A 32-year-old male construction worker from rural Jharkhand presents to the primary health centre with fever, chills, and sweating for 3 days. He reports working outdoors in the evening and early morning. On examination, temperature is 39.5°C, splenomegaly is noted, and thick blood smear shows P. vivax parasites. The patient asks about the risk of recurrence. Which statement best explains the epidemiological pattern of his infection?

Question

Accepted Answer

D. P. vivax causes tertian fever with a 48-hour cycle; recurrence is due to hypnozoites in the liver that can activate months to years later. ## Epidemiology of P. vivax Malaria

**Key Point:** P. vivax is the most common cause of malaria in India and has a unique relapse pattern due to hypnozoites (dormant liver forms) that can reactivate months to years after the primary attack.

### Clinical Presentation
- **Fever pattern:** Tertian (every 48 hours) — fever on days 1, 3, 5, etc.
- **Periodicity:** Synchronized rupture of infected RBCs occurs every 48 hours
- **Typical cycle:** Fever, chills, sweating lasting 8–10 hours, followed by defervescence

### Pathophysiology of Relapse
1. **Hypnozoites** are dormant forms in hepatocytes that escape the initial attack of antimalarials
2. **Reactivation** can occur weeks to months (even years) after the primary infection
3. **Trigger factors:** Immunosuppression, stress, or concurrent illness may precipitate relapse
4. **Prevention:** Primaquine (8-aminoquinoline) is required to eliminate hypnozoites and prevent relapse

### Epidemiological Significance in India

| Feature | P. vivax | P. falciparum |
|---------|----------|---------------|
| Fever pattern | Tertian (48 hrs) | Quotidian or irregular |
| Hypnozoites | Present (relapse common) | Absent (no relapse) |
| Severity | Milder | Severe, cerebral malaria |
| Geographic distribution | Pan-India, especially plains | Forest/tribal areas |
| Relapse risk | 20–40% without primaquine | None |

**Clinical Pearl:** In endemic areas like Jharkhand, P. vivax accounts for ~60% of malaria cases. The relapse pattern makes it epidemiologically significant for sustained transmission — each relapse can serve as a reservoir for mosquito infection.

**High-Yield:** Primaquine is mandatory for P. vivax (and P. ovale) to prevent relapse. G6PD deficiency screening is essential before primaquine administration in endemic populations [cite:Park 26e Ch 10].

### Why Relapse Occurs
- Hypnozoites are sequestered in the liver and are not exposed to blood-stage antimalarials (chloroquine, artemisinin derivatives)
- Only 8-aminoquinolines (primaquine, tafenoquine) are effective against hypnozoites
- Without primaquine, the patient is at risk of clinical relapse 2–12 months later

Answer

A. P. vivax causes quartan fever with a 72-hour cycle; the patient will have fever every fourth day indefinitely without treatment

Answer

B. P. vivax parasites remain in the bloodstream for life; recurrence is inevitable despite antimalarial therapy

Answer

C. P. vivax only causes acute illness; once treated, there is no risk of relapse or recurrence in endemic areas

Explanation

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