Malaria

Slide 1 · Malaria

From Plasmodium life cycle to organ pathology

Mechanisms • Morphology • Clinicopathologic correlations

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What determines the severity of malaria?

The liver stage amplifies parasites before symptoms begin.

Rupture of infected erythrocytes drives febrile attacks and anemia.

In P. Falciparum, adhesion of infected red cells compromises the microcirculation.

Tissue injury reflects parasite burden, perfusion failure, and host inflammation.

Slide 3 · Malaria is an intraerythrocytic protozoal infection

Plasmodium is an intracellular parasitic protozoan.

Human infection alternates between hepatic and erythrocytic stages.

Disease results from circulating parasitized RBCs and systemic responses.

The erythrocytic stage explains characteristic clinical paroxysms.

Slide 4 · Five human-infecting Plasmodium species

Species

Robbins emphasis

P. falciparum

High parasitemia; severe malaria and cerebral involvement

P. vivax

Hypnozoites; Duffy-related red-cell invasion

P. ovale

Latent hepatic hypnozoites and relapse

P. malariae

Usually lower parasitemia

P. knowlesi

Listed among human malarial parasites

Slide 5 · The published burden reflects a major global disease

247 million

Estimated malaria cases in 2021

619,000

Estimated malaria deaths in 2021

Historical figures reproduced (2021 estimates); Not a current surveillance update.

Slide 6 · The African region bears most documented cases

95% of estimated cases and 96% of deaths to the WHO African region (2021).

Malaria is a major cause of mortality in children younger than 5 years there.

Vectors are also distributed across Asia and Latin America.

Geography informs exposure history but does not determine an individual diagnosis.

Slide 7 · The mosquito bite starts human infection

Infected female Anopheles

Sporozoites in blood

Hepatic infection

Erythrocytic cycle

Vector-mediated transmission introduces sporozoites, not erythrocytic schizonts.

Vector: Female Anopheles mosquito

Slide 8 · Transmission is not limited to mosquito bites

Infected female Anopheles mosquitoes are the principal vector.

The textbook also records transmission by blood transfusion.

Contaminated needles offer another blood-borne route.

A travel history is informative, but blood exposure is also relevant.

Slide 9 · Uncomplicated malaria has a multisystem symptom complex

Fever and chills may occur with headache and muscle aches.

Fatigue is common; Gastrointestinal symptoms may accompany illness.

Nausea, vomiting, and diarrhea are nonspecific associated features.

Symptoms alone do not identify the infecting Plasmodium species.

Slide 10 · Severe malaria involves organ dysfunction

Renal failure is a major severe manifestation.

Seizures, confusion, and coma signal cerebral involvement.

Severe anemia and pulmonary edema occur particularly with P. Falciparum.

An individual patient may develop several organ complications together.

Slide 11 · The life cycle crosses three biological compartments

Mosquito salivary gland

Human hepatocyte

Human erythrocyte

Mosquito blood meal

The human hepatic stage is initially silent; Blood stages generate symptoms.

Slide 12 · Sporozoites are the infectious mosquito-derived form

Sporozoites are present in female mosquito salivary glands.

A blood meal transfers sporozoites into the human circulation.

They invade hepatocytes shortly after entering the bloodstream.

HUMAN HEPATIC PHASE

Injected sporozoites

Hepatocyte invasion

Asexual amplification

Merozoites enter blood

Schematic: Hepatocytes precede the erythrocytic infection

Slide 13 · Hepatic invasion initiates asymptomatic amplification

Sporozoites bind to the hepatocyte surface before entering.

Host attachment involving thrombospondin/properdin-related receptors.

Infected liver cells support asexual parasite multiplication.

The exoerythrocytic stage is typically clinically silent.

Slide 14 · One infected hepatocyte can release many merozoites

Release of up to 30,000 merozoites per infected hepatocyte.

Merozoites are the progeny that begin erythrocytic infection.

This amplification precedes the symptomatic blood stage.

