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IN THE 1950s and 1960s, health officials in Brazil had brought malaria
in their country under control. Transmission of the parasite that causes
malaria had virtually stopped in the most densely populated central and
coastal regions. Although malaria continued in the Amazon region, few people
were exposed to it there, so it did not seem to pose a large threat.

Brazil controlled the disease by spraying the walls inside houses with
insecticides to kill the mosquitoes that carry the malaria parasite. This
strategy was particularly effective against the species of mosquito that
prefer to stay inside buildings, rather than resting outdoors.

Similar public health programmes reduced theL incidence of malaria in
much of Venezuela, Guyana and Surinam (especially in the lowland coastal
areas), as well as in Brazil. Unfortunately, this trend did not last. Over
the past 10 years, the numbers of cases of malaria throughout the Amazon
region, particularly in Brazil, has risen almost exponentially. In 1983,
more than 297 000 cases of malaria were reported in Brazil, almost 287 000
of them from Amazonia. By 1988, those figures had risen to about 560 000
and almost 500 000 respectively.

To help Brazil to counter the epidemic, the World Bank has lent the
country $99 million (around Pounds sterling 60 million). The money will
partly help to develop the Brazilian agency in charge of controlling malaria,
the Superintendency for Public Health Campaigns (SUCAM). It will also pay
for Brazil to monitor how many people catch malaria, to treat patients,
run education projects and improve drainage, including eliminating sites
where mosquitoes can breed. Finally, it will allow SUCAM to buy materials
and equipment for applying pesticides.

Malaria is one hardship that those desperate to benefit from the riches
of the Amazon have to tolerate. One of the most obvious reasons for the
sudden change in the statistics has been the huge influx of immigrants to
the Amazon region, most of whom have no immunity to malaria. The populations
of the Amazon states grew 5 per cent a year between 1970 and 1980; in most
states, the population has doubled during the 1980s. In the state of Rondonia,
which has attracted more immigrants than other areas, the population has
increased by more than 1200 per cent between 1950 and 1980.

People have been attracted to the region for many reasons. The building
of the Transamazon highway, begun in the late 1960s, made it easier to enter
the Amazon basin, allowing people to establish farms and settlements. Settlers
in Rondonia founded more than 30 000 new farms within 10 years. People have
also been drawn by the prospects of finding gold and by jobs in mining.

Many settlers have no immunity to malaria, probably because they come
from areas where the disease has remained under control. The association
with new settlers colonising the area has brought the nickname ‘frontier
³¾²¹±ô²¹°ù¾±²¹â€™.

The rising incidence of malaria also has a knock-on effect in Brazil
outside the Amazon. People who go to Amazonia to work, and return home,
infected with the parasite, to areas where malaria is absent, can spark
off local epidemics. In 1987, SUCAM had to divert resources to silence 29
new outbreaks of malaria outside the Amazon region.

Settlers are vulnerable to being bitten by malarial mosquitoes because
they live in makeshift shelters with no walls to stop the insects entering.
Miners, particularly, wear minimal clothing and many live in camps beside
streams where mosquitoes can breed, on boats or even on rafts, if the operation
involves dredging for minerals on the river bed.

The push into the Amazon jungle has created additional opportunities
for mosquitoes to breed. Anopheles darlingi, the most important vector of
malaria in the region, generally breeds in pools of stagnant water, as well
as at the edges of streams and rivers protected from the current. And after
a river has flooded, water remains trapped along the banks, providing ideal
breeding grounds for mosquitoes.

New roads through the Amazon region create similar habitats: construction
workers building roads dig channels on either side of the highway to raise
it to a suitable level. When these flood, the mosquito moves in to lay eggs.
Culverts dug beneath the road to drain water away become blocked, so flooding
again results.

In areas where farmers have cleared forests to cultivate the land, the
soil erodes and washes down into the main rivers. There, it silts up the
banks, increasing their height and making it harder for water to drain away
after flooding.

Mining itself can generate breeding sites for mosquitoes. Sites where
there has been opencast mining can fill with water, again encouraging mosquitoes
to breed.

Once bitten by a parasite-carrying mosquito, anyone who catches malaria
in the Amazon region has few opportunities for treatment. Miners move around
a great deal in search of work, and many mines are accessible only by air.
Even in the most densely populated areas, there are few health centres.

The species of parasite which is the most common cause of malaria in
the Amazon is Plasmodium falciparum. This is the most severe form of malaria.
It is often fatal if not treated. In the Amazon, it is resistant to most
antimalarial drugs, including chloroquine.

