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Malaria: Clinical Features, Diagnosis, Pathophysiology & Complications

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Causative Organisms

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Pathophysiology

Hepatic Stage (Clinically Silent)

1. Sporozoites injected by mosquito bite travel to the liver within minutes
2. Two surface proteins - thrombospondin-related adhesive protein and circumsporozoite protein - bind heparan sulfate proteoglycans on hepatocytes
3. Sporozoites enter hepatocytes and differentiate into merozoites (liver schizonts)
4. After 1-4 weeks (or 2-10 days), hepatocytes rupture, releasing thousands of merozoites into the bloodstream

P. vivax and P. ovale form hypnozoites - dormant, metabolically inactive liver stages that can reactivate weeks to years later, causing relapse. Standard antimalarials (except primaquine/tafenoquine) do not eliminate hypnozoites.

Erythrocytic Stage (Symptomatic Phase)

1. A lectin-like molecule on the merozoite surface binds sialidated glycophorin on RBCs
2. Merozoite invaginates into RBC within a digestive vacuole → differentiates into trophozoite
3. Trophozoites follow two paths:
   • → Gametocytes (sexual forms; infect mosquito when it bites)
   • → Schizonts → lyse RBC → release merozoites → infect new RBCs

Mechanism of Severe Disease (P. falciparum Specific)

• Infected RBCs express PfEMP1 (Plasmodium falciparum erythrocyte membrane protein 1), concentrated in knob-like extensions on the RBC surface
• PfEMP1 binds endothelial adhesion molecules: ICAM-1, VCAM-1, CD36
• This causes cytoadhesion - parasitized RBCs stick to capillary endothelium
• Result: microvascular occlusion, tissue hypoperfusion, and end-organ damage
• Note: sequestration also reduces measured parasitemia and can cause false-negative smears

Fever Mechanism

• Synchronized rupture of RBCs releases merozoites plus pyrogenic substances (hemozoin, cytokines, TNF-α, IL-1)
• Fever coincides with each burst of merozoite release
• Early in infection, cycles may be asynchronous (no periodicity); periodicity develops over time

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Clinical Features

Prodrome / Non-specific Phase

• Malaise, headache, myalgia, fatigue, nausea, vomiting
• Upper respiratory symptoms (can mimic influenza)
• Abdominal pain, diarrhea
• Fever is common but not universal at initial presentation; when present, it is often continuous early on

Classic Febrile Paroxysm (3 Stages)

1. Cold stage - sudden onset of rigors and chills (15-60 min)
2. Hot stage - high fever 39-41°C, headache, nausea (2-6 h)
3. Sweating stage - drenching sweats, temperature falls, patient feels exhausted

Species-Specific Notes

• P. falciparum: fever pattern is often irregular; can progress to severe malaria within hours to days
• P. vivax / P. ovale: tertian fever, milder but relapse risk
• P. malariae: quartan fever, insidious; can cause immune-complex nephrotic syndrome years later

Signs on Examination

• Fever (may be low-grade or absent in early disease)
• Splenomegaly (chronic infection → massive splenomegaly)
• Hepatomegaly
• Pallor (anemia)
• Jaundice (hemolysis)
• Thrombocytopenia (common, often used as a diagnostic clue)

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Complications

1. Cerebral Malaria (P. falciparum)

• Parasitized RBCs (with PfEMP1 knobs) adhere to cerebral capillary walls → sludging, microvascular occlusion, capillary leakage, petechial hemorrhages
• Clinical: altered consciousness, obtundation → coma, seizures (often >2 generalized), fever
• Most common cause of death in malaria
• Mortality high especially in children; neurologic sequelae rare in survivors
• Corticosteroids (dexamethasone) are contraindicated - they worsen outcomes

2. Severe Anemia

• Two mechanisms:
  • Direct: mature merozoites lyse parasitized RBCs
  • Indirect: auto-antibodies destroy unparasitized RBCs; increased reticuloendothelial activity; suppressed erythropoietin response
• Hemoglobin < 7 g/dL = marker of severe malaria

