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Journal of Clinical Microbiology, November 2002, p. 4161-4165, Vol. 40, No. 11
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.11.4161-4165.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Evaluation of an Enzyme-Linked Immunosorbent Assay (ELISA) with Affinity-Purified Em18 and an ELISA with Recombinant Em18 for Differential Diagnosis of Alveolar Echinococcosis: Results of a Blind Test
Akira Ito,1* Ning Xiao,1,2 Martine Liance,3 Marcello O. Sato,1 Yasuhito Sako,1 Wulamu Mamuti,1,4 Yuji Ishikawa,1 Minoru Nakao,1 Hiroshi Yamasaki,1 Kazuhiro Nakaya,5 Karine Bardonnet,6 Solange Bresson-Hadni,6 and Dominique A. Vuitton6
Department of Parasitology,1
Animal Laboratory for Medical Research, Asahikawa Medical College, Asahikawa, Japan,5
Sichuan Institute of Parasitic Diseases, Chengdu,2
Department of Parasitology, Xinjiang Medical University, Urumqi, China,4
Laboratoire de Parasitologie-Mycologie, Hôpital Henri Mondor AP-HP, et Université Paris 12, Paris,3
Université de Franche-Comté, WHO Collaborating Center on Prevention and Treatment of Human Echinococcosis, Besançon, France6
Received 3 May 2002/
Returned for modification 9 July 2002/
Accepted 30 July 2002

ABSTRACT
Alveolar echinococcosis (AE) is the most potentially lethal
parasitic zoonosis of the nontropical areas in the northern
hemisphere, where cystic echinococcosis (CE) is also endemic.
Both AE and CE are highly endemic in China, and both serologic
detection of echinococcosis, either AE or CE, and differentiation
of AE from CE are crucial problems. Evaluation of Western blot
analysis (WB) and enzyme-linked immunosorbent assay (ELISA)
for the Em18 antigen, using affinity-purified and recombinant
Em18, was carried out "blindly" using 60 human sera from patients
diagnosed in France. The results were compared with those obtained
using a commercially available
Echinococcus WB immunoglobulin
G (IgG) kit developed in France. The Em18 WB and
Echinococcus WB IgG showed very similar results for detection of AE. Both
affinity-purified Em18 or a recombinant Em18 WB and
Echinococcus WB IgG seem useful for identification of AE, and the latter
seems appropriate for both AE and CE, whereas affinity-purified
Em18 ELISA and the newly developed recombinant Em18 ELISA appear
to be suitable for detection of AE, especially for epidemiological
surveys.

INTRODUCTION
Alveolar echinococcosis (AE), caused by the metacestode of the
fox tapeworm,
Echinococcus multilocularis, is the most potentially
lethal parasitic zoonosis of the nontropical areas in the northern
hemisphere, where cystic echinococcosis (CE), caused by the
metacestodes of the dog tapeworm,
E. granulosus, is also endemic.
For example, both AE and CE are highly endemic in China (
8,
19) and serological detection of echinococcosis, either AE or
CE, and differentiation of AE from CE are crucial problems,
since the pathogenicity of these two types of echinococcosis
and the treatment of patients with these diseases are critically
different (
14,
16).
In Japan and France, immunoblotting (Western blotting [WB]) assay systems have been developed for differentiation of AE from other diseases (4-7). The Asahikawa Medical College (AMC) group in Japan has focused on the detection of antibody response to the Em18 antigen (approximately 18 kDa) extracted from protoscoleces of E. multilocularis (4, 9, 15) and has tried to purify Em18, which shows a single band in WB, and to make it available for enzyme-linked immunosorbent assay (ELISA), using preparative isoelectric focusing (PIEF). Since purification of Em18 by PIEF takes longer and the yield is not as great, we have shifted to purification of Em18 by affinity chromatography (AffEm18) and production of a recombinant Em18 (RecEm18) for WB and ELISA (7, 9, 10, 13, 18). Echinococcus WB immunoglobulin G (IgG) (EchWB IgG; LDBIO Diagnostics, Lyon, France), which has a high sensitivity for the detection of both AE and CE, is basically very similar to the AMC system since it also focuses on differentiation of AE and CE based on different banding patterns including antigen B (most predominant at 8 and 26 to 28 kDa), Em16, and Em18 in crude antigens. The merit of the latter system is that it detects both AE and CE on a single strip based on the difference in the banding patterns. In this paper, we report blind test results from AffEm18 and RecEm18 WB and AffEm18 and RecEm18 ELISA using 60 serum samples prepared in France for further evaluation of the usefulness of Em18 serology for identification of AE.

