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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 92, Num. 5, 1997, pp. 609-612
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Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 92(5),
September/October 1997, pp. 609-612
V International Symposium on Schistosomiasis
Hotel MIridien, Salvador, BA, Brazil
October 10, 1995
Organizers
Edgar Marcelino de Carvalho Luiz Antonio Freitas, Italo Sherlock
Manoel Barral Neto, John David Marilda S Goncalves, Jose Carlos Bina
Mitermayer Galvao dos Reis, Lain Pontes de Carvalho Zilton A Andrade
Why the International Schistosomiasis Symposia?
Zilton A Andrade
Code Number:OC97114
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Opening Address
We are here assembled for the V International Symposium on
Schistosomiasis. We are people interested on a particular subject, who came
from different areas of Brazil and from abroad. About one year ago China,
another country where the disease is also endemic, organized its I
International Symposium on Schistosomiasis. Several similar symposia have
been organized in Egypt, the last one quite recently.
Since the direct aim of such Symposia is not to establish public health
policies, nor to draw the lines for a control program to government
agencies, we might as well wonder from where comes the motivation for such
meetings.
Schistosomiasis is a parasitic disease that presents a well known
transmission cycle. Its epidemiological cycle contains weak points which
could be easily blocked if public health authorities in endemic countries
would be willing to concentrated efforts on prophylaxis. Schistosomiasis is
a disease that can be cured with highly specific and effective drugs,
administered by mouth in one single dose, practically without
contraindications. Even in its advanced stage, with extensive hepatic
fibrosis and severe destruction of the intrahepatic portal vein system,
drug treatment can benefit the patient. Medical resources to deal with this
disease are therefore available. Schistosomiasis now ranks with intestinal
helminthiasis as the most easily curable parasitic diseases. The situation
of schistosomiasis in Brazil now is highly illustrative of the fact that
medical resources alone are not sufficient to control endemic diseases
which are rooted in socio-economical problems.
Why are we now and again involved in an international symposium on
schistosomiasis?
Perhaps for the same reason that some national and foreign agencies are
giving financial support to studies on schistosomiasis. The WHO TDR
Programme includes schistosomiasis among its six priorities. For several
years the Rockefeller Foundation's "Great Neglected Diseases" Program
maintained schistosomiasis as a main target for research. The Edna-Clark
Foundation gave great stimulus to the studies leading toward a vaccine
against schistosomiasis. Similar studies are constantly being supported by
the American NIH, the Brazilian CNPq and FINEP, etc. Why such everlasting
interest over a parasitic disease that has already disappeared from several
endemic areas of the world regardless of official medical measures, but
simply by the advent of socio-economic improvement?
If we ask such question at blank point to the people gathered in this
room tonight, the main answer probably would be: because there are numerous
people still infected with schistosomes. That is a good reason, indeed.
However, we do not really know how many are they. The estimated WHO figure
of 200 million is frequently repeated. But even if we assume that it is
correct, we do not understand what it really means. We do not know how many
of those infected people will present health problems. We are far from
knowing which is the real impact that this parasitic disease cause in
different countries, as compared for example to the losses caused by
unemployment, by wastage, by pollution, by social inequalities, etc.
Why again the insistence with the International Symposium?
To find the correct answer, we should analyze what have occurred in our
previous meetings. Simply, an exchange of scientific information. The
involved individuals are stimulated by the existence of a parasitic disease
presenting considerable potential for scientific research. There are good
experimental models and several basic and applied problems to be
investigated. Several of them seem simple at the surface but many are
complex and involve basic aspects of medicine and biology. They function as
potent attractive for researchers. The challenge is accepted not by sheer
dilettantism. The scientists as well as the health planners know that the
solution of the problems connected with schistosomiasis will lead to
scientific progress in general and in particular to the improvement of
laboratories located in underdeveloped areas, and, last but not least, to
better means to control or even eradicate schistosomiasis. This challenge
is thus the main reason for and explains the success and persistence of the
International Symposia on Schistosomiasis.
The Symposia are also international because there are similar problems
presented by the disease in different geographic areas and there are
research interests shared by scientists living in non-endemic areas of the
world as well. The existence of basic research problems attract colleagues
from the best equipped laboratories located in places where schistosomiasis
does not occur. The exchange with them is mutually advantageous.
