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JOURNAL OF CLINICAL MICROBIOLOGY, Sept. 1992, p.
2269-22740095-1137/92/092269-06$02.00/0
Evaluation of an Immunoenzymatic Assay Detecting
SpecificAnti-Toxocara Immunoglobulin E for Diagnosis
andPosttreatment Follow-Up of Human Toxocariasis
J.-F. MAGNAVAL,1* R. FABRE,2 P. MAURIERES,l J.-P. CHARLET,3 AND
B. DE LARRARD4Laboratoire de Parasitologie, Centre Hospitalier
Universitaire Purpan, F-31059 Toulouse Cedex, 1 Bioinova,F-78370
Plaisir,2 Service dI'nformatique et Statistiques Medicales, Centre
Hospitalier Universitaire HotelDieu, F-31052 Toulouse Cedex,3 and
Laboratoire de Biologie Medicale, F-31800 Saint Gaudens, 4
France
Received 18 February 1992/Accepted 8 June 1992
In order to complete the immunodiagnosis of human toxocaral
disease, an immunoenzymatic assay withexcretory-secretory antigens
from Toxocara canis larvae was developed for the detection of
specific immuno-globulin E (sIgE enzyme-linked immunosorbent assay
[ELISA]). The specificity of the assay was evaluated inpatients
presenting with various allergic or helminthic diseases. The
sensitivity was assessed in patientsexhibiting clinical and
biological symptoms indicative of toxocariasis, serodiagnosis of
which was made by theWestern blot (WB; immunoblot) procedure that
used the same antigen as that used in the sIgE ELISA but
thatdetected specific IgG. The value of the sIgE ELISA for
posttreatment follow-up was tested in two groups ofpatients: one
group was treated with diethylcarbamazine; the other group was not
treated with DEC. Resultsshowed that the specificity and
sensitivity of the sIgE ELISA were moderate. Thus, the sIgE ELISA
appearedto be insufficient for properly ensuring the serodiagnosis
of toxocariasis when it is used alone. However, sIgEELISA might be
an interesting complementary method for the detection of specific
IgG. It was the only assaythat was found to be positive in sera
from some hypereosinophilic patients. sIgE ELISA values
decreasedsignificantly among the patients treated with DEC,
indicating that this test would be useful for
posttreatmentfollow-up assessment.
Toxocariasis is a parasitic zoonosis caused by infestationof
humans with larvae of Toxocara canis, the commonroundworm in dogs,
and possibly, larvae of T. cati, acommon ascarid species of cats
(16, 22). Two syndromeshave been identified: visceral larva migrans
(3) and ocularlarva migrans (21). Results of recent studies suggest
that thedisease frequently assumes the features of a syndrome
thatcomprises chronic weakness, abdominal pain, various signsof
allergy, and hypereosinophilia (11, 18, 30). Moreover,toxocariasis
has been found to be a cofactor for epilepsy (1)and has been
proposed as a possible etiology in variousneurologic syndromes
(25).These data have been obtained by sensitive and specific
serodiagnostic methods by using excretory-secretory anti-gens
from T. canis larvae (TES-Ag) (6). These methods arethe TES-Ag
enzyme-linked immunosorbent assay (TESELISA) (7, 14) and, more
recently, the Western blot (WB;immunoblot) procedure (20), both of
which detect immuno-globulin G (IgG) specific for TES-Ag. However,
clinicalsigns of allergy and increased levels of total IgE in
manycases of toxocariasis (11, 13, 18) indicated that IgE
specificfor TES-Ag (sIgE) would be present. Brunello et al. (5)
andDesowitz et al. (8) detected IgE antibodies for larval
extractsof T. canis in patients with toxocariasis and
asthmaticchildren. In 1986, Genchi et al. (10) used a
radioimmunoas-say with TES-Ag for the immunodiagnosis of
toxocariasisand showed that this assay is valuable for the
diagnosis ofocular larva migrans (9). In 1986, Oliver et al. (23)
demon-strated that sIgE is detectable by ELISA.
