Leishmaniasis

Slide 1 · Leishmaniasis

Pathogenesis, morphology and clinicopathologic correlation

Pathology and clinical correlations

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Differentiate the promastigote and amastigote stages within the sandfly–mammal cycle.

Explain Leishmania survival in phagocytes and the opposing Th1/Th2 immune responses.

Recognize the morphology and clinical consequences of four disease forms.

Connect disease distribution and pathology to source-supported diagnostic approaches.

Slide 3 · Leishmaniasis is an intracellular protozoal disease

Caused by Leishmania, a kinetoplast-containing protozoan parasite.

Produces chronic inflammation in skin, mucous membranes or viscera.

Transmission occurs through bites of infected sandflies.

Disease phenotype reflects both the infecting parasite and the host.

Slide 4 · Three major tissue compartments

Localized infection

Skin lesions may begin at the site of inoculation.

Mucosal disease can involve nasopharyngeal structures.

Tissue inflammation may evolve into granulomas.

Disseminated infection

Macrophages can transport infection through the mononuclear phagocyte system.

Spleen, liver and marrow may become heavily involved.

Systemic inflammatory and hematologic consequences dominate.

Slide 5 · The four recognized morphologic forms

Form

Principal distribution

Defining lesion pattern

Visceral

Mononuclear phagocyte system

Systemic organ enlargement and cytopenias

Cutaneous

Exposed skin

Papule evolving into a slow ulcer

Mucocutaneous

Nasopharyngeal mucosa

Destructive mucosal inflammation

Diffuse cutaneous

Extensive skin

Progressive widespread nodules with foamy macrophages

Slide 6 · Endemicity spans multiple regions

The source identifies the Middle East, South Asia, Africa and Latin America as endemic regions.

“Old World” and “New World” are geographic groupings, not clinical diagnoses.

Exposure history should be interpreted in relation to local transmission ecology.

Slide 7 · Social conditions influence transmission

Leishmaniasis is associated with poverty in endemic regions.

The text describes epidemics following forced migration of people with low immunity.

Movement into an area of intense sandfly transmission changes opportunities for infection.

Slide 8 · Disease burden as reported

Measure

Textbook estimate

Interpretive caution

Cutaneous cases per year

0.6–1 million

Reported estimate; Not presented as a 2026 live count

Visceral cases per year

50,000–90,000

Reported global estimate

Deaths per year

More than 20,000

Reported in the source in context of visceral disease

Slide 9 · Leishmania is a kinetoplastid parasite

The organism contains a distinctive kinetoplast: Mitochondrial DNA concentrated into a specialized structure.

It alternates between an extracellular vector stage and an intracellular mammalian stage.

Recognition of stage and compartment is central to understanding pathogenesis.

Slide 10 · The two developmental forms

Promastigote

Extracellular form in the sandfly.

Slender and flagellated.

Transmitted during an infectious sandfly bite.

Amastigote

Round intracellular stage within mammalian macrophages.

Lacks an external flagellum.

Proliferates in phagolysosomal compartments.

Slide 11 · Transmission cycle at a glance

Sandfly blood meal

Ingests infected host cells

Vector stage

Development as promastigotes

Sandfly bite

Promastigotes enter the dermis

Macrophages

Amastigotes multiply

The next sandfly blood meal can reacquire infection from an infected host.

Slide 12 · Vectors and parasite diversity

The text identifies more than 90 sandfly species as vectors.

Approximately 21 Leishmania species infect humans, according to the textbook.

Parasite identity contributes to geographic distribution and tissue phenotype.

Slide 13 · The mammalian reservoir interface

Reservoir mammals

Rodents are listed as reservoirs.

Dogs can harbor infection.

Foxes are another example.

Transmission bridge

Sandflies feed on infected mammalian hosts.

Vector acquisition starts a developmental cycle within the insect.

Infected vectors can subsequently transmit to people.

Slide 14 · Events within the sandfly

Uptake

Amastigote-bearing host cells

Transformation

Amastigote → promastigote

Amplification

Promastigote multiplication

Transmission

Infectious forms at a subsequent bite

Slide 15 · What happens at the bite site?

Infected sandfly

Inoculates promastigotes

Dermal exposure

Sandfly saliva accompanies inoculation

Host phagocytes

Macrophages internalize organisms

The source attributes enhanced infectivity to sandfly saliva.

