Onchocerciasis

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Lecture topics

Onchocerciasis: A tissue-centered infection
A compartmental view of infection
Onchocercoma: Capsule architecture
Epidermal atrophy: Tissue loss
Why the skin pattern is not one lesion
Anterior chamber involvement
Ivermectin and developmental stage
Source and boundaries

Slide index & full transcript (63 slides)

Text from the original slides, in presentation order. Diagrams and images remain in the viewer above.

Slide 1 · Onchocerciasis

Pathogenesis, morphology, and clinicopathologic consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Onchocerciasis: A tissue-centered infection

Onchocerca volvulus is a filarial nematode.

Infection has a characteristic subcutaneous nodule and cutaneous inflammatory disease.

Microfilariae can injure the cornea and intraocular tissues, causing loss of vision.

Core distinction

Adult worms and microfilariae occupy different pathological roles.

Slide 3 · Learning outcomes

Identify the parasite, vector, and river-associated exposure setting.

Explain why microfilarial inflammation dominates tissue damage.

Recognize onchocercomas, chronic skin changes, and progressive eye lesions.

Relate ivermectin activity and treatment-associated inflammation to parasite stage.

Emphasis: Mechanism → morphology → organ damage.

Slide 4 · The etiologic organism

The disease is attributed to Onchocerca volvulus.

O. Volvulus belongs to the filarial nematodes.

Adult parasites and their microfilariae produce distinct patterns of tissue involvement.

Core distinction

Name the species, then locate its adult and immature forms.

Slide 5 · Filarial context: Two sites of disease

Lymphatic filariasis

Onchocerciasis

Adult parasites in lymphatic channels

Adult parasites in dermis

Lymphedema / elephantiasis

Dermatitis / ocular injury

Avoid transferring elephantiasis mechanisms directly to onchocerciasis.

Slide 6 · Black flies transmit the parasite

Black fly habitat

Human exposure

Dermal infection

Skin / eye disease

The source identifies black flies as the vectors.

Reported transmission locations include Africa, South America, and Yemen.

The local vector habitat is central to geographic risk.

Vector ecology helps explain the disease distribution.

Slide 7 · Why “river blindness”?

Fast-moving water

Black fly habitat

Transmission to people

Potential eye damage

Black flies have habitats near fast-moving water.

Human incidence is therefore higher near rivers.

The name links transmission ecology to a severe ocular outcome.

River proximity predicts exposure context—not the anatomical site of injury.

Slide 8 · The distribution

Africa, South America, and Yemen as transmission settings.

The description emphasizes blindness in sub-Saharan Africa.

These are textbook statements, not a current surveillance map.

Core distinction

Distribution statements should be dated to the edition being taught.

Slide 9 · Elimination is location-specific

The text reports WHO-declared elimination in Colombia, Ecuador, Mexico, and Guatemala.

Elimination in named countries does not imply elimination everywhere.

Historical program achievements must be separated from present-day surveillance.

Core distinction

Textbook claim; No independent current-status verification performed.

Slide 10 · Mass ivermectin campaigns

Community treatment

Immature-stage killing

Lower disease burden

Need for repeat dosing

A large decline in incidence to mass ivermectin administration.

Campaign impact is described for Africa and South America.

Continued treatment is conceptually linked to persistence of adult parasites.

Public-health effect and individual parasitologic clearance are different endpoints.

Slide 11 · A compartmental view of infection

Dermis

Adult worms mate

Subcutaneous onchocercoma

Skin

Microfilariae accumulate

Chronic dermatitis

Eye

Microfilariae disseminate

Keratitis / inflammation

Dermis: Adult worms mate and persist.

Skin: Offspring microfilariae accumulate.

Slide 12 · Adult worms establish the dermal focus

Adult worms

Fibrous capsule

Fibrous enclosure

Adult parasites

Mixed inflammatory cells

Fibrin

Simplified nodule schematic — not a histology image

Adult male and female parasites mate in the dermis.

Host cells accumulate around these adult worms.

Slide 13 · Reproduction creates a mobile disease stage

Adult mating

Microfilariae produced

Skin accumulation

Inflammatory injury

Inseminated adult females produce microfilariae.

Microfilariae collect in skin rather than remaining confined to the adult nodule.

Their distribution explains lesions beyond the original nodule.

Adult persistence can seed ongoing microfilarial exposure.

