents false reassurance.

Detect complications by the anatomic presentation.

Slide 66 · Integrative pathogenesis map

1 Soil egg exposure

2 Gut hatching

3 Larval lung passage

4 Swallowing

5 Adult jejunal habitat

6 Egg output / obstruction / ductal migration

Schematic: Sequence is conceptual, not a time-scaled or anatomic diagram

Slide 67 · Three mechanisms, three clinical outcomes

Biologic action

Tissue / organ consequence

Clinical result

Larvae migrate through lungs

Eosinophilic pulmonary inflammation

Loeffler pneumonitis

Adults accumulate in intestinal lumen

Mechanical interruption of transit

Intestinal obstruction

Adults enter bile ducts

Ductal obstruction / inflammation

Cholangitis or pancreatitis

Slide 68 · High-yield synthesis

Think in stages: Swallowed egg → migrating larva → luminal adult.

Larval phase: Pulmonary inflammation, often before stool eggs appear.

Adult phase: Frequent silence, but heavy burdens obstruct the bowel.

Ectopic adult migration: Biliary and pancreatic complications.

Slide 69 · Four errors worth avoiding

Incorrect assumption

All soil-transmitted worms enter through the skin.

Early stool-negative infection excludes Ascaris.

Eosinophil-rich inflammation identifies species.

Every adult worm infection is symptomatic.

Correct interpretation

Ascaris infection begins by swallowing eggs.

Prepatent lung-phase infection may be stool-negative.

Inflammation is supportive but nonspecific.

Many infections are asymptomatic.

Slide 70 · References and provenance

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026. Chapter 17, “The Gastrointestinal Tract,” p. 725.

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026. Chapter 8, “Infectious Diseases,” p. 362.

CDC DPDx. Ascariasis. Laboratory morphology, parasite biology and diagnosis (page reviewed July 19, 2019). https://www.cdc.gov/dpdx/ascariasis/

Visuals: original editable PowerPoint schematics. No synthetic specimen or unlicensed textbook photomicrograph reproduced.