MATERIALS AND METHODS
Serology.
AffEm18 was prepared as follows. Protoscoleces of
E. multilocularis were homogenized in 0.1 M Tris-HCl (pH 7.5) containing 0.5 M
NaCl and 1% NP-40. After centrifugation, the resulting supernatant
was incubated at 37°C for 1.5 h and applied to an affinity
resin column (Hi Trap NHS-activated HP; Amersham Pharmacia Biotech)
coupled with anti-Em18 polyclonal antibody. After unbound proteins
were washed off with 0.1 M Tris-HCl (pH 7.5) containing 0.15
M NaCl and 1% NP-40, Em18 was eluted with 0.1 M glycine-HCl
(pH 2.6). The eluates were pooled and used for further experiments.
For AffEm18 WB and AffEm18 ELISA, 2.5-µg samples per mini
sodium dodecyl sulfate-polyacrylamide gel (6 cm wide) (Tefco,
Tokyo, Japan) and 250 ng per well (Maxisorp; Nunc, Copenhagen,
Denmark) were used, respectively. A RecEm18 produced at AMC
(
9) was also used for this project. For RecEm18 WB and RecEm18
ELISA, 350 ng per mini sodium dodecyl sulfate-polyacrylamide
gel and 50 ng per well were used, respectively. WB and ELISA
were carried out as reported previously (
5,
6,
15). Cutoff values
for AffEm18 ELISA and RecEm18 ELISA were determined as four
times the optical density (OD) of a pool of serum samples from
40 healthy Japanese adults. EchWB IgG was carried out as specified
by the manufacturer in France (
15). Briefly, the WB banding
patterns are differentiated into six groups, P1 to P5 and Neg;
P1 and P2 are specific to CE; P3 is specific to AE, P4 and P5
are either CE or AE, and Neg is neither AE nor CE.
Serum samples.
A total of 60 human sera, numbered from 1 to 66 (lacking numbers 55, 57, 59, 61, 63, and 65) was shipped to AMC with no clinical background information included. After performing serological examinations at AMC, the investigators were informed that the samples included 19 active AE and 1 inactive AE after treatment (see Results), 35 CE, 3 neurocysticercosis (NCC), 1 polycystic echinococcosis (PE) due to E. vogeli, and 1 false-positive sample found at mass screening. Surgical and pathological confirmations were carried out on all patients whose sera were tested, either in Paris or in Besançon, France.