Slide 16 · The macrophage is the replication niche

Promastigote uptake

Phagocytosis by macrophage

Acidic compartment

Stage differentiation is induced

Amastigote stage

Rounded intracellular organisms

Replication

Progeny accumulate

Slide 17 · Amastigote structure: What to recognize

Intracellular organism model

Amastigotes are rounded organisms within macrophages.

The kinetoplast is a mitochondrial DNA-containing structure distinct from the nucleus.

The drawing conveys location and components; It is not a substitute for a stained preparation.

Blue dot: Parasite nucleus Red dot: Kinetoplast

Original editable schematic — not a histologic or clinical specimen

Slide 18 · Intracellular amplification and spread

Viable macrophage

Amastigotes replicate

Host-cell death

Progeny organisms released

New macrophages

Additional infection established

The cycle increases parasite-containing phagocytes within an infected tissue.

Slide 19 · What determines dissemination?

Parasite factors

Different Leishmania species have different clinical associations.

Virulence strategies favor survival in innate immune cells.

The source ties parasite identity to extent of spread.

Host factors

Host immune response limits or permits intracellular persistence.

Effective T-cell function is needed to clear infection.

Immunodeficiency can exacerbate infection.

Slide 20 · Species grouping

Grouping

Examples in the source

Regional framing

Old World

L. Major, L. Tropica, L. Donovani, L. Infantum

Parts of Asia, Middle East, Africa, southern Europe

New World

L. Mexicana, L. Braziliensis, L. Chagasi

Mexico, Central America, South America

Slide 21 · Human disease is not confined to classic endemic regions

The text notes some cases in Texas and Oklahoma.

Geography informs suspicion but does not independently establish a diagnosis.

Clinical pattern and tissue or molecular detection remain necessary.

Slide 22 · Leishmania actively modifies innate defense

Survival is not explained solely by passive macrophage uptake.

The source identifies parasite surface factors and subversion of neutrophil defenses.

Additional adaptations involve phagolysosomal conditions, iron handling and immune signaling.

Slide 23 · Two prominent promastigote virulence factors

Lipophosphoglycan

Abundant surface glycoconjugate.

Interferes with the complement pathway.

Supports early survival at host entry.

Gp63 protease

Zinc-dependent surface proteinase.

Cleaves host enzymes described as important to defense.

Illustrates enzymatic subversion of host responses.

Slide 24 · Complement interference supports early entry

Promastigote surface

Lipophosphoglycan

Host interface

Complement pathway interference

Consequence

Enhanced opportunity for parasite survival

This is a mechanistic schematic of the textbook description, not a complete complement cascade.

Slide 25 · Gp63: Protease-mediated host interference

Promastigote

Surface Gp63

Protease activity

Cleavage of host enzymes

Host response

Perturbation of defense pathways

The source does not enumerate specific enzyme substrates; None are inferred here.

Slide 26 · Neutrophil escape has several routes

Parasites interfere with formation of phagolysosomes and fusion with neutrophil granules.

They may occupy intracellular compartments protected from lytic mechanisms.

They can resist reactive oxygen species-mediated toxicity.

Slide 27 · Neutrophil extracellular trap evasion

NET formation

Host extracellular DNA-based defense

Parasite adaptations

Endonucleases and protease-resistant surface molecules

Potential result

Reduced effectiveness of NET-mediated killing

The textbook explicitly describes parasite digestion of NETs.

Slide 28 · Amastigotes resist the phagolysosomal environment

Expected host function

Macrophage phagolysosomes are antimicrobial compartments.

Acidity contributes to the hostile environment.

Killing depends on functional phagocyte defenses.

Source-described adaptation

Amastigotes alter phagolysosomal conditions.

Maintenance near pH 6.5 versus typical pH 4.5.

The stated mechanism supports persistence despite ingestion.

Slide 29 · The iron contest occurs inside infected cells

Parasite acquisition

ZIP-family iron transporter

Local substrate

Iron entry into phagolysosome

Host response

Inflammatory iron restriction

The same intracellular compartment is a source of nutrients and a site of antimicrobial restriction.

Slide 30 · Host defense counteracts parasite iron uptake

Proinflammatory cytokines inhibit cellular iron absorption.

The host downregulates transferrin receptors.

Iron is also removed from the phagosomal compartment.

