Community study of toxoplasma antibodies in urban and rural schoolchildren aged 4 to 18 years.

Abstract

To estimate the prevalence of toxoplasma antibodies in schoolchildren and their association with clinical and environmental data, antibody titres were measured in 1276 children aged 4 to 18 years attending primary and secondary schools. Environmental and clinical data were obtained by questionnaire. Altogether 12.8% (163/1276) of children had antibodies to Toxoplasma gondii with no difference between the sexes. Seroprevalence was higher in country children (16.6% (50/302)) than town children (10.2% (75/737)). The proportion testing positive increased with age in both town and country children. No association with cat ownership was found. Toxoplasma seropositivity was associated with a positive toxocara titre, having had a bitch whelp in the past two years, and having an unwormed dog at home. Lack of energy or tiredness in the last 12 months were the only clinical features associated with a positive titre.

Full text

Page 1

Community study of toxoplasma antibodies in
urban and rural schoolchildren aged 4 to 18 years
Mervyn R H Taylor, Bernadette Lennon, Celia V Holland, Mary CaVerkey
Abstract
To estimate the prevalence of toxoplasma
antibodies in schoolchildren and their
association with clinical and environmen-
tal data, antibody titres were measured in
1276 children aged 4 to 18 years attending
primary and secondary schools. Environ-
mental and clinical data were obtained by
questionnaire.Altogether
1276) of children had antibodies to Toxo-
plasma gondii with no diVerence between
the sexes. Seroprevalence was higher in
country children (16.6% (50/302)) than
townchildren (10.2%
proportion testing positive increased with
age in both town and country children. No
association with cat ownership was found.
Toxoplasma seropositivity was associated
with a positive toxocara titre,having had a
bitch whelp in the past two years,and hav-
ing an unwormed dog at home. Lack of
energy or tiredness in the last 12 months
were the only clinical features associated
with a positive titre.
(Arch Dis Child 1997;77:406–409)
12.8%(163/
(75/737)). The
Keywords: toxoplasma; seroprevalence; community
Toxoplasmosis is an important infection of
humans. The natural host of Toxoplasma gondii
is the cat. Congenital infection of the human
fetus may cause abortion, blindness, mental
retardation, and other neurological disease
while acquired infection is usually more benign
in the immunocompetent subject.
While the seroprevalence of toxoplasmosis in
adults, especially pregnant women, has been
recorded in many studies, we have found no
community based study of toxoplasma sero-
prevalence in schoolchildren in the British Isles
and only one in Europe.1We record here the
seroprevalence of T gondii infection in 1276
schoolchildren.
Subjects and methods
STUDY POPULATION
The investigation formed a sequel to a report of
Toxocara canis infection in schoolchildren in
which details of the study population are
given.2In that study, 30 schools were randomly
selected from the Department of Education’s
list of schools for the county of Dublin and the
adjoining counties of Wicklow and Kildare.
