Acute Transient Infections

Slide 1 · Acute (Transient) Infections

Virologic mechanisms · organ pathology · clinical interpretation

COVID-19 • Measles • Mumps • Poliomyelitis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Explain why most acute viral infections resolve yet reinfections differ among viruses.

Trace key cellular events in SARS-CoV-2, measles, mumps and poliovirus infections.

Recognize the characteristic tissue injury and major clinical complications.

Connect clinical syndromes and pathology with targeted diagnostic approaches.

Slide 3 · Transient infection: An immunologic outcome

Acute viral infection

Innate + adaptive responses

Pathogen clearance

Clinical resolution

“Transient” describes usual pathogen clearance, not uniformly mild clinical disease.

Severe organ damage may occur before the infection is controlled.

Schematic temporal sequence, not a quantitative time course

Slide 4 · Why reinfection risks differ

Virus-related features

Host-related features

Limited antigenic diversity can support durable protection against repeat infection.

New genetic variants can reduce recognition of prior immune responses.

Waning protection is especially relevant to some respiratory and gastrointestinal viruses.

Effective clearance of one episode does not guarantee lifelong protection.

Slide 5 · Different viruses, different patterns of repeat infection

Illustrative virus

Source emphasis

Clinical implication

Mumps

One genetic subtype

Usually durable protection after infection

Influenza

New variants arise periodically

Repeat infection can occur

Respiratory / GI viruses

Immunity may decline with time

Reinfection despite previous exposure

Slide 6 · Four archetypes within acute viral disease

Infection

Usual entry / spread

Principal teaching pathology

COVID-19

Respiratory

Alveolar injury; Inflammation; Thrombosis

Measles

Airborne; Lymphatic / hematogenous

Rash, giant cells, immune suppression

Mumps

Respiratory; Hematogenous

Parotitis; Orchitis; Pancreatitis

Poliomyelitis

Fecal–oral; Possible CNS spread

Motor-neuron injury and paralysis

Slide 7 · COVID-19 illustrates acute cytopathic viral infection

SARS-CoV-2 infection ranges from asymptomatic infection to life-threatening organ injury.

The respiratory tract is a major portal of entry and site of clinically important disease.

Outcome depends on viral replication, immune containment and inflammatory injury.

Severe disease can include coagulation abnormalities and extrapulmonary manifestations.

Slide 8 · SARS-CoV-2 genome and structural components

Genome

Structural proteins

Single-stranded, positive-sense RNA genome; Approximately 30 kilobases.

Viral RNA is translated by host ribosomes after cell entry.

Spike and membrane proteins are located in the lipid envelope.

Nucleocapsid protein associates with viral RNA.

Spike protein mediates host-cell entry and is a central target of neutralizing antibodies.

Slide 9 · Spike-mediated entry: Receptor to fusion

S1 receptor-binding domain

ACE2 engagement

TMPRSS2 cleavage

S2-mediated fusion

RNA entry

ACE2 is expressed by epithelial cells, including respiratory epithelium.

The spike subunits perform distinct receptor-binding and fusion functions.

Selected molecular steps in viral entry

Slide 10 · SARS-CoV-2 receptor-binding domain

The receptor-binding domain (RBD) is part of spike subunit S1.

RBD engagement of ACE2 is the first depicted step in cellular attachment.

Neutralizing antibodies against spike—especially RBD—can block infection of host cells.

Antigenic changes affecting spike help explain some patterns of immune escape.

Slide 11 · After attachment: Membrane fusion is activated

Spike bound to ACE2

TMPRSS2 proteolysis

S2 conformational activity

Viral/host membrane fusion

Entry requires more than simple receptor attachment.

The host protease-dependent activation step links the surface receptor to RNA delivery.

Mechanistic schematic; Cell membrane not drawn to scale

Slide 12 · Intracellular RNA replication

Positive-sense RNA inside cell

Translation of viral proteins

RNA-dependent RNA polymerase

New viral RNA genomes

Replication involves a double-stranded RNA intermediate.

Viral RNA and replication intermediates are potential innate immune stimuli.

Selected steps; Does not depict the complete replication cycle

Slide 13 · Type I interferon: An early restriction mechanism

Viral RNA sensing

Type I IFN production

Antiviral state in cells

Restriction of replication

Interferon activity limits replication in infected and neighboring cells.

Severe disease may follow impaired production or signaling of type I IFN.

Simplified antiviral response

Slide 14 · Innate sensing creates evolutionary pressure

Host detects

Virus counters

Viral RNA structures can activate innate RNA receptors.

