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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 102, Num. s1, 2007, pp. 71-74
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Memórias
do
Instituto
Oswaldo
Cruz,
Vol.
102,
No.
Suppl.
I,
2007,
pp.
71-74
Epidemiological
and
social
determinants
of
Chagas
disease
and
its
control
in
the
Amazon
countries
-
Group
discussion
Antonio Carlos Silveira
Ministério da Saúde, 70736-020 Brasília,
DF,
Brasil
E-mail:
atcrs@uol.com.br
Received
4
July
2007
Accepted
3
September
2007
Code
Number:
oc07136
The emergence of Chagas disease transmission in the Amazon region is a new challenge for controlling the disease. It takes on special importance, considering that: (i) vector transmission in homes in many other areas has now been brought under control, or at least that the technology available for control presents proven efficiency; (ii) the transmission patterns are different; (iii) some of its epidemiological and social determinants or risk conditions are unknown.
The enzootic transmission cycle of Trypanosoma cruzi has long been known in the Amazon region. Carlos Chagas himself already recognized flagellates isolated from monkeys of the species Saimiri scirius as T. cruzi, in the year 1924 (Chagas 1924). Following this, many other animal reservoirs were identified (Deane 1961, 1964). The triatomine fauna is also very diversified and natural infection has been observed in several of the species present (Barret 1988, Coura et al. 1994, Schofield 2002).
However, the domestic transmission cycle has not become established in an evident manner or on a large scale. With the progressive human occupation of the region, introduction of non-autochthonous species or colonization by native species as a result of human predatory action on the natural environment were considered likely (Silveira et al. 1984, Barret 1988, Silveira 1997). So far, it has not been possible to confirm this. Nonetheless, autochthonous cases started to be recognized in the Amazon region, including in countries without a history of occurrences of this disease (Shaw 1969, Rambajan 1984, Beauder 1985). Moreover, increasing numbers of such cases have been found over recent years (Valente 2005). On the one hand, this may be ascribed to possible new events or environmental changes. On the other hand, this is certainly due to the greater attention that has been given to studying the disease and performing disease surveillance in this region, even if done non-systematically.
The means of transmission in the Amazon region do not correspond to those that are recognized as characteristic of the endemic disease, with "installation and permanence" of the vector in the home. The known autochthonous cases are produced by the following means of transmission: (i) oral transmission, which indirectly or passively may be understood as vectorial, provided that it only occurs by means of contamination of foods by the feces of infected triatomines; (ii) vectorial transmission in the home, without colonization, by means of periodic or regular incursions by specimens that invade the home; (iii) vectorial transmission outside of the home, by means of frequent human entry into forests and contact with wild triatomines, as occurs with Rhodnius brethesi in the case of extraction activities relating to the piaçaba palm tree.
The peculiarities of Chagas disease in the Amazon region require the adoption of a surveillance model differing from what has been followed in historically endemic areas, in which it is fundamentally centered on entomological surveillance.
Likewise, in conceptualizing a surveillance and control model for the disease in this region, the following must be considered: (i) the extent of the Amazon territory and the operational difficulties implied; (ii) the fact that it is not recognized as a public health problem in that region; (iii) the resources already installed in the region that mat serve for preventing endemic Chagas disease.
GROUP
ACTIVITIES AND DISCUSSION
The
group discussion was preceded by a presentation by the reporter
on this topic (Marcelo Aguilar), which was developed following a
sequence that considered: (i) the delimitation of the Amazon according
to different criteria (hydrographic, ecological, and biogeographic);
(ii) characterization of the Amazon scenario from the points of
world, national and population geopolitics; (iii) land occupation
patterns; (iv) structural (environmental) elements of the disease;
(v) country-by-country detailing of the existing knowledge about
vectors, reservoirs, infection, and the disease in humans.
This
presentation was accompanied by a complementary presentation by
the president of the session (Antonio C Silveira) covering: (i)
matters relating to the "exceptional" means of transmission
in the region and the approach towards them, which implies the production
of knowledge; (ii) the resources already in place and their possible
utilization for surveillance of Chagas disease, as a condition for
enabling the proposed actions (primarily and essentially supported
by the malaria surveillance system); (iii) the means of institutional
integration and organization and shared activities between countries:
technical meetings in Palmarí, 2002, and within the Amazon
Initiative (AMCHA), 2004 and 2005.
In the
discussion on the topic, the participants contributed a variety
of data and information on their practices in the projects and fields
in which they are active, and with regard to their knowledge of
the situation in the countries that make up the region. These contributions
were considered in formulating the conclusions and recommendations
presented by the reporter (M Aguilar) at the final plenary session,
which are to a large extent included in the report herein presented.