As a matter of fact, the control of schistosomiasis or even its
eradication does not depend anymore on new strictly medical advances, but
on public health political priorities aimed at the harmonious
socio-economical improvement of the population, with full employment and a
better quality of life for the population as a whole. However, the
challenge of this parasitic infection continues in other fields and this
has to do with us. During a WHO meeting in Nairobi, Kenya, I jokingly said
that schistosomiasis was doing more for immunology than vice-versa.
We were then at a moment where the advancements with experimental in
vivo and in vitro research with schistosomules had brought new
data to antibody-mediated immunity, which involved complement activity and
the role of several effector-cells, such as macrophages, cytotoxic
T-lymphocytes, eosinophils, neutrophils, mast-cells and even platelets.
Accumulated data were so impressive that studies on schistosomiasis became
the main leading movement toward the development of the new field of
immunopathology of parasitic disease. Indeed, such studies everywhere
stimulated the investigations about the function and significance of the
eosinophil leukocytes, a subject which continues up to the present.
During a long time the granuloma of tuberculosis was considered the
prototype of all granulomas. Nowadays, knowledge on schistosomal periovular
granuloma is the most advanced of all. Schistosomal periovular granuloma is
the best studied, the best known and represents the basic example for the
understanding of the general pathology of this peculiar type of
inflammation. Although, different host reactivity in early and late
infection has been recongnized since a long time ago in studies on
tuberculosis, it was the schistosomal periovular granuloma that allowed for
the sound investigation on the phenomenon now called immunological
modulation. The in vivo and in vitro models of granulomas
formed around the eggs of Schistosoma mansoni turned possible the
dissection of the several factors involved in the origin and evolution of
periovular granulomas, and in its immunological modulation. With the new
advances on the role of T-helper-cell subpopulations and their citokines,
the adhesion molecules and the biology of the extracellular matrix, the
unitary lesion of schistosomiasis (granuloma) keeps on giving model and
stimuli to new advances of importance for general pathology, medicine and
biology.
Another great impact to medical science, in my opinion still not
sufficiently appreciated by researchers from other areas, concerns the
observation on extracellular matrix degradation which follows the curative
treatment of schistosomiasis in man and in experimental animals. Although
this subject had been extensively studied in physiology and pathology of
connective tissues, especially in rheumatic diseases, in post-partum uterus
involution, in tumor metastasis, etc., the matrix degradation in these
instances was considered as a focal and limited phenomenon. Dense
cicatricial fibrosis was a different matter, and was considered
irreversible.
Now, with ultrasonography facilitating the observations on
post-chemotherapy hepatic fibrosis involution in hepatosplenic patients
submitted to mass treatment in the field, previous clinical and
pathological findings on extracellular matrix degradation were confirmed
and extended. Similar degradation of fibrosis is currently being documented
in the liver of patients with visceral leishmaniasis, and in the murine
heart in experimental Chagas' disease.
Another aspect that may have a significance beyond our expectation, refers
to the type of matrix degradation seen in advanced schistosomiasis. In
general, more is known about matrix formation than about its degradation.
Data on the latter concerning the participation of several proteases and
metallo-proteases, with interference of excitatory and inhibitory factors
originated from studies made in animal models presenting what we may call
"acute" matrix degradation, in which the involution of fibrosis occurs from
1-2 up to 28-30 days. In chronic schistosomiasis extracellular matrix
degradation is partial and occurs in 2 to 4 years after treatment in man or
in 4 to 6 months in the mouse. This is a type that we may call "chronic"
degradation. Are "acute" and "chronic" matrix degradation the same? We do
not know. We should remember that hepatic post-chemotherapy fibrosis
degradation in schistosomiasis is accompanied by a complex set of vascular
re-arrangements, leading to the return of portal pressure toward normal,
with disappearance of esophageal varices, diminution of splenomegaly and so
on. These are aspects that may have considerable practical and conceptual
importance.
