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146 • JID 2006:194 (15 July) • Wildig et al.
MAJOR ARTICLE
Parvovirus B19 Infection Contributes to Severe
Anemia in Young Children in Papua New Guinea
James Wildig,
1,a
Pascal Michon,
2,a
Peter Siba,
3
Mata Mellombo,
2
Alice Ura,
2
Ivo Mueller,
2,3
and Yvonne Cossart
1
1
Department of Infectious Diseases and Immunology, University of Sydney, Australia;
2
Papua New Guinea Institute of Medical Research,
Madang, and
3
Papua New Guinea Institute of Medical Research, Goroka
(See the editorial commentary by Pasvol, on pages 141–2.)
Background. Severe anemia (hemoglobin level, !50 g/L) is a major cause of death among young children,
and it arises from multiple factors, including malaria and iron deficiency. We sought to determine whether infection
with parvovirus B19 (B19), which causes the cessation of erythropoiesis for 3–7 days, might precipitate some cases
of severe anemia.
Methods. Archival blood samples collected in the Wosera District of Papua New Guinea, from 169 children
6 months–5 years old with severe anemia and from 169 control subjects matched for age, sex, and time were
tested for B19 immunoglobulin M (IgM) by enzyme immunoassay and for B19 DNA by nested polymerase chain
reaction (PCR). A total of 168 separate samples from children in the Wosera District were tested for B19 IgG.
Results. A strong association between acute B19 infection (positive by both IgM and PCR) and severe anemia
was found (adjusted odds ratio, 5.61 [95% confidence interval, 1.93–16.3]). The prevalence of parvovirus B19 IgG
reached
190% in 6-year-olds.
Conclusions. B19 infections play a significant role in the etiology of severe anemia in this area of malarial
endemicity. Given the high levels of morbidity and mortality associated with severe anemia in such regions, the
prevention of B19 infection with a vaccine might be a highly effective public health intervention.
Severe anemia (hemoglobin level, !50 g/L) is very com-
mon among young children in regions where malaria
is endemic [1], accounting for an estimated 1 million
child deaths per year [2]. The etiology of severe anemia
in these children is complex, with a variety of factors—
including malaria and iron deficiency—contributing [3].
Parvovirus B19 (B19) is common worldwide; anti-
body studies have indicated that
150% of people are
infected during childhood. Higher rates have been re-
ported among children in some tropical areas [4, 5].
Outbreaks occurring at 3–6-year intervals have been
described [5, 6].
Received 20 December 2005; accepted 16 February 2006; electronically pub-
lished 14 June 2006.
Potential conflicts of interest: none reported.
Financial support: Biotrin International, Ireland (parvovirus IgM and IgG test
kits); PanBio Limited (Australia; assistance with shipping); University of Sydney,
Faculty of Medicine Postgraduate Research Support Scheme; and Daphne Goulston
Scholarship (travel assistance to J.W.).
a
J.W. and P.M. contributed equally to the study.
Reprints or correspondence: Dr. Yvonne Cossart, Dept. of Infectious Diseases
and Immunology, University of Sydney, D06, Sydney NSW 2006, Australia
(ycossart@infdis.usyd.edu.au).
The Journal of Infectious Diseases 2006;194:146–53
2006 by the Infectious Diseases Society of America. All rights reserved.
0022-1899/2006/19402-0003$15.00
B19 is tropic for red blood cell precursors in the
bone marrow, with acute infection causing impaired
erythropoiesis for 7–10 days and complete cessation for
3–7 days. The effect of this on hemoglobin level varies
by individual. In healthy adults, a decrease in hemo-
globin level of ∼20 g/L will occur [7, 8], whereas larger
decreases have been described in persons with iron de-
ficiency [9] and malaria [10, 11]. In persons with sickle-
cell disease [12] and other hemolytic disorders, a pre-
cipitous decrease in hemoglobin levels can be induced
through the combination of a high rate of red blood
cell destruction and complete cessation of red blood
cell production caused by B19. This has been termed
“transient aplastic crisis.”