Double-stranded RNA intermediates are an important signal of replication.

Viral RNA can be modified to resemble host RNA.

Replication intermediates can be hidden within membrane-bound compartments.

Viral proteins interfere with interferon-generating pathways.

Slide 15 · RNA capping and methylation reduce sensing

New viral RNA

Phosphate removal

Capping + methylation

Less innate recognition

These modifications help viral RNA resemble cellular RNA.

Reduced recognition favors viral survival during early infection.

Mechanistic simplification of one immune-evasion route

Slide 16 · Membrane sequestration of viral RNA

Protected replication environment

Innate immune consequence

Host endoplasmic reticulum membranes form double-membrane vesicles around viral RNA.

Replication intermediates remain sequestered in these compartments.

Double-stranded viral RNA becomes less accessible to cytoplasmic RNA sensors.

The viral RNA endonuclease additionally limits accumulation of immunostimulatory intermediates.

Slide 17 · Impaired type I interferon defense and severity

The source describes multiple viral proteins that reduce IFN generation or signaling.

Autoantibodies directed against type I IFNs are associated with increased risk of severe COVID-19.

Inherited abnormalities of IFN production or signaling provide a parallel susceptibility mechanism.

The link illustrates the importance of early innate restriction.

Slide 18 · Respiratory exposure and transmission

Transmission routes

Conditions increasing exposure

Virus moves person-to-person via respiratory particles, including droplets and aerosols.

Inhalation exposure is relevant, including at longer distances in poorly ventilated environments.

Indoor gatherings and prolonged close contact favor transmission.

Shared living settings and institutions can facilitate spread.

Transmission may precede symptom onset.

Slide 19 · Infectiousness is not synonymous with symptoms

Incubation period

Presymptomatic shedding

Symptomatic infection

Declining viral burden

The excerpt associates highest upper respiratory viral levels with early infection.

Individuals without symptoms may transmit SARS-CoV-2.

Schematic course; Timing varies between patients and variants

Slide 20 · Clinical spectrum of acute COVID-19

SARS-CoV-2 infection

No evident symptoms

Fever / cough / fatigue

Respiratory dysfunction

Systemic inflammation

Mild or self-limited disease

Severe disease → ARDS / organ injury

Clinical categories are illustrative; Boxes are not proportional

Slide 21 · Risk of severe COVID-19 is heterogeneous

Host characteristics

Comorbid conditions

Older age is emphasized as the strongest risk factor in the text.

Pregnancy and immunocompromise can increase vulnerability.

Unequal access to prevention and care influences observed risk.

Lung and cardiovascular disease.

Diabetes, obesity and smoking.

Cancer and chronic kidney or liver disease.

Slide 22 · Severe COVID-19: Excessive inflammatory response

Active respiratory infection

Inflammatory cytokines rise

Disordered immune-cell profile

Tissue injury and organ dysfunction

TNF and IL-6 are emphasized in the source.

Lymphopenia and abnormalities of myeloid cells accompany severe disease.

Conceptual sequence; Multiple feedback pathways exist

Slide 23 · Lymphopenia and immune dysregulation

Described cellular findings

Pathologic significance

Reduced T-cell and NK-cell numbers occur in severe cases.

Myeloid cell populations may be dysregulated.

Antiviral defense may be compromised even while inflammatory responses are amplified.

This combination distinguishes immune dysregulation from a simple “strong” response.

Slide 24 · Pulmonary injury: From inflammation to ARDS

Lung infection / inflammatory injury

Diffuse alveolar damage

Impaired oxygen exchange

Hypoxemic respiratory failure

Alveolar-capillary dysfunction links histologic lesions to dyspnea and hypoxia.

Severe respiratory failure can progress to multiorgan dysfunction.

Causal interpretation of the source-described morphology

Slide 25 · Diffuse alveolar damage in severe COVID-19

Normal gas-exchange surface

Diffuse alveolar damage

Thin alveolar barrier

Hyaline membrane

Alveolar edema and fibrinous hyaline membranes impair diffusion.

Congested capillaries, type II pneumocyte hyperplasia and microthrombi compound dysfunction.

Schematic — not histology

Slide 26 · Why hyaline membranes compromise gas exchange

Observed lesion

Physiologic effect

Edema fluid accumulates in alveolar spaces.

Fibrinous material lines alveolar walls as hyaline membranes.

Some alveoli collapse and alveolar ducts dilate.

Air–blood diffusion is impeded.