Slide 14 · The eye is an additional target

Cornea

Punctate → sclerosing keratitis

Anterior chamber / ciliary body

Iridocyclitis ± glaucoma

Choroid and retina

Atrophy → loss of vision

Linking factor

Microfilarial inflammation

Anatomical site map; Not a scaled anatomical drawing

Microfilariae disseminating into the eye chambers.

Ocular inflammation can affect the cornea, anterior chamber, and posterior structures.

Slide 15 · The core pathogenic principle

Microfilariae

Host inflammatory response

Tissue injury

Functional deficit

Clinical disease is primarily attributed to inflammation induced by microfilariae.

Immature parasite degeneration is prominent in corneal inflammatory injury.

Host inflammatory responses are central to the destructive phenotype.

Organ damage is not simply the physical presence of worms.

Slide 16 · Adults versus microfilariae

Adult worms

Microfilariae

Predominantly dermal nodules

Distributed through skin

Fibrous capsule + mixed cells

Diffuse dermatitis and eye inflammation

Source of progeny

Key inflammatory effector stage

Different parasite stages explain distinct pathology patterns.

Focal process

Distributed process

Adult worm in capsule

Microfilariae beyond nodule

Localized subcutaneous nodule

Dermatitis and ocular lesions

Distinguish focal structural lesions from distributed inflammatory lesions.

Slide 23 · Cutaneous disease: The clinical pattern

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Morphologic pattern

Epidermis + dermis

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

A chronic, itchy dermatitis.

Pigment may become focally darker or reduced.

Slide 24 · Pruritus reflects an inflammatory skin disease

Skin microfilariae

Inflammatory response

Chronic dermatitis

Pruritus / remodeling

Itch is included in the primary cutaneous morphology.

The source places dermatitis downstream of microfilarial inflammation.

Persistent irritation can coexist with longer-term tissue remodeling.

Pruritus and architectural changes belong to one pathological process.

Slide 25 · Cutaneous pigment may increase or decrease

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Pigment change

Epidermis + dermis

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

Both focal darkening and loss of pigmentation are reported.

The patterns may coexist with scale.

Slide 26 · “Leopard,” “lizard,” and “elephant” skin

These terms for chronic onchocercal skin patterns.

They refer to visible alterations in pigmentation, scale, and surface architecture.

The labels describe appearance; They are not separate etiologic entities.

Core distinction

Use descriptive morphology rather than assuming distinct pathogens.

Slide 27 · Epidermal atrophy: Tissue loss

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Tissue atrophy

Epidermis + dermis

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

Areas of epidermal atrophy are described.

The source also reports breakdown of elastic fibers.

Slide 28 · Elastic-fiber breakdown

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Elastic fiber injury

Dermal matrix

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

Degeneration of elastic fibers is specifically included in the skin lesion.

The dermal matrix is therefore involved, not just the epidermal surface.

Slide 29 · Hyperkeratosis in chronic dermatitis

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Hyperkeratosis

Epidermal keratin

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

Some skin regions become hyperkeratotic.

Hyperkeratosis may coexist with hyperpigmentation.

Slide 30 · Pigment incontinence

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Pigment change

Epidermis + dermis

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

Dermal pigment incontinence.

This is distinct from a simple visual description of darker skin.

Slide 31 · Dermal atrophy and fibrosis

Epidermal surface

Epidermis: Focal atrophy ↔ hyperkeratosis

Dermis: Elastic-fiber injury, pigment incontinence, fibrosis

Focus: Tissue atrophy

Epidermis + dermis

Schematic tissue layers

Schematic: Relative layer positions, not diagnostic microscopy

The dermis can become atrophic and fibrotic.

Loss of normal tissue and deposition of fibrous tissue may coexist.

Slide 32 · The patchwork morphology of skin disease

Relatively atrophic foci

Thickened / pigmented foci

Epidermal atrophy

Hyperkeratosis

Elastic-fiber breakdown

Hyperpigmentation

Dermal atrophy

Pigment incontinence / fibrosis

Alternating patterns are an explicit finding.

Slide 33 · Cutaneous structure–function reasoning

Inflammation

Epidermal change

Dermal remodeling

Pigment / scale / texture

Microfilarial inflammation produces chronic dermatitis.

Ongoing injury is associated with epidermal and connective-tissue alterations.

The clinical surface changes are the visible readout of underlying morphology.