After initial contact with B19, viral replication leads
to a dense viremia that starts to decline once specific
IgM is produced on day ∼9 [8]. Virus-induced bone-
marrow suppression begins to recover on day ∼16, and
the lowest hemoglobin level occurs soon after (figure
1) [7, 13, 14]. Thus, the simultaneous detection of B19
IgM and DNA is strongly indicative of acute infection.
B19 IgM usually becomes undetectable after 2–4 months,
depending on the initial level of response [15], although
persistence for up to 9 months has been reported [16].
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Parvovirus B19 and Anemia in Children • JID 2006:194 (15 July) • 147
Figure 1. Timing of changes in clinical and virological parameters dur-
ing acute parvovirus B19 infection in the immunocompetent individual.
Data are from various sources [7, 12–15]. RBC, red blood cell.
The rate of decrease in viremia is less predictable. The half-life
of B19 in blood is not known, but, even though the virus may
become undetectable soon after infection, clinical studies using
highly sensitive nested or real-time polymerase chain reaction
(PCR) methods have shown that B19 DNA can often be de-
tected 6 months or even longer after the onset of illness in
patients who have become IgM negative [17]. After infection,
IgG persists; thus, a person usually is infected only once in a
lifetime.
In 1990, it was suggested that B19 infection might be a
causative factor in some cases of severe anemia among young
children in areas where malaria is endemic [4]. In that study,
which was conducted in the Republic of Niger and apparently
coincided with a B19 infection outbreak, 54% of children with
severe anemia (hematocrit level,
!20%) showed evidence of re-
cent B19 infection. No control group was assessed, so rates of
B19 infection in children with and without anemia could not be
compared. Two subsequent studies, from Malawi [18] and Kenya
[3], found little evidence of acute B19 infection in any children
(anemic or control) over the course of 1 year of testing. In the
present article, we present the results of a retrospective case-
control study linking B19 infection to severe anemia in a highly
malarious area [19] of Papua New Guinea (PNG).
PATIENTS, MATERIALS, AND METHODS
Both case patients and control subjects were selected from ar-
chival blood samples collected between 1996 and 2002 from
children 6 months–6 years old who presented with presumptive
malaria (measured fever or reported febrile illness with no ob-
vious respiratory cause) at 2 health centers in Wosera District,
East Sepik Province, PNG. These samples had been collected
as part of ongoing routine malaria morbidity surveillance at
the PNG Institute of Medical Research malaria vaccine trial
site. Hemoglobin was measured at the time of sample collection
using the HemoCue system (HemoCue). Malarial infection was
defined as the detection of malarial parasites by microscopic
examination of the blood film; the different species of malaria
parasite were distinguished and examined individually in the
statistical analyses. All children were treated in accordance with
PNG national guidelines for malaria infection and severe ane-
mia (antimalarial treatment and oral or intramuscular iron
supplementation).
After samples lacking hemoglobin readings were excluded,
there were 11,441 samples with age, sex, blood-slide readings,
and hemoglobin measurement data available. Children with
hemoglobin levels of ⭐50 g/L (the World Health Organization
[WHO]–recommended cutoff for severe anemia]) were selected
as case patients. A control group of children with hemoglobin
levels of
150 g/L was selected and matched for age (83% within
1 month), sex, and time (most within 3 months and all with-
in 1 year). When spoiled or lost samples were excluded, 169
matched pairs of samples were available for testing. The mean
age of case patients and control subjects was 2.87 and 2.84
years, respectively, and 47.9% of children in both groups were
male (table 1). These pairs were tested for the presence of both
B19 IgM and DNA, because either can be a unique marker of
recent B19 infection, and the finding of both in the same spec-
imen is strongly indicative of acute infection. A total of 168
separate consecutive samples from children 6 months–10 years
old who presented to the same health centers in late 2000 with
presumptive malaria were subsequently selected for testing for
B19 IgG.