Sporozoite enters hepatocyte

Asexual multiplication

Hepatocyte ruptures

Merozoites circulate

Slide 15 · Hypnozoites provide a mechanism for relapse

P. Vivax and P. Ovale can persist as latent hepatic hypnozoites.

Dormant forms may produce recurrent malaria weeks to months later.

Relapse is not explained solely by the ongoing RBC cycle.

P. Vivax / P. Ovale hepatic infection

Latent hypnozoite persists

Later renewed blood infection → relapse

Slide 16 · The hepatic and blood stages have distinct roles

Hepatic stage

Erythrocytic stage

Begins with sporozoite invasion

Begins with merozoite invasion

Asexual multiplication in hepatocytes

Trophozoite → schizont in RBCs

Asymptomatic in Robbins description

Fever and chills follow RBC rupture

Hypnozoites in vivax/ovale

Gametocytes may enter mosquito

Slide 17 · Merozoites invade red cells by receptor interaction

Merozoites use lectin-like adhesion molecules.

They bind sialic acid residues on erythrocyte glycophorin.

Active membrane penetration initiates an intracellular RBC stage.

Erythrocyte

Merozoite attachment precedes membrane penetration

Schematic — not a Giemsa-stained micrograph

Slide 18 · An intracellular digestive vacuole supports parasite growth

Within infected erythrocytes, parasites reside in a membrane-bound digestive vacuole.

Secreted enzymes hydrolyze host hemoglobin.

Hemoglobin consumption is part of trophozoite development.

Hemozoin pigment later accumulates in tissue macrophages.

Slide 19 · Trophozoites and schizonts are distinct blood stages

Merozoite entry

Ring trophozoite

Multinucleated schizont

RBC rupture

Schematic parasite stages; Diagnostic interpretation requires authentic blood-smear microscopy

Slide 20 · The trophozoite has a single chromatin mass

The ring/trophozoite follows successful erythrocyte invasion.

Its single chromatin mass distinguishes it from the later schizont.

Giemsa-stained peripheral blood permits stage recognition.

Erythrocyte

Early intraerythrocytic stage: One chromatin mass

Schematic — not a Giemsa-stained micrograph

Slide 21 · The schizont contains multiple chromatin masses

Schizonts show multiple chromatin masses.

Each chromatin mass develops toward an individual merozoite.

Mature blood stages precede RBC lysis and reinvasion.

Early trophozoite

Growing parasite

Schizont

Merozoites

Schematic parasite stages; Diagnostic interpretation requires authentic blood-smear microscopy

Slide 22 · RBC rupture perpetuates parasitemia and symptoms

Parasite maturation in RBC

Erythrocyte lysis

Merozoite release

Invasion of further RBCs

Repeated cycles propagate infection and host inflammatory responses

Slide 23 · Cytokine release explains malarial fever

Clinical paroxysms coincide with merozoite release.

Host mediators, including TNF, drive fever.

The fever is a host response—not a direct heating effect of parasites.

Infected RBC ruptures

Merozoites and parasite products released

Host cells produce TNF and other cytokines

Fever, chills and rigors

Slide 24 · Fever periodicity varies among parasite species

Paroxysmal attacks can recur with erythrocytic schizogony.

Periodicities within an approximately 24–72-hour range.

The interval depends on the parasite species.

A fixed fever schedule is not required to suspect malaria.

Slide 25 · Gametocytes sustain transmission back to mosquitoes

Blood-stage parasites

Sexual differentiation to gametocytes

Mosquito takes blood meal

Mosquito cycle continues

Gametocytes are the human blood forms infective to mosquitoes.

Slide 26 · A compartment-specific view prevents stage confusion

Biological form

Compartment / role

Sporozoite

Female mosquito salivary glands → hepatocytes

Merozoite

Released from liver or RBC; invades red cells

Trophozoite

Growing intracellular erythrocytic stage

Schizont

Asexual dividing blood-stage parasite

Gametocyte

Blood-stage sexual form infective for mosquito

Hypnozoite

Latent hepatic form in P. vivax/P. ovale

Slide 27 · Lower parasitemia is typical of several non-falciparum species

P. Vivax, P. Ovale, P. Knowlesi and P. Malariae with lower parasitemia.

These infections may still produce anemia and splenic changes.