3. Blackwater Fever

• Complication of chronic/acute falciparum malaria
• Massive intravascular hemolysis → hemoglobinemia → hemoglobinuria (black/dark red urine) → acute tubular necrosis and renal failure
• Also associated with jaundice

4. Acute Kidney Injury

• From microvascular occlusion, hemoglobinuria, hypovolemia
• Criteria for severe malaria: creatinine > 3 mg/dL or blood urea > 20 mmol/L

5. Pulmonary Complications

• Range from mild cough to ARDS / acute lung injury
• Bilateral opacities on CXR mimicking pulmonary edema
• Alveolar macrophages contain hemozoin (brown degradation product of hemoglobin)
• Most susceptible: children, pregnant women, non-immune travelers

6. Hypoglycemia

• P. falciparum parasites are metabolically active and consume glucose
• Worsened by anorexia, malnutrition, and quinine infusion (stimulates insulin release)
• Glucose < 40 mg/dL = severe malaria criterion; especially dangerous in children

7. Metabolic Acidosis / Lactic Acidosis

• From tissue hypoperfusion (microvascular occlusion) and impaired hepatic lactate clearance
• Bicarbonate < 15 mmol/L or lactate > 5 mmol/L = severe malaria

8. Hepatosplenomegaly

• Mononuclear phagocyte hyperplasia causes splenomegaly
• Kupffer cells in liver distended with parasites and malarial pigment (hematin)
• Parasitized RBCs adhere to splenic sinusoids → impaired splenic immunity

9. DIC / Spontaneous Bleeding

• Multifactorial: thrombocytopenia, coagulation factor consumption

10. High-Output Cardiac Failure

• Due to severe anemia (compensatory)

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WHO Criteria for Severe Malaria (key thresholds to memorize)

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Diagnosis

1. Thick & Thin Blood Smears (Gold Standard)

• Thick smear: concentrated - higher sensitivity for detection
• Thin smear: species identification and estimation of parasitemia
• Each Plasmodium species has distinct trophozoite morphology on Giemsa stain
• Repeat smears every 12-24 h if initial is negative (due to sequestration/low parasitemia in falciparum)

2. Rapid Diagnostic Tests (RDTs)

• Detect P. falciparum HRP2 antigen or pan-malarial pLDH
• Useful in resource-limited settings; quick turnaround
• False negatives possible with low parasitemia or when sequestration is high

3. PCR

• Most sensitive; useful for species confirmation and mixed infections
• Not point-of-care; used when smear/RDT results are unclear

4. Other Labs (Supportive)

• CBC: thrombocytopenia (nearly universal), hemolytic anemia, leukopenia or normal WBC
• Blood film: hemolytic anemia picture
• LFTs: elevated bilirubin, mild transaminase elevation
• Renal function: AKI in severe disease
• Glucose: hypoglycemia
• Lactate: elevated in severe disease
• Urinalysis: hemoglobinuria (blackwater fever)

5. Radiology

• CXR in severe disease: bilateral symmetric opacities (ARDS pattern)

Key Clinical Clue: Travel History

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Key Points Summary

• P. falciparum is the deadliest species; P. vivax/ovale cause relapse via hypnozoites
• Pathogenesis hinges on PfEMP1-mediated cytoadhesion of infected RBCs to endothelium → microvascular occlusion → multi-organ failure
• Classic fever periodicity (48 h / 72 h) often absent in falciparum - do not use absence of periodicity to exclude the diagnosis
• Cerebral malaria + blackwater fever = the two most feared complications
• Diagnosis by blood smear; repeat if negative; do NOT wait for periodicity to develop
• Primaquine required to eradicate hypnozoites in P. vivax/ovale - check G6PD first (risk of hemolysis)
• Corticosteroids are harmful in cerebral malaria

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Chikungunya: Clinical Features, Pathophysiology & Complications