Fifteen schools agreed to take part. Consent
forms and questionnaires were sent to parents
for completion. Questionnaires were returned
for 2818 children and 2134 of these provided
venepuncture blood samples from which hae-
matology results were obtained. Bloodspots
from the venepuncture specimens were taken
onto Guthrie cards from 1276 children’s sam-
ples in seven schools. There were 652 girls and
624 were boys, which is similar to the sex
distribution of the 1991 national census for this
age range. The ages of those providing Guthrie
card samples was from 4 to 18 years. Ages are
given as completed years of age so that ‘6 years’
denotes a child >6 and <7 years of age.
Children were designated as having an urban
or rural residence depending on the location of
the school as children attend their local
primary school. Written parental consent had
been obtained for venepuncture but blood was
taken only if the child consented at the time of
phlebotomy. Parents of some smaller children
were present when blood was taken. The study
was approved by the ethics committee of the
Federated Dublin Voluntary Hospitals and St
James’s Hospital.
TOXOPLASMA SEROLOGY
The modified latex agglutination test for T
gondii antibody (Eiken Toxoreagent) was used
to screen the Guthrie card samples. Equivalent
serum titres are 4.13 times higher than the
results obtained using this method.3A titre of
>1:4 is regarded as positive. Toxocara titres
were measured as previously reported.2
QUESTIONNAIRE DATA
Questionnaire data were available from the
toxocara study questionnaire and the replies
provideddata forlifetime
asthma, eczema, hay fever, earth eating, thumb
or finger sucking, convulsion; the presence, in
the past two years of cats, dogs, birds, fish, and
the birth of puppies in and around the home;
the 12 month prevalence of abdominal pain,
nausea, vomiting, headache, cough, wheeze,
poor appetite, lack of energy or tiredness,
behaviour upset, fever, and skin rash. Those
with a dog at home were asked whether it was
wormed once a year (or more often). The ?2
test was used for statistical analysis.
prevalence of
Results
Altogether 12.8% (163/1276) of samples
tested positive. There was no diVerence
between the sexes: girls 12.7% (83/652), boys
12.8% (80/624). The prevalence of positive
results increased significantly with increasing
age (?225.82, df 11, p = 0.0069 after combin-
ing age groups 4 and 5 and 16, 17, and 18 to
provide adequate numbers; table 1).
Altogether 87.2% (1113/1276) of the study
population had negative titres, 1.6% (20) had
titres >1:4 and <1:16, 1.9% (24) had titres
Archives of Disease in Childhood 1997;77:406–409 406
Department of
Paediatrics, Trinity
College Dublin and the
National Children’s
Hospital, Harcourt
Street, Dublin
M R H Taylor
Department of
Microbiology, Rotunda
Hospital, Dublin
B Lennon
Department of
Zoology, Trinity
College Dublin
C V Holland
Royal College of
Surgeons in Ireland,
Dublin, Department of
Microbiology, Rotunda
Hospital and the
Children’s Hospital,
Temple Street, Dublin
M CaVerkey
Correspondence to:
Dr M R H Taylor,
Department of Paediatrics,
National Children’s Hospital,
Harcourt Street, Dublin 2,
Ireland.
Accepted 21 June 1997