To complicate matters further, traditional methods of controlling malaria
may not work well in the Amazon. The species of mosquito responsible for
transmitting most cases of malaria in the Amazon forests looks exactly the
same as the species that spreads malaria in the lowland areas of Venezuela
and Guyana. Yet while the latter spent most of its time inside dwellings,
where it was easy to spray it with insecticide, the Amazonian variety prefers
to be outside. It enters shelters and buildings, feeds on its victim, and
flies out again to lay its eggs.

No one knows why the mosquitoes behave differently. This species of
mosquito may have originally lived outdoors and fed on animals in the forest,
but then had to adapt to an indoor life, feeding on humans, when the forest
and its animals disappeared. An alternative theory is that insecticides
have put pressure on A. darlingi to evolve its outdoor habit. However, this
hypothesis contradicts the observation that malaria is worse when people
first colonise an area, when they tend to live outdoors.

Whatever the reason, the mosquitoes’ dislike of remaining inside dwellings
makes it difficult to control their numbers with insecticide. The loan from
the World Bank includes a portion for spraying inside houses with DDT, a
pesticide banned in much of the developed world. According to World Bank
News (2 June, p 3): ‘The use of DDT, the pesticide recommended by the World
Health Organization for malaria-control operations, will pose no negative
environmental impact.’ The amounts being used, says the newsletter, ‘will
be minimal compared with those previously used in agricultural spraying’.
The loan includes allocations for training on safe techniques when spraying
and for monitoring the use of the pesticide.

Albert Heier, a spokesman for the Environmental Protection Agency in
Washington DC, says that the US banned DDT because of its persistence in
the food chain, and because insects became resistant to it. Nevertheless,
he believes that the benefits of DDT would outweigh its risks in a country
with a huge outbreak of malaria.

DDT is not the only insecticide that the Brazilian authorities will
employ. Even if the others, such as synthetic pyrethroids, have better reputations
for their impact on the environment, it is still important to evaluate the
effectiveness of spraying. Apart from the outdoor habit of A. darlingi,
another difficulty is that there are no walls to spray in many dwellings.
To counter this problem, officials in some places have adopted a policy
of making curtains out of locally produced raffia to resemble walls, and
spraying these. Evaluation of the impact of this strategy will be difficult,
because scientists know very little about the habits of the mosquitoes of
the forests.

Brazil’s experience of malaria in the Amazon raises the issue of how
little attention is generally paid to the impact of development projects
on health. The World Bank, which provided loans for many of the projects
in the Amazon basin, has recently set up an environment department. Visvanathan
Rajagopalan, a vice-president of the World Bank, says the department’s function
is to examine ways of managing natural resources, improving conservation
and the ecological impact of projects. ‘These things are receiving much
greater attention than in the past,’ he says.

Bernhard Liese, also with the World Bank, points out that in Brazil
no one understood the intricate factors contributing to the malaria epidemic
in the Amazon until it had been going on for some time. Disorderly development,
with many families moving in each day by any possible means of transport,
made it difficult to evaluate what was going on. ‘Amazonia really is a wild
west, a frontier,’ he says.

It took time for SUCAM to learn that frontier malaria was a completely
new type of malaria, Liese adds. Although the disease concentrates in areas
of settlements and gold mines, the epidemic dies down after three or four
years, when water around the settlement becomes too polluted for the mosquitoes
to lay their eggs in it.

The World Bank maintains that, even though it lays down strict rules
about the ways in which countries can spend its loans, it cannot stipulate
that they take measures to reduce adverse effects on health when carrying
out projects. That is up to the country concerned, the bank believes.

Not everyone agrees. Bruce Rich, a senior attorney with the Environmental
Defense Fund, an independent organi sation based in Washington DC, which
focuses on environment and development in the third world, and particularly
the role of the World Bank, holds a different view. He says that the World
Bank, which since the early 1980s has loaned hundreds of millions of dollars
to Brazil for development of the Amazon region, ‘has a direct responsibility
for this disaster’. Of the latest loan, for the control of malaria in the
Amazon, Rich says: ‘For a country like Brazil, that’s a very expensive way
of standing still.’

Further reading ‘Human migration and the spread of malaria in Brazil’,
A. Cruz Marques, Parasitology Today, 1987, vol 3, p 166.

Report on a Technical Consultation on Research in Support of Malaria
Control in the Amazon Basin, available on request from the Tropical Disease
Research Programme of the World Health Organization, 1211 Geneva 27, Switzerland.