Histology explains the visible skin phenotype.

Slide 34 · Cutaneous recognition: What to describe

Record pruritus and scaling as inflammatory symptoms/signs.

Describe whether pigmentation is increased, decreased, or mixed.

Distinguish atrophic from hyperkeratotic regions and note dermal fibrosis.

Core distinction

These are morphology descriptors, not a validated diagnostic algorithm.

Slide 35 · Why the skin pattern is not one lesion

Subcutaneous lesion

Cutaneous diffuse lesion

Encapsulated adult worms

Microfilaria-related inflammation

Mixed infiltrate

Pigment and keratin changes

Focal nodule

Patchy tissue remodeling

Separate lesion type, anatomical site, and parasite stage.

Slide 36 · Ocular injury: Multiple anatomical targets

Cornea

Punctate → sclerosing keratitis

Anterior chamber / ciliary body

Iridocyclitis ± glaucoma

Choroid and retina

Atrophy → loss of vision

Linking factor

Microfilarial inflammation

Anatomical site map; Not a scaled anatomical drawing

The cornea is affected by punctate and later sclerosing keratitis.

Anterior chamber and ciliary body may develop iridocyclitis.

Slide 37 · Early corneal change: Punctate keratitis

Initial microfilarial injury

Punctate keratitis

Sclerosing opacity

Punctate stage · Conceptual corneal schematic, not a clinical image

The initial described corneal lesion is punctate keratitis.

It appears as small, fluffy corneal opacities.

Slide 38 · Why microfilariae cloud the cornea

Degenerating microfilariae

Eosinophilic infiltration

Punctate opacity

Reduced transparency

Degeneration of microfilariae occurs in the cornea.

The degenerating parasites elicit an eosinophilic infiltrate.

Inflammation accompanies the punctate, fluffy opacities.

Parasite degeneration → inflammation → loss of corneal clarity.

Slide 39 · Eosinophils in early corneal disease

Initial microfilarial injury

Punctate keratitis

Sclerosing opacity

Eosinophilic inflammation · Conceptual corneal schematic, not a clinical image

The infiltrate accompanying degenerating microfilariae includes eosinophils.

This connects ocular pathology to host inflammatory response.

Slide 40 · Corneal disease can become sclerosing

Initial microfilarial injury

Punctate keratitis

Sclerosing opacity

Sclerosing opacity · Conceptual corneal schematic, not a clinical image

Progression from punctate to sclerosing keratitis.

The later lesion opacifies the cornea.

Slide 41 · The limbal starting point

Initial microfilarial injury

Punctate keratitis

Sclerosing opacity

Limbal onset of sclerosis · Conceptual corneal schematic, not a clinical image

Corneal disease

Chorioretinal disease

Punctate → sclerosing keratitis

Choroid / retina involvement

Opacified optical tissue

Posterior tissue atrophy

Transparency compromised

Loss of retinal function associated with tissue loss

Two major patterns: Loss of clarity versus tissue atrophy.

Slide 48 · A site-based ocular damage map

Cornea

Punctate → sclerosing keratitis

Anterior chamber / ciliary body

Iridocyclitis ± glaucoma

Choroid and retina

Atrophy → loss of vision

Linking factor

Microfilarial inflammation

Anatomical site map; Not a scaled anatomical drawing

Cornea: Punctate keratitis and sclerosing opacity.

Anterior segment: Iridocyclitis with glaucoma.

Slide 49 · Vision loss has more than one mechanism

Cornea: Opacity

Anterior: Glaucoma

Posterior: Atrophy

Visual impairment

Corneal damage changes optical transparency.

Anterior intraocular inflammation is associated with glaucoma.

Posterior chorioretinal atrophy is another route to loss of vision.

Separate the three lesion pathways when teaching blindness.

Slide 50 · Mazzotti reaction: A treatment-linked change

Keratitis may be accentuated by antifilarial treatment.

This treatment-associated exacerbation is called the Mazzotti reaction.

It underscores inflammation during parasite-directed therapy.

Core distinction

Anti-parasitic efficacy does not mean inflammation always subsides immediately.

Slide 51 · Ivermectin and developmental stage

Ivermectin treatment

Immature-stage killing

Adults persist

Repopulation possible

Ivermectin kills immature worms, not adults.

It does not eradicate the adult reproductive reservoir described in the dermis.