Stored plasma from the selected samples was tested for B19
IgM or IgG using the Biotrin Parvovirus B19 IgM or IgG EIA
kit (Biotrin International). The reaction wells were washed with
200–220 mL of wash solution per use, depending on the avail-
able equipment. Plasma samples that were stained with red
blood cells during the collection or storage process were in-
cluded. Otherwise, specimens were tested in accordance with
the manufacturer’s instructions. The IgM EIA kit has a reported
sensitivity of 86% and a specificity of 95% [20], and the IgG
EIA kit has a reported sensitivity and specificity of 100% [21].
These kits have been shown to have good specificity when they
are tested on serum samples from people with other infections
[22] and in comparison with other kits [23]. All case-control
samples were tested for IgM in duplicate (or in triplicate, if
the first 2 results differed). Case and control specimens were
tested side by side in 96-well plates. Because the samples were
stored at a remote field location, a portable Axiom M6 Mini-
photometer with a 450-nm filter (Axiom) was used to measure
the optical density of the test reactions. To allow for the mea-
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148 • JID 2006:194 (15 July) • Wildig et al.
Table 1. Comparison of age, hemoglobin (Hb) level, and malarial parasitemia in
case patients and control subjects.
Characteristic
Case patients
(Hb level, ⭐50 g/L)
(n p 169)
Control subjects
(Hb level,
150 g/L)
(n p 169)
Male sex 81 (47.9) 81 (47.9)
Age, mean SE, years 2.86 1.22 2.84 1.22
Hb level, mean SE, g/L 43 789 17
Plasmodium species found by microscopy
P. falciparum 123 (72.8) 67 (39.6)
P. vivax 17 (10.0) 27 (15.0)
P. malariae 2 (1.2) 4 (2.4)
P. ovale 0 (0.0) 1 (0.6)
Mixed infection
a
8 (4.7) 9 (5.3)
NOTE. Data are no. (%), unless otherwise indicated.
a
Mixed infection included 7 P. falciparum/P. vivax and 1 P. falciparum/P. malariae infection in case
patients and 1 each of P. falciparum/P. vivax, P. falciparum/P. malariae, and P. falciparum/P. vivax/P.
malariae infection in control subjects.
sured precision of the reading device, the equivocal range was
extended to 0.8–1.2 times the cutoff optical density.
DNA samples were extracted separately from plasma and
erythrocyte pellets of the selected samples (when available) us-
ing the QIAmp 96 DNA blood kit (Qiagen). Two oligonucle-
otide primer pairs were designed on the basis of the B19 ge-
nomic sequence (GenBank accession number NC_000883) and
used in a nested-PCR approach. Briefly, 1 mL of DNA template
(or PCR product from first-round PCR) was amplified by PCR
with 0.5 U of Ta q DNA polymerase (Invitrogen) and supplied
buffer, 1.5 mmol/L MgCl
2
, and 200 mmol/L each dNTP in
2 consecutive 15-mL reactions, using oligonucleotide primers
(400 nmol/L each) specific for human erythrovirus genotype 1
(B19), as follows: first-round forward primer B19-1F (5
-CTG
TGG TTT TAT GGG CCG CC-3
) and reverse primer B19-1R
(5
-AGG TGT GTA GAA GGC TTC TTC CC-3
), followed by
nested forward primer B19-2F (5
-GGG AAA AGC TTG GTG
GTC TGG G-3
) and reverse primer B19-2R (5
-GCG CGG GGT
TTC AGT GTT CC-3
). Both reactions consisted of 2 min at
94C and 35 cycles of 30 s at 94C,30sat60C, and 1 min
at 72C. To ensure specificity, PCR products of the expected
sizes for both reactions were originally sequenced and checked
with the DNA database, to verify that the appropriate target
was amplified. A sample with a positive PCR result in either
plasma or the erythrocyte pellet was regarded as positive for
statistical analysis.
Statistical analyses. To account for matching, the case-
control data were analyzed with either McNemar’s x
2
test or
with conditional logistic regression. Correspondence between
PCR and EIA results and the prevalence of malarial infections
was tested using Pearson’s x
2
test. All analyses were done using
Stata statistical software (version 7.0; StataCorp). Stata software
uses an uncorrected numerator for the McNemar’s test—that
is, . An age-specific prevalence curve for IgG data
2
(n ⫺ n )
12 21
was fitted using a generalized additive model for binomial data
involving fourth-order splines of the S-PLUS package (version
6.0; Insightful).
