Coccidioidomycosis

Slide 1 · Coccidioidomycosis

PATHOGENESIS · TISSUE MORPHOLOGY · CLINICOPATHOLOGIC INTEGRATION

An endemic dimorphic fungal infection

From inhaled arthroconidia to tissue spherules

Mechanisms • morphology • clinical distribution

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Identify the two Coccidioides species and the principal entry route.

Explain innate immune evasion and the role of T-cell immunity.

Recognize nonbudding endospore-containing spherules and tissue reactions.

Connect host risk factors with pulmonary and disseminated disease.

Slide 3 · The etiologic organisms

Coccidioides immitis and Coccidioides posadasii cause the infection.

Both belong to the group of geographically endemic fungal pathogens.

Species-level distinction is not required to recognize the characteristic tissue spherule.

C. Immitis

Etiologic species

C. Posadasii

Etiologic species

Slide 4 · Why this is an endemic mycosis

Endemic mycoses arise from fungi associated with specific regions.

They can produce systemic illness even in otherwise healthy people.

Coccidioides infection is acquired through inhalation of environmental spores.

Geographic

Exposure

Airborne

Spores

Pulmonary

Infection

Simplified conceptual sequence

Slide 5 · Geographic exposure

The described endemic setting includes the southwestern and western United States and Mexico.

Exposure history is therefore etiologically informative.

A positive response to a fungal skin test is common in endemic populations description.

Region

Southwestern / western US

Region

Mexico

Slide 6 · Fungal morphology depends on context

Molds consist of hyphae and can form airborne conidia.

Dimorphic fungi occupy different morphologic states under environmental versus host conditions.

For Coccidioides, tissue diagnosis hinges on spherules—not conventional budding yeasts.

Environmental

Fungus

Inhaled

Arthroconidia

Tissue

Spherule

Simplified conceptual sequence

Slide 7 · Arthroconidia: The infective form

The infectious units inhaled from the environment are arthroconidia.

Their small size permits access to the respiratory tract.

Their interaction with alveolar macrophages as an early pathogenic step.

Segmented environmental filament — schematic

Airborne arthroconidia

Slide 8 · The respiratory portal of entry

Inhalation establishes the exposure-to-lung sequence.

Alveolar macrophages encounter the incoming arthroconidia.

The pulmonary lesion is the starting point for the clinicopathologic spectrum.

Inhalation

Alveolar

Macrophage

Lung

Lesion

Simplified conceptual sequence

Slide 9 · First-line defense: The macrophage

Phagocytosis normally brings microbes into an intracellular compartment.

That compartment ordinarily participates in the delivery of killing mechanisms.

Coccidioides arthroconidia can subvert this defense step.

Blocked fusion

Lysosome

Schematic phagosome with arthroconidium

Slide 10 · Phagosome–lysosome fusion is blocked

After engulfment, infective arthroconidia impede phagosome–lysosome fusion.

The consequence is resistance to intracellular killing.

This mechanism helps account for the organism’s infectivity.

Blocked fusion

Lysosome

Schematic phagosome with arthroconidium

Slide 11 · Immune evasion changes the initial balance

Entry and uptake do not automatically eliminate the fungus.

Blocked fusion permits survival despite contact with a host phagocyte.

Subsequent disease depends on the organism–host immune interaction.

Macrophage

Uptake

Fusion

Interference

Persistence

Risk

Simplified conceptual sequence

Slide 12 · Two connected immune responses

Innate macrophage mechanisms confront inhaled fungal elements.

Cell-mediated immunity becomes important in containing persistent fungal material.

A delayed-type hypersensitivity response is a prominent feature of Coccidioides infection.

Innate

Macrophage uptake

Adaptive

T-cell / DTH response

Slide 13 · Delayed-type hypersensitivity (DTH)

DTH is a T-cell–mediated inflammatory response to antigen.

Previously sensitized hosts can mount a delayed cutaneous reaction.

This explains how an asymptomatic infected person may still have a positive skin test.

Fungal

Antigen

T-cell

Recognition

Delayed

Skin response

Simplified conceptual sequence

Slide 14 · DTH is not identical to clinical disease

An immune response indicates recognition of fungal antigen.

Most infected people remain asymptomatic.

Therefore a positive skin reaction should not be equated with active pulmonary or disseminated disease.

Immune evidence

DTH / skin-test positivity

Disease evidence

Compatible pathology / clinical lesion

Slide 15 · Cell-mediated inflammation: The Th1 axis

In immune granulomas, persistent microbial antigens can stimulate T cells.

Th1-associated cytokines, particularly interferon-γ, activate macrophages.

Macrophage activation links antigen recognition to containment of persistent material.

