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haemoglobin with successive episodes of malaria caused by reinfection and
relapses. Despite these limitations, the association between vivax infection
and severe anaemia is strong, particularly in infancy ( Tjitra et al., 2008 ; Poe-
spoprodjo et al., 2009 ; Genton et al., 2008 ).
Severe anaemia associated with P. vivax infection tends to be even
more strongly skewed to childhood than P. falciparum , and in regions with
comparatively high endemicity, the first year of life in particular ( Poespo-
prodjo et al., 2009 ). In Papua, Indonesia, 36% of all infants under the age
of 3 months, who were admitted to hospital with vivax malaria, had severe
anaemia (haemoglobin <5 g/dl) compared with 18% of infants with P. falci-
parum malaria ( Poespoprodjo et al., 2009 ). Across the border in Papua, New
Guinea, 1.6% of all children with vivax malaria presenting to community
clinics had severe anaemia ( Genton et al., 2008 ). At a hospital in Delhi,
India, 20% (7/35) of children with vivax malaria diagnosed in the paedi-
atric outpatient or emergency department had severe anaemia ( Kaushik
et al., 2012 ) and in Manaus, Brazil, 9% of children of 0-14-years old were
admitted to an intensive care unit with vivax malaria fulfilled criteria for
severe anaemia ( Lanca et al., 2012 ). None of the seven children with severe
anaemia in the latter study subsequently died.
Cross-sectional data show that the apparent severity of haematological
morbidity associated with P. vivax in childhood is not simply due to selection
bias. In the D'Entrecasteaux Islands, children between 0 and 6 years of age
with vivax malaria had a significantly lower mean haemoglobin concentra-
tion (8.7 g/dl) than children with P. falciparum (9.0 g/dl) ( Spencer, 1966 ).
One speculative reason for the significant haematological morbidity
associated with vivax malaria in early childhood is that there is a greater
pool of young red blood cells (RBCs) in circulation and thus more potential
host cells susceptible to invasion (Douglas et al., 2012). A further potential
explanation is that severe vivax-associated anaemia in childhood is a con-
sequence of multiple additive haematological insults from frequent relapses.
However, severe anaemia is commonly seen in children <2 months of age
in Papua, Indonesia ( Poespoprodjo et al., 2009 ). Multiple relapses cannot
explain severe anaemia at such an early age. Sustained parasitaemia, initially
subclinical, from congenital malaria may be an alternative explanation in
this age group.
Infection with gastrointestinal helminths can cause anaemia through
chronic blood loss. There is good evidence that mixed infection with hook-
worm and falciparum malaria causes an additive reduction in haemoglobin
in preschool children ( Brooker et al., 2007 ). To our knowledge, only one
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