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The Virus & Vector

• Virus: Chikungunya virus (CHIKV) is a single-stranded positive-sense RNA alphavirus of the family Togaviridae, genome ~12 kb
• Vectors: Aedes aegypti and Aedes albopictus (the latter is now indigenous to many regions worldwide, including Europe and the Americas)
• Hosts: Humans are the primary host during epidemics; a sylvatic cycle exists between jungle primates and mosquitoes (Aedes africanus, A. furcifer-taylori)
• Transmission routes (non-vector):
  • Blood transfusion (documented, rare)
  • Needlestick / occupational (laboratory workers)
  • Intrapartum (when mother viremic at delivery) - dangerous for neonates
  • Rare in utero transmission (mainly 2nd trimester)
  • Breastfeeding: viral RNA found in milk but no infant infection documented
• Geography: Sub-Saharan Africa, India, SE Asia, Pacific and Indian Ocean islands, Caribbean, Americas (since 2013 when first detected in the Western Hemisphere)
• Incubation period: 3-7 days (range 1-12 days)
• The name derives from the Kimakonde/Makonde language meaning "to become contorted" or "that which bends up" - describing the stooped posture from severe joint pain

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Pathophysiology

Viremia & Innate Immune Response

• CHIKV causes a brief viremia lasting 5-7 days
• Controlled primarily by type I interferon (IFN-α/β) and antibodies
• The innate response clears the acute viremia but does not always prevent chronic musculoskeletal disease

Cellular Tropism - Key Concept

• Primary target cells: fibroblasts - synovial fibroblasts, skin fibroblasts, muscle epimysial fibroblasts
• Also infects: epithelial cells, endothelial cells, hepatocytes, neurons, astrocytes
• Cellular receptor: MXRA8 (matrix remodeling-associated protein 8, also called limitrin) - binds the viral E2 surface protein
• CD147 also contributes to E2 binding
• Notably, immune cells (monocytes, lymphocytes, dendritic cells, NK cells) are generally not permissive for productive CHIKV replication

Synovial / Joint Pathology

• CHIKV antigens detected in: skeletal muscle epimysium, joint capsule cells, dermis
• Persistent viral antigen or remnants in synovial tissue drives chronic inflammation
• Tenosynovitis and enthesopathy (rather than classical synovitis) are the dominant findings on ultrasound in chronic disease
• MRI findings in post-CHIKV arthritis: joint effusion, bony erosion, marrow edema, synovial thickening, tendonitis, tenosynovitis
• Mechanism of chronicity: ongoing fibroblast infection + local cytokine/chemokine milieu; pain has both nociceptive and neuropathic components

Why Arthritis Persists

• Most patients do NOT develop autoantibodies (RF and anti-CCP usually negative)
• Yet ~1/3 may meet ACR criteria for RA
• This is a virus-driven inflammatory arthropathy, distinct from classic seropositive RA
• Predictors of non-recovery: age >45 years, severe initial joint pain, pre-existing osteoarthritis

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Clinical Phases

Phase 1 - Acute (Days 1-10)

• Abrupt onset, typically >39°C (102°F)
• Lasts several days to a week, may be biphasic (brief improvement then recurrence)

• Occurs in up to 100% of patients who develop a rash; ~40-50% of all infected
• Bilateral, symmetric polyarthralgia - mainly small joints: hands (MCPs, PIPs), wrists, ankles, feet (MTPs)
• More proximal joints (knees, shoulders, elbows) also affected
• Pain appears on days 3-5 of illness; can be severe and debilitating
• Swelling, stiffness, warmth present
• The stooped, contorted posture = pathognomonic appearance

• Headache (~70%)
• Myalgia
• Nausea and vomiting (~60%)
• Fatigue / lethargy
• Conjunctivitis
• Lymphadenopathy (adenopathy common)

Phase 2 - Subacute (Weeks 2-12)

• Acute fever resolves but joint pain persists or recurs
• Symptoms fluctuate - patients often perceive relapses as reinfection
• Tenosynovitis develops
• Neuropathic features can emerge: Raynaud phenomenon, erythromelalgia, severe acral coldness

Phase 3 - Chronic (>3 months, up to years)

• Arthralgia is the most frequent chronic symptom
• Polyarthritis, tenosynovitis, enthesopathy persist
• Some develop progressive erosive arthritis resembling RA (without RF/anti-CCP)
• Variable prevalence: some studies report >50% still symptomatic at 6 months; some persist years
• Risk factors for chronicity: age >50 years, arthritis during acute phase, severe or prolonged initial illness