Persistent

Antigen

Th1 cell

Response

Macrophage

Activation

Simplified conceptual sequence

Slide 16 · Why granulomas form

Granulomas represent attempts to contain an agent difficult to eradicate.

They contain aggregates of activated macrophages, often with lymphocytes.

Macrophages may become epithelioid and fuse into giant cells.

Central spherule

Schematic granuloma

Slide 17 · The cellular composition of a granuloma

Epithelioid macrophages are the principal constituent.

Multinucleated giant cells may be present.

Peripheral T lymphocytes support the immune organization of the lesion.

Central spherule

Schematic granuloma

Slide 18 · What a giant cell contributes diagnostically

A giant cell is produced by the fusion of activated macrophages.

The Robbins coccidioidomycosis figure describes spherules within a giant cell.

An identifiable organism supplies etiologic specificity beyond the granuloma pattern alone.

Multinucleated giant cell (schematic)

Slide 19 · The inflammation can injure tissue

Persistent antigen-driven macrophage activation is not harmless.

Granulomatous inflammation can damage normal structures while containing pathogens.

Coccidioides lesions may coexist with a pyogenic component.

Containment

Granulomatous reaction

Injury

Pyogenic / mixed response

Slide 20 · Possible outcomes after inhalation

Most infections remain clinically asymptomatic.

A minority produces recognizable lung lesions.

Rare progressive infection can involve multiple extrapulmonary tissues.

Exposure /

Infection

Pulmonary

Lesion

Rare

Dissemination

Simplified conceptual sequence

Slide 21 · The relative frequencies

Skin-test reactivity above 80% in endemic-area populations.

It reports lung lesions in approximately 10% of infected individuals.

It describes disseminated infection in fewer than 1% of infected individuals.

>80%

Skin-test reaction in endemic-area populations

~10%

Lung lesions among infected individuals

<1%

Disseminated infection among infected individuals

Different denominators and descriptions; Not additive

Slide 22 · How to interpret these estimates

The three percentages use different clinical descriptions and should not be summed.

The figures reflect the textbook’s narrative estimates rather than a contemporary cohort analysis.

Disease frequencies must be interpreted in the setting of host immunity and the population sampled.

Slide 23 · Asymptomatic infection is common

Infection and inflammatory sensitization may occur without illness.

Absence of symptoms does not negate prior exposure.

The asymptomatic majority contrasts with the much smaller group with progressive lesions.

Frequent

Exposure + immune sensitization

Less frequent

Pathologically evident disease

Slide 24 · Pulmonary disease is the principal focus

The lung is the initial site reached following inhalation.

Coccidioides is among the causes of chronic granulomatous pneumonia listed by Robbins.

Recognition of organisms helps distinguish fungal infection from noninfectious granulomas.

Central spherule

Schematic granuloma

Slide 25 · Chronic pneumonia as parent context

Chronic pneumonia as commonly granulomatous.

Mycobacteria and certain dimorphic fungi can produce this pattern.

Pulmonary histology must therefore integrate inflammatory architecture with organism morphology.

Pattern

Granulomatous pneumonia

Cause

Infectious organism must be identified

Slide 26 · Host immunity influences disease extent

T-cell function supports granulomatous responses to persistent organisms.

Suppression of T-lymphocyte immunity is a risk factor for dissemination.

Host factors therefore affect the probability of disease progression.

T-cell

Competence

Containment

Response

Extent of

Infection

Simplified conceptual sequence

Slide 27 · Pregnancy as a dissemination risk

Robbins specifically flags infection acquired during the second or third trimester.

This is a host-state risk factor for disseminated infection.

Pregnancy-related susceptibility should be considered when assessing progressive disease in an endemic setting.

Period named

Second / third trimester

Concern

Risk of dissemination

Slide 28 · HIV-associated T-cell impairment

HIV infection may suppress T-lymphocyte immunity.

That impaired immunity is associated with an increased risk of dissemination.

A disseminated presentation should be understood as an interaction between pathogen and host defenses.

Host factor

HIV / low T-cell function

Risk

Disseminated Coccidioides

Slide 29 · Organ transplantation and immune suppression

Post-transplant immunosuppression is explicitly listed as a dissemination risk.

Immunosuppressive drugs are another named risk setting.

A history of immune-modifying treatment is essential clinicopathologic context.

Transplant /

Medication

T-cell

Suppression

Dissemination

Risk

Simplified conceptual sequence

Slide 30 · Risk factors: A unified framework

Risk setting

Mechanistic / clinical implication

Second / third trimester

Increased dissemination risk

HIV infection

T-lymphocyte immune suppression

Organ transplant treatment

Therapeutic immunosuppression

Other immunosuppressive drugs

Reduced cellular defenses

Slide 31 · Tissue phase: A nonbudding spherule

The Coccidioides tissue form is a thick-walled spherule.