Splenic rupture and nephrotic syndrome are described as uncommon outcomes.

Lower parasitemia does not imply absence of clinical significance.

Slide 28 · P. Falciparum can infect erythrocytes of any age

Falciparum infection is not restricted to young or old red cells.

Broader host-cell availability supports greater parasitemia.

Parasite burden alone does not explain microvascular injury.

P. Falciparum

Access to a broad RBC age range → potentially high parasite load

Other species

Restricted age subsets → lower RBC fraction available

Slide 29 · Falciparum virulence has two major mechanisms

Cell-entry advantage

Infection of RBCs at multiple ages raises parasite burden

Vascular adhesion

PfEMP1-bearing infected RBCs adhere in small vessels

High parasitemia plus sequestration drive severe pathology

Slide 30 · PfEMP1 remodels the infected RBC surface

Falciparum erythrocyte membrane protein 1 (PfEMP1) is parasite-derived.

PfEMP1 associates with protruding knobs on infected RBCs.

This change allows adhesion to endothelial molecules.

Erythrocyte

Adhesive PfEMP1 is displayed in surface knobs

Schematic — not a Giemsa-stained micrograph

Slide 31 · Endothelial ligands participate in sequestration

Ligand named in Robbins

Role in falciparum pathology

CD36

Endothelial adhesion partner for PfEMP1

ICAM-1

Endothelial adhesion partner for PfEMP1

VCAM-1

Endothelial adhesion partner for PfEMP1

E-selectin

Endothelial adhesion partner for PfEMP1

Thrombospondin

Adhesion-associated ligand

Slide 32 · Sequestration and rosetting are related but distinct

Both are described for P. Falciparum infection.

Adhesion impedes blood passage through microvessels.

The consequence is local hypoperfusion, not merely anemia.

Sequestration

Infected RBC attaches to vascular endothelium

Rosetting

Infected RBC clusters with other RBCs

Slide 33 · Microvascular obstruction produces ischemia

Adherent parasitized red cells accumulate in small vessels.

Local perfusion falls when flow is obstructed.

Ischemia follows impaired oxygen delivery to tissue.

Parasite-infected RBCs

Adherent parasitized cells narrow functional microvascular flow

Schematic

Slide 34 · Cerebral malaria is a microcirculatory disorder

PfEMP1-mediated adhesion

Small cerebral vessel sequestration

Reduced perfusion and hypoxia

Neurologic dysfunction

Mechanistic chain underlying confusion, seizures and coma

Slide 35 · Parasite GPI-linked proteins activate inflammation

Falciparum GPI-linked parasite proteins are released from infected red cells.

They include merozoite surface-associated antigens.

Host cells respond by producing cytokines.

Inflammatory signaling complements the mechanical effects of sequestration.

Slide 36 · Cytokines contribute to systemic tissue injury

Cytokine production follows exposure to parasite components.

Reactive nitrogen intermediates add inflammatory injury.

Organ dysfunction can reflect more than vascular occlusion.

Fever

Host inflammatory mediators promote febrile response

Cell injury

Reactive nitrogen species contribute to tissue damage

Slide 37 · Inflammation can intensify vascular sequestration

Cytokines induce expression of endothelial PfEMP1 ligands.

More adhesion receptors facilitate sequestration.

Sequestration then contributes to local ischemia.

Infected RBCs release GPI-linked antigens

Host cytokine response

More endothelial adhesion receptors

Greater RBC sequestration

Slide 38 · Falciparum infection produces several clinical end points

Pathogenic process

Major clinical consequence

High erythrocytic parasite burden

Severe anemia

Cerebral microvascular sequestration

Seizures, confusion, coma

Systemic / microcirculatory injury

Renal failure

Inflammation and vascular dysfunction

Pulmonary edema; possible death

Slide 39 · Host resistance is intrinsic or acquired

These mechanisms operate at different biological levels.

