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Acta Médica Costarricense
versão On-line ISSN 0001-6002versão impressa ISSN 0001-6012
Acta méd. costarric vol.55 no.2 San José Abr./Jun. 2013
Original
Current
status in
Rebeca Varela-Villalobos, Johana
Rojas-Granados, Idalia Valerio-Campos, Misael
Chinchilla-Carmona
Project executed by the Department of Investigation and the Cathedra of Medical Parasitology.
University
of Medical Science Universidad
de Ciencias Médicas
(UCIMED),
Support
Sources: UCIMED,
MICIT, CONICIT.
Abstract
Background:
Toxoplasmosis
is usually an asymptomatic chronic disease which can eventually cause
problems
for humans, such as abortion and eye damage. Therefore, it is important
to know
about possible infection sources for humans. The objective of this
study is to
review the literature related to transmission through meat products and
to
compare the infection level for Toxoplasma
gondii in meat for human consumption to
that occurred
10 years ago.
Methods: laboratory
animals were fed with ground meat or chorizo (a type of sausage)
obtained from
various suppliers of this product and immunological techniques were
used to
determine whether the animals’ contamination with the parasite came
from
eating such products.
Results
and conclusions: In
4% of the animals fed with ground meat or sausage, there were traces of
antibodies against T. gondii. This
result is
significantly lower than the one reported twelve years ago using the
same
method. After a historical analysis of the subject, the conclusion is
that
there has been a reduction in meat infected with T. gondii.
Keywords: Toxoplasmosis,
Toxoplasma gondii,
transmission, epidemiology, meat.
The more
severe problems will manifest in newborns2
and in cases where there are significant immunosuppresants
treatment-induced immune problems3,4 or due to weakening
diseases
such as cancer, leukemia and AIDS, etc.5 In the latter,
infections
tend to be disseminated and can mean the final cause of very serious
injuries
and even death.6
For the
tendency towards chronic or latent stages of
this disease in
In Costa
Rica, studies performed by Madrigal et al,13
added sausages as a potential source of infection for this
parasite in
human beings, this aspect was also contemplated in Reyes et al work,13
proposing a new model of transmission.
Given
this, grounded meat was chosen, a product
derived from bovine and sausages made with pork (chorizo), both very
common in
the diet of a good number of people in the general population, to
determine its
potential as an infection source for toxoplasmosis. The results
obtained in this
study and the comparative analysis of these with similar observations
in
previous years, are the main reason for this work.
Methods
Fifty
samples of
An in vivo
model was used for the possible detection
of T. gondii, previously
described14 using
laboratory animals. To made this model, white Swiss mice were used, to
which
were administrated a certified commercial concentrate and ad libitum water, maintain in any case according to
the
regulations issued by No 7451 Law of Animal Welfare. A group of 5
animals for
every sample were fed with uncooked meat, with a prior 18 to 24 hours
fasting
period, with the objective of promoting the intake of the products
under study.
The mice remained in contact with the supplied material in a period of
time
require to ensure the full consumption of it. All the animals in our
laboratory
were monitored regularly for the presence of T. gondii,
so the negativity for this parasite is guaranteed.
After two
months, the mice were sacrificed and bled
from the heart to obtain the serum which is then subsequently be
studied for
the presence of antibodies against T.gondii.
Also, under the microscope, between blade and slide, 6 portions
took from
different regions of the brain of each animal were checked, in order to
determine if there were cysts of the parasite. Additionally, portions
of brain,
lung, liver, spleen, heart, kidney, diaphragm and pectoral muscle, and
the eye
were fixed in 10% formalin. Histological sections stained with hematoxylin-eosin were studied for the presence
of
parasite.
The serum
obtained was studied through CIA (Carbon Immuno
Assay) for sensibility and specificity,15
as well as with Sabin-Feldman
confirmatory technique.16 Both techniques are widely known
and had
been described in multiples studies. As a positive control, positive
serums for
T. gondii were used (American Type
Culture
Collection, ATCC, 50174). Tachyzoites from
RH strain
were used in CIA tests.