Ethics approval. Ethics approval for the study was given
by the PNG Medical Research Advisory Committee, and that
for the IgM testing was given by the University of Sydney
Human Ethics Committee.
RESULTS
For each specimen, 2 independent B19 diagnostic results were
obtained: the presence or absence of B19 IgM or DNA. Positive
results for both in the same specimen were regarded as strongly
indicative of an acute B19 infection.
Of 169 case patients with hemoglobin levels of
!50 g/L, 51
(30.2%) were positive, 95 (56.2%) were negative, and 23
(13.6%) had equivocal results for B19 IgM, whereas, of control
subjects, 21 (12.4%) were positive, 126 (74.6%) were negative,
and 22 had equivocal results (13.0%). All analyses were done
once with equivocal readings considered to be negative and
once with all case-control pairs with equivocal IgM values omit-
ted from the analysis. Because the results of both analyses did
not differ significantly (data not shown), only results from the
former analyses (equivocal p negative) will be presented.
Acute B19 infection, defined as both IgM EIA and PCR
positivity, showed the strongest association with severe anemia
(odds ratio [OR], 5.0). Independently, only IgM positivity (OR,
3.0)—and not PCR positivity (OR, 1.25)—was significantly as-
sociated with severe anemia (table 2). If only the samples with
the highest optical-density values in IgM testing (i.e.,
13 times
the cutoff value) were considered, 25 of 26 were from case
patients, and 21 of these were also positive by PCR (figure 2).
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Parvovirus B19 and Anemia in Children • JID 2006:194 (15 July) • 149
Table 2. Association of parvovirus B19 IgM and polymerase chain reaction (PCR) pos-
itivity with severe anemia.
IgM PCR IgM + PCR
a
Control subjects
+ ⫺ + ⫺ + ⫺
Case patients
+ 6 45 11 35 1 25
⫺ 15
103 28 95 5 138
Significance
OR (95% CI) 3.00 (1.64–5.79) 1.25 (0.74–2.13) 5.00 (1.88–16.7)
McNemar’s x
2
test (P) 15.0 (!.001) 0.8 (.38) 18.1 (!.001)
NOTE. Data are the no. of matched case-control pairs. +, positive; ⫺, negative; CI, confidence interval;
OR, odds ratio.
a
Only double-positive samples were scored as positive. Double positivity is indicative of acute parvovirus
B19 infection.
Figure 2. Evidence of acute parvovirus B19 infection in case patients and control subjects. Optical density readings for B19 IgM testing (as multiples
of the cutoff optical density value) were plotted against hemoglobin (Hb) levels for case patients and control subjects. Gray-shaded area, equivocal
range (0.8
! OD ! 1.2); black points, polymerase chain reaction (PCR)–positive samples; white points, PCR-negative samples.
No clear temporal clustering of either IgM- or PCR-positive
samples was observed.
In the case patients, but not in the control subjects, PCR
positivity was significantly associated with IgM positivity (table
3). Among the case patients, 14.8% were positive for IgM only,
11.8% were positive for B19 PCR only, and 15.4% were positive
for both, compared with 8.9%, 19.5%, and 3.6%, respective-
ly, in control subjects ( [df, 3]; ). The ORs
2
x p 19.5 P ! .001
(vs. double-negative samples) for association with severe ane-
mia were 5.32 for both IgM and PCR–positive results, 1.89 for
IgM-positive results only ( ), and 0.61 for PCR-positiveP p .075
results only (table 4).
Malarial infections were significantly more frequent in case
patients (150/169 [88.8%]) than in control subjects (108/169
[63.9%]) ( ). Significantly more of these were P. fal-P
! .0001
ciparum infections (131/150 [87.3%]) than non–P. falciparum
infections (76/108 [70.4%]) ( ) (table 1). Both P. fal-P p .001
ciparum and non–P. falciparum infections were associated with
an increase in risk of severe anemia, compared with that in
uninfected children (OR, 5.75 [95% confidence interval {CI},
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150 • JID 2006:194 (15 July) • Wildig et al.