In most countries, strict legal and technical regulations
areapplied to radioimmunoassays that use isotopically labeled
* Corresponding author.
reagents. Thus, we perfected for the first time an ELISA forthe
detection of sIgE (sIgE ELISA); we then assessed thespecificity of
this test in sera from patients presenting withvarious allergic or
helminthic diseases or containing immuneanti-blood group
antibodies. Then, we studied the value ofsIgE ELISA for the
serodiagnosis of toxocariasis in serafrom patients suspected of
having the disease. The serodi-agnosis of this zoonosis was based
on the results of a WBassay that detected IgG for TES-Ag. WB was
chosen since itis well correlated with TES ELISA; moreover, it
seemedmore specific. Banding patterns that included
low-molecu-lar-weight bands appeared to be specific for toxocaral
infes-tations; high-molecular-weight bands were found to bepresent
at significant levels only when sera from patientswith various
helminthic diseases were tested, 33% of whichyielded positive
results by TES ELISA (20). Finally, theeffectiveness of sIgE ELISA
for use in follow-up assess-ments of treated patients was
evaluated.
MATERIALS AND METHODS
TES-Ag. Cultivation of T. canis larvae was carried out bythe
prototype method of de Savigny (6) that was modified byBowman et
al. (4). In culture vials, the larval density was1,000 larvae ml-',
and the RPMI 1640 medium (Intermed,Venissieux, France) in the
vials, supplemented with 1%glutamine, was renewed every week. The
supernatants werefiltered on Whatman no. 1 filter paper and were
frozen at-70°C. After thawing, the batches were pooled, dialyzed
for48 h in distilled water (Visking dialysing tube C 75; PolyLabo,
Strasbourg, France), and then freeze-dried in 5-mlvials. Before
each pool was used, the protein titer wasmeasured by the method of
Lowry et al. (17).
Positive and negative reference samples. A positive refer-
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2270 MAGNAVAL ET AL.
ence serum pool was made from the sera of 30 patientspresenting
with toxocariasis that was positively serodiag-nosed by WB, namely,
a typical seven-band pattern (20). Anegative reference serum pool
was made from the sera of 30children (age, 3 to 6 months) referred
to the Laboratory ofParasitology by the Department of Paediatrics
for toxoplas-mosis serology. Titers of total IgE in the positive
andnegative reference pools were 2,760 and 3.1 kIU
liter-1,respectively, as determined by radioimmunoassay in
theDepartment of Nuclear Medicine, Centre Hospitalier
Uni-versitaire Purpan. Evaluation of the reproducibility of thesIgE
ELISA was done by testing positive and negativereference pools two
times a week for 19 weeks.Human sera from patients with allergic
diseases (group 1).
Sera were obtained from 41 patients attending the Depart-ment of
Dermatology and Allergy for various symptoms ofallergy (asthma [n =
15], eczema [n = 16], or chronicurticaria [n = 10]). Group 1
patients exhibited sensitizationto various allergens (antibiotics,
house dust mites, pollens,and foods) as shown by
radioallergosorbent tests, patchtests, or prick tests. Only seven
patients had atopic eczema.The mean total IgE value was 912.4 kIU
liter-1 (95%confidence interval [CI], 555.1, 1,499.6; range, 10 to
11,000kIU liter-1).Human sera with immune anti-A and/or anti-B
blood group
or heterophilic antibodies (group 2). Sera were obtained from12
patients with immune anti-A hemagglutinins, 3 patientswith both
anti-A and anti-B immune antibodies, and 5patients with
heterophilic anti-sheep erythrocyte antibodies.Human sera from
patients with various helminthic diseases
(group 3). We collected in the Laboratory of Parasitology175
serum samples from patients with anisakiasis (n = 2);cystic
hydatidosis (n = 7); fascioliasis (n = 5); variousfilariases (n =
22); a history of living in an African country,hypereosinophilia,
and a negative parasitological checkupbut a positive serodiagnosis
for filariasis by fluoroimmunoas-say (n = 22); various
schistosomiases with a positive sero-diagnosis and/or direct
evidence of parasite eggs (n = 24);strongyloidiasis with a positive
stool examination (n = 28);hypereosinophilia with a negative
parasitological checkupexcept positive serodiagnosis for
strongyloidiasis (n = 9);and positive stool examination forAscaris
lumbricoides (n =7), hookworms (n = 6), pinworms (n = 22),
tapeworms (n =9), and whipworms (n = 12).With these sera, WB with
TES-Ag was negative or dis-
played the high-molecular-weight banding pattern only.Human sera
from patients presenting with a clinical and/or
a biological syndrome evocative of toxocariasis (group 4).