These responses oppose parasite nutrient acquisition as.

Slide 31 · MicroRNAs contribute to immune disruption

Posttranscriptional gene regulation through microRNAs.

It refers to microRNAs in the parasite and host cells.

Altered cellular signaling is linked to disturbance of protective immunity.

No individual microRNA species or validated target is specified in the source.

Slide 32 · T-helper polarization and infection control

Th1-dominant response

Parasite-specific CD4+ T cells contribute to control.

IFN-γ activates macrophages.

Activated phagocytes become better able to kill parasites.

Th2-dominant response

Susceptible mouse strains show Th2 predominance.

Th2 cytokines impair effective macrophage killing.

Infection control is correspondingly weakened.

Slide 33 · Protective cellular immunity acts through macrophages

Parasite-specific CD4+ Th1

Cellular immune response

IFN-γ

Macrophage-activating signal

Macrophage effector state

Increased parasite killing

This protective mechanism in experimental models and humans.

Slide 34 · A Th2-biased response may favor persistence

Th2-predominant response

Susceptibility in animal models

Reduced macrophage microbicidal activity

Inadequate intracellular clearance

Continued infection

Parasite persistence

Slide 35 · Avoid interpreting Th1 and Th2 as an absolute binary

The textbook uses Th1–Th2 polarization to explain major determinants of susceptibility.

The cited direct strain comparisons are from mice.

Human phenotypes also depend on parasite species and broader immune status.

Th1 and Th2 are teaching mechanisms here, not stand-alone diagnostic tests.

Slide 36 · T-cell dysfunction aggravates leishmaniasis

Impaired T-cell function increases vulnerability to intracellular organisms.

The source compares this susceptibility with mycobacterial, Histoplasma and Toxoplasma infections.

An immune response is necessary for durable parasite clearance even when effective drugs exist.

Slide 37 · HIV coinfection is clinically important

The source notes that many individuals with leishmaniasis are coinfected with HIV.

Compromised cellular immunity may worsen intracellular parasite control.

A systemic leishmanial phenotype should be interpreted in the context of immune competence.

Slide 38 · Disease extent shapes the pathologic phenotype

Extent

Dominant host tissue

Characteristic consequence

Localized dermis

Skin macrophages

Cutaneous papule and ulceration

Mucosal disease

Nasopharyngeal tissue

Inflammatory destruction and scarring

Widespread dermis

Skin macrophages

Disseminated nodular lesions

Systemic dissemination

Mononuclear phagocyte system

Organomegaly, marrow dysfunction, inflammation

Slide 39 · Visceral leishmaniasis is the most severe form

The source describes untreated visceral leishmaniasis as almost always fatal.

Macrophage infection becomes widespread in mononuclear phagocyte organs.

The clinical syndrome combines systemic inflammation, enlargement of organs and cytopenias.

Slide 40 · Systemic macrophage involvement drives visceral disease

Amastigote infection

Macrophages parasitized

Organ infiltration

Spleen, liver and marrow

Tissue dysfunction

Organomegaly, cytopenias and systemic inflammation

Slide 41 · The visceral syndrome has a recognizable cluster

Fever and weight loss reflect systemic illness.

Hepatosplenomegaly and lymphadenopathy reflect mononuclear phagocyte organ involvement.

Pancytopenia signals hematologic consequences.

No single component is pathognomonic; The source recommends parasite detection.

Slide 42 · Spleen: Gross enlargement and structural disruption

Schematic of marked splenomegaly

That the spleen may reach approximately 3 kg.

Phagocyte expansion and plasma-cell accumulation distort normal splenic architecture.

Organ enlargement is part of the systemic mononuclear phagocyte response.

Original editable schematic — not a histologic or clinical specimen

Slide 43 · Spleen: Parasitized macrophages dominate

Simplified cellular model

Phagocytic cells are enlarged and filled with organisms.

Numerous plasma cells are present.

Normal splenic architecture may be obscured by the infiltrate.

Blue dot: Parasite nucleus Red dot: Kinetoplast

Original editable schematic — not a histologic or clinical specimen

Slide 44 · Bone marrow infiltration contributes to blood-count changes

The source describes marrow crowded by parasite-containing phagocytic cells.

Visceral disease is clinically marked by pancytopenia.

Marrow infiltration provides a tissue-level explanation for hematologic compromise, although causation is not exclusive.