Surviving adult parasites can produce additional microfilariae.

This slide follows the textbook’s stage-based wording.

Slide 52 · Why repeat treatment is needed

Adults survive

New microfilariae

Potential recurrent injury

Repeat treatment

Adult parasites are not killed by ivermectin as.

Microfilariae can recur while adults remain reproductively active.

The text therefore describes retreatment every 3–6 months until symptoms resolve.

Regimen quoted; Not a current prescribing guideline.

Slide 53 · Treatment: Parasite and host response

Parasitologic effect

Inflammatory consequence

Reduction in immature stages

Keratitis may intensify

Adults can persist

Mazzotti reaction is named

Retreatment may be needed

Ocular injury still requires recognition

Keep pathogen control separate from transient tissue inflammation.

Slide 54 · Skin and eye: A unifying mechanism

Skin

Eye

Pruritus + scaling

Punctate keratitis

Pigment / keratin change

Sclerosing corneal opacity

Dermal atrophy / fibrosis

Iridocyclitis / chorioretinal atrophy

One etiologic process produces contrasting organ morphologies.

Slide 55 · Onchocerciasis versus lymphatic filariasis

Lymphatic filariasis (parent text)

Onchocerciasis (topic text)

Adults occupy lymphatic channels

Adults mate in dermis

Chronic lymphedema / elephantiasis

Subcutaneous onchocercoma

Lymphatic remodeling

Dermatitis and eye damage

Do not interpret “elephant skin” as equivalent to lymphatic elephantiasis.

Slide 56 · Morphology-based differential reasoning

A subcutaneous fibrous nodule with adult worms favors onchocercoma.

Chronic pruritic pigmentary dermatitis points to a broader cutaneous process.

Corneal eosinophilic inflammation and chorioretinal atrophy indicate separate ocular compartments.

Core distinction

These are source-based lesion associations—not formal diagnostic test criteria.

Slide 57 · Case 1: Chronic skin disease near a river

An individual from a river-associated exposure area has intense itch and patchy light / dark scale.

A subcutaneous nodule is present alongside diffuse dermatitis.

Question: Which parasite stage explains each lesion?

Interpret the adult nodule and microfilarial inflammation separately.

Slide 58 · Case 1: Compartment-specific explanation

Adult worms

Fibrous capsule

Fibrous enclosure

Adult parasites

Mixed inflammatory cells

Fibrin

Simplified nodule schematic — not a histology image

Adult worms surrounded by a fibrous capsule and mixed cells produce an onchocercoma.

Skin microfilariae account for the inflammatory, pigmentary dermatitis.

Slide 59 · Case 2: Progressive visual impairment

A patient with relevant exposure develops punctate, fluffy corneal opacity.

Later, corneal opacity extends from the limbal region.

Question: Identify the morphological stages and the inflammatory trigger.

Differentiate early punctate from later sclerosing keratitis.

Slide 60 · Case 2: Clinicopathologic explanation

Initial microfilarial injury

Punctate keratitis

Sclerosing opacity

Inflammation precedes sclerosis · Conceptual corneal schematic, not a clinical image

Degenerating microfilariae evoke an eosinophilic infiltrate.

Punctate keratitis precedes sclerosing, opacifying keratitis.

Slide 61 · Five interpretation pitfalls

Mistaking adult worm nodules for the primary cause of every manifestation.

Treating “leopard / lizard / elephant skin” as separate infections.

Assuming keratitis is the only ocular lesion.

Assuming ivermectin eliminates dermal adult worms.

Confusing lymphatic elephantiasis with cutaneous onchocerciasis.

Each mistake arises from ignoring site, stage, or morphology.

Slide 62 · Integrated pathology: What to retain

Agent and ecology: O. Volvulus transmitted by black flies near running water.

Parasite stages: Adults form nodules; Microfilariae drive inflammation.

Skin: Pruritus, pigment / scale changes, atrophy, hyperkeratosis, and fibrosis.

Eye: Punctate → sclerosing keratitis; Anterior / posterior inflammatory damage.

This slide synthesizes facts established across the lecture.

Slide 63 · Source and boundaries

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

Chapter 8, “Onchocerciasis,” printed pp. 365–366.

Related comparison: preceding “Lymphatic Filariasis” section, pp. 364–365.

Epidemiologic statements and treatment intervals reproduce the supplied textbook, not a contemporary guideline.