The study of schistosomiasis may go well beyond its frontiers, providing
for a great deal of inter-disciplinary collaboration. Unfortunately, some
of such subjects have provoked a fleeting interest, giving the impression
that its potential has been exhausted. Ramon y Cajal said that there are
not such thing as exhausted questions, but only exhausted individuals. The
potential for some multidisciplinary studies on schistosomiasis do remain,
as we shall see below. One example is represented by renal involvement in
hepatosplenic schistosomiasis. The concept of glomerulonephritis mediated
by immune-complexes appeared before it was possible to demonstrate the
presence of antigen in the renal glomeruli. Renal involvement in quartan
malaria allowed the demonstration of malarial antigen in the lesions. Soon
afterwards, the presence of schistosomal antigen (s) was documented in the
kidneys of both man and experimental animals. In subjects living in endemic
areas the presence and intensity of proteinuria showed positive correlation
with hepatosplenic schistosomiasis, even in those presenting normal renal
function. One study made in Sudan failed to show any correlation between
hepatosplenic schistosomiasis and renal disease. However, I would like to
remark that schistosomal glomerulopathy has been subjected to, let us say,
the "Koch' s postulate" test. In Brazil, schistosomal glomerulopathy
affects 15 to 20% of hepatosplenic patients, as seen in clinical and
pathological studies made in several medical centers. Several histological
types may appear, but all are known to be associated with the nephrotic
syndrome, the main clinical manifestation of the condition. Morphological
evidences of pre-clinical forms of renal involvement have been demonstrated
in biopsy material taken during splenectomy in young people. The presence
of antibodies and antigens have been shown by immuno-histology. The full
glomerular lesion has been reproduced in monkeys and rabbits, especially
when they are infected with S. japonicum. However, there is much
more needing investigation. The clinical significance of renal involvement,
its geographic variations and the influence of co-factors are among them.
Let us hope that research on the relationship between schistosomiasis and
renal disease be soon resumed.
Another challenge is represented by the pathogenesis of the hepatosplenic
form of schistosomiasis. There is no clear explanation why some infected
people develop systematized periportal fibrosis, the so-called "pipestem"
fibrosis of the liver, as Symmers called it 91 years ago. In hyperendemic
areas the proportion of hepatosplenic patients may reach 4-12%, which means
that a large majority of heavily infected people living under the same
environmental conditions fail to develop severe disease. Hepatosplenic
patients present heavy worm load, but with mild to moderate worm burden
will develop the severe form of the disease. On the other hand, only a
fraction of heavily infected people will evolve to hepatosplenic
schistosomiasis. The role of the spleen has been emphasized in some
studies, but "pipestem" fibrosis of the liver can occur in the absence of
splenomegaly. These cases are now more frequently seen, probably due to the
use of ultrasonography. There are interesting data pointing to a modulatory
defect due to an abnormal response in the generation of anti-idiotypic
antibodies, but some of our recent results to be presented in this
Symposium failed to give support to such possibility. But, it is not only
the pathogenesis of the advanced forms of schistosomiasis that have excited
the efforts and ingenuity of the scientists. Their association with viral
and bacterial infections sometimes reveals peculiar characteristics.
Problems related to viral hepatitis and septicemic salmonelosis are
examples known by all of you. Further studies are needed to clarify
host-parasite relationship in such situations.
The goal of an effective and practical vaccine against schistosomes has
appeared to us intermittently as very near or too far distant. Much effort
and money have been expended on it. Although a large body of collateral
data on basic knowledge have been produced, it is my opinion that the goal
of a vaccine remains elusive. The question is to know whether we really
need a vaccine. This question is a sensitive one, but we have not so far
attempted to rationally answer it. Of course, the obtaining of such vaccine
will be a breakthrough that will stimulate the whole field of
anti-parasitic research.
Up to this point I have mentioned some facts about schistosomiasis research
that have stimulated investigators in several parts of the world. The
motivation they have to accept the challenge and to come to the meetings to
report to and to learn from colleagues, is the same that moves men and
women of science since Galilei.
In the fields, hospitals and medical clinics there are intense activities
to minimize the defficiencies of our public health assistance and to lessen
patient suffering. Many individuals in these institutions go beyond their
routine and accumulate valuable experience to help the fight against
schistosomiasis. Applied research has always been a significant part of our
Symposia.
Let us hope this Symposium will keep the same high standard of the previous
ones. To achieve this there has been much dedication from the Organizing
Committee, its President, the Fundacao Oswaldo Cruz support and the
enthusiastic response of the Brazilian and foreign investigators.
Tomorrow we will initiate our scientific activities. Let the scientific
progress appear in a cordial and stimulating environment, so all of us will
be looking forward to new advances and to the continuation of this
activities in the next Symposium. Things being so, the V International
Symposium on Schistosomiasis would certainly reach its main objectives.
Copyright 1997 Fundacao Oswaldo Cruz
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