Serawere collected from 150 patients attending the
ConsultationOffice in the Laboratory of Parasitology. None of the
group4 patients had ever lived outside of France; only 3
patientshad traveled overseas as tourists. For all patients
repeatedstool examinations, including examinations by
Baerman'smethod, were negative for intestinal helminthiasis, as
wereserological checkups for the autochthonal parasitic
diseasescystic hydatidosis, fascioliasis, and strongyloidiasis. A
se-rodiagnostic test for trichinosis is no longer included in
thepanel of tests for autochthonal parasitic diseases. From 1975to
1977, serodiagnostic tests for trichinosis were systemati-cally
carried out on over 12,000 serum samples referred tothe Laboratory
of Parasitology, but only two cases of coverttrichinosis were
detected. For the three patients who hadtraveled overseas,
parasitologic examinations of blood, skin,and urine were found to
be negative, and serodiagnostic testsfor tropical diseases (i.e.,
amoebiasis, filariasis, malaria, andschistosomiasis) were also
negative. In 138 patients, serodi-
agnostic tests for toxocariasis by WB exhibited a
typicalseven-band pattern that included low-molecular-weightbands.
For 12 patients, results of WB remained negative.The date of onset
of toxocariasis was estimated. On
average, the duration of the disease before consultation atthe
Laboratory of Parasitology was 4.8 months (95% CI, 4.1,5.6]). The
main clinical features were chronic weakness(76%), abdominal pain
(36.5%), cough (26.5%), and varioussigns of allergy, the most
frequent of which was pruritus(40%). The clinical level of illness
was quantified by using aclinical score system performed in the
Laboratory of Para-sitology (mean, 7; 95% CI, 6.2, 8.2). The mean
eosinophilcount was 784 cells ,ul-1 (95% CI, 676, 901), and the
meanlevel of total IgE was 510 kIU liter-1 (95% CI, 399, 653).Human
sera from patients included in a therapeutic trial
(group 5). Sera from 60 patients from group 4 were obtainedfor
inclusion in a therapeutic trial. Twenty-eight patientswere treated
with diethylcarbamazine (DEC), and 32 pa-tients were not treated
with DEC. These two batches of serawere similar since, before
treatment, no significant differ-ence was found (Mann and Whitney's
test) between thevalues of dur'ation of disease before
consultation, clinicalscore, eosinophil count, WB results, and
total and specificIgE levels. According to epidemiologic findings
(11), thefollowing advice was given to patients so that they
couldavoid possible reinfestation: deworming of any pet threetimes
a year, enclosing kitchen gardens, and careful hand-washing before
meals. These patients were examined againfor a control checkup from
2 to 3 months after the firstconsultation.WB procedure. The WB
procedure used in this study has
been described elsewhere (20). Briefly, electrophoresis ofTES-Ag
was carried out in a gel containing 10% polyacryl-amide and 7.5 ,ug
of TES-Ag per lane. Transfer (semidrytype) lasted for 45 min under
0.2 to 0.4 V cm-1. Forimmunodetection, sera were diluted at 1:100.