Page 2

>1:16 and <1:64, and 9.3% (119) had titres
>1:64 There was an overall rise in the
proportion of children with titres of >1:64
(equivalent to a serum titre of >1:264) with
increasing age (fig 1).
Country children were more commonly
seropositive than town children (table 1).In the
population examined the oldest country child
was 13.35 years, so the town/country compari-
son was made for children <13.35 years. Alto-
gether 16.6% (50/302) country children were
positive while the figure for town children was
10.2% (75/737) (?28.239, df 1, p = 0.0041,
diVerence = 6.4%, 95% confidence interval
(CI) 1.7% to 11.1%).
Positive results were no more common in
those with a cat, dog, bird, or fish in or around
the house in the past two years. There was no
association between seropositivity and having a
bitch whelp at any time. However 32.5% of
those who were seropositive had a bitch whelp
in the past two years while the figure was
16.9% for those who were seronegative (?2
5.526, df 1, p = 0.0187, diVerence = 16.6%,
95% CI 0.4% to 30.8%). There was a
significant association between having a posi-
tive toxocara titre (>1:50) and having a
positive toxoplasma titre (?235.74, df 1, p <
0.0001). Of the toxoplasma positive children
51.9% (82/158) were toxocara positive while
28.3% (304/1075) of the toxoplasma negative
children were toxocara positive (diVerence
=23.6%, 95% CI 15.4% to 31.9%).
There was an association between not
worming dogs once a year or more often and a
positivetoxoplasma
wormed their dogs 11.3% (50/444) tested
positive while 19.2% (29/151) who did not
were positive (?26.176, df 1, p=0.013 diVer-
ence = 7.9%, 95% CI 1.0% to 14.8%).
Toxoplasma infection does not cause eosi-
nophilia, but more seropositive (45.3%) than
seronegative children (35.8%) had an eosi-
nophil count of >0.4 × 109/l (?25.458, df 1, p
= 0.0195, diVerence = 9.5%, 95% CI 1.3% to
17.7%). However this association was not
significant at higher cut oV levels for the
eosinophil count, which are more appropriate
values for eosinophilia.4
Of the clinical features examined by ques-
tionnaire only the answer to one question was
associated with a positive titre (In the last 12
months has your child had any of the
following?—lack of energy or tiredness.) Of the
seronegative children 14.5% (158/1093) com-
plained of lack of energy or tiredness while
21.3% (34/160) of the seropositive children did
so (?24.966, df 1, p = 0.0259, diVerence =
6.8%, 95% CI = 0.12% to 13.5%). There was
no significant diVerence in the proportion
reporting lack of energy or tiredness between
those with titres >1:4 and <1:64 and those
with titres >1:64 but the numbers in the
first group were small (fig 1). There was
no association with earth eating or digit
sucking.
titre. Ofthosewho
Discussion
The major application of testing Guthrie card
samples is to study congenital disease; however
the samples may also be used for other applica-
tions. The modified latex agglutination test for
T gondii antibodies when used on Guthrie card
eluates detected 98.8% of positive serum sam-
ples, with 100% specificity when compared to
the standard latex agglutination test. The two
eluates in which antibody was not detected
came from patients with equivocal results by
the standard test.3The standard Eiken latex
test has been found to have a sensitivity of 99%
and a specificity of 81%.5Other methods for
detecting toxoplasma antibodies (such as the
IgM immunosorbent agglutination assay) can
detect low levels of specific antibody which
may not be detected by the toxoplasma dye test
or latex agglutination test.6In the same study
comparison of dye test results obtained from
filter paper eluates and from serum samples
showed that the lowest level of toxoplasma spe-
cific IgG detected from filter paper eluates was
10 IU. This lower limit may also apply to the
latex agglutination test applied to Guthrie card
samples in which case antibody levels below 10
IU will have been falsely recorded as negative
and so the recorded seropositivity rate will be
lower than that which would have been found
using blood samples and the toxoplasma dye
test. While Guthrie card samples can be tested
for specific IgM this estimation was not under-
taken in the present study because of the cost
involved.
We have found no reports of community
based studies of toxoplasma antibody levels in
Table 1
in each age group
Number and percentage of schoolchildren testing positive for T gondii antibodies
Age group
(years)
All childrenCountry Town
NoNo (%) positive NoNo (%) positive NoNo (%) positive
4+5
6
7
8
9
10
11
12
13
14
15
16–18
96
103
126
122
122
149
167
132
73
69
65
52
6 (6.3)
7 (6.8)
18 (14.3)
16 (13.1)
12 (9.8)
17 (11.4)
26 (15.6)
23 (17.4)
3 (4.1)
16 (23.2)
9 (13.8)
10 (19.2)
40
37
51
33
37
38
37
26
3
3 (7.5)
3 (8.1)
7 (13.7)
8 (24.2)
4 (10.8)
3 (7.9)
13 (35.1)
9 (34.6)
0
56
66
75
89
85
111
130
106
70
69
65
52
3 (5.4)
4 (6.1)
11 (14.7)
8 (9)
8 (9.4)
14 (12.6)
13 (10)
14 (13.2)
3 (4.3)
16 (23.2)
9 (13.8)
10 (19.2)
Figure 1
Titres of >1:4 and <1:16 are recorded as 1:4,those >1:16 and <1:64 as 1:16,and those
>1:64 as 1:64.Equivalent serum titres are 4.13 times higher than those from the Guthrie
cards,so that a titre of >1:64 is equivalent to a serum titre of >1:264.
The percentage of children with antibody titres to T gondii in each age group.
18
16
12
14
10
6
8
4
2
0
1:4
Age (years)
1:161:64
% Children
4+56789 101112 13141516–18
Community study of toxoplasma antibodies
407

