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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 106, Num. s1, 2011, pp. 105-106
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Memórias do Instituto Oswaldo Cruz, Vol. 106, Special Issue, pp. 105-106
Original Article
The
prospect of eliminating malaria transmission in some regions of Brazil
Pedro Luiz Tauil+
Programa de Pós-Graduação
em Medicina Tropical, Faculdade de Medicina, Universidade de Brasília,
Brasília, DF, Brasil
+ Corresponding author: pltauil@unb.br
Received 19 April
2011
Accepted 8 June 2011
Code Number: oc11146
Abstract
This paper discusses
malaria epidemiology and control in Brazil as well as the prospect of interrupting
transmission in some areas of the country. The concepts of receptivity and vulnerability
of an area to malaria transmission are analysed to predict where elimination
might occur in a near future. Outside of the Amazon Region and in the oriental
states of the Amazon, such as Tocantins, Maranhão and Mato Grosso, it
is likely that malaria transmission can be eliminated with the development and
sustained use of a good surveillance system.
Key words:
malaria - Brazil - elimination - prospects
Doctor Robert D
Newman, director of the World Health Organization's (WHO) Global Malaria Programme,
recently stated in the WHO Bulletin (Newman 2011) "that eradicating malaria
is the only morally acceptable end-goal, one that will take 40 years or more
to achieve. Today, it is possible to reduce malaria in the places where it is
worst and to eliminate it from the fringes where it is already low. But it is
not possible to take the centre of Africa and reduce malaria to zero with today
tools".
The incidence of
malaria is influenced by political, economic, social, ecological and biological
factors. The absence of effective control measures, such as an efficacious and
safe vaccine, also plays a role. For these reasons, one could say that Dr. Newman's
statement is also valid in Brazil.
Malaria incidence
in Brazil varies throughout the country. For the last 40 years, the disease
was concentrated in the Amazonian Basin Region, which includes the states of
Acre, Amapá (AP), Amazonas, Maranhão (MA), Mato Grosso (MT), Pará,
Rondônia, Roraima and Tocantins (TO). Currently, greater than 99% of reported
cases in the country occur in these states.
The Amazon Region
possesses several environmental characteristics that favour the transmission
of malaria and make the disease control difficult. The first of these factors
is the abundance of the Anopheles (Nyssorhynchus) darlingi
mosquito, which is the main malaria vector in the country. Clean, hot and slow-moving
water is the main breeding site for the mosquito. In addition, temperatures
above 16ºC, low altitude, high humidity and rainfall are all favourable
conditions for the survival of the mosquito, which seeks shelter in the surrounding
forests. All of these characteristics are found in the Amazon Region and make
this region highly receptive to malaria transmission.
Related to these
environmental factors, there are social and economic determinants of malaria
transmission. For example, provisional houses, which are often missing complete
exterior walls, are found in areas that have experienced deforestation, recent
colonisation and not mechanical mineral exploitation. Without exterior walls,
the mechanical barriers to mosquito bites are practically non-existent. In the
absence of complete exterior walls, insecticide spray cannot be applied. In
addition, the low population density and long distances between localities make
access to these areas difficult and transportation costly.
The cases of malaria
have been concentrated in this region since the early 1970s. These cases have
been directly related to the intense, but disorganised, occupation of the region
by migrants from other Brazilian regions. These immigrants moved with encouragement
from the government and envisioned economic development as the ultimate goal.
Even within the
Amazon Region, the incidence levels of malaria vary by location. Malaria is
concentrated in areas where groups of people move in search for better living
conditions. These areas include the periphery of large cities and sites of recent
colonisation, mining, agricultural projects, construction of roads and hydroelectric
plants.
In 2007, more than
80% of malaria cases were reported in 60 municipalities. This is only 7.4% of
the 807 municipalities in the Brazilian Amazon Region, according to data from
the National Programme of Malaria Control of the Ministry of Health in 2008.
This unequal distribution is related to the migration of people to specific
regions. In general, areas with high transmission levels are those where people
have just recently arrived. In these areas, the houses are precarious and work
conditions are poor. The people that move here live next to the forests and
water collections that support malaria transmission.
In Brazil, 333,424
malaria cases were reported in 2010 and, of these, 332,310 (99.7%) were contracted
in the Amazon Region. Of the cases reported in the extra-Amazon Region, 85%
were imported from the Amazon or from other endemic countries, and only 168
cases were autochthonous. Transmission outside of the Amazon is rare and is
restricted to small residual foci or new foci with low rates. These remaining
disease foci are the result of reintroduction of the parasite from patients
who where infected in areas where the vector is still present. In 2010, the
states of Espírito Santo, Paraná and São Paulo (SP) reported
the majority of the malaria cases (45, 42 and 20, respectively).
