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Chagas disease has left millions of South Americans crippled by heart
disease and other chronic disorders. It kills tens of thousands every year.

But within 10 years, Triatoma infestans – the insect which spreads the
parasite that causes the disease – could be virtually wiped out by an ambitious
plan to spray more than eight million homes with insecticide.

The aim is to stop the human suffering caused by the disease and save
millions of pounds in health care cost and lost income.

Foundations for the scheme were laid in July, when government representatives
from Brazil, Paraguay, Uruguay, Bolivia, Argentina and Chile adopted a resolution
calling for action to eradicate T. infestans. Peru is also expected to become
involved.

The countries have agreed to set up an intergovernmental commission
for Chagas disease, to raise and administer funds and coordinate the plan.
Under the aegis of the Pan-American Health Organization and part-funded
Trby the European Community, a meeting next month in Montevideo, Uruguay,
is expected to approve a draft action plan and a structure for the commission.

The intention is to spray every home in areas known to be infested with
T. infestans (see Map), in the biggest insect control programme to be mounted
in the world since the attempt to eradicate malarial mosquitoes in the 1960s.

The malaria campaign failed, but international programmes to control
other insect-borne diseases have since had much greater success. For example,
the West African onchocerciasis control programme brought together 11 countries
in the fight against one of the principal causes of blindness in the world.
By targeting insecticides against the blackflies that transmit onchocerciasis,
and treating sufferers with drugs, the incidence of the disease has been
reduced sharply over the past decade.

By comparison, the programme to eradicate Chagas disease will cover
an area six times larger, involving parts of Argentina, Brazil, Bolivia,
Chile, Paraguay, Uruguay and southern Peru. In this region, transmission
by T. infestans accounts for 80 per cent of Chagas disease cases. Other
insects found in homes across South America do spread the parasite that
causes Chagas disease, but these are expected to be destroyed by the measures
taken against T. infestans.

Apart from an area of Bolivia, where it lives in the wild and feeds
on guinea pigs, T. infestans lives almost exclusively in people’s houses
and outbuildings, particularly in underdeveloped rural areas. This makes
it an easy target for insecticides.

During the day, the bugs – which resemble large bedbugs and can grow
to a length of about 2.5 centimetres – hide in cracks and crevices. At night,
they emerge to suck blood from sleeping people. There may be more than 1000
bugs living in one small house. Since each bug sucks blood once every four
to nine days, every person living in the house may be bitten by 25 bugs
or more each night.

The adult bugs take so much blood at each meal – a third of a millilitre
– that they can contribute to chronic anaemia in their victims. But the
consequences are frequently much more serious.

Many bugs are infected with the protozoan parasite Trypanosoma cruzi,
the cause of Chagas disease. As the bug takes its meal of blood, it defecates
the remains of its last meal, along with the parasites, onto its victim’s
skin. When the person scratches the bite, the bug’s faeces can be rubbed
into the wound, allowing the parasite to enter the bloodstream.

The chances of becoming infected after a single bite are remote, perhaps
1 in 10 000. But someone who may suffer thousands of bites a year has a
high risk of eventually becoming infected.

According to WHO estimates, about 500 000 people become infected with
T. cruzi every year, 300 000 of them children. Between 10 and 15 per cent
of them die during the fever typical of the acute phase of Chagas disease.

The rest become chronically infected. The parasite circulates in the
bloodstream, invading cells in most of the organs of the body. It concentrates
particularly in heart muscle and the muscle and nerves of the gastrointestinal
system. It replicates inside the cells, ruptures them, and goes on to colonise
others.

After some years, the walls of the heart can weaken and may eventually
burst. The oesophagus, colon and other parts of the digestive tract widen
and the walls grow thin. The muscles in the wall become unable to push food
along the gut and blockages are common. Those affected lose the capacity
to swallow and defecate normally. People with Chagas desease become progressively
weaker and unable to work and often die from heart failure and digestive
complications.

There are two drugs, benznidazole and nifurtimox, which are thought
to cure up to 70 per cent of cases of infection. But they must be given
within the first few days of infection. Unfortunately, people rarely know
they are infected this soon after a bite because the acute phase takes some
days to show its presence. The main application for the drugs is after laboratory
incidents in which someone has been accidentally inoculated with the parasites.
The drugs are also very expensive and have unpleasant side effects.

The WHO estimates that between 16 million and 18 million people in South
America are infected with T. cruzi. Another 90 million are at risk, more
than half of them in the area where T. infestans is endemic.