Table 3. Prevalence of viremia in case patients and control sub-
jects with and without parvovirus B19–specific IgM antibody.
IgM antibody result
Case patients
Control
subjects
Overall
+ ⫺ + ⫺ + ⫺
PCR result
+ 26 20 6 33 32 53
⫺ 25 98 15 115 40 213
Significance
x
2
test
a
(P) 20.8 (!.001) 0.4 (.52) 18.1 (!.001)
NOTE. +, positive; ⫺, negative.
a
x
2
test for the association between IgM and polymerase chain reaction
(PCR) results.
Table 4. Risk of severe anemia associated with parvovirus B19 and Plas-
modium infection status.
Positive result
B19 only
B19 + Plasmodium
OR (95% CI) P OR (95% CI) P
P. falciparum 5.84 (1.90–12.0) !.001
Non–P. falciparum species 1.86 (0.77–4.50) .169
B19, IgM only 1.89 (0.94–3.81) .075 1.89 (0.88–4.08) .102
B19, PCR only 0.61 (0.31–1.21) .158 0.50 (0.23–1.09) .082
B19, IgM + PCR 5.32 (2.00–14.1) .001 5.53 (1.90–16.1) .002
NOTE. All odds ratios (ORs) were calculated by (multivariate) conditional logistic regression,
in comparison with B19 (and Plasmodium)–negative samples. CI, confidence interval; PCR,
polymerase chain reaction.
2.93–11.26]; for P. falciparum infection and OR, 2.16P ! .001
[95% CI, 0.94–5.00]; for non–P. falciparum infection).P p .07
We then investigated the interaction between B19 and ma-
larial infections in detail (table 4). Multivariate analyses showed
that the risks of severe anemia associated with Plasmodium and
B19 infections were independent of each other ( [df,
2
x p 7. 5 7
6]; , likelihood-ratio test). Acute B19 infection (i.e., PCR-P p .27
and IgM-positive results) was associated with an increase in the
risk of severe anemia comparable to that associated with P. fal-
ciparum infections (multivariate OR, 5.53 vs. 5.84) (table 4).
In the serum samples from 168 children 1–10 years old from
the study area, the age-specific prevalence of B19 IgG was found
to increase rapidly during the first years of life (figure 3), with
60% of children
!2 years old already positive for B19 IgG.
Levels continued to increase until age 6 years, when the prev-
alence of IgG plateaued at ∼90%.
DISCUSSION
The present results demonstrate that acute B19 infection is a
major contributor to severe anemia in young children in the
study area, where malaria is endemic. Indeed, the association
found between acute B19 infection (defined as both B19 IgM
and PCR positivity) and severe anemia (multivariate OR, 5.53)
is comparable to that found between P. falciparum infection (a
leading cause of anemia in areas of endemicity) and anemia
(multivariate OR, 5.84).
This finding contrasts the situation in developed countries,
where B19-induced severe anemia is rare, except in individuals
with hemolytic disorders. A possible reason for this geograph-
ical difference is that, in tropical areas of developing countries,
an underlying mild-to-moderate level of anemia is very com-
mon in young children [3]. Cross-sectional surveys in the Wo-
sera and neighboring populations of PNG found that 5%–11%
of children had a hemoglobin levels of
!7 g/dL (I.M., unpub-
lished data). This anemia arises from multiple factors, such as
malnutrition (including iron deficiency), current and past ma-
laria, and other infections, including hookworm [24]. B19 in-
fection causes a 20-g/L decrease in hemoglobin level, even in
previously healthy adult volunteers without hemolytic disease
[7]. Thus, when acute B19 infection strikes children in a pop-
ulation where anemia is common, the resulting decrease in
hemoglobin level, when superimposed on a preexisting mod-
erate level of anemia, may be the proverbial “last straw” that
pushes an already low hemoglobin level below the 50-g/L level
that defines severe anemia, even in the absence of hemolysis.