RESULTS
AffEm18 WB and AffEm18 ELISA.
Figure
1a shows the results obtained using AffEm18 WB. Although
we could obtain a single band of Em18 by PIEF (
9,
10,
11), AffEm18
WB showed two bands, the lower of which was Em18. As summarized
in Fig.
1a and Table
1, all 19 strongest responders (3+) were
patients with active AE which showed the P3 profile in EchWB
IgG. However, seven weak responders were found from six patients
with CE (samples 2, 4, 6, 16, 18, and 45) and one with PE (sample
62). The CE samples showed the P2 profile except for one (sample
4), which showed P5, whereas one PE sample (sample 62) showed
a P3 profile similar to that of all the AE samples in EchWB
IgG. Sample 2 was from a Turkish CE patient with numerous cysts
in the liver. Sample 4 was from a patient with CE in the liver
from whom the CE lesion was partially removed in Algeria in
1979 but for whom a clinical recurrence occurred in France in
1990 (the number of cysts removed in Algeria was unknown); at
the time of sampling (1999), he had one hepatic CE with biliary
involvement, and protoscoleces were found in the cyst fluid.
Sample 6 was from a patient with two cysts in the liver. Sample
16 was from a patient with bone and muscle CE. Sample 18 was
from a patient with one small ovarian cyst with anaphylaxis
following surgery. Sample 45 was from the same patient (patient
18) without recurrence 3 years after stopping albendazole therapy.
Figure
2a shows the results obtained using AffEm18 ELISA. Using
this test, it was much easier to differentiate the 19 patients
with active AE from others including the one with inactive AE
(patient 31). With all 19 active-AE samples, an OD
405 higher
than 0.56 was observed, whereas with one CE sample (sample 2;
OD
405, 0.27) and one PE sample (sample 62; OD
405, 0.22) the
OD
405 was at the borderline of the cutoff value (0.21). The
inactive-AE sample posttreatment (sample 31) was negative.
RecEm18 WB and RecEm18 ELISA.
Figure
1b shows the results obtained using RecEm18-WB. Samples
from all 19 AE patients showed a strong clear band (3+), and
samples from 1 CE patient (sample 2) and 1 PE patient (sample
62) showed a very faint band (1+) similar to that observed using
AffEm18 WB. Figure
2b shows the results obtained using RecEm18
ELISA. The patterns from AffEm18 ELISA (Fig.
2a) and from RecEm18
ELISA (Fig.
2b) appeared to be very similar except for the one
inactive-AE patient (sample 31; OD
405, 0.25) and two additional
CE patients (samples 11 and 50; OD
405, 0.25 and 0.36, respectively),
which became weakly positive. All other sera from patients with
active AE were higher than 0.42 under the cutoff value at 0.23.
Patient 31 had a progressive AE (average size of the lesions,
7/4 cm, confirmed histologically) diagnosed in 1999; the curative
nature of the partial hepatectomy performed in 1999 was, however,
doubtful. From 1999 to 2000, the patient was treated with albendazole,
and from the beginning of 2000, the treatment was switched to
mebendazole. So far, there has been no recurrence, and the antibody
level, quite significant with a P3 profile using EchWB IgG at
diagnosis, became very low and then negative using the same
test after treatment.

