Page 180 - 80 guidelines for the treatment of malaria_opt

nd
Guidelines for the treatment of malaria – 2 edition

ANNEX 9
treatment of PlasmODium vivax, P. OvalE
and P. malariaE infections

a9.1 introduction

Plasmodium vivax is the second major human malaria species; estimates of its contribution
to the malaria cases worldwide range from 8–41% (1,2,3), and it is the dominant species of
malaria in many areas outside Africa. It is prevalent in the Middle East, Asia, the Western
Pacific and Central and South America. It is rarer in Africa and almost absent from West
Africa due to the high prevalence of the Duffy negative phenotype (3). In most areas
where P. vivax is prevalent, malaria transmission rates are low and, therefore, the affected
populations achieve only a partial immunity to this parasite. Consequently, people of all
ages, adults and children alike, are at risk of acquiring P. vivax infections (3). Where both
P. falciparum and P. vivax prevail, the incidence rates of P. vivax tend to peak in people of a
younger age than those of P. falciparum (4). The other two human malaria parasite species,
P. malariae, which is prevalent at low levels in nearly all malaria endemic areas of the world,
and P. ovale, which has the most limited distribution of all the species and is prevalent in
Africa, New Guinea and the Philippines (5).
Among the four species of Plasmodium that affect humans, only P. vivax and P. ovale
have the ability to form hypnozoites (dormant parasite stages in the liver that can result
in relapse infections weeks to months after the primary infection). P. vivax preferentially
invades reticulocytes, and this may lead to anaemia. Repeated infections lead to a chronic
anaemia that can be debilitating, thereby impairing human and economic development
in affected populations. In areas where both P. falciparum and P. vivax co-exist, intensive
malaria control efforts often result in having a rapid and major impact on P. falciparum
(leaving P. vivax as the residual malaria burden, as it is more resilient to interventions). As a
result P. vivax is increasing in some regions of the world (3). Appropriate case management
of P. vivax malaria will help to minimize the global malaria burden.
Although P. vivax has been traditionally known to be benign malaria, it causes a severe
and debilitating febrile illness. Vivax malaria can also result in severe disease with life-
threatening end-organ involvement similar to severe and complicated P. falciparum
malaria illness. Recent studies in Papua province, Indonesia (6), and Papua New Guinea
(7) highlight P. vivax as a major cause of malaria morbidity and mortality, particularly in
young infants and children, accounting for nearly as high a proportion of severe malaria

166