By contrast, children in developed countries with normal he-
moglobin levels are untroubled by a transient 20-g/dL decrease
in hemoglobin level. Clearly, any children in PNG with a he-
molytic disorder would have an even larger decrease in he-
moglobin levels if they developed B19 infection, and they might
be even more prone to B19-induced severe anemia. Although
hemoglobin S is not known to occur in PNG, glucose-6-phos-
phate-dehydrogenase (G6PD) deficiency has been noted to be
present in 8.7% of people in a nearby region [25]. It is thus
conceivable that at least part of the excess risk of severe anemia
after B19 infection is concentrated in children with G6PD de-
ficiency. Other red blood cell polymorphisms that are common
in PNG include the Gerbich blood group and a-orb-thal-
assemia [26]. However, among 306 children with genotypic data
available, Gerbich blood group (band 3 deletion) and a-thal-
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Parvovirus B19 and Anemia in Children • JID 2006:194 (15 July) • 151
Figure 3. Age-specific prevalence of parvovirus B19 IgG in 168 children from the study area who were !10 years old. All children were selected
from among patients with presumptive malaria attending the Kunjingini health center during the second half of 2002. The age-specific mean (solid
line) and binomial SEs (dashed lines) were predicted using fourth-order regression splines. White circles, IgG-negative children; black circles, IgG-
positive children.
assemia were not significantly associated with an increase in
the risk of severe anemia associated with B19 infection (P.M.,
unpublished data).
Data on the prevalence of B19 IgM and DNA in children
living in tropical areas is very limited. Although studies of adult
blood donors in the United States have indicated a prevalence
of B19 IgM of ∼ 1%, we found a much higher prevalence of
B19 IgM, 12%, in the control population. The characteristics
of our control group may offer some explanation for this, in
that they were children, they had had a recent febrile illness,
and they lived in PNG. IgG studies have indicated that B19
infection is much more common in children living in tropical
areas. Indeed, our IgG testing showed that 90% of children in
the Wosera District had evidence of previous B19 infection by
age 6 years. Furthermore, B19 causes a febrile illness, so the
febrile children used as control subjects were more likely to
have had IgM from an acute infection than were asymptomatic
children. These factors help to explain the high prevalence of
IgM and, thereby, the high number of equivocal results in our
study. With a high rate of positive results, numerous samples
will be from children who were recently positive and whose
antibody levels are decreasing, passing through the equivocal
range as they fall.
Some studies have indicated that IgM testing yields more
false-positive results in populations with other infections or
autoantibodies. It is true that a number of the children sampled
in the present study were likely to have had other infections,
whereas the rate of autoantibodies in this population was not
known. However, although older IgM assays had problems with
specificity under these circumstances, the Biotrin B19 IgM and
IgG EIA kits that we used have been shown to perform well
with regard to specificity in such samples. Moreover, because
case patients and control subjects were selected from the same
population, the false-positive rates should have been similar in
both and should not have had a major influence on the cor-
relation found between B19 infection and severe anemia.
The introduction of sensitive PCR tests for B19 in recent
years has revealed that many patients retain detectable DNA
for weeks or months after specific IgM becomes undetectable,
at ∼3 months after infection [13, 27]. This may well explain
the high prevalence of B19 DNA that we found in both case
patients and control subjects. The average age of the children
in our study was a little less than 3 years, when the prevalence
of B19 IgG is already 60%. Assuming an added PCR persistence
of 3 months the after the loss of IgM, protection for the first
6 months of age by maternal antibody, and an endemic pattern
of infection, random testing of 3-year-olds in this environment
would be expected to detect B19 DNA in 10% of them. We
detected a not-dissimilar rate of 15.6%.
Although many of the children with severe anemia tested
positive for both B19 IgM and DNA, our study revealed nu-
merous children who tested positive for only 1 of the 2. Given
the complex temporal nature of the association between levels
of viremia and IgM (figure 1), this is not surprising. At least
2 studies have demonstrated similar discrepancies between PCR
and IgM test results in B19 infection, and those researchers
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152 • JID 2006:194 (15 July) • Wildig et al.
recommended that both be used to diagnose of recent infection
[14, 28]. The fact that the double-positive specimens showed
the strongest correlation with severe anemia is expected, be-
cause this pattern of results is most likely to be seen around
the time of hemoglobin suppression (figure 1).