For that pro-cedure, we used Auroprobe BL Plus and Intense BL
kits(Amersham, Paris, France), in which anti-human IgG waslabeled
with gold and the detection of immune complexeswas enhanced by a
silver coprecipitation.
sIgE ELISA procedure. Ninety-six-well microtitrationpolystyrene
plates (Immunoplate, Poly-Labo Block; Nunc,Strasbourg, France) were
loaded with a TES-Ag solution (50,ul per well) containing 2.5 ,ug
of protein ml- in a 0.1 Mcarbonate-bicarbonate buffer (pH 9.6). The
plates weremaintained for 18 h at 25°C in a moist chamber. Then,
theantigenic solution was discarded and the plates were washedthree
times with phosphate-buffered saline (PBS)-Tween(0.05% Tween 20; pH
7.2) buffer; they were dried and finallystored at -70°C. All test
reagents, including anti-human IgEconjugate labeled with
3-galactosidase, were part of thePhadezym Rast kit (Pharmacia, Bois
d'Arcy, France). Serafrom patients and the negative reference pool
were testedundiluted; positive reference pool sera were tested
undilutedand at 1:10, 1:100, and 1:1,000 dilutions. All diluted
andundiluted sera were tested in duplicate. Sera (50 ,ul per
well)were incubated at 25°C for 3 h. The plates were washed
threetimes with PBS-Tween (0.05% Tween 20; pH 7.2) buffer.Fifty
microliters of the anti-IgE conjugate solution wasadded to each
well, and the plates were maintained at 25°Cfor 16 h in a moist
chamber. Then, they were washed threetimes with PBS-Tween buffer. A
total of 150 ,ul of thesubstrate
(o-nitrophenyl-0-D-galactopyranoside solution)was added to each
well, and the plates were incubated at37°C for 2 h. Finally, the
reaction was stopped by theaddition of 50 ,u of the blocking
solution to each well. The
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IMMUNODIAGNOSIS OF TOXOCARIASIS 2271
TABLE 1. Assessment of the cross-reactivity of sIgE ELISA
No. of patients whose sera were infectedGroup with the following
titers (TU liter-'):
.1 25 .10 .20 .50
1 (allergic patients) 41 13 13 5 1 0
2 (immune isohemaggluti- 20 7 1 0nins)
3 (helminthiasis) 175 89 54 36 23 10Anisakiasisa 2 0
Cystic hydatidosisb 7 3 3 1 1 1
Fascioliasisb 5 4 2 2 2 1
Filariasis caused by: 22 13 12 9 7 3Bancroftiasis 3 1 0Loiasis 4
3 3 1 0Mansonella perstans 6 5 5 5 4 1Mansonella strepto- 1 1 1 1 1
1
cercaOnchocerciasis 8 3 3 2 2 1
Occult filariasisb 22 12 6 3 2 1
Schistosomiasisa,b 24 12 7 3 1 0
Strongyloidiasisa 28 18 10 8 5 1
Strongyloidiasisb 9 4 2 1 0
Intestinal helminthiasisa 56 23 12 9 5 3Ascaridiasis 7 4 1
0Hookworms 6 2 1 1 0Pinworms 22 8 6 4 2 2Tapeworms 9 2 1 1 1
0Whipworms 12 7 3 3 2 1
Total 236 109 68 41 24 10
a Diagnosis by direct evidence of parasite.b Diagnosis by
serology.
plates were read at 420 nm with a Multiskan photometer(Flow
Laboratories, Puteaux, France).The following steps were done with
software written in the
Laboratory of Parasitology. The software was compiled
inGW-Basic. This software read the optical densities (ODs)from
every pair of wells and calculated the means. When adifference of
over 10% was found between the two ODscorresponding to the same
pair of serum samples, the pair ofserum samples was discarded and
tested again. The negativepool was read at first and its average OD
at 420 nm (OD420)was substracted from the values of other sera.
Then, anundiluted positive reference pool of sera and 1:10, 1:100,
and1:1,000 dilutions of serum were read, and a positive refer-ence
curve was constructed. Results for patient sera wereexpressed in
units. According to Voller et al. (31), thismethod yields the
second best result when various systemsthat give ratios for
positive versus negative serum sampleswere tested. In Pharmacia's
system of units, the positivereference serum was heterologous and
contained IgE frompatients sensitized to birch tree flower
allergens. Thus, wepreferred to use a homologous system; our
positive refer-
20 *18.7
1614
12 ..% 10.