Slide 45 · Hepatic disease evolves during progression

Macrophage involvement accompanies visceral dissemination.

The liver enlarges during systemic disease.

In late stages, the source describes increasingly fibrotic hepatic tissue.

Histologic severity should be considered in relation to disease duration.

Slide 46 · Dissemination can extend beyond the core organs

Parasite-containing phagocytes may be present in lung tissue.

Gastrointestinal tract, kidneys and pancreas may be involved.

The testes are also listed among potential locations.

This distribution is described in advanced visceral involvement, not as universal disease.

Slide 47 · Kala-azar: The pigmentation association

Cutaneous hyperpigmentation in some patients of South Asian ancestry.

The designation “kala-azar” refers to “black fever” in Hindi.

Pigmentation is a clinical correlate; Diagnosis should not depend on its presence.

Slide 48 · Renal pathology may be immune mediated

The source reports immune complex–mediated mesangioproliferative glomerulonephritis.

Amyloid deposition may occur in advanced disease.

These lesions illustrate that organ injury may extend beyond direct parasite-containing macrophage infiltrates.

Slide 49 · Serious consequences of visceral infection

Infectious complications

Life-threatening secondary bacterial infections occur in advanced disease.

The text gives pneumonia and sepsis as examples.

Tuberculosis is also mentioned.

Hematologic complications

Thrombocytopenia contributes to bleeding risk.

Hemorrhage can be fatal.

Cytopenias coexist with extensive organ involvement.

Slide 50 · Cutaneous lesions change with time

Papule

Induration at exposed skin

Shallow ulcer

Slowly expands

Chronic ulcer

Heaped-up margins

Involution

Often heals with scarring

The source reports spontaneous healing over approximately 6–18 months in typical disease.

Slide 51 · Cutaneous ulcers are slowly progressive

Stylized skin surface (not a lesion photo)

Papule

Expanding ulcer

Involution/scar

Exposed skin is a typical site.

A papule becomes an enlarging superficial ulcer with raised margins.

The time course can be prolonged before involution.

Original editable schematic — not a histologic or clinical specimen

Slide 52 · Cutaneous histology reflects cellular immune response

Granulomatous inflammation is reported in the lesion.

Multinucleated giant cells are often prominent.

Parasites may be few in this inflammatory pattern.

Low organism conspicuity on a section does not by itself rule out disease.

Slide 53 · Localized cutaneous disease may involute

Many lesions healing without treatment.

A 6–18-month timeframe is reported for typical involution.

Healing and the residual scar are distinct from absence of a prior infection.

Clinical outcomes vary with form, so this course should not be generalized to visceral disease.

Slide 54 · Mucocutaneous disease has a regional distribution

Robbins particularly highlights Brazil, Ethiopia and Peru.

The target is nasopharyngeal mucosa rather than skin alone.

Damage to mucosal structures can produce major disfigurement.

Slide 55 · Mucocutaneous lesions can be destructive

Moist lesions may be ulcerating or nonulcerating.

Progressive disease may destroy and disfigure nasopharyngeal tissue.

The clinical risk reflects lesion location and local tissue destruction, not just parasite count.

Slide 56 · Mucocutaneous inflammation changes over time

Early disease

Parasite-bearing macrophages

Inflammatory infiltrate

Lymphocytes and plasma cells

Later lesions

Granulomas; Fewer parasites

Outcome

Scarring; Possible reactivation

Slide 57 · Mucosal reactivation can occur after remission

The text describes lesions that remit and scar.

Reactivation may occur after long intervals.

The mechanisms of reactivation are not currently understood.

Avoid claiming a predictable recurrence interval or molecular trigger.

Slide 58 · Diffuse cutaneous disease spreads through the skin

Diffuse cutaneous leishmaniasis is described as rare.

It has been reported in Ethiopia, neighboring East Africa and Central and South America.

The lesion begins as one skin nodule and progresses to widespread nodularity.

Slide 59 · Diffuse cutaneous histology has a high parasite burden

Foamy macrophages: Conceptual model

Foamy macrophages form aggregates within the lesions.

The cells may be densely packed with Leishmania organisms.

This contrasts with the pauciparasitic granulomas described for localized cutaneous disease.