Chagas disease puts a tremendous drain on already overstretched health
services. A course of drugs to correct the erratic heartbeat common to sufferers,
costs about $200 a year. Corrective surgery for damage to the digestive
tract can cost up to $2000. And implanting a cardiac pacemaker can cost
more than $6000.

In the seven countries involved in the programme, the potential savings
are huge. An unpublished study in Chile recently put the direct costs of
Chagas disease, including those on the health service, at $36 million a
year. But the full costs are much greater. Estimates of the productivity
of those who would be saved from the disease if transmission is halted stand
at around $1200 million every year.

The plan that South American officials will discuss next month builds
on progress that some countries, notably Brazil, have already made in combating
T. infestans. The Brazilians combined spraying with follow-up inspections
in the target area to ensure the bug did not return. Chris Schofield, an
expert on Chagas disease, who used to work for the Tropical Disease Research
Programme at the WHO in Geneva, says the Brazilian programme was splendidly
successful. ‘They eliminated T. infestans from 80 per cent of the affected
area,’ he says.

But the programme lost impetus after changes at the Ministry of Health.
The bug started to return. Joao Carlos Pinto Dias, former director of Chagas
disease control at the Ministry of Health in Brazil, says: ‘From that experience
we realised that the key problem was no longer technical but administrational
and political. In all Latin American programmes against Chagas disease the
best results have clearly depended on continuity.’

The international programme was designed to ensure that continuity in
an area where political instability is endemic – an international project
is less likely to be interrupted by a change of government in a single country.
‘If things are not going well in one country, the programme can, we hope,
be supported by neighbouring countries,’ says Pinto Dias.

In the affected zone, every dwelling, whether or not it is known to
be infested, will be sprayed with pyrethroid insecticides. More than eight
million will be treated at an average cost of $30 per house. Altogether,
124 tonnes of insecticide will be needed.

The pyrethroids used will include cypermethrin, cyfluthrin, deltamethrin
and cyhalothrin. Schofield says these have all passed international safety
tests and are registered for public health use. They break down quickly
in soil, he says, and are not expected to pose any environmental hazard.
Spraying needs to be done just once in the initial ‘attack’ phase of the
programme.

One year later, the success of the spraying will be evaluated. Community
workers will search houses for bugs and ask householders if they have seen
any. While this is going on, a programme to educate people in the affected
areas will be in progress. Householders will be able to report any sightings
of bugs to local information posts. Inspectors will visit these posts regularly
and arrange to have houses resprayed as necessary. This ‘vigilance’ phase
is expected to last up to six years.

Schofield says the synthetic pyrethroids that will be used are highly
effective against T. infestans. The bugs reproduce very slowly – they have
only one or two generations a year. Consequently, strains resistant to pesticides
are slow to emerge. Mosquitoes, by contrast, became impossible to eradicate
because of the rapid spread of resistance to insecticides.

Even in the laboratory, scientists have found it very difficult to breed
strains of T. infestans that are resistant to pyrethroids, Schofield says.
Nevertheless, live bugs collected from houses during the vigilance phase
will be reared in a reference laboratory in order to monitor whether resistance
to the insecticides used is developing.

No problems are anticipated in gaining cooperation from local people.
The experience from Brazil suggests that, once people know what the authorities
hope to achieve by spraying, they usually welcome it. Schofield adds: ‘In
many houses, the spraying will get rid of other pests, such as cockroaches,
fleas and bedbugs, at least temporarily, so people are often very keen to
have their houses sprayed.’

The programme, which will also include measures to prevent transmission
via transfusion of infected blood, is expected to take up to 10 years. The
health ministers anticipate that the cost will lie between $180 million
and $370 million. The lower figure supposes that Brazil has already achieved
control of the insect in 85 per cent of its affected area. The upper figure
assumes that infestation in Brazil returns to 1983 levels before eradication
attempts begin.

Pinto Dias estimates that, even if the cost is $370 million, the benefits
will be enormous. Considering just the medical savings, the financial benefits
are expected to be equivalent to investing the money spent at an annual
interest rate of 14 per cent.

And at the end of the commission’s 10-year lifetime, those involved
hope to have achieved more than just the eradication of Chagas disease.

‘Chagas disease is not an isolated problem,’ Pinto Dias says. ‘Our approach
to controlling it will help to build community organisations and our experience
in Brazil shows that, from this platform, these communities can start to
tackle other problems, such as basic health needs and the relationship of
the community to the state.’

Sharon Kingman is a writer who specialises in health and medical matters.