PHA-Exchange> Malaria May Be Twice As Prevalent As Previously Thought

[Claudio]

From: "Vern Weitzel" <vern.weitzel at undp.org>
http://www.nature.com/news/2005/050307/full/050307-10.html

Published online: 8 March 2005;

Malaria map paints stark picture
Study suggests the disease may afflict twice as many people as thought.

Helen Pearson

The number of malaria cases worldwide may be close to double that previously
estimated, according to
a new tally of the killer disease.

The study, which is one of the most comprehensive efforts to map the
prevalence of malaria, shows
that over half a billion people could have the disease. This elevated count
could increase pressure
on governments to pump money into prevention efforts.

Malaria, which is caused by a mosquito-borne parasite, is one of the world's
biggest infectious
killers. But it has been tough to figure out exactly how many people succumb
to the disease. Earlier
estimates relied to some extent on health clinics that voluntarily report
their cases. But this can
be inaccurate because many people with malaria do not go to clinics - and
many clinics do not submit
figures.

In the new study, published in Nature1, Robert Snow at the Wellcome Trust
Research Laboratories in
Nairobi, Kenya, and his colleagues created a computer model to build a
detailed world map showing
how many people are likely to be experiencing malaria symptoms.

To do this, they first divided the world into regions in which the disease
is present, based on
medical advice to travellers. They excluded areas above a certain altitude,
where the parasite is
less able to survive, and very built-up areas where there is less clean
water in which mosquitoes
can breed.

The team refined this map by adding estimates of the population density in
each area, the risk of
picking up an infection from a mosquito bite, and medical reports on the
likelihood that an
infection would blossom into the full-blown fever and other symptoms. "Then
we pressed a button and
the number came out," Snow says.

Best estimate

The researchers reckon that there were around 515 million clinical cases of
malaria in 2002,
although the actual figure could lie anywhere between 300 and 660 million.
This is not far off
double the estimate of 273 million cases produced by the World Health
Organisation (WHO) in 1998.
And in areas outside Africa, the new figures are at least three times as
high as those previously
estimated by the WHO.

Snow's numbers are still only a rough approximation of malaria's prevalence.
But "it's probably the
best estimate we have", says Andrew Spielman, a specialist in tropical
infectious diseases at
Harvard School of Public Health in Boston. "It's known to be a terrible
burden and now it appears
it's even more terrible than we thought."

Snow hopes that the new study will help work out the amount of money,
medicines and other resources
needed to combat malaria. Without it, for example, pharmaceutical companies
struggle to know how
many drugs to make and public health agencies find it hard to gauge how well
they are curbing the
disease. The map could also help guide where in the world money and aid
should be targeted.

International momentum

The report comes at a time when international momentum to tackle malaria is
building. For example,
the Global Fund to Fight AIDS, Tuberculosis and Malaria, which coordinates
government and private
funding, has channelled $3.1 billion into these diseases since its
establishment in 2002.

Even so, public health researchers and advocates say that they need more.
They point out that unlike
other infectious diseases such as HIV and tuberculosis, we already know how
to defeat malaria using
simple measures such as insecticide-treated bed nets and drugs. Spielman
predicts that some groups
will use the study as "ammunition" to ask for more funding.

Experts at the WHO say they are now working with Snow's team to refine their
own estimates of
malaria's incidence. The WHO's new figures, which are due to be published
later this year, lie
between 350 and 500 million and largely overlap with Snow's, says Eline
Korenromp, who works for the
organization's malaria-monitoring unit in Geneva, Switzerland.

References

    1. Snow R. W., Guerra C. A., Noor A. M., Myint H. Y. & Hay S. I. Nature
doi:10.1038/nature03342
(2005).