The tests
were repeated in triplicate to validate the
results, which were compared with those of previous studies and
discussed from
the epidemiological point of view of toxoplasmosis.
Results
Of the 100
CIA tests, 50 were from meat and 50 from
chorizo, 4 of each groups were positive.
From these
eight samples, two from each product were confirmed with Sabin-Feldman
test.
This data indicated a positivity percentage of 4% for each meat product
studied
(Table 1). To the
same samples studied with CIA tests, we performed the
Sabin-Feldman test (dilutions of 1:2 to 1:16), where only 4 of the 8
samples
were tested positive.
Looking at
table 2, we can
appreciate that the
majority of the analyzed samples of both, meat and chorizo, came from
independent establishments. Also, the positive ones with Sabin-Feldman
confirmatory test came from the same type of establishments.
In
relation with the histological analysis of the
tested animals’ organs, a direct evidence of infection for T. gondii was not found, however it is
important to
emphasize that the reviewed 6 sections from each animal brain were also
negative.
In table
3, some additional data is added, according
to the place’s hygiene where the samples were collected. As it can be
seen, from the 50 meat samples analyzed, 48% of the establishment had a
good
appearance and all were kept cooling chambers; on the contrary, chorizo
samples
from 54% of the establishments looked in fair or bad conditions.
Furthermore,
only 32 of 50 establishments conserved the products in cooling
chambers, which
leads to the presence of flies in a greater degree than with meat.
Discussion
The
original concept for T. gondii
transmission involved the ingestion of meat products as the main
system,
especially since Jacobs17 demonstrated the presence of the
parasite
in hamburgers. Subsequently and following the elucidation of Toxoplasma life cycle, in which
it was
determined that one of the developmental stages is the oocyst
that is eliminated in the feces of cats;18, 19 it was
considerate
that the ingestion of the oocysts from the
ground,
were another route of ingestion in the human being. Such hypothesis
were
postulated in Costa Rica in very complete epidemiological studies were
meat
products were not taken into consideration as a source of infection.9,10
Rather,
it was implied that the ingestion of this parasite oocysts,
were the most important system of infection for the human being.
However, in
latter studies, the presence of T. gondii
in
meat and pork was confirmed,20,21
opening
the possibility for these foods as another important source of
infection.
These
findings, plus others found positive for the
presence of this parasite in certain type of sausages, induced studies
to be
performed, in relation of the prevalence of toxoplasmosis in human
beings with
the ingestion of meat products.22 Knowing the presence of T.
gondii oocysts
on the ground,
in relationtothegreaterorlesserpresenceofcats,thatdisseminate
those stages on the ground, also Arias et al22 demonstrated
that such prevalence was related always with the presence of meat and
sausages
ingestion, independently of the number of these felines.
All of
above, lead to the confirmation of the new
hypothesis proposed by the authors, of a new concept for the
transmission of
this parasitic infection in Costa Rica12 were the ingestion
of meat
and some sausages acquired increasing importance in the transmission of
toxoplasmosis. However, given the increase in the export of meat, it
was
establish a new and more strict control measures in the management of
these and
consequently of sausages.23, 24
The
findings informed in these recent studies,
although scarce, related to the conditions of the places of collection,
with
them seems to be demonstrated that these measures have influenced, at
least in
part, in reducing the presence of T. gondii
in
those foods. In fact it took 100 samples, 50 of grounded meat and 50 of
chorizo
to find only 4% of positivity in each of the products studied. This
contrasts
markedly with similar studies in the past,13,
21 were positivity observed was greater (8-40%), even when
obtained with
a lower number of samples of 38 and 40, lower than the one used in this
study.
Thanks:
This work was sponsored by the Department of
investigation and the Cathedra of Medical Parasitology
of the
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