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The Rash

• ~90% of bullous cases occur in children <1 year of age; 17% of children vs only 3% of adults
• Flaccid or tense, non-hemorrhagic blisters that rupture easily
• Nikolsky sign positive
• Genitalia, palms, soles spared
• Can involve up to 80% of BSA (resembles toxic epidermal necrolysis)
• High viral titers in blister fluid
• Biopsy: intraepidermal blister with acantholytic cells
• Management: burn-unit approach; skin grafting usually not required; most recover

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Laboratory Findings

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Diagnosis

1. Clinical (Preliminary)

• Acute febrile illness + severe bilateral symmetric polyarthralgia + travel/residence in endemic area
• Consider alongside dengue and Zika (cocirculation in same regions)

2. RT-PCR (First Week - Viremic Phase)

• Performed on serum during the first 5-7 days of illness
• Most sensitive test in acute phase
• Also detects viral RNA in blister fluid

3. Serology (After Day 5-7)

• IgM antibodies: appear toward end of first week; persist 30-90 days (sometimes longer)
  • Positive IgM alone may reflect past infection if long-persisting
• IgG neutralizing antibodies: develop within weeks; persist long-term; confirm immunity
• Plaque-reduction neutralization test (PRNT): quantifies neutralizing antibodies; used to distinguish cross-reactive antibodies from related alphaviruses (Mayaro, O'nyong-nyong)
• Seroconversion (IgM → IgG rise) confirms diagnosis

4. Immunohistochemistry

• Detects viral antigen in fixed tissue at reference labs (CDC)

Dengue vs Chikungunya - Distinguishing Features

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Complications

Common

• Persistent polyarthritis / chronic arthropathy (most common overall complication)
• Hepatitis (elevated transaminases)
• Neuropathic pain (Raynaud, erythromelalgia)

Neurological (Rare but Most Severe)

• Meningoencephalitis
• Myelitis
• Guillain-Barré syndrome
• Cranial nerve palsies

Other Rare Complications

• Uveitis, retinitis
• Myocarditis
• Nephritis
• Bullous/vesiculobullous skin lesions (esp. infants)
• Hemorrhage

High-Risk Groups for Severe Disease

• Neonates exposed perinatally (intrapartum transmission during maternal viremia - can be life-threatening)
• Older adults (>65 years)
• Persons with hypertension, diabetes, cardiovascular disease, kidney disease

Mortality

• Rare (~1 in 1000 infected patients); most cases are self-limiting

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Treatment

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Prevention

• No licensed vaccine (as of 2024, though candidates in trials)
• Vector control: eliminate Aedes breeding sites (standing water), insecticide spraying
• Personal protection: insect repellent (DEET), long sleeves/pants, screened/air-conditioned rooms, avoid outdoor activity at peak mosquito feeding times (dawn and dusk for Ae. aegypti; daytime for Ae. albopictus)
• Febrile/viremic patients should be protected from mosquito bites to prevent onward transmission
• Blood and organ donor screening

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Key Points to Remember

1. CHIKV = alphavirus, Togaviridae; vector = Aedes aegypti and Ae. albopictus
2. Incubation 3-7 days; viremia 5-7 days (IFN + antibodies clear it)
3. Primary target = synovial and skin fibroblasts (via MXRA8 receptor)
4. Hallmark: acute high fever + severe bilateral symmetric polyarthralgia (mainly small joints of hands and feet)
5. Rash in 50-75%; morbilliform, appears day 2; bullous eruption is a pediatric emergency
6. Lymphopenia + thrombocytopenia are typical lab findings
7. Diagnose by RT-PCR (first week) then IgM serology (after day 5-7)
8. Chronic arthritis in up to 50% at 6 months; RF and anti-CCP usually negative
9. Rare but severe: meningoencephalitis, GBS, neonatal severe disease
10. Treatment: paracetamol first (avoid NSAIDs until dengue excluded); no antiviral; hydroxychloroquine/MTX for chronic arthritis
11. No vaccine; prevention = vector control + personal protection

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