What are the different types of malaria?

Types of Malaria

Malaria in humans is caused by six species of Plasmodium parasites: P. falciparum, P. vivax, P. ovale wallikeri, P. ovale curtisi, P. malariae, and P. knowlesi. 1

The Six Main Species

Plasmodium falciparum

• Most virulent species and responsible for the majority of malaria-related deaths, particularly in sub-Saharan Africa 1, 2
• Accounts for approximately 69.8% of malaria cases in imported malaria to the United States 3
• Can rapidly progress to severe (complicated) malaria with life-threatening complications including cerebral malaria, severe anemia, metabolic acidosis, and multi-organ failure 1
• Predominant species in Africa, where it causes the highest mortality burden 1, 2

Plasmodium vivax

• Second most common species globally and the predominant cause of malaria outside of Africa, particularly in Southeast Asia and South America 2
• Historically considered benign but now recognized to cause severe disease including acute respiratory distress syndrome, cerebral malaria, and multi-organ failure 2
• Unique characteristic: forms dormant liver-stage hypnozoites that cause relapsing infections weeks to months after initial infection 1, 2
• Essentially absent in most of Africa due to inherited lack of Duffy antigen receptor on red blood cells required for parasite invasion 2
• Accounted for 74.6% of locally acquired mosquito-transmitted malaria outbreaks in the United States from 1957-2003 1

Plasmodium ovale (two subspecies)

• Two distinct subspecies: P. ovale wallikeri and P. ovale curtisi 1
• Traditionally considered rare and causing mild illness 4
• Also forms dormant liver hypnozoites causing relapsing infections similar to P. vivax 1
• Recent PCR-based diagnosis reveals these infections may be more common than previously recognized, often occurring as mixed infections 4
• Accounted for 5.2% of imported malaria cases in the United States in 2018 3

Plasmodium malariae

• Causes chronic, low-level parasitemia that can persist for years 4
• Traditionally thought to cause mild disease, but sensitive PCR diagnosis shows low-level infection is more common than previously recognized 4
• Accounted for 2.6% of imported malaria cases in the United States in 2018 3
• Often occurs as part of complex mixed infections with other Plasmodium species 4

Plasmodium knowlesi

• Simian (monkey) parasite that causes a significant portion of human malaria cases in parts of Southeast Asia 1
• First imported case to the United States since 2008 was identified in 2018 3
• Can cause severe disease with rapid parasite multiplication 5

Additional Considerations

Mixed Species Infections

• Infections with two or more Plasmodium species can occur and accounted for less than 1% of cases in the United States in 2018 3
• PCR-based diagnosis reveals mixed infections are more common than microscopy alone suggests 4

Other Rare Simian Species

• Other simian Plasmodium species restricted to South America and Southeast Asia can occasionally infect humans 1

Clinical Pitfall

All species can cause severe disease and death if not diagnosed and treated promptly, though P. falciparum carries the highest mortality risk 1, 2. The historical classification of P. vivax, P. ovale, and P. malariae as "benign" is outdated and clinically dangerous 2.