To better understand why malaria has
become such a threat and what can be
done to stop the disease, it helps to know
a little biology. Malaria is caused by
four closely related parasites, the deadliest of which is Plasmodium falciparum,
which has a particular fondness for
anopheles mosquitoes. The parasites enter the bloodstream when an infected
mosquito bites a human. Then they multiply inside the host’s liver and red blood
cells. (That’s why pregnant women, who
make lots of blood to nourish their growing fetus, are especially vulnerable.)
Eventually the red blood cells burst with
a new generation of parasites, causing
fever, shivering, pain and sometimes
death. The cycle of transmission is complete when another mosquito bites an infected person and picks up more parasites.
You might expect that one bout of
malaria would lead to lifelong protection
against the disease. But for complicated
reasons, that is not the case. The illness
tends to be less severe in adults who are
continually exposed to the parasites. But
when young children become infected,
they are much more likely to suffer severe
anemia and convulsions that may lead to
permanent brain damage and death.
For decades, the best treatment for
malaria was an inexpensive medication
called chloroquine, first discovered in
Germany in 1934 by a researcher working
for Bayer. Chloroquine was so effective that
it seemed it might vanquish malaria forever.
But by the 1970s, the drug had been used so
widely to treat all kinds of fevers, not just
those caused by malaria, that the malaria
parasites became resistant and doctors
had to turn to a second medication, called
sulfadoxine-pyrimethamine, or SP. But
within five years, the parasites started to
develop resistance to SP as well. Today resistance to both drugs is rampant in many
parts of Africa, where resistant malaria parasites are the leading cause of death.
At the same time, efforts to control
anopheles mosquitoes have been more or
less abandoned. Part of the problem was
the realization that malaria could never be
completely eradicated from tropical regions the way it had been in the U.S. and
other countries in temperate zones. There
was also a growing backlash against DDT, a
pesticide that is highly effective at attacking mosquitoes but whose indiscriminate
use in agriculture killed many fish, beneficial insects and birds. Although only
small amounts of DDT are needed to control malaria – usually in indoor-spraying
campaigns – its toxic reputation made cashstrapped governments in Africa, which often
must rely heavily on international donors,
hesitant to use it.
So much for how things got so bad. The
silver lining to all this heartache is that the
outlines of a workable solution have at long
last emerged. No one is promising an end
to all deaths from malaria. But doctors estimate that hundreds of millions of people
could be spared the illness and the mortality rate could be cut in half. The catch: although astonishingly inexpensive (at least
by the industrial world’s standards), an effective response is still beyond the financial
resources of the poorest nations of the
world, particularly those in Africa. There
simply can be no progress without help
from the developed world.
To be successful, any antimalaria campaign must do two things: treat the illness
and prevent the transmission of parasites.
Several pilot studies conducted in Africa
have proved that combination therapy, in
which at least one of the medications is derived from a plant called Artemisia annua,
or sweet wormwood, easily destroys drugresistant malarial parasites in the bloodstream. Using several drugs at once, often
in the same pill, greatly decreases the risk
that the parasites will become resistant.
As an added bonus, artemisinin, the active
ingredient in Artemisia annua, acts very
quickly, further decreasing the chances of
drug resistance.
The full three-day course of treatment with artemisinin-based combination therapy costs from $1 to $10 a person,
depending on whether it is purchased in
the public or private sector. Unfortunately, that’s at least 10 times the price
of current, albeit ineffective, treatment
programs. Most impoverished African
governments simply cannot afford to foot
the entire bill for combination therapy
and the training required to give it, and
the same holds true for the majority of
their private citizens, many of whom already spend a third of their income on
malaria treatment.
Although nearly every developed country and most major international aid organizations have said they are ready to
help finance artemisinin-based treatment
in Africa, that support has not always been
forthcoming. Some health experts believe
a report on artemisinin-containing therapy due out from the U.S. Institute of
Medicine this week will dissolve any lingering reluctance.
And what about prevention? Many
African countries are working to sell or distribute low-cost insecticide-impregnated
mosquito nets. These function as traps for
mosquitoes, which are attracted by the
carbon dioxide that sleepers exhale and
are then killed by the insecticide. The nets
are portable, so they can be taken along by
their owners if they need to move. In villages where at least 80% of pregnant
women and children under age 5 sleep
beneath insecticide-impregnated mosquito
nets, the rate of illness for all residents has
dropped dramatically. Unfortunately, only
1% or 2% of people in malarial zones sleep
under mosquito nets. Also, most nets need
to be retreated every six months, and they
are less effective in areas where anopheles
mosquitoes bite all day long instead of just
at night.
A more controversial but nonetheless
effective method of reducing transmission
is to spray DDT inside huts and other buildings. Intriguingly, DDT is often better at repelling mosquitoes than killing them. This
requires much less pesticide than was once
sprayed on crops and swamps. Indeed, if
DDT had been used only for medicinal purposes, it might never have acquired its
toxic reputation. An international antipesticide treaty that took effect last May
makes an exception for the use of DDT in
malarial areas, but some health experts
are worried that the bureaucratic headache of applying for an exemption will
limit the effectiveness of DDT.
Recent experience in South Africa
shows just how well DDT can work. In 1996
the South African government, under pressure from international and domestic environmental groups, decided to phase out its
use of DDT in residential spraying and rely
instead on pesticides containing pyrethroid
chemicals. Unfortunately, it turned out that
many anopheles mosquitoes in South Africa
were resistant to pyrethroids. The number
of cases of malaria, which had been hovering between 8,000 and 13,000 a year, grew
steadily worse, and by the year 2000 it had
reached 64,000 cases, with 423 deaths.
When the government reintroduced DDT
spraying in the middle of that year, the results were dramatic. The number of cases
fell almost immediately. By the end of 2001,
when doctors began treating their patients
with Coartem, a single, multidrug pill that
includes an artemisinin derivative, the
number of cases had been cut in half. In
2003 the number of deaths was down to 146.
Even environmentalists had to admit
that DDT was necessary. “I wasn’t very happy about it, but we are what you’d call
pragmatic conservationists,” says Gerhard
Verdoorn, chairman of South Africa’s Endangered Wildlife Trust, which had earlier
lobbied the South African government to
drop the pesticide and now helps train the
350 or so DDT sprayers who are employed
each year. “We can’t just look after animals
and not care if people die.”
That’s the kind of attitude that will make
a difference in the battle against malaria. The
know-how to control the disease already
exists. What is not so clear is whether there
is the necessary commitment – financial and
political – to make it happen. — With reporting
by Simon Robinson/Johannesburg