It does not reproduce by the budding pattern of ordinary tissue yeasts.

The spherule may contain numerous small endospores.

Schematic: Endospore-containing spherule

Slide 32 · Approximate spherule diameter

A spherule diameter of 20–60 µm.

Size is assessed together with wall thickness and internal endospores.

Do not infer organism identity from a round shape alone.

20–60 µm

Slide 33 · The diagnostic role of the thick wall

A prominent boundary defines the mature tissue spherule.

The wall encloses multiple endospores when the spherule is mature.

This internal organization differentiates it from a single budding yeast cell.

Schematic: Prominent enclosing wall

Slide 34 · Endospores develop within the spherule

A mature spherule contains numerous smaller endospores.

Endospores are a defining internal feature’ morphology description.

The parent spherule and its contained elements should be interpreted together.

Schematic: Endospore-containing spherule

Slide 35 · Rupture releases endospores

A spherule can rupture and discharge endospores.

This may place multiple small fungal elements into adjacent tissue.

Robbins explicitly associates rupture with an additional pyogenic reaction.

Intact

Released endospores

Slide 36 · Why neutrophils enter the lesion

The source links pyogenic inflammation to spherule rupture.

Released endospores are therefore associated with an acute inflammatory component.

This explains why granulomatous and neutrophil-rich foci can coexist.

Spherule

Rupture

Endospore

Release

Pyogenic

Response

Simplified conceptual sequence

Slide 37 · Three inflammatory patterns are possible

Pure granulomatous inflammation.

Pure pyogenic inflammation.

A mixed granulomatous–pyogenic lesion.

Granulomatous

Macrophage aggregates

Pyogenic

Neutrophil-rich response

Mixed

Both components

Slide 38 · One infection, variable tissue reactions

The lesion’s cellular composition is not fixed across all sites.

Granulomatous, pyogenic and mixed responses can each occur.

The defining fungal structure remains the most direct morphologic clue.

Variable

Host inflammatory pattern

Characteristic

Coccidioides tissue spherule

Slide 39 · The source figure: What to look for

Robbins Fig. 8.50 describes a well-defined granuloma.

A large multinucleated giant cell contains two small spherules.

Higher magnification demonstrates intact and ruptured endospore-bearing forms.

Multinucleated giant cell (schematic)

Slide 40 · A stepwise tissue-recognition checklist

First: Identify the inflammatory pattern.

Second: Search for thick-walled nonbudding spherules.

Third: Determine whether internal endospores or rupture are present.

Fourth: Connect morphology with the relevant exposure and immune setting.

Pattern

Spherule

Endospores

Host context

Slide 41 · Morphology: What is specific and what is not

Granulomatous inflammation alone is not species-specific.

A pyogenic reaction alone is likewise not etiologically specific.

Thick-walled spherules containing endospores provide the distinctive tissue clue.

Nonspecific

Granulomas / neutrophils

Characteristic

Nonbudding endospore-filled spherules

Slide 42 · The diagnosis belongs to the lesion

Fungi can be detected by histologic examination.

Definitive fungal identification sometimes requires culture.

In a granulomatous lesion, organism detection is stronger evidence than morphology of inflammation alone.

Histologic

Pattern

Fungal

Structures

Etiologic

Assessment

Simplified conceptual sequence

Slide 43 · Granulomatous differential diagnosis

Tuberculosis and sarcoidosis can also produce granulomatous lesions.

Several dimorphic fungi produce granulomatous pulmonary inflammation.

Identification of the causative agent is the key safeguard against pattern-only diagnosis.

Inflammation

Common pathway

Organism

Differential discriminator

Slide 44 · Histoplasma: A contrasting fungal form

Small thin-walled tissue yeasts measuring approximately 3–5 µm.

The yeasts may remain within phagocytes and persist in tissue.

Their size and yeast morphology contrast with the larger Coccidioides spherule.

Histoplasma

Coccidioides

Small tissue yeasts

Spherule with endospores

Slide 45 · Blastomyces: A second contrasting form

A round thick-walled yeast measuring approximately 5–15 µm.

Broad-based budding is a characteristic structural clue.

Coccidioides spherules do not show broad-based budding.