42-0- q
13.4
10.7
2~~~~~
o -_e17 c O,In oIn~~ ~Toxoca Units I I
FIG. 1. Repartitioning of sIgE ELISA values in sera from
150patients with toxocariasis.
ence pool contained 1,000 units of IgE for TES-Ag liter-'.This
unit was named the Toxocara unit (TU). The softwarereported OD420
of patient sera on the positive referencecurve and converted them
into TU liter-'. The technicalcutoff value was 1 TU liter-'.
Statistical analysis. Statistical analysis was conducted byusing
an i386/387 computer with statistical software (North-west
Analytical, Portland, Oreg.). All the calculations weremade with
logarithmic values of data, so geometric meansare given.
RESULTS
Serological examinations. Thirty-eight tests of the undi-luted
positive reference pool showed a mean OD420 of 0.992(95% CI, 0.968,
1.016; range, 0.898 to 1.173; variation, 1%).At a 1:1,000 dilution,
i.e., 1 TU, the mean OD420 of thepositive reference pool was 0.050
(95% CI, 0.046, 0.054;range, 0.030 to 0.070; variation, 5%). The
negative referencepool exhibited a mean OD420 of 0.003 (95% CI,
0.002, 0.004;range, 0.000 to 0.018; variation, 100%).Among sera
from patients in group 1, 2, and 3, WB with
TES-Ag yielded negative results (all groups) or displayedonly
high-molecular-weight banding patterns (group 3). Theresults of
sIgE-ELISA are presented in Table 1. Sera fromgroups 1 to 3
exhibited very low values, especially sera fromallergic patients or
those containing immune isohemaggluti-nins or heterophilic
antibodies. Sera from patients in group 3had the highest sIgE
values, but the maximum value did notexceed 100 TU liter-'.
Figure 1 shows sIgE results for group 4 patients. Sera from131
of 150 (81.3%) patients with clinical toxocariasis werereactive in
the sIgE-ELISA at 21 TU liter-', while serafrom 138 (92%) patients
were positive in the WB assay. Ahigh proportion (18.7%) of sera
from patients found to bepositive by WB were negative by sIgE
ELISA; sera from 12patients (8%) presenting with a negative WB
result displayedhigh titers for total IgE (range, 181 to 37,162 kIU
liter-') andsIgE (range, 276 to 25,000 TU liter-l).An assessment of
the efficacy of the sIgE ELISA for the
follow-up of treated patients was carried out on the resultsfor
group 5 patients, as was the evaluation of the efficacy ofDEC.
Results from statistical analysis. A study of the specificityand
sensitivity of the sIgE ELISA was conducted on theresults for
patients in groups 1 to 4. Five cutoff values weretested: 1, 5, 10,
20, and 50 TU liter-'. The first valuecorresponded to the technical
threshold (Table 2).
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2272 MAGNAVAL ET AL.
TABLE 2. Assessment of sensitivity and specificity ofsIgE
ELISA
sIgE ELISA Percentcutoff value(TU liter-') Sensitivity
Specificity
.1 81.3 53.8
.5 67.9 76.2
.10 55.9 82.6
.20 53.2 89.8250 41.9 95.8
The correlation of the sIgE ELISA with other parameters,i.e.,
clinical (duration of disease before consultation andclinical
score) or biological (eosinophilia and total IgE level),was studied
for the results for group 4 patients by usingSpearman's rank test
and multivariate regression analysis.No positive or negative
correlation was found between sIgEvalues and duration of disease
before consultation, clinicalscore, or eosinophil count (Spearman's
coefficient values[0.052, 0.014, and -0.199] not significant). A
strong corre-lation between sIgE and total IgE was found
(Spearman'scoefficient, 0.469; Z statistic, 6.16; P <
0.001).
In group 5 patients (therapeutic trial), at the controlcheckup
significant variations were found for the clinicalscore (control
group and treated patients), eosinophil count(control group and
treated patients), total IgE (controlgroup), and sIgE (treated
patients) (Table 3).