The contributions are enumerated according to the specific subject
dealt with and the authors:
Transmission
by R. brethesi in the Negro river region (Barcelos, state of Amazonas,
Brazil) - Dr José Rodrigues Coura gave a report on the
situation, starting from the initial investigations and highlighting
in particular that: (1) the transmission was basically caused by
invasion of the dwellings by the vectors. The dwellings were precarious
and temporary, and did not serve as a physical barrier against "visits"
by the insects. This differed from some other observations that
attributed greater importance to contact with the vector by humans
during their piaçaba extraction activities (Silveira
& Passos 1985); (2) serological diagnosis presents great difficulties,
which has meant that the criterion for diagnostic confirmation is
that the serum should present three positive reactions; (3) in the
most recent studies carried out in the area, infection with the
strains Z1 and Z3 of T. cruzi was observed; (4) chronic cardiopathy
is unquestionably documented in autochthonous cases, which suggests
that transmission is not a recent occurrence in the region.
Oral
transmission - Dr Roberto Salvatella made the specific proposal
that outbreaks of Chagas disease due to oral transmission should
be prevented and managed by means of food safety methodology, and
that this form of the parasitosis should be considered to be a foodborne
disease. For this, it needs to be proposed that studies on outbreaks
should be done by means of epidemiological studies on foodborne
diseases, with surveys of the critical points and risk analysis
on the foods implicated in such transmission, investigation of factors
favoring transmission by certain foods (temperature, hygiene, preparation,
conservation, and others); development of appropriate domestic technologies
for managing and preparing these foods and dissemination of information
for prevention, directed towards the population.
Regarding
the peculiarities and specificities of vectorial transmission in
the region - One comment of a more general nature that was made
(Dr Pedro Albajar) was on the great diversity of situations and
conditioning factors for the occurrence of the disease in this region.
In other words, the Amazon region cannot be treated as a homogeneous
ecological-epidemiological area.
Specifically
with regard to the knowledge of acute cases among the adult population,
Dr Aluízio Prata made the timely remark that, because of
the lack of domestic vectors, a longer exposure or contact time
between humans and vectors would be needed, since the continuous
risk of vectorial transmission that characterizes transmission in
places where there is colonization of homes does not exist.
Regarding
Chagas disease in the Bolivian Amazon region - Dr Faustino Torrico
indicated that Chagas disease in the Bolivian Amazon region is not
a priority, because of the extensive endemic area in the remainder
of the country, with high levels of transmission in some areas,
despite the intensive chemical control actions that are being carried
out. This means, however, that little is known about the disease
in the Amazon region.
Concerning
the importance that R. stali might have (sometimes referred
to as a potential vector in the Departments of Beni and Pando),
he indicated the need to promote more systematized investigations
in order to demonstrate its capacity for transmitting T. cruzi.
Finally,
Dr Torrico mentioned that human occupation of the Amazon region
is taking place rapidly and without control. The population has
quadrupled over the last decade.
Regarding
Chagas disease in the Colombian Amazon region - Dr Felipe Guhl
made reference to the presence of Triatoma maculata in the
Departments of Casanare and Arauca. Furthermore, R. brethesi and R. pictipes are triatomine species in the Colombian Amazon
region that could have some participation in transmitting T.
cruzi to humans.
On the
other hand, he commented that one additional problem in the Colombian
Amazon region is drug trafficking, with all its implications for
surveillance and control over the disease.
Domestication
of T. maculata in the state of Roraima (Brazil) - Dr José
Rodrigues Coura and his coworkers gave a report on recent investigations
in the city of Boa Vista, capital of the state of Roraima (Brazil),
in which high rates of infestation by T. maculata were found
in homes in the urban area. This veritable "invasion"
could be explained by the overpopulation of pigeons in the city.
Specimens examined did not show natural infection by T. cruzi,
which is understandable because of the preferential association
of the species with birds. Even so, this massive infestation may
represent a future risk, since T. maculata is considered
to be a secondary vector of importance in some countries, such as
in Venezuela.
A final
comment from the reporter for the topic, Dr Marcelo Aguilar, was
in relation to the need to approach the investigation, surveillance
and control of Chagas disease in the Amazon region starting from
what he called "hotspots". The territorial extent of the
region and the great diversity and complexity that exist would justify
this proposal, which is in accordance with what was defined at the
Technical Meeting held in Palmarí, 2002, on the strategies
to be followed for future actions.
According
to what had been agreed at that time, it would be recommendable
to integrate entomological, seroprevalence and clinical studies
for characterizing the known foci of transmission according to the
degree of human impact. The definition given would be areas (generally
concentric) in which the environmental degradation is progressively
lower: strongly altered urban/semiurban center; surrounded by urban
areas with a high degree of intervention, which in turn are surro-unded
by cultivated areas; isolated farms (frequently with residues of
secondary forest) that are bordered by forested areas that are preserved
to a greater or lesser extent. It is considered that this type
of focus should be respected, since it will allow fuller understanding
of the processes that produce the disease in the region.