Functional gas exchange surface is reduced.

Hypoxemia develops as injury becomes extensive.

Slide 27 · Microvascular thrombosis compounds lung injury

Inflammation / endothelial injury

Procoagulant state

Arteriolar + capillary thrombi

Worsened tissue perfusion

Thrombi are reported in pulmonary arterioles and alveolar capillaries in severe cases.

Thrombosis and alveolar injury can jointly aggravate respiratory dysfunction.

Schematic; Magnitude and timing are not quantified

Slide 28 · Coagulopathy: Increased clot formation

Potential activating factors

Disease expression

Endothelial injury can expose tissue factor.

Inflammation favors coagulation activation.

Antiphospholipid antibodies are described in some severe cases.

Shift toward thrombosis rather than normal hemostatic equilibrium.

Thrombi may affect small and larger blood vessels.

Coagulopathy is one component of systemic severe COVID-19.

Slide 29 · Impaired fibrinolysis sustains thrombi

PAI-1 increased

TPA / urokinase inhibited

Reduced plasmin formation

Less fibrin breakdown

The source describes reduced fibrinolytic activity in severe disease.

Inhibiting fibrin clearance augments the prothrombotic shift.

TPA: Tissue plasminogen activator; PAI-1: Plasminogen activator inhibitor 1

Slide 30 · Severe COVID-19 is a multisystem disorder

Affected domain

Examples

Respiratory

ARDS with diffuse alveolar damage

Vascular / coagulation

Thrombosis; Systemic vasculitis

Inflammatory

HLH-like features; Elevated acute-phase response

Musculoskeletal

Myositis and arthritis

Slide 31 · MIS-C follows acute SARS-CoV-2 infection

Prior SARS-CoV-2 infection

Delayed inflammatory syndrome

Mucocutaneous / GI / CNS findings

Cardiac involvement ± shock

Onset commonly 2–6 weeks after acute disease in children.

Myocardial dysfunction and coronary artery dilation are among the cardiac manifestations.

Multisystem inflammatory syndrome in children (MIS-C)

Slide 32 · HLH-like changes in severely affected adults

Some adults show hemophagocytic lymphohistiocytosis-like features.

Cytopenias, hemophagocytosis and elevated acute-phase reactants can occur.

This inflammatory phenotype is not unique to SARS-CoV-2.

Associated pathology must be interpreted within the clinical syndrome.

Slide 33 · Postacute sequelae: Long COVID

Clinical manifestations

Interpretive cautions

Persistent fatigue, weakness, dyspnea, chest pain or cough may occur.

Impaired memory or concentration and psychological symptoms are also described.

Definitions differ among studies.

A relapsing–remitting course is described in persistent cases.

Persistent symptoms alone do not establish ongoing viral replication.

Slide 34 · Viral variants arise through genomic change

Mutation / indel

Recombination

Altered viral genome

New variant properties

Variants may differ in efficiency of transmission or immune escape.

Spike changes can alter recognition by infection- or vaccine-induced antibodies.

The figure does not imply all variants increase disease severity

Slide 35 · Immune escape: Lesson from Omicron

Viral characteristic

Population-level implication

The many spike-protein alterations in Omicron.

Some changes reduce binding by previously generated antibodies.

Prior immunity may not prevent all infections.

Immune escape is distinct from the intrinsic severity of disease.

Variant descriptions in this source refer to the 2021–2022 period.

Slide 36 · Diagnosis: Viral antigen versus nucleic acid

Principle

Target

Specimen / interpretation

Antigen detection

Nucleocapsid protein

Antibody-based test on nasal material

Nucleic-acid amplification

SARS-CoV-2 RNA

PCR-based detection of viral sequences

Slide 37 · Clinical application: Respiratory illness with hypoxia

Illustrative case: A patient with confirmed SARS-CoV-2 infection develops increasing dyspnea, hypoxia and evidence of systemic inflammation.

Interpretation question

Which pulmonary lesion best connects this presentation to severe COVID-19?

Details to integrate

Confirmed infection

Hypoxemia

Systemic inflammation

Slide 38 · Case interpretation: Diffuse alveolar damage

Most consistent interpretation

ARDS with diffuse alveolar damage

Alveolar edema and hyaline membranes reduce effective gas exchange.

Type II pneumocyte hyperplasia reflects alveolar epithelial injury.

Pulmonary microvascular thrombi may further impair oxygenation.

Slide 39 · Measles: Airborne infection with systemic dissemination

Measles is an acute systemic infection caused by a Paramyxoviridae RNA virus.