DISCUSSIONWhen it is used routinely and intensively, sIgE
ELISA
appears to be a simple and easy-to-use method. The use
ofundiluted sera avoided the tiresome procedure of massdilutions
and probably contributed to the excellent reproduc-ibility of the
method.The intrinsic specificity of the sIgE ELISA was good,
since this test reacted at a very low average level (mean, 2.1TU
liter-', 95% CI, 1.5, 2.9) with sera from allergic patientswhen the
mean value of total IgE in the sera was high (912.4kIU liter-'; 95%
CI, 555.1, 1,499.6). Nonspecific adsorptionof total IgE onto the
polystyrol solid phase did not occur.When Oliver et al. (23) tested
58 serum samples from atopicor asthmatic patients that exhibited
total IgE levels of.1,000 kIU liter-', they also found that the
sIgE ELISAwas nonreactive. Thus, the good statistical agreement
foundbetween sIgE and total IgE levels in patients in group 4 maybe
due to the marked stimulation of IgE synthesis that hasbeen shown
in many patients with helminthiases, includingtoxocariasis (13, 15,
24).
In 1983, Smith et al. (27) demonstrated that TES-Agcontains
blood group-like antigens; they stated that sera with
immune isohemagglutinins could cross-react and thus
yieldfalse-positive results in the serodiagnosis of
toxocariasiswhen sera were tested by TES ELISA (26). In 1985,
Glick-man and Schantz (12) showed that sera containing high
titersof such haemagglutinins were not reactive when tested byTES
ELISA, and we corroborated this point when weassessed the WB
procedure for the serodiagnosis of toxo-cariasis (20). In the
present study, neither sIgE ELISA wasaffected by such immune
hemagglutinins.
Testing of sera from patients presenting with varioushelminthic
diseases showed that the sIgE ELISA reacted ata low mean level (3.1
TU liter-'; 95% CI, 2.6, 3.8), although23.8% of these sera had .5
TU liter-'. Those positivitiescould be due to concurrent minor
toxocaral infestations,because that zoonosis is widespread. In a
previous study,examination of sera from such patients by WB
revealed that6.7% (8 of 118 serum samples) displayed typical
patterns(20).
Analysis of the results from group 4 patients, showed thata
majority of the patients (52.1%) exhibited moderate values(from 1
to 100 TU liter-') and a high proportion of negativeresults (18.7%)
was found. These two factors produced amoderate mean titer for the
sIgE ELISA (49.8 TU liter-1).Genchi et al. (9) have hypothesized
that the synthesis of sIgEremains at a low level during the acute
phase of toxocaralinfestation. Statistical analysis of data for
group 4 patients,which indicated that there is no relationship
between thesIgE level and parameters such as the estimated duration
ofthe disease, the clinical score, and/or eosinophilia, does
notagree with the hypothesis of Genchi et al. (9). The synthesisof
sIgE for a given parasite is probably genetically
regulated,although this point remains unclear (24).The wide range
of sIgE ELISA values in 138 patients with
toxocariasis showing a positive WB result suggested that thetwo
methods correlated poorly. Since the antigens that weretransferred
to the nitrocellulose sheet might be different fromthose that
adhered to the ELISA plate, we studied thecorrelation between the
detection of specific IgG by the TESELISA and that by sIgE ELISA.
TES ELISA values wereavailable for 43 patients in group 3 and for
13 patients ingroup 4. These sera were tested by TES ELISA in a
previousstudy (20). The results for the 43 serum samples
frompatients in group 3 showed a lack of correlation between thetwo
methods (Spearman's coefficient, 0.19, Z statistic, 1.22).Among the
13 serum samples from patients in group 4, areverse quantitative
correlation was found (Spearman's co-efficient, patients in -0.475,
Z statistic, -1.634; P = 0.05).Moreover, using the data published
by Genchi et al. (9,
10), we assessed the quantitative correlation between theTES
ELISA (IgG) and radioimmunoassay with TES-Ag(sIgE) for sera from 21
patients; Spearman's rank test was
TABLE 3. Statistical analysis of the kinetics of various
parameters in patients in group 5'
Eosinophilia (celis 1-J) Total IgE (kIU liter-) sIgE ELISA titer
(TU liter-1)Consultation DEC-treated Untreated DEC-treated
Untreated DEC-treated Untreated
patients patients patients patients patients patients
First 1,005 803 574 840 68 157Second 287 415 527 724 48
79Wilcoxon's signed rank test 2.75 (P < 0.001) 2.75 (P = 0.006)
NSb 2.2 (P = 0.03) 2.46 (P = 0.01) NS
(Z statistic)a Values are means.b NS, not significant.
