19 Further information is provided in Annex 10.
P. vivax, the second most important species causing human malaria, accounts for about 40% of malaria cases worldwide and is the dominant malaria species outside Africa. It is prevalent in endemic areas in the Middle East, Asia, Oceania and Central and South America. In Africa, it is rare except in the Horn and it is almost absent in West Africa. In most areas where P. vivax is prevalent, malaria transmission rates are low, and the affected populations therefore achieve little immunity to this parasite. Consequently, people of all ages are at risk. The other two human malaria parasite species P. malariae and P. ovale are generally less prevalent but are distributed worldwide especially in the tropical areas of Africa.
Among the four species of Plasmodium that affect humans, only P. vivax and P. ovale form hypnozoites, parasite stages in the liver that can result in multiple relapses of infection, weeks to months after the primary infection. Thus a single infection causes repeated bouts of illness. This affects the development and schooling of children and debilitates adults, thereby impairing human and economic development in affected populations. The objective of treating malaria caused by P. vivax and P. ovale is to cure both the blood stage and the liver stage infections, and thereby prevent both relapse and recrudescence. This is called radical cure. Infection with P. vivax during pregnancy, as with P. falciparum, reduces birth weight. In primigravidae, the reduction is approximately two-thirds of that associated with P. falciparum (110 g compared to 170 g), but this adverse effect does not decline with successive pregnancies as with P. falciparum infections. Indeed, in the one large series in which this was studied, it increased. Reduction in birth weight (<2500 g) increases the risk of neonatal death.