There is one recognized serotype of measles virus in the source.

Infection can affect skin, lymphoid organs, lung, intestine and the CNS.

Severe outcomes are more likely with malnutrition, inadequate access to care or impaired cellular immunity.

Slide 40 · Measles is transmitted efficiently by aerosols

Aerosolized respiratory secretions

Upper airway exposure

Initial local replication

Lymphoid dissemination

Measles is described as highly efficient at airborne transmission.

Susceptible unvaccinated persons are prominent in outbreaks.

Transmission / initial dissemination diagram

Slide 41 · Measles receptor usage explains cell tropism

SLAMF1

Nectin-4

Present on activated lymphocytes, dendritic cells and monocytes.

Supports early infection of immune cells.

Located on the basal surfaces of epithelial cells.

Associated with respiratory epithelial infection and viral shedding.

Slide 42 · Measles spreads beyond the respiratory tract

Respiratory epithelium

Local lymphoid replication

Viremia

Multiple organ sites

Dissemination reaches conjunctiva, skin, lymphatic system, small vessels and CNS.

Systemic involvement explains the combination of exanthem and internal-organ complications.

Selected organs; Not exhaustive

Slide 43 · The measles rash is immune-mediated

Viral dissemination to skin

Virus-specific T-cell response

Perivascular inflammation

Typical exanthem

T-cell responses help contain infection and also contribute to rash formation.

Rash may be less evident in patients with impaired cell-mediated immunity.

Mechanistic model from source

Slide 44 · Measles skin rash: Pathologic substrate

Macroscopic distribution

Microscopic pattern

Blotchy reddish-brown eruption.

Affects face, trunk and proximal extremities.

Dilated dermal blood vessels.

Dermal edema.

Mononuclear perivascular infiltrates.

Slide 45 · Koplik spots: Diagnostic oral mucosal lesions

Clinical location

Tissue findings

Oral mucosa near openings of Stensen ducts.

Characteristic finding in measles described as pathognomonic by the source.

Mucosal necrosis and neutrophil-rich exudate.

Associated neovascularization in affected mucosa.

Slide 46 · Warthin–Finkeldey multinucleated giant cells

Lymphoid-organ response

Distinctive cytology

Follicular hyperplasia and prominent germinal centers.

Multinucleated giant cells within lymphoid tissue.

Eosinophilic inclusions in nuclei and cytoplasm.

Similar giant cells may be observed in lung or sputum.

Slide 47 · Measles-associated immunosuppression

Measles infection

Reduced lymphocyte responses

Impaired delayed hypersensitivity

Secondary infections

Immune suppression may be transient yet profound.

Secondary bacterial and viral infections account for important morbidity and mortality.

Immune consequences in the source

Slide 48 · Severe and complicated measles

Organ system

Examples

Respiratory

Croup and pneumonia

Gastrointestinal

Diarrhea; Protein-losing enteropathy

Ocular

Keratitis, scarring and possible blindness

CNS

Encephalitis; Rare delayed syndromes

Slide 49 · Late neurologic complications of measles

Subacute sclerosing panencephalitis

Measles inclusion-body encephalitis

Rare delayed complication associated with altered viral persistence.

Source describes defective viral particle formation and cell-to-cell spread.

Rare complication particularly noted with immunocompromise.

Illustrates possible neurologic injury beyond the acute exanthem.

Slide 50 · Measles diagnosis: Syndrome and virology

Clinical findings may suggest the diagnosis, particularly in a compatible outbreak setting.

Serologic testing provides an additional diagnostic approach.

PCR can detect measles viral RNA in respiratory secretions or urine.

Morphologic findings should complement—not replace—appropriate virologic testing.

Slide 51 · Clinical application: Febrile exanthem

Illustrative case: A susceptible patient has an acute febrile respiratory illness followed by a widespread rash and characteristic oral mucosal lesions.

Interpretation question

Which mechanisms produce the rash, and why can secondary infections follow?

Details to integrate

Airborne infection

Oral lesions

Systemic exanthem

Slide 52 · Case interpretation: Measles immunity and injury

Most consistent interpretation

T-cell-mediated rash with transient immune suppression

Viremia disseminates the virus to the skin and other organs.

A cellular immune response contributes to perivascular inflammation and rash.

Diminished lymphocyte function predisposes to secondary infection.

Slide 53 · Mumps: Systemic infection with salivary tropism

Mumps is a Paramyxoviridae infection characteristically associated with painful salivary gland swelling.