CONCLUSIONS
AND RECOMMENDATIONS
The conclusions from the meeting can be considered in summary
to be that:
1. Despite
the severe environmental changes that have occurred, generated by
the different types of productive occupation of land in the Amazon
region, there is insufficient evidence of an imminent risk of domestic
colonization by the vectors that maintain a transmission profile
in the way that is seen the original endemic areas. So far, just
a few situations of incipient domestication have been documented,
relating to species like T. maculata, P. geniculatus, P. herreri,
R. neglectus, and R. stali, in restricted areas of Brazil,
Bolivia, and Peru.
2. The
selective deforestation caused by different types of land occupation
in the Amazon region has been associated with areas of transmission
of T. cruzi, with an accumulated risk that is directly proportional
to individuals' ages, which is compatible with an endemic profile
for the disease. These situations occur mainly where R. robustus,
R. pictipes, and R. brethesi are in contact with the
population, without neglecting the importance of other potential
vector species. These situations should especially be watched, since
they are the ones presenting greatest risk of transmission to human
populations.
3. There
are sufficient documented observations to have established that
endemic transmission exists, although at low levels. However, there
have been proven occurrences of severe clinical forms. This situation
has been described in Sucumbíos (Ecuador), Guianía
(Colombia), Cayenne and Cacao (French Guiana), and the upper and
middle Negro river regions of the state of Amazonas (Brazil).
4. These
elements characterize a very particular epidemiological profile
that requires a differentiated approach. This demands the development
of methodologies and techniques suitable for the distinct parasite
circulation dynamics of the region.
5. In
addition to the particular transmission patterns, the development
of new instruments and methods for surveillance and control must
take into consideration the existing opportunities represented by
the resources already installed, especially the malaria surveillance
services that exist in most of the populated areas of the Amazon
region, and the operational difficulties caused by the extent of
the territory and in many cases by its inaccessibility. In this
respect, it cannot be expected that surveillance for Chagas disease
in this region will be set up and implemented extensively, because
of the fact that it is not recognized as a problem and consequently
does not represent a priority.
6. Chagas
disease has already been recognized as an emerging problem in several
countries, and the scientific community and control organizations
have mobilized in search of shared and coordinated action. As a
concrete result from these proposals, a first international meeting
of a technical nature was held in Palmarí, Brazil, in 2002,
at which some guidelines for the investigation, surveillance, and
assessment of the control possibilities were established. At this
meeting, it was proposed to set up an Intergovernmental Initiative
for Surveillance and Prevention of Chagas Disease in the Amazon
Region (AMCHA), and PAHO/WHO was designated to be the Technical
Secretariat. There were meetings in Manaus (Brazil) in 2004 and
in Cayenne (French Guiana) in 2005. At these meetings there was
a consensus regarding: (a) an international surveillance network/system
adapted to the Amazon subregion; (b) measures for surveillance and
prevention of Chagas disease in the Amazon region; (c) proposals
for diagnoses and clinical studies regarding Chagas disease in the
Amazon region; (d) investigations relating to improvement of epidemiological
information, diagnoses, and treatments for the disease.
It was
agreed that the strategy for implementing the initiative should
have an incremental nature, starting with progressive characterization
and demonstration of the risks.
Insofar
as the recommendations could be considered applicable to the topic,
they were put into sequence according to the guidelines, for group
discussion ("Guidelines for Discussion Groups"):
Neglected
or emerging matters/Additional knowledge for formulating surveillance
and control policies
As already
mentioned, it is absolutely necessary to gain new knowledge, thereby
seeking to improve the actions proposed for surveillance and control
of Chagas disease in the Amazon region.
To set
up (or implement) a regular system for surveillance and control
of Chagas disease in this region, the services should be instrumentalized
to adopt the model that has already been formulated and taken as
the consensus by the countries participating in the "AMCHA"
initiative, in which the surveillance objectives are: (i) the disease/infection;
(ii) the vectors; and (iii) the environment.
These
three aspects of the surveillance should be integrated by progressive
development of a standardized georeferencing method for acute cases,
in relation to the known distribution area for the vectors (or potential
vectors) and their preferred ecotope(s). The information generated
should be centralized in a database, using a geographic information
system that is fed with the data gathered by remote sensing and
data obtained by direct collection in the field.
It is
evident that, because of the dimensions of the Amazon region, it
cannot be expected that comprehensive intervention for surveillance
and control of Chagas disease will be established immediately. The
initial recommendation is to work on the critical areas already
identified as presenting frequent transmission of T. cruzi ("hotspots"),
at which the epidemiological characteristics of the disease should
be studied in depth. Implementation of the proposed actions in these
areas will make it possible to validate the recommended technical
procedures and actions, with gradual expansion for them.