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IMMUNODIAGNOSIS OF TOXOCARIASIS 2273
not significant (Spearman's coefficient, 0.078; Z
statistic,0.35).From these findings it can be inferred that an
assay that
detects sIgE should not be used alone, but it appears to be
agood complement to a method that detects IgG for TES-Ag.In fact,
sera from 12 of 150 patients in group 4 were stronglypositive for
TES-Ag by sIgE ELISA only.
Prophylactic measures must be used in association withdrug
therapy for toxocariasis. When treated and controlpatients
exhibited clinical and biological disturbances (onaverage, 4.6
months [95% CI, 3, 4.4] and 3.6 months [95%CI, 3.4, 7] after the
presumed onset of disease, respectively),a significant decrease in
the clinical scores and eosinophilcounts was found in both groups 2
months after the firstconsultation. A remarkable point is the
significant decreasein sIgE ELISA only in the DEC-treated group,
indicatingthat for posttreatment follow-up assessment, the
sIgEELISA could be more valuable than ELISAs that detectIgG. The
levels of specific IgG did not vary significantly, andthis result
is in agreement with the results of previous studiesin two groups
of children, in which Bass et al. (2) assessedthe efficacy of
thiabendazole versus that of placebo andchecked the TES ELISA
results 1 year later. Only a slightdecrease in the average TES
ELISA values was found insera from the two groups.For a long time
it remained a question whether anthel-
minthics are effective for the treatment of
toxocariasis.Previous reports describing the results of therapeutic
trialswith various benzimidazoles showed that these drugs did
notaffect the kinetics of biological parameters (2, 19, 28). In
thisstudy, the results for group 5 patients proved the efficacy
ofDEC, especially its effect on the sIgE ELISA level. More-over,
when the values of the parameters were comparedamong the two groups
at the time of consultation forcontrols, DEC was found to be more
effective (P = 0.03 byMann and Whitney's one-tailed test; Z
statistic, 1.9) oneosinophilia, a biological parameter that appears
to becorrelated with the presence of viable larvae in body
tissues(29).According to the results of this study, in the
Laboratory of
Parasitology the WB procedure remains the first-line assayfor
the serodiagnosis of human toxocariasis. A serum samplefound to be
negative for helminthic diseases by our panel ofserodiagnostic
tests and by WB is tested by sIgE ELISA. Adiscrepancy (i.e.,
negative WB and positive sIgE ELISA), ifany, is interpreted in
three ways when the patient's casehistory is not available. When
sIgE ELISA values rangefrom 1 to 100 TU liter-', physicians are
told to ask forrepeated stool examination, including an examination
by theBaerman's method, plus other direct examinations when
thepatient lived in or was a native of a tropical country. Whenthe
sIgE titer lies between 100 and 500 TU liter-', a
secondserodiagnosis is carried out, when possible, 1 month
later.Patient sera that exhibit titers of more than 500 TU
liter-'are classified as toxocariasis cases.
ACKNOWLEDGMENTS
We thank F. Giordano (Department of Dermatology,
CentreHospitalier Universitaire Purpan, Toulouse), Y. Marty
(RegionalBlood Bank, Toulouse), J. Fabre (Department of Nuclear
Medicine,Centre Hospitalier Universitaire Purpan, Toulouse), and D.
Hosford(Institut Henri-Beaufour, Paris) for help. We also thank A.
Galasso,J. Jezequel, M.-J. Touchard, M. Vidal, G. Carriere, E.
Dubly, andA. Thuries for technical assistance.
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