10. RISK FACTORS FOR UNCOMPLICATED AND
SEVERE VIVAX MALARIA
As in falciparum malaria ( Miller et al., 2002 ), host, parasite and socio-
geographic factors may explain the variance in the overall risk of severe
disease and death in vivax malaria, as well as specific severe manifestations.
10.1. Host Risk Factors
Young age is a risk factor for both uncomplicated and severe vivax malaria
(Section 7 ) ( Poespoprodjo et al., 2009 ), with infants and young children
at increased risk of severe anaemia (see Douglas et al., 2012 for review).
Gender may also influence risk of severe disease from P. vivax , with a higher
risk of hospitalisation in females apparent in both adults and children
( Tjitra et al., 2008 ; Kochar et al., 2010 ). This association needs confirmation
in other large series. Adults and children with malnutrition and other co-
morbidities are also at increased risk of severe and fatal disease (Section 7 ).
10.2. Haematinic Replacement
Iron deficiency protects against P. falciparum infection and severe disease ( Gwa-
maka et al., 2012 ) and supplementation may increase the risk of high parasi-
taemia infections ( Nyakeriga et al., 2004 ; Sazawal et al., 2006 ). Although there
are fewer data for P. vivax infection, a link has been reported between iron
supplementation and morbidity in vivax malaria, with haematinic treatment
during pregnancy being associated with an increased risk of maternal vivax
malaria ( Nacher et al., 2003 ). In children, the evidence is less clear. Sixteen
weeks of supplemental iron in prepubescent Papua, New Guinean school
children provided an overall haematological benefit compared with placebo
and did not affect the risk of vivax-associated morbidity ( Harvey et al., 1989 ).
A randomized trial from Peru demonstrated that iron plus zinc supplemen-
tation decreased morbidity (not otherwise specified) associated with vivax
malaria in children under 5 years of age, however iron supplementation alone
increased morbidity in those older than 5 years ( Richard et al., 2006 ).
10.3. Host Genetics
Genetic polymorphisms have been associated with both increased risk
(alpha and beta thalassaemia ( Williams et al., 1996 ; O'Donnell et al., 2009 ))
and decreased risk (Duffy antigen negativity ( Miller et al., 1976 ) and G6PD
deficiency ( Leslie et al., 2010 )) of P. vivax parasitaemia. The rarity of mor-
bidity from P. vivax in West Africa is attributed to the high prevalence of