Where do most cases of malaria occur (including transmission)?
Most cases of malaria occur in tropical Africa (West and Central Africa).
Transmission also occurs in other tropical and subtropical regions such as South and Southeast Asia, and Central and South America
Describe the etiology
Eukaryotic parasites (belonging to the Sporozoa group)
Species that affect humans 
Plasmodium falciparum: most virulent and causes the most severe disease, i.e., falciparum malaria; dominant in Africa
Plasmodium vivax: the most common of the less virulent species and causes milder disease; dominant in endemic areas outside Subsaharan Africa (e.g., Southeast Asia)
Plasmodium ovale and Plasmodium malariae: less common and cause milder disease 
Plasmodium knowlesi: found in Southeast Asia and can cause severe malaria; possibly zoonotic and often misidentified as other species due to morphological similarities. 
Vector: the female Anopheles mosquito
When can a partial resistance against malaria be seen?
Carriers of sickle‑cell mutation
Individuals with either certain Duffy antigens or no Duffy antigens are resistant to P. vivax and P. knowlesi 
Other hemoglobinopathies (e.g., thalassemia, HbC)
Infection with malaria subsequently leads to the development of specific Plasmodium antibodies that result in partial immunity for a limited amount of time (less than a year)
Describe the pathophysiology.
Asexual development in humans
Transmission of Plasmodium sporozoites via Anopheles mosquito bite → sporozoites travel through the bloodstream to the liver of the host
Liver: sporozoites enter hepatocytes → sporozoites multiply asexually → schizonts are formed containing thousands of merozoites → release of merozoites into the bloodstream
Circulatory system (two possible outcomes)
Merozoites enter erythrocytes → maturation to trophozoites → red cell schizonts are formed containing thousands of merozoites → release of merozoites into the bloodstream (which causes fever and other manifestations of malaria) → penetration of erythrocytes recurs
Merozoites enter erythrocytes → differentiation into gametocytes (male or female)
Sexual development in female Anopheles mosquito
A mosquito bites an infected human and ingests gametocytes → gametocytes mature within the mosquito intestines → sporozoites are formed and these migrate to the salivary glands → transmission of sporozoites to humans via mosquito bite
See also “Developmental stages of Plasmodium in RBCs.”