DISCUSSION
Em18 WB, using either AffEm18 or RecEm18, appears to be as reliable
as EchWB IgG. The overall results can be summarized as follows.
(i) EchWB IgG identified 19 active AE cases correctly and 1
PE case as AE with the banding pattern P3, 30 CE cases as CE
(P1 or P2), and one NCC and 5 CE cases as either AE or CE (P5);
(ii) AffEm18 WB detected 19 AE cases showing very strong responses
and 6 CE and 1 PE cases as AE showing weak responses; (iii)
RecEm18 WB detected 19 AE cases as strong positive and 1 CE
case (from sample 2) and 1 PE case (from sample 62) as very
weak positive, similar to AffEm18-WB; and (iv) AffEm18 ELISA
and RecEm18 ELISA differentiated 18 AE cases (lack of data from
sample 33 [strong positive AE, due to lack of sufficient volume
sample]) and 20 AE cases from all others, respectively, and
the specificity and sensitivity of the former appeared to be
very similar to but a little bit higher than those of the latter.
The AE case (from sample 31) which was thoroughly negative at
AMC except in RecEm18 ELISA (which gave a borderline result)
could be considered an inactive AE case following treatment
(
2,
12). In abortive cases, Em2 ELISA remains positive but becomes
negative when Em II/3-10 ELISA or Em18 WB is used (
3,
12). After
surgery or long-term medical treatment, very specific antibodies
have also been shown to disappear earlier while those detected
using cross-reacting
Echinococcus antigens remained longer (
1).
Based on these results, it may be concluded that (i) AffEm18 WB, RecEm18 WB, and EchWB IgG are highly reliable for detection of AE, although they are not completely species specific (13); (ii) EchWB IgG is useful for detection of both AE and CE in Europe; and (iii) none of the three tests can qualitatively differentiate PE patients from AE patients. However, we expect that AffEm18 ELISA or RecEm18 WB may more easily differentiate AE from other diseases, including CE, especially in epidemiological surveys. Since PE is endemic exclusively in Latin America but not in the Northern Hemisphere, serological differentiation of AE and PE is not required for epidemiological studies. However, we need more samples of PE for evaluation of antibody responses in patients with PE.
The antibody response to Em18, which has been conceived to be highly specific to AE, is now considered to be at least in part ascribed to the critical differences in antigen release or presentation of Em18 in patients with AE, CE, and PE, due to different pathological features of Echinococcus infections. The E. granulosus metacestode grows in a double-walled cyst by endogenous budding: the outer layer is formed by fibrous tissue from the host and the inner laminated layer of the parasite. In contrast, the E. multilocularis metacestode grows by exogenous budding and has the potential to spread to contiguous vital structures, and the parasite tissue lacks a clear barrier from the adjacent host tissues. So far, the CE cases which showed antibody responses to Em18 were those with complicated or multiple cysts exclusively, but not those with a single cyst (13). Therefore, it is rather easy to expect similar responses from PE cases involving polycystic lesions. This study also recorded that the CE patient showing the highest response (patient 2) had numerous cysts in the liver. Although these CE cases were seropositive by AffEm18 WB and RecEm18 WB, it is evident that the response was much weaker than that of AE cases and that the OD value in ELISA was also much lower than for AE cases (7, 13). EchWB IgG using a single strip should be highly reliable in Europe, although a minority of CE cases may exhibit P4 or P5 profiles, which are serologically indistinguishable from AE. Minor cross-reactivity with neurocysticercosis and schistosomiasis has also been reported; however, such patients are basically rare in Europe except among immigrants or refugees from Latin America, Africa, or Asia (5-7).
The sensitivity of Em18 WB using Em18 purified by PIEF or affinity chromatography using polyclonal antibodies against Em18 should be more reliable in detecting AE patients in Japan than are other serological assays using crude antigens for ELISA and WB. The AMC group was asked by clinicians to check sera from 33 persons suspected of having AE in Japan over the last 2 years. AMC identified 28 patients as having AE and 5 others as not having AE based on the simple criterion of the presence or absence of an antibody response to Em18 by WB. All these were later confirmed by pathological testing to be 100% correct. The non-AE sera were from two patients with hemangioma, one with a hepatic cyst, one with fascioliasis, and one with CE who was born and resided until 5 years old in Argentina (9, 11). Em18 serology using either WB or ELISA seems sufficient for screening and identification of AE patients in Japan and is expected to be highly useful in China, where both AE and CE are highly endemic. Both Em18-WB and EgCF (cyst fluid of E. granulosus) ELISA have been used for differentiation and identification of AE and CE together with ultrasound examination for epidemiological surveys in China (13, 17). EchWB IgG might be much simpler for identification of AE and CE at once in China, but the occurrence of false-positive cases in patients with schistosomiasis japonica, paragonimiasis, and other trematodiases and cestodiases, especially cysticercosis, all of which are still more common than echinococcosis in China, should be studied.

ACKNOWLEDGMENTS
This study was supported in part by grants-in-aid from the Japan
Society of Promotion of Science (12557024 and 14256001) and
by the NIH (1 R01 TW01565-01) (principal investigator, P. S.
Craig) to A. Ito.

FOOTNOTES
* Corresponding author. Mailing address: Department of Parasitology, Asahikawa Medical College, Midorigaoka-Higashi 2-1-1-1, Asahikawa 078-8510, Japan. Phone: 81-166-68-2420. Fax: 81-166-68-2429. E-mail:
akiraito{at}asahikawa-med.ac.jp.


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Journal of Clinical Microbiology, November 2002, p. 4161-4165, Vol. 40, No. 11
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.11.4161-4165.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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