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schoolchildren in the British Isles and only one
in Europe.1Huldt et al in a community based
study of 15 to 16 year old Scandinavian
children found a seroprevalence of 19% in girls
and 14% in boys.1An exact seroprevalence rate
for other age groups was not recorded. In con-
trast to the present study they reported that
antibodies were more common in girls than
boys at all ages. Walker et al reported data from
small numbers of hospital based South York-
shire children gathered into five year age
groups over the years 1988–90.7They used the
Eiken Toxoreagent latex agglutination test for
analysis.All of their rates were lower than those
of the equivalent age group in the present study
(table 2).Etheredge and Frenkel examined 760
Panamanian children aged 0 to 12 years from
13 localities and reported values from 0% to
45%.8They failed to find an association with
age or sex.The zero prevalence rates were from
three islands where toxoplasma infection was
not found in the local cats.Huldt et al found no
association between antibody titres and the
presence of cats in the family or the consump-
tion of raw meat by family members.1
The reason for the rise in quantitative titres
(fig 1) with age is not clear. An hypothesis
would be that the increase is a reflection of
increasing ‘exposure years’ as the children get
older. Multiple minor infections might at first
produce low antibody levels and later higher
levels.
Frenkel et al, in a study of toxoplasma trans-
mission to children, reported a relative risk for
contact with nursing dogs which was higher
than the relative risk for cats.9It is of interest
that this association between nursing dogs and
toxoplasma antibodies should be found both in
Panama and in Europe.In the present study no
association was found with any of the pets or
working dogs in or around the home, other
than for having had a bitch whelp in the past
two years and for having unwormed dogs.
Frenkel et al suggested that dogs might be
instrumental in mechanical transmission by
eating or rolling in cat faeces,9but this hypoth-
esis seems tenuous as in their data dog contact
alone was associated with a seropositivity rate
of 4.2% and no contact with dog or cat was
associated with a rate of 14.4%. However, the
association with dog contact is further sup-
ported by the association between toxoplasma
and toxocara seropositivity. It may be that this
association and the association with unwormed
dogs indicate an alternative route of infection
involving dogs or are merely markers for
suboptimal animal husbandry and lax hygiene
where animals are concerned. The lack of
association with cat ownership suggests that
either most infection is acquired through the
food chain or other routes of ingestion or that
environmental contamination by cats is so
widespread that owning a cat has little eVect on
the level of exposure to toxoplasma infection.
No information on the children’s feeding hab-
its was available from the questionnaire.
With the exception of the 10 year age group,
in all age groups up to 12 years a higher
proportion of country children than town chil-
dren had titres >1:64 (table 1). By the age of
13 years the cumulative percentage of country
children with titres >1:64 was 12.4% (37/299)
while that for town children was 7.1%
(51/719). These findings are in keeping with
those of French et al who showed (in adults) a
negative association with animals with a 9.4%
seroprevalence in stock handlers with intimate
animal contact but little land contact and a
34.9% seroprevalence rate in adults working
the land.10Beattie also reported a higher preva-
lence of dye test positivity in adult country
dwellers than town dwellers.11
The finding of lack of energy or tiredness in
21.3% of seropositive children is in keeping
with the report of Beverley and Beattie that
fatigue was a common and, in some cases, a
long continued feature.12Their study group of
30 subjects included both adults and children.
In the present study the questionnaire only
inquired about the previous 12 months regard-
ing this symptom.
Using the data it is possible to extrapolate
beyond the data envelope to obtain an estimate
of the congenital infection rate. This extrapola-
tion extends two years below the youngest
group of subjects and involves data which show
considerable year to year variation. Any esti-
mate is likely to be crude. If the seropositivity
rate is extrapolated using all the data an
estimate for 1 year olds is 2.2% seropositive
and for those 6 months old 1.6% ( y = 1.181x
+ 1.016. R squared for this regression = 43.4%
(y = the percentage of children seropositive and
x = the age in years)). If the country children
are excluded in an attempt to reduce variation
in the data these figures become 0.9% and
0.3% (y = 1.222x −0.336;R2for this regression
= 44.7%). We do not regard these figures as
providing anything more than an indication
that the congenital toxoplasmosis rate may be
low.Taking logarithms and applying non-linear
regression models do not help the fit of the
curve.
We thank the children, parents, and schools; the National Chil-
dren’s Hospital staV (especially Mrs B McNulty and Miss L
Thompson); Dr Myra O’Regan, Mr J P Larragay and the Com-
puter Laboratory staV, Trinity College Dublin for their
assistance.
This work was supported by the Garfield Weston Foundation,
the New Moorgate Trust Fund, the Sir Samuel Scott of Yews
Trust, the Trinity Trust, the Ladies’ Guild of the National Chil-
dren’s Hospital and the Child Health Foundation,Children’s
Hospital, Temple Street, Dublin.
1 Huldt G, Lagercrantz R, Sheehe PR. On the epidemiology
of human toxoplasmosis in Scandinavia especially in
children. Acta Paediatr Scand 1979;68:745-9.
2 Holland CV, O’Lorcain P, Taylor MRH, Kelly A. Sero-
epidemiology of toxocariasis in school children.Parasitology
1995;110:535-45.
Table 2
hospital based South Yorkshire7series and in the present
study.The absolute values are given in brackets.Both
studies used the Eiken Toxoreagent latex agglutination test
for analysis.The children in the present study were aged 4
to 18 years
Seroprevalence rate,as a percentage,reported in a
Age (years)
South Yorkshire
1988–90 (hospital
study)
Ireland 1992–3
(community study)
0–5
6–10
11–15
16–20
3.3 (3/92)
7.4 (4/81)
10.5 (8/76)
10.6 (10/94)
6.3 (6/96)
11.3 (70/622)
15.2 (77/506)
19.2 (10/52)
408
Taylor,Lennon,Holland,CaVerkey

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Community study of toxoplasma antibodies
409