(Eh) y metanólico (Em) de Pera distichophylla sobre un aislado de ...

microscopy applying the Ritchie’s modified technique
was difficult, as the sediment had become
very thick, while in Sheather’s modified technique,
owing to the sugar solution with high concentration,
the sediment on the microscope slide was
clear and easily readable. As an alternative to improve
the reading of the slabs in the Ritchie’s modified
technique, Carvalho et al., (2002) suggest the
dilution of the material obtained with a drop of salt
solution for obtainment of clearer fields of reading.
Thus, we suggest that Ritchie’s modified technique
is not used in the processing of soil samples, as it
may lead to false negative results, owing to excess
residues in the fields of reading.
ELISA showed a larger number of positive
samples compared to the microscopic techniques in
the survey of G. lamblia, E. histolytica and Cryptosporidium
sp. These results are in keeping with the
studies performed with fecal samples in the city of
Belém, State of Pará, for which ELISA was considered
the most sensitive technique for detecting
G. lamblia in children’s feces by Machado et al.,
(2001) and for detecting E. histolytica in feces of
dwellers of the Metropolitan Region by Silva et al.,
(2005).
In this study, the agreement between microscopic
and ELISA techniques allowed to confirm species
of protozoa which could not be identified by
microscopy. This fact was substantiated by cysts
of Giardia sp. confirmed for G. lamblia and
four-nucleus amoeboid cysts confirmed for E.
histolytica. The confirmation of species of protozoa
through the enzyme immunoassay was possible
due to the use of species-specific kits.
The degree of agreement between the microscopic
techniques and ELISA in soil samples was
not ascertained, as protozoa G. lamblia, E. histolytica
and Cryptosporidium sp. were detected only
in the enzyme immunoassay, and the microscopy
did not find any compatible structure.
The high sensitivity of the enzyme immunoassay
in water and soil samples may be explained by the
fact that this technique is capable of capturing
surface antigens, given that the integrity of the cyst
and oocyst is not necessary. On the other hand, in
microscopic techniques, the integrity of the cysts
and oocysts of protozoa is essential for the diagnosis.
The high efficiency of the enzyme immunoassay is
also the result of its ability to detect small amounts
of antigens, which stand as low parasite load. This
Rev. Ibero-Latinoam. Parasitol. (2012); 71 (1): 90-96
COMPARISON OF TECHNIQUES IN ENVIRONMENTAL SAMPLES
may facilitate the detection of antigens in water,
since these antigens are usually at low loads, owing
to high dilution.
Vidal and Catapani (2005) reported that the
main disadvantages of enzyme immunoassays are
related to the high cost compared to the traditional
microscopic techniques. In this study, for each
sample, ELISA cost BRL 25.00 in average, while
Sheather’s technique modified by Huber et al.,
cost BRL 0.37, and Ritchie’s technique modified
by Young et al., cost BRL 0.55. In addition to this,
the enzyme immunoassay, as a specific kit, does
not detect other parasites, and the identification of
parasite in ELISA does not ensure its feasibility.
Comparing the results of ELISA with other immunological
techniques is necessary; these techniques
include the direct immunofluorescence,
which uses monoclonal antibodies with high sensitivity,
and is capable of detecting undivided cysts
and oocysts. Still, ELISA has the advantage of being
less costly than immunofluorescence, is swifter,
facilitating concomitant analysis of a number of
samples, and is easy to handle. Nonetheless, it has
been subject to few tests in environmental samples.
Other relevant factors to be considered would be
the need for less technology infrastructure, as some
kits may be processed by visual reading and do not
require a trained operator to identify the evolutionary
parasitic forms.
The consensus is that the identification of a given
parasite must be confirmed by a parasitological
laboratory technique. It is recommended, however,
the combination of techniques with different
principles to increase the probability of detection
of evolutionary forms of protozoa and helminths,
taking into account the morphological variability
they present. However, based on the results
found, we suggest the use of immunoenzymatic
technique for monitoring the water quality or for
investigating environmental contamination, as
the mere detection of antigens may indicate risk
of infection and, chiefly, the occurrence of fecal
source contamination, with the possible presence
of other pathogens.
REFERENCES
1. CARVALHO FM, FALCÃO AO, ALBUQUERQUE
MC, SILVA P, BASTOS OMP, UCHÔA CM. 2002.
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