The present objectives
of the National Programme of Malaria Control include interruption of malaria
transmission in urban areas of the Amazon Region, which is a prospect that seems
to be reachable. At the same time, some states in the eastern Amazon Region
(TO, MA and MT) are reporting a decreasing number of new malaria cases every
year, which allows us to visualise a possible interruption in transmission in
the near future.
In areas where
transmission of malaria has already been interrupted, the National Programme
aims to keep transmission rates at zero. In the case that outbreaks do occur
in these areas, the National Programme aims to use a surveillance system for
early detection.
It is worthwhile
to remind ourselves of two principles of malaria epidemiology: receptivity and
vulnerability. Receptivity refers to the presence of conditions that are ideal
for disease transmission, specifically the existence of a minimum density of
competent vectors. Vulnerability refers to the probability that infected people
from endemic areas enter the region and introduce the parasite.
In Brazil, the
receptivity of regions outside of the Amazon is decreasing substantially every
year with increasing deforestation and fewer breeding sites for the An. (Nys)
darlingi mosquito. In the forests along the Atlantic, particularly in the
Southeast and South Regions, from the state of Rio de Janeiro to the north of
the state of Rio Grande do Sul, the vector Anopheles (Kerteszia) cruzii
still exists. This mosquito proliferates in water collections in bromeliads.
Along the coastline, from AP, in the north Region, to SP, it is possible to
find the Anopheles (Nyssorhynchus) aquasalis, which breeds in brackish
water. Other malaria vectors of the albitarsis species are found in other
regions of the country.
Therefore, regions
outside of the Amazon do exhibit receptivity and require a sensitive surveillance
system to detect early cases of malaria to provide immediate treatment and to
prevent local transmission. Areas that are visited by a large number of people
from endemic areas become more vulnerable to malaria transmission and must undergo
active and effective surveillance. Well-trained individuals who have fieldwork
experience are an important resource needed to achieve the objective of interrupting
malaria transmission.
In the Amazon Region,
urban areas and other important municipalities are highly receptive, as these
areas still have forests and breeding sites for mosquitoes primarily in the
periphery of the cities. Moreover because of the high rates of travel from rural
to urban areas, these areas are still vulnerable to introduction of the parasite
by symptomatic and asymptomatic carriers of Plasmodium sp.
Any program of
disease control aims to reduce the mortality and severity of disease (Tauil
1998). In the case of malaria, these objectives are being met in Brazil. The
number of malaria deaths is decreasing, with less than 100 cases per year in
the last five years. Additionally, the rate of hospitalisation due to malaria,
a proxy for disease severity, is decreasing; in 2010 there were approximately
5,000 cases.
The National Programme
aims to reach these objectives by employing the strategies of early diagnosis
and immediate treatment of confirmed cases. Recent data show that more than
60% of cases start treatment within 48 h of the onset of symptoms.
More ambitious
objectives, such as the reduction of disease incidence, elimination of transmission
and eradication are being pursued adding integrated measures of vector control
to early detection and treatment of cases looking for reducing the time parasites
remains in the blood of people as sources for mosquitoes infections. These methods
include the use of impregnated bed nets and improvements in epidemiological
surveillance for early detection and treatment. New drugs and shorter treatment
schedules are necessary to overcome drug resistance and improve patient compliance.
In the last few
years, the incidence of malaria in Brazil has been declining. Disease elimination,
which is defined as the absence of autochthonous cases in a predetermined area
with the use of control activities (Evans 1985), is being achieved in Brazil
outside of the Amazon. Here, only a small number of residual cases are being
reported. However, eradication, which is defined as the absence of autochthonous
cases in a predetermined area without the use of any control activity (Henderson
1980, Fenner et al. 1988, Forattini 1988, Oliveira-Ferreira et al. 2010), is
still a remote objective due to the continued receptivity and vulnerability
of a very large portion of Brazil.
References
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DA, Arita I, Jezek Z, Ladnyi ID 1988. Smallpox and its eradication, World
Health Organization, Geneva, 1460 pp.
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Varíola, erradicação e doenças infecciosas. Rev
Saude Publ 22: 371-374.
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Smallpox eradication. Public Health Rep 95: 422-426.
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Learning to outwit malaria. Bull World Health Organ 89: 10-11.
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in Brazil: an overview. Malar J 9: 115.
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Copyright © 2011 - Instituto Oswaldo Cruz - Fiocruz
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