What are the diagnosis and treatment options for malaria vivax?

Diagnosis and Treatment of Plasmodium vivax Malaria

The gold standard for diagnosing P. vivax malaria is microscopic examination of Giemsa-stained thick and thin blood films, while first-line treatment consists of chloroquine followed by primaquine for radical cure after G6PD testing. 1

Diagnosis

Diagnostic Methods

• Microscopy: Gold standard for malaria diagnosis

  • Allows detection of parasites, species identification, and quantification of parasitemia
  • Thick films for parasite detection
  • Thin films for species identification

• Rapid Diagnostic Tests (RDTs):

  • Complementary to microscopy
  • Sensitivity for P. vivax: 66-91%
  • Specificity for P. vivax: 98-100% 2, 1
  • Limitations: False negatives with low parasitemia, non-falciparum species

• Nucleic Acid Amplification Tests (NAATs):

  • 10-100 times more sensitive than microscopy or RDTs
  • Detection limit: ~0.2-6 parasites/μL
  • Particularly useful for:
    • Very low parasitemia
    • Mixed infections
    • Usually restricted to specialized laboratories 2

Diagnostic Algorithm

1. Obtain blood samples for thick and thin smears
2. Perform RDT for rapid initial assessment
3. Confirm with microscopy for species identification and parasitemia quantification
4. Consider PCR/LAMP for cases with suspected low parasitemia or mixed infection

Treatment

Uncomplicated P. vivax Malaria

Blood Schizontocidal Treatment (Acute Phase)

• First-line: Chloroquine 1, 3

  • Adult dosing: 600 mg base (1000 mg salt) orally, followed by 300 mg base (500 mg salt) at 6,24, and 48 hours
  • Pediatric dosing: 10 mg/kg on days 1-2 and 5 mg/kg on day 3 1

• For chloroquine-resistant P. vivax (from Papua New Guinea, Indonesia, Sabah):

  • Artemisinin-based combination therapies (ACTs)
  • Dihydroartemisinin-piperaquine (preferred) or artemether-lumefantrine 1
  • Mefloquine can be used at a dose of 1250 mg (five tablets) as a single oral dose 4

Anti-Relapse Therapy (Hypnozoitocidal)

• Primaquine (after G6PD testing):

  • Dosing: 30 mg base daily for 14 days (preferred in most guidelines)
  • Alternative: 15 mg base daily for 14 days
  • Reduces relapse risk by approximately 80% 1, 3

• Tafenoquine (where available):

  • Single 300 mg dose after G6PD testing 1

Special Populations

Pregnant Women

• Chloroquine alone for blood-stage treatment
• Primaquine and tafenoquine are contraindicated during pregnancy
• Defer anti-relapse therapy until after pregnancy 1

Children

• Chloroquine: 10 mg/kg on days 1-2 and 5 mg/kg on day 3
• Primaquine: 0.3 mg/kg/day for 14 days (after G6PD testing) 1
• Mefloquine: 20-25 mg/kg body weight (not to exceed adult dose) 4

Monitoring and Follow-Up

• Monitor parasitemia daily until cleared 1
• Follow up to detect recurrence or delayed complications
• Consider ECG monitoring for patients on medications with potential QT effects
• Regular blood glucose checks (hypoglycemia is common)
• Monitor renal function and electrolytes 1

Common Pitfalls and Caveats

1. Failure to test for G6PD deficiency before primaquine administration

   • Can lead to life-threatening hemolysis in G6PD-deficient patients
   • Mandatory before administering primaquine or tafenoquine 1

2. Missing radical cure with primaquine

   • P. vivax has dormant liver stages (hypnozoites) that cause relapses
   • Mefloquine and chloroquine only treat blood stages but do not eliminate hypnozoites 3, 4
   • Without primaquine, relapse rates are high

3. Not considering geographic resistance patterns

   • Chloroquine resistance is increasingly common in Southeast Asia and parts of Oceania
   • Treatment should be adjusted based on region of acquisition 1

4. Inadequate diagnosis

   • Low parasitemia in P. vivax can lead to false negatives
   • Mixed infections may be missed without proper microscopy or molecular testing 2

5. Underestimating severity

   • P. vivax was historically considered "benign," but can cause severe disease
   • Severe manifestations should be treated as medical emergencies with IV artesunate 2, 1

By following this diagnostic and treatment approach, clinicians can effectively manage P. vivax malaria while minimizing the risk of treatment failure and relapse.