Intrinsic resistance is related to erythrocyte phenotype.

Acquired resistance does not necessarily prevent reinfection.

Intrinsic resistance

Inherited RBC traits reduce productive parasite infection

Acquired resistance

Repeated exposure develops partly protective immunity

Slide 40 · Heterozygous RBC variants can confer an advantage

Selected inherited RBC variants reduce susceptibility to productive Plasmodium infection.

Some confer protection in heterozygous carriers but cause disease in homozygotes.

This can maintain otherwise harmful variants in endemic populations.

The benefit varies with the variant and parasite context.

Slide 41 · Globin variants are one protective category

Hemoglobin S and hemoglobin C among protective globin variants.

The source identifies heterozygous-state protection as an evolutionary pattern.

The diagnosis and pathobiology of each hemoglobinopathy remain distinct.

Hemoglobin S (HbS)

Hemoglobin C (HbC)

Thalassemias

Other RBC traits

Inherited RBC variation → reduced productive infection in some heterozygous carriers

Slide 42 · Thalassemias form a second resistance category

α- and β-thalassemias reduce globin-chain production.

They are listed among erythrocyte traits that may inhibit malaria.

Protection is not equivalent to eliminating infection risk.

The source does not assign a single molecular protective mechanism to all variants.

Slide 43 · Enzyme and membrane variants also affect susceptibility

G6PD deficiency is the red-cell enzyme example.

DARC, band 3, and spectrin appear among membrane-related examples.

Protective mechanisms for many listed traits are incompletely understood.

G6PD deficiency

Duffy / DARC absence

Band 3 variants

Spectrin variants

Inherited RBC variation → reduced productive infection in some heterozygous carriers

Slide 44 · Duffy antigen illustrates receptor-specific resistance

Duffy (DARC) in P. Vivax entry.

Duffy-negative populations historically show reduced susceptibility.

Do not generalize this receptor model to every Plasmodium species.

P. Vivax targets the RBC Duffy antigen

Duffy absence changes the available entry receptor

Susceptibility to classical vivax invasion is reduced

Slide 45 · Repeated exposure produces partial clinical immunity

Endemic exposure can generate partially protective immune responses.

Individuals may have fewer symptoms even with persistent or repeated infections.

Antibodies and T lymphocytes contribute to reduced manifestations.

This is partial immune protection—not sterile lifelong immunity.

Slide 46 · Antigenic variation permits immune escape

PfEMP1 and other surface antigens are recognized

Parasites express alternate antigen-encoding genes

Newly expressed surface proteins change antigenicity

Existing antibody responses may become less effective

P. Falciparum expresses variable surface-antigen repertoires

Slide 47 · Malaria immunity has several effector components

Antibodies against Plasmodium antigens help limit disease.

T lymphocytes contribute to adaptive resistance.

Cytotoxic T lymphocytes may play a role against falciparum infection.

Parasite antigenic switching challenges durable protective responses.

Slide 48 · The peripheral blood smear is central to diagnosis

Giemsa-stained peripheral blood is the morphologic diagnostic specimen.

Intraerythrocytic asexual parasite forms are identifiable.

Microscopic recognition connects the lifecycle directly with diagnosis.

Accurate interpretation depends on genuine slide morphology.

Slide 49 · Blood-stage forms have different nuclear patterns

Invaded RBC

Ring trophozoite

Schizont

Cell lysis

Schematic parasite stages; Diagnostic interpretation requires authentic blood-smear microscopy

Slide 50 · Antigen-based rapid diagnostic tests provide early evidence

Immunochromatographic tests detect parasite antigens.

These as useful for a rapid response.

Robbins specifies confirmation with blood-smear examination.

Assay availability and use should be interpreted within the relevant diagnostic setting.