With
regard to the particular situation of family outbreaks of Chagas
disease due to oral transmission, it is recommended, as suggested
by Dr Roberto Salavatella, that these should be treated on the basis
of food safety methods. In such cases, for the purposes of prevention,
it is taken that Chagas disease is a foodborne disease.
Concerning
the production of additional knowledge, it is proposed (as already
identified at meetings of the AMCHA initiative) that investigation
projects should be developed as a matter of priority, taking the
following into account (a) categorical proof for the transmission
route(s) of the focused outbreaks (micro-epidemics) that have been
described, with identification of the risk factors implicated; (b)
identification of the ecological, cultural, economic and social
factors, and contingencies involved in interactions between humans
and triatomines, including seeking to elucidate situations such
as the incidence of human infection due to invading vectors that
do not colonize the dwelling; the possibility of vectorial transmission
outside the home (apart from the transmission already known through R. brethesi); and in outbreaks due to oral transmission;
(c) studies on the distribution of vector species, starting from
characterization of the natural environments and ecotopes in which
they have been found, with the aim of predicting their presence
in areas with similar ecological-physiographic characteristics;
(d) studies on the physical patterns of homes and their vulnerability
to invasion or colonization by tria-tomines, thereby seeking to
define the risk that exists; (e) studies on wild triatomines that
are recognized as potential vectors, in areas close to or connected
with human settlements; (f) specific studies on R. prolixus and R. robustus, with the aim of greater understanding of
their differences and interactions, and their potential for hybridization
in nature; (g) the possible influence of chemical control activities
against malaria vectors in relation to repelling triatomines; (h)
identification of possible clinical peculiarities of Chagas disease
in the region.
Capacitation
and technology transfer projects
With
regard to capacitation needs, it is recommended that the projects
implemented should take the following into consideration:
1. Training
for laboratory personnel who work on the epidemiological surveillance
of malaria, so that they can recognize T. cruzi. The most
important source of information for identifying acute cases is certainly
the data "resulting" from parasitological diagnoses from
thick drops of peripheral blood, stained using the Walker/Giemsa
method. These tests, which are carried out extensively for malaria
surveillance and so far have been allowing sporadic or "random"
detection of T. cruzi, should be used routinely for Chagas
disease surveillance in this region.
Examination
of fresh peripheral blood offers practical advantages and may be
faster and more sensitive, with regard to viewing the parasite in
movement, especially considering that cases with low levels of parasitemia
are common. Nonetheless, from the perspective of carrying out wide-ranging
surveillance action on Chagas disease, together with malaria surveillance,
there would not be any procedure other than what is routinely adopted
for diagnosing malaria.
When
autochthonous acute cases of Chagas disease are identified, it may
be recommendable that, over the course of the investigations, fresh
blood tests are performed on contacts related to the case.
2. Strengthening
of the capacities for clinical and laboratory diagnosis, thereby
determining the significance of the cross-correlated results and
defining a protocol for serological diagnosis.
How
to achieve capacitation and technology transfer
To capacitate
the laboratory personnel, it is proposed that, where there is regular
training for technicians working within malaria surveillance (which
is considered to be the practice within malaria programs), a week
on T. cruzi identification should be inserted into the course
program.
In addition
to T. cruzi investigation, it is considered recommendable
to include information on epidemiology and biosafety in the program
content. The target public would be technicians involved in diagnosing
malaria (of high school or university level).
In other
situations in which there is no possibility of integrating such
material in malaria courses, areas considered to be a priority will
have to be selected for promoting capacitation. These will be based
on histories, occurrences of autochthonous cases, seroprevalence
data that may be available, and the opportunities and facilities
that may exist.
For
clinical and auxiliary medical personnel, it is suggested that courses
directed towards the areas of greatest risk should be promoted,
with identification of services that could act as reference centers
for Chagas disease patient care, and whose trained professionals
would serve as multipliers for extending the knowledge to primary
healthcare services.
Implementation
of the dissemination of information
Considering
the limited existing knowledge and its fragmentation, it is fundamental
that a supranational body be created, to bring together and regularly
disseminate the information generated.
In this
respect, the Internet program that ALCUE Health proposes to create
may take on a role of prime importance in surveillance and control
for Chagas disease in the Amazon region, as an instrument to be
used regularly by the AMCHA initiative.
Availability
of the information necessary and its sufficiency
As already
mentioned several times, Chagas disease in the Amazon region is
an emerging public health problem that follows transmission patterns
that are largely unknown. The knowledge accumulations are restricted
to certain areas and episodic events, although tending towards some
continuity, which may mean that endemic Chagas disease is becoming
permanently established in the region. The operating models for
surveillance and control that have so far been formulated and incompletely
developed must be refined and possibly redefined as the determining
conditions for the occurrence of Chagas disease in the Amazon region
become known.
Copyright
2007
Instituto
Oswaldo
Cruz
-
Fiocruz
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