Viral spread can extend beyond the salivary glands to testis, pancreas, CNS and ovary.

Infection begins in the respiratory tract and is disseminated via lymphoid tissue and blood.

The resulting organ pathology often reflects edema and inflammation.

Slide 54 · Mumps viral envelope proteins

Hemagglutinin–neuraminidase

Fusion glycoprotein

One surface glycoprotein combines hemagglutinin and neuraminidase functions.

Supports interactions required for infection.

The other surface glycoprotein mediates cell fusion.

Both are part of the description of mumps as an enveloped paramyxovirus.

Slide 55 · Mumps: Respiratory entry to salivary gland

Respiratory exposure

Draining lymph nodes

Lymphocyte replication

Viremia

Salivary gland infection

Activated T cells are highlighted as targets during lymphoid replication.

Infected duct epithelial cells desquamate and inflame the gland.

Pathogenesis flow

Slide 56 · Mumps parotitis: The edema–injury relationship

Parotid duct–acinar unit

Duct epithelial injury + desquamation

Interstitial edema + mononuclear infiltrate

Mechanism of gland enlargement and tenderness

Schematic

Slide 57 · Parotid histology: Interstitial inflammation

Interstitial compartment

Ductal compartment

Edema and lymphocytes, macrophages and plasma cells.

Inflammatory expansion compresses normal acini and ducts.

Neutrophils and necrotic debris may accumulate within duct lumens.

Focal epithelial injury and desquamation occur.

Slide 58 · Mumps orchitis: Swelling within a rigid capsule

Testicular infection

Edema + mononuclear inflammation

Pressure under tunica albuginea

Perfusion compromise

Focal infarction / atrophy

Hemorrhage may accompany acute testicular inflammation.

Severe tissue destruction can result in scarring and impaired fertility.

Structural explanation of potential irreversible injury

Slide 59 · Pancreatitis and encephalitis in mumps

Pancreas

Central nervous system

Infection of pancreatic acinar cells can liberate digestive enzymes.

Enzymatic injury may cause parenchymal/fat necrosis and neutrophilic inflammation.

Encephalitic pathology can show perivenous demyelination.

Perivascular mononuclear cuffing is described.

Slide 60 · Mumps diagnosis: Clinicopathologic integration

Parotid pain and swelling are prominent clinical clues.

Clinical assessment is often sufficient for a presumptive diagnosis.

Serology or viral RNA detection in saliva can provide confirmation.

Urine or CSF may be examined in selected clinical settings.

Slide 61 · Clinical application: Parotitis and testicular pain

Illustrative case: A patient has painful bilateral parotid swelling followed by testicular enlargement and pain.

Interpretation question

Why can orchitis threaten testicular viability?

Details to integrate

Salivary duct injury

Edema

Encapsulated testis

Slide 62 · Case interpretation: Mumps orchitis

Most consistent interpretation

Inflammatory edema compromises perfusion within the tunica albuginea

Viremia permits spread to extra-salivary organs.

Interstitial edema and inflammation increase testicular tissue pressure.

Ischemic injury can produce infarction followed by atrophy or scarring.

Slide 63 · Poliovirus: Usually controlled, occasionally neuroinvasive

Poliovirus is a nonenveloped RNA enterovirus transmitted chiefly by the fecal–oral route.

Most infections are asymptomatic or mild and self-limited.

A small minority progress to motor-neuron involvement and paralysis.

Spinal and bulbar involvement have distinct functional consequences.

Slide 64 · Poliovirus enters through the gastrointestinal route

Fecal–oral exposure

Pharyngeal and intestinal mucosa

Tonsils / Peyer patches

Lymphatic spread

Transient viremia

Infections may also follow exposure to pharyngeal secretions.

Local lymphoid replication precedes systemic dissemination.

Early pathogenesis sequence

Slide 65 · CD155 mediates poliovirus attachment

Viral receptor

Tissue implications

Poliovirus binds the cell-surface receptor CD155.

The source describes CD155 on epithelial cells, lymphocytes and neurons.

Receptor expression makes multiple tissue compartments potentially susceptible.

Neuronal infection is clinically important only when viral spread reaches the CNS.

Slide 66 · Antibodies usually contain poliovirus infection

Pharynx + intestinal mucosa

Tonsils + Peyer patches

Lymph nodes → blood

Contained infection in most hosts

CNS entry in a small minority

Antibody response usually contains systemic spread.