Slide 51 · Molecular testing improves parasite detection

PCR and related molecular assays are more sensitive than conventional microscopy in the source.

Species confirmation may assist selection of appropriate therapy.

A very low parasitemia result does not by itself establish symptomatic disease.

Methods should be chosen for a defined diagnostic question.

Slide 52 · The meaning of a positive test depends on context

Clinical suspicion

Giemsa microscopy

Rapid antigen assay

Molecular species support

These are complementary methods, not a single universally mandated sequence.

Slide 53 · Spleen enlargement reflects red-pulp congestion

Parasitized red cells acquire altered membrane proteins.

Splenic macrophages recognize and remove abnormal erythrocytes.

Congestion and red-pulp hyperplasia contribute to splenomegaly.

Marked enlargement in P. Falciparum infection.

Slide 54 · Macrophage clearance links blood infection to spleen

Parasite proteins alter the erythrocyte membrane

Splenic macrophages recognize abnormal RBCs

Engulfment of parasitized erythrocytes

Red-pulp expansion and pigment accumulation

Slide 55 · Hemozoin gives chronically infected tissues dark color

Hemozoin is a granular brown-black malarial pigment.

The pigment occurs within phagocytic cells.

It as faintly birefringent.

Pigmented macrophages help explain the gray-black spleen.

Slide 56 · Chronic splenic infection remodels the organ

The chronically involved spleen may become increasingly fibrotic.

The capsule and trabeculae become thickened.

A brittle, enlarged spleen.

Structural remodeling follows prolonged congestion and phagocytic activation.

Slide 57 · The liver becomes enlarged and pigmented

The liver may enlarge as infection progresses.

Kupffer cells contain pigment, parasites and cellular debris.

Pigment may also appear within hepatocytes.

Kupffer cells

Parasites, debris, hemozoin

Parenchyma

Some pigment deposition

Slide 58 · Renal pathology combines congestion and hemoglobin injury

Kidneys may be enlarged and congested.

Pigment is described within glomerular structures.

Hemoglobin casts occur in tubules.

Renal vessels

Congestion

Glomeruli

Scattered pigment

Tubules

Hemoglobin casts

Slide 59 · Pigmented phagocytes are not confined to one organ

Bone marrow

Pigmented phagocytes

Lymph nodes

Pigmented phagocytes

Lungs

Pigmented phagocytes

Subcutaneous tissues may also contain pigmented cells

Slide 60 · Cerebral vessels accumulate parasitized RBCs

P. Falciparum–infected red cells may pack cerebral small vessels.

The finding provides a morphologic correlate of sequestration.

Local vascular stasis produces tissue hypoxia.

Parasite-infected RBCs

Microvascular sequestration → impaired cerebral perfusion

Schematic

Slide 61 · Perivascular ring hemorrhages signal focal injury

The source describes ring hemorrhages around involved brain vessels.

Their formation is thought to reflect local hypoxia and stasis.

These are tissue lesions, distinct from the bloodstream parasite stage.

Vascular occlusion and hemorrhage may coexist.

Slide 62 · Dürck granulomas accompany cerebral malaria

Small focal inflammatory reactions may surround compromised vessels.

Robbins calls these malarial or Dürck granulomas.

More severe hypoxia leads to neuronal degeneration and softening.

Meningeal inflammation may be scant.

Slide 63 · Chronic anemia may impair myocardial oxygen delivery

Progressive anemia and circulatory stasis can cause focal myocardial hypoxia.

Some hearts show focal interstitial inflammatory infiltrates.

The myocardial findings are not described as pathognomonic.

Cardiac injury is a secondary consequence of systemic infection.

Slide 64 · Pulmonary edema, shock, and DIC mark critical disease

Pulmonary edema can be a fatal complication in a nonimmune host.

Shock with disseminated intravascular coagulation is also described.

Fatal disease may occur without all classic morphologic lesions.

Severity assessment must integrate clinical organ dysfunction.