Our finding of a significant association between acute B19
infection and severe anemia is reminiscent of the observations
in Republic of Niger [4] but contrasts with the results of 2
other studies, from Malawi [18] and Kenya [3]. The fact that
no association was found in these latter articles is likely to have
stemmed from the short duration of the studies, which seems
to have coincided with periods of low B19 transmission in the
respective communities. Indeed, in the Malawi study, only 13%
of children were B19 IgG positive, whereas, in the Wosera Dis-
trict, 60% of children were IgG positive by age 2 years. B19
often occurs in outbreaks separated by long periods of inactivity
in both temperate and tropical areas [5, 29, 30]. The present
study, which used archival samples collected over the course
of a 6-year period, was able to achieve sufficient sample size
to clearly demonstrate the association between B19 and severe
anemia. However, the use of archival specimens also meant that
the choice of control subjects in this retrospective analysis was
limited by the availability of samples. Both case patients and
control subjects were obtained from the same population of
children presenting to health centers with presumptive malaria
(i.e., recent fever with no obvious respiratory cause) between
1996 and 2002. Because acute B19 infection is accompanied by
fever [31], it is likely to be more common among these clini-
cal control subjects than among asymptomatic children in the
community. The presumably higher prevalence of B19 infection
in the available control subjects is likely to affect the estimates
of the association of B19 infection with severe anemia in a
conservative way, so the association is likely to be less pro-
nounced in the present study than would have been the case
if asymptomatic control subjects from the community had been
used for comparison.
Our study was based in the Wosera District, an area where
malaria is highly endemic [19], and P. falciparum infection is
an important risk factor for severe anemia. Interestingly, anal-
ysis of the results showed that the association of B19 infection
with severe anemia is not altered by malarial infections and
that the effects of both are additive. However, longitudinal
studies in young African children have shown that hemoglobin
levels are more closely related to average parasitemia during
the preceding 90 days than to concurrent infections [32]. In
addition, hematological responses after symptomatic malarial
infections are often characterized by an initial decrease in he-
moglobin levels, followed by an eventual recovery through in-
creased erythropoiesis [33]. The interaction of B19 and acute
malaria infections may thus be strongest when B19-induced
erythropoietic suppression coincides with the period of in-
creased erythropoiesis during the 1–4 weeks after treatment
rather than with the acute malarial episode. The interactions
between the 2 infections can thus only be properly investigated
in longitudinal studies. The present results nevertheless indicate
that controlling B19 infection is likely to lower the risk of severe
anemia in all children, irrespective of their malaria status.
Severe anemia is a major cause of morbidity and mortality
in young children in areas where malaria is endemic [2]. Treat-
ment with blood transfusion is limited in availability, is costly
to patients and health-care facilities, and carries the risk of
transmission of bloodborne pathogens, including HIV (even
when anti-HIV screening is performed) [34]. Clearly, the pre-
vention of severe anemia should be a major priority [35].
Further studies are needed to estimate the effects of B19 in-
fection in other regions where malaria is endemic. However,
the strength of the association between B19 and severe anemia
observed in the present study indicates that the prevention of
B19 infections is likely to result in a significant reduction in
the burden of severe anemia in young children in these regions.
Efforts to develop a safe and effective vaccine [36] against B19,
which are already under way, should be strengthened, with the
view of its possible use in the prevention of severe anemia
among young children, alongside other measures, including
malaria control and nutritional supplementation.
Acknowledgments
We thank the staff of the Papua New Guinea Institute of Medical Re-
search in Goroka, Madang, and Maprik; the staff of the Department of
Infectious Diseases, University of Sydney; Lawrence Rare and the health
center surveillance nurses, for the collection of the samples; Thomas Adi-
guma, for managing the databases and helping with the selection of control
subjects; and Livingstone Tavul, for helping with DNA extraction.
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