Schematic

Slide 67 · Neuroinvasion targets motor neurons

Bloodstream / possible axonal entry

Central nervous system access

Motor-neuron infection

Loss of motor function

Source proposes hematogenous spread or retrograde axonal transport.

The basis for failed containment in the small affected minority remains uncertain.

Both neuroinvasion routes are presented as possible, not proved in a given case

Slide 68 · Spinal versus bulbar poliomyelitis

Type

Primary region

Functional consequence

Spinal

Motor neurons in spinal cord

Limb-muscle weakness or paralysis

Bulbar

Brainstem motor structures

Potential impairment of respiration and related functions

Slide 69 · Polio immunization: Two vaccine approaches

Inactivated poliovirus vaccine

Oral attenuated poliovirus vaccine

Injected preparation containing inactivated virus.

Antibodies protect against poliovirus serotypes.

Live attenuated oral vaccine has been used to support eradication.

Rare genetic reversion can yield pathogenic vaccine-derived strains.

Slide 70 · Why eradication has been achievable

Humans are the only natural host emphasized by Robbins.

The virus has comparatively limited genetic variation.

Antibody responses induced by vaccination neutralize poliovirus.

Sustained immunization is essential because wild and vaccine-derived circulation can occur.

Slide 71 · Poliovirus diagnosis depends on virologic detection

Viral culture is a described diagnostic method.

Viral RNA can be detected in throat secretions or stool.

Serology may support diagnosis, depending on context.

Anatomic and neurologic localization is needed to interpret suspected paralytic disease.

Slide 72 · Clinical application: Febrile illness with paralysis

Illustrative case: Following an initial nonspecific febrile illness, a patient develops acute limb weakness involving motor function.

Interpretation question

What anatomic target explains paralytic poliomyelitis?

Details to integrate

Enteric replication

Systemic spread

Motor weakness

Slide 73 · Case interpretation: Motor-neuron involvement

Most consistent interpretation

Poliovirus replication in spinal or brainstem motor neurons

Early mucosal and lymphoid replication can be clinically inconspicuous.

Neuroinvasion occurs in a small minority despite usual antibody control.

Neuron injury links CNS infection directly to weakness and paralysis.

Slide 74 · Comparison: Entry routes and initial sites

Virus

Predominant acquisition

Early replication / receptor

SARS-CoV-2

Respiratory particles

ACE2-bearing respiratory epithelium

Measles

Airborne aerosols

Respiratory tract; SLAMF1-positive immune cells

Mumps

Respiratory droplets

Respiratory tract and draining lymphocytes

Poliovirus

Fecal–oral

Pharyngeal / gut mucosa; CD155

Slide 75 · Comparison: Dominant tissue injury

Virus

Morphologic signature

Clinical consequence

SARS-CoV-2

Diffuse alveolar damage; Microthrombi

ARDS / hypoxia

Measles

Perivascular rash; Multinucleated giant cells

Exanthem; Secondary infection risk

Mumps

Salivary interstitial edema, duct injury

Parotitis; Orchitis / pancreatitis

Poliovirus

Motor-neuron infection

Spinal or bulbar paralysis

Slide 76 · Common theme: Pathology depends on host response

Syndrome

Direct viral effects

Host-mediated component

COVID-19

Infection of respiratory epithelial cells

Cytokine injury, coagulation disturbance

Measles

Dissemination across organs

T-cell-mediated rash; Altered immunity

Mumps

Duct/acinar infection

Edema, inflammation, ischemia

Poliomyelitis

Motor-neuron infection

Antibody containment protects most hosts

Slide 77 · Clinical reasoning: Localize before identifying the virus

Identify syndrome

Localize organ injury

Consider entry/spread

Select virologic confirmation

The same virus can cause distinct organ syndromes.

Histologic patterns are interpreted together with exposure history and molecular tests.

Conceptual diagnostic reasoning, not a treatment guideline

Slide 78 · High-yield distinctions among four infections

SARS-CoV-2: ACE2 / spike-mediated entry; Severe alveolar and thromboinflammatory injury.

Measles: Airborne dissemination, cell-mediated rash and transient immune suppression.

Mumps: Salivary duct injury with possible orchitis, pancreatic and CNS involvement.

Poliovirus: Enteric replication with rare motor-neuron neuroinvasion.

Slide 79 · Final integration: four diagnostic questions

What route allowed infection, and which cell type first supported replication?

How did the virus disseminate from its primary site to injured organs?

Which findings reflect direct cytopathic injury, host inflammation or both?

Which clinical specimen and laboratory method can establish the responsible virus?