Blue dot: Parasite nucleus Red dot: Kinetoplast

Original editable schematic — not a histologic or clinical specimen

Slide 60 · Localized versus diffuse cutaneous pathology

Feature

Localized cutaneous

Diffuse cutaneous

Clinical extent

Papule → localized ulcer

Progressively widespread nodules

Characteristic cells

Granulomas and giant cells

Aggregates of foamy macrophages

Organism burden

Few parasites in described lesions

Many organisms within macrophages

Natural history in source

Typical involution over months

Continued dissemination across skin

Slide 61 · Compare four leishmanial disease patterns

Form

Lesion or organ distribution

Signature microscopic or clinical clue

Visceral

Spleen, liver, marrow

Macrophage infiltration; Organomegaly and pancytopenia

Cutaneous

Localized exposed skin

Granulomas with giant cells; Few parasites

Mucocutaneous

Nasopharyngeal tissue

Inflammation evolves to granulomas and scarring

Diffuse cutaneous

Widespread skin nodules

Foamy macrophages packed with amastigotes

Slide 62 · The source recognizes three diagnostic approaches

Histologic examination can demonstrate tissue involvement and intracellular organisms.

Culture is listed as a diagnostic method.

PCR is also listed for detection of infection.

The text does not provide assay performance, optimal specimen algorithms or validated thresholds.

Slide 63 · Recognize parasite-containing macrophages

Schematic macrophage with amastigotes

Look for intracellular rounded forms within infected macrophages.

Each kinetoplast-containing protozoan has structures that help identify the stage.

This model is not a Giemsa stain and cannot establish a morphologic diagnosis.

Blue dot: Parasite nucleus Red dot: Kinetoplast

Original editable schematic — not a histologic or clinical specimen

Slide 64 · A tissue pattern alone does not identify Leishmania

Granulomatous inflammation is a tissue reaction, not a species-specific finding.

The diagnostic suspicion rests on compatible epidemiology, lesion pattern and direct testing.

When parasites are sparse, culture and PCR among additional approaches.

Slide 65 · Case application: Visceral disease

A patient from an endemic region develops fever, weight loss, marked splenomegaly and pancytopenia. Tissue evaluation identifies macrophages containing intracellular kinetoplastid organisms.

Interpretation

Most consistent form: Visceral leishmaniasis.

The mechanism combines systemic macrophage involvement with marrow and splenic pathology.

The source supports histology, culture and PCR as diagnostic approaches.

Slide 66 · Case application: A chronic skin ulcer

An exposed-skin papule slowly becomes a shallow ulcer with raised margins. A biopsy shows granulomas and giant cells, but only rare candidate parasites.

Interpretation

The pattern is compatible with localized cutaneous leishmaniasis.

A low parasite burden can accompany a strong granulomatous response.

Direct diagnostic evaluation is still needed; Morphology alone is not a species determination.

Slide 67 · Case application: A destructive mucosal lesion

A patient with relevant geographic exposure has a nasopharyngeal lesion that progresses to local destruction and later scars; The biopsy shows inflammatory cells and evolving granulomas.

Interpretation

The distribution raises mucocutaneous leishmaniasis as a consideration.

A later granulomatous phase may contain fewer visible parasites.

The source acknowledges reactivation after prolonged intervals without a defined mechanism.

Slide 68 · Case application: Progressive diffuse nodules

A single skin nodule gradually progresses to widespread nodules. Histologic sections show collections of foamy macrophages containing numerous amastigotes.

Interpretation

This is the source-described pattern of diffuse cutaneous leishmaniasis.

Prominent foamy, organism-packed macrophages contrast with localized pauciparasitic granulomas.

Slide 69 · Mechanistic synthesis: From vector to clinical syndrome

Sandfly promastigotes enter dermis and convert to macrophage amastigotes.

Survival depends on interactions with complement, neutrophils and intracellular phagocyte defenses.

Th1-dependent macrophage activation opposes persistence; Impaired cellular immunity increases susceptibility.

Parasite–host interaction and distribution generate distinct tissue patterns.

Slide 70 · Reference and interpretive boundaries

Primary: Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed. (2026), Chapter 8, “Leishmaniasis,” pp. 357–359.

The supplied Markdown is derived from extracted textbook text and includes column interleaving.

This deck excludes neighboring babesiosis, malaria and trypanosomiasis material.

No original chapter PDF or licensed source micrograph was provided; all illustrations are native editable schematics.