Blastomyces

Coccidioides

Broad-based bud

Spherule with endospores

Slide 46 · Dimorphic fungi: Tissue-morphology table

Organism

Key tissue form

Approximate diameter

Coccidioides

Thick-walled nonbudding spherule with endospores

20–60 µm

Histoplasma

Small thin-walled yeasts

3–5 µm

Blastomyces

Thick-walled broad-based budding yeast

5–15 µm

Slide 47 · Comparing the inflammatory patterns

Infection

Robbins-described pulmonary response

Coccidioidomycosis

Granulomatous / pyogenic / mixed

Blastomycosis

Suppurative granulomas

Histoplasmosis

Often necrotizing granulomas

Slide 48 · Dissemination extends beyond the lung

Disseminated infection is uncommon description.

Skin and meninges are frequently involved when spread occurs.

Rare progressive disease can involve other organs and lymphoid tissues.

Pulmonary entry

Lung

Meninges

Skin

Bone / nodes

Adrenals /

Spleen / liver

Slide 49 · Skin involvement

The skin is a frequently named site of disseminated Coccidioides infection.

Skin lesions belong in the differential diagnosis in a patient with relevant exposure.

The same spectrum of granulomatous, pyogenic, or mixed inflammation may be seen.

Site

Skin

Expected pathology

Variable inflammatory pattern

Slide 50 · Meningeal involvement

The meninges are a frequently affected site in dissemination.

Coccidioides among endemic fungi that can involve the CNS.

CNS fungal involvement often follows widespread dissemination, especially with impaired immunity.

Primary

Exposure

Disseminated

Infection

Meningeal

Pathology

Simplified conceptual sequence

Slide 51 · Other sites of progressive disease

Bones and lymph nodes as possible sites.

Adrenals, spleen, and liver may also be involved.

Organ distribution demonstrates that the disease can become systemic rather than remain pulmonary.

Pulmonary entry

Lung

Meninges

Skin

Bone / nodes

Adrenals /

Spleen / liver

Slide 52 · Anatomic site does not fix histologic pattern

Across listed sites, inflammation may be granulomatous.

A pyogenic response may dominate in other areas.

Mixed lesions require deliberate search for the Coccidioides spherule.

Lung

Variable

Skin / meninges

Variable

Other organs

Variable

Slide 53 · From lung to multiorgan disease: Synthesis

Entry begins with inhaled arthroconidia.

Macrophage evasion is an early pathogen advantage.

Suppressed T-cell immunity favors spread beyond the pulmonary focus.

Inhalation

Host defense

Interaction

Systemic

Involvement

Simplified conceptual sequence

Slide 54 · Case 1 — pulmonary granuloma

Teaching vignette (hypothetical): A patient has lived in an endemic part of the southwestern United States.

A lung biopsy shows granulomatous inflammation with a large nonbudding spherule.

Question: Which additional morphologic feature best supports Coccidioides?

Slide 55 · Case 1 — interpretation

Numerous internal endospores favor Coccidioides.

Spherule rupture may explain a superimposed neutrophil-rich reaction.

Geography supports the setting, but the tissue structure is the decisive pathologic clue.

Schematic: Endospore-containing spherule

Slide 56 · Case 2 — concern for dissemination

Teaching vignette (hypothetical): A patient receiving immune-suppressing transplant treatment develops a pulmonary lesion.

Additional assessment identifies meningeal involvement.

Question: Which host mechanism helps explain the broader distribution?

Slide 57 · Case 2 — interpretation

Transplantation-associated suppression of T-cell immunity as a risk factor.

Meningeal involvement is consistent with disseminated disease.

A regional pulmonary process has become a systemic clinicopathologic problem.

T-cell

Suppression

Dissemination

Risk

Meningeal

Involvement

Simplified conceptual sequence

Slide 58 · Case 3 — a misleading granuloma

Teaching vignette (hypothetical): A biopsy is initially reported as “granulomatous inflammation.”

A large thick-walled round organism with internal bodies is subsequently recognized.

Question: Why does the organism matter more than the generic granuloma label?

Slide 59 · Case 3 — interpretation

Granulomatous inflammation is shared by multiple infections and inflammatory diseases.

The nonbudding endospore-containing spherule supplies etiologic specificity.

The pathologic report should distinguish response pattern from identified organism.

Pattern

Granulomatous inflammation

Etiology

Coccidioides spherule

Slide 60 · Five concepts that integrate the disease

Inhaled arthroconidia initiate infection.

Interference with phagosome–lysosome fusion promotes intracellular persistence.

T-cell immunity and DTH shape the host response.

Endospore-containing nonbudding spherules define tissue morphology.

Rare dissemination favors skin, meninges, and other organs in susceptible hosts.

Slide 61 · Reference and figure provenance

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

Supporting Robbins material: granulomatous inflammation, delayed-type hypersensitivity, chronic pneumonia, and CNS fungal infections.

All displayed organism and immunopathology diagrams are original, editable, simplified schematics—not photomicrographs.