Overall for scolex antigen were mainly of the

Overall a good
correlation between ELISA positivity and EITB positivity against SA was
observed followed by with that of ESA and MBA. The correlation has also been
reported by Molinari et al (2002)
during the comparison of ELISA OD values and number of bands developed in EITB
using ESA wherein the researchers have recorded increase in the number of bands
in EITB proportionate to increase in OD value while working on NCC patients.

It was observed that the samples positive for
scolex antigen were mainly of the patients who revealed calcified lesions on
CT/MRI. Gupta et al. (2002) showed
that calcified lesions are not dead parasites, as these incite perifocal
inflammation and edema formation. The calcified cyst containing a scolex are
the one that have their antigenicity intact and are able eliciting an immune
response in the host (Gupta et al, 2002). Schantz et al. (1994) reported that the appearance of
anti-cysticercus antibodies in serum occurs at different intervals after
infection due to qualitative and quantitative changes in the somatic and ES
antigens released at various stages of development of the parasite. Sahu et
al., (2009) observed positive ELISA result in 100% of cases (9/9) with active
lesions and 73.33% of cases (11/15) with degenerating lesions employing ES
antigens of Cysticercus cellulosae as
against 50% and 38.46% in our study. Active NCC is defined
in most of the cases as ring enhancing lesion (REL) in imaging. The CT scan
sometimes may not detect presence of live parasites due to their isodense
appearance which may be present along with degenerating larvae (Zee et al., 2000). This may attribute to the
variations in results of serology and neuroimaging.

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            Some of the patients’ sera reacted
with ESA although showing calcification/ degeneration on imaging. This may be
due to the fact that, the antibody developed against the live cyst might
persist in the circulation even after the initiation of degenerative process of
the parasite which attributes to the positive serology (Harrison et al., 1989? Garcia et al., 1997? Sciutto et al., 2007).

            ELISA
has more sensitivity and specificity when done in CSF. However, lumbar puncture
should not be performed only for doing serological tests because of associated
pain and invasiveness and getting an ethical concern has its own limitations. The
sensitivity of EITB in case of single enhancing or calcified lesion, which is
more common in Indian condition, is much lower. However, we did not observe any definite pattern when immunodominant
bands were compared between antigens with that of the type, number or location
of the lesions. Further studies may be conducted employing purified antigens
and CSF as parallel sample.   

Serology
should be used in conjunction with neuroimaging. Serology and neuroimaging
evaluate different aspects of the disease and may disagree in some patients.
Intestinal tapeworm carriers, naturally cured individuals or non-neurologic
infections have normal brain imaging (Erhart et al., 2002) but may be seropositive while individuals with only
inactive lesion like calcification or those with a single cerebral lesion test
seronegative (Ohsaki et al., 1999)

PCR
was not reported earlier taking blood as a clinical sample for molecular
diagnosis of neurocysticercosis targeting large subunit rRNA gene (LSU rRNA) of
Taenia solium. This was the first
attempt in this context. The gene is
specific and conserved for taenid cestodes and the primer TBR-3 was selected
from the conserved region and TBR-6 from semi-conserved region of the LSU
rRNA gene which are being used in the present study. This gene has been
targeted for detection of cysticercosis in pigs in validation of meat
inspection (Sreedevi et al.,
2011) and species specific
identification of Taenia solium and Taenia saginata (Jardim et
al., 2006). Although PCR has been carried out taking CSF as clinical
sample by Almeida et al. (2006) and
Michelet et al. (2011) who observed
96.7% and 90-100% PCR positivity in 30 and 121 radiologically
and clinically confirmed NCC patients respectively targeting a highly repetitive element pTsol9 of the genome of Taenia solium.  

Immunocompetent NCC patients might be
antibody-negative due to the negative response, anergy (Ito et al., 2006). Detection of highly
specific circulating antigens or specific DNA in CSF may be alternative tools (Ito
et al., 2006; Michelet et al., 2011). PCR could be useful for the
diagnosis of cysticercosis at the time of non-availability of imagery
techniques.

Regardless
of the technique used, detection of T. solium specific antibodies in serum only
indicates exposure to the parasite and not necessarily established infection,
resulting in a transient antibody response (Garcia et al., 2001). Antibody-
detection assays can remain positive long after the parasite has been
eliminated by immune mechanisms and/or antiparasitic therapy (Dorny et al.,
2003). Antigen detection assays as well as molecular techniques can improve the
diagnostic efficacy as it can detect the presence of viable parasites and is
useful in NCC treatment follow-up.

Conclusion

This is the first report of
detection of NCC in epileptic patients in Nagpur, India using SA, ESA and MBA
by three different diagnostic tests- ELISA, EITB and PCR. Overall, EITB was
reported to be very specific and discriminating, nevertheless the results
reported by different researchers seemed not to be agreed well. Although
different immunodominant bands were detected by EITB, the methods used in
antibody detection by ELISA and EITB should be used in conjunction with
clinical findings and neuroimaging methods in the diagnosis of NCC. The serum
based ELISA against SA and ESA have more potential, further, they are less
expensive than EITB and PCR assays. PCR seems to be a promising tool and should
be evaluated taking CSF from confirmed NCC patients. The
serum based techniques are quite helpful in endemic areas where the imaging
techniques are not available and (or) the cost involved in CT/MRI is not
affordable by the lower socio-economic strata.

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