Slide 65 · The organ lesions follow a shared causal framework

Organ

Dominant Robbins lesion

Pathophysiologic link

Spleen

Congestion, red-pulp hyperplasia, pigment

RBC clearance

Liver

Pigmented Kupffer cells

Phagocytic sequestration

Kidney

Congestion, pigment, hemoglobin casts

Perfusion + hemoglobin injury

Brain

Parasitized RBCs, hemorrhages, hypoxic lesions

Microvascular obstruction

Heart

Focal hypoxic changes

Anemia and stasis

Slide 66 · Malaria and babesiosis share a diagnostic resemblance

Feature

Malaria

Babesiosis

Blood-stage form

Intraerythrocytic parasites

Rings may resemble falciparum

Hemozoin

Present in malaria tissue pathology

Absent in Babesia

Tetrads

Not a defining malaria feature

Maltese-cross tetrads may appear

Vector

Female Anopheles

Ixodes ticks

Contrast relies on the separate Robbins Babesiosis passage (pp. 357–358).

Slide 67 · Case: Fever after exposure in an endemic region

A returning traveler reports episodic fever, chills, headache and fatigue. A peripheral blood sample is available.

Reasoning questions

Which stages are likely to be seen in a Giemsa-stained blood film?

Why do febrile episodes coincide with erythrocyte rupture?

How would parasite species confirmation change interpretation?

Slide 68 · Case: Coma with falciparum parasitemia

A patient with confirmed P. Falciparum infection develops confusion and seizures. Microvascular congestion is suspected.

Reasoning questions

Explain how PfEMP1 changes infected RBC behavior.

Name the vascular adhesion and perfusion consequences.

Predict the cerebral histologic lesions.

Slide 69 · Case: Malaria recurs after apparent resolution

Weeks after an initial episode, a patient develops another febrile illness following P. Vivax infection.

Reasoning questions

Which hepatic parasite form accounts for a true relapse?

Why is a purely erythrocytic explanation incomplete?

Which other human Plasmodium species shares hepatic latency?

Slide 70 · Circumsporozoite antigen is a vaccine target

RTS,S/AS01 recommendation for children in moderate- to high-transmission P. Falciparum regions.

The antigen is displayed before liver-cell infection.

This is a prevention mechanism rather than an erythrocytic treatment.

Circumsporozoite surface protein

Sporozoite recognition

Hepatic entry phase

RTS,S/AS01 targets the pre-hepatic circumsporozoite stage.

Slide 71 · Control faces both vector and parasite resistance

Public-health control is impeded by resistant mosquito vectors.

Antimalarial drug resistance is a separate parasite problem.

The textbook specifically identifies artemisinin resistance.

Vector challenge

Insecticide-resistant mosquitoes

Parasite challenge

Artemisinin-resistant Plasmodium

Slide 72 · Clinical severity arises through several converging routes

Erythrocyte infection

RBC loss / anemia

Adhesion / sequestration

Organ hypoxia and injury

Inflammatory cytokines independently aggravate symptoms and tissue injury.

Slide 73 · Four distinctions organize the pathology of malaria

Sporozoite infects hepatocytes; Merozoite infects erythrocytes.

Trophozoite and schizont are asexual blood stages; Gametocytes maintain transmission.

Falciparum severity reflects parasite burden plus microvascular adhesion.

Hemozoin and parasitized RBCs connect the blood infection to organ morphology.

Slide 74 · Assess your understanding

Why does the exoerythrocytic phase usually lack fever?

Why does P. Falciparum cause disproportionate cerebral injury?

What causes hepatosplenic dark pigment in chronic infection?

Which species can relapse through latent hepatic hypnozoites?

Slide 75 · Reference and source limitations

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

Chapter 8, Infectious Diseases: Malaria and adjacent parasitic-infection context.

The extracted Markdown interleaves figure captions and Babesiosis text; content was separated by context.

No original chapter PDF or licensed photomicrographs were supplied; all presented figures are explicit native conceptual schematics.