84 Science & technology The EconomistOctober 12th 2019
2 One such shift may be to screen the
whole population of high-burden coun-
tries. A study published recently in the New
England Journal of Medicinetested this idea
in part of Vietnam. Researchers collected
saliva from people once a year for three
years—and offered treatment to the infect-
ed. If this intervention were widely de-
ployed it could, they calculate, decrease
prevalence by 15% a year, rather than the
3-7% typical in currently affected places.
What would really transform prospects
for tb, though, would be a vaccine. Here
there is good news and bad. The good is
that a vaccine made by GlaxoSmithKline, a
big drug company, has showed promising
results in a trial in southern Africa. The bad
is that since this result was published 18
months ago little has happened.
In the case of malaria there has been
great progress. Between 2000 and 2015
6.8m deaths were averted and 20 countries
eliminated the disease altogether. How-
ever, malaria is now on the rise again. The
fund says this is because spending on pre-
vention has stalled in countries with rapid
population growth.
On top of that, there is concern about
increasing resistance to insecticides
among the mosquitoes that spread the ma-
larial parasite. In particular, these insecti-
cides are used to coat bednets employed to
keep mosquitoes away from people when
they are asleep. Here, a new bednet called
the “Interceptor G2” will help. It is coated
with two insecticides instead of one. Resis-
tance is also on the rise, though, to the
drugs used to treat people infected with
malaria. The most successful and widely
deployed of these are based on a chemical
called artemisinin, but in parts of South-
East Asia resistance to artemisinin is
spreading. If such resistance were to
spread from there to India and Africa it
could be a catastrophe.
The fund’s third target is aids. As with
malaria, there has been much progress.
The number of new cases is falling every
year and the number of lives saved by anti-
retroviral therapy is rising. But, again, de-
mography is moving the goalposts. In sub-
Saharan Africa, the number of young peo-
ple is expected to increase by 40% over the
next decade. And the young, who are the
most sexually active part of the population,
are those most at risk of infection by hiv,
the aids-causing virus.
The lesson from malaria, where con-
stant funding levels have led to a decline in
the amount of money available per person,
is that if spending does not increase, hiv
will bounce back—taking human lives with
it. Moreover, the burden of infection will
fall heavily on girls and women, 1,000 of
whom are infected every day around the
world. In sub-Saharan Africa, for example,
girls and young women aged 15-24 are now
eight times more likely than men of thesame age to be infected, because of sexual
violence, lack of economic opportunity
and educational disadvantages.
All these problems are solvable with in-
novation, effort and cash. But there also
has to be political will. That seems to be
forthcoming. Britain, one of the fund’s big-
gest supporters, pledged £1.4bn ($1.7bn) in
advance of the meeting in Lyon. That is a
16% increase on the last three-year round.
Other countries are also upping their con-tributions. Denmark’s has increased by
16.6%, Sweden’s by 14%, Italy’s by 15%, Ger-
many’s by 17.6% and Canada’s by 15.7%. As
The Economist went to press, an American
congressional delegation was proposing to
offer $1.56bn a year—a 15% increase. This
would provide a third of the fund’s needs.
There are few guarantees in life. But it is
safe to say that if the Global Fund receives
all the cash that it has been promised, it
will be money well spent. 7T
ougherthananyfibremadeby
humans and extraordinarily good at
transmitting vibrations to the predators
that weave it, spider silk has been a
source of inspiration for the develop-
ment of everything from scaffolding for
regenerating bones to bulletproof vests,
remote sensors and noise reducers. Yet
one of its most remarkable attributes, its
resistance to decay, has received little
attention. Some researchers speculate
that spider silk keeps hungry bacteria at
bay by being laced with antibiotics. But
work by Wang Pi-Han and Tso I-Min at
Tunghai University, in Taiwan, pub-
lished in the Journal of Experimental
Biology, suggests this is not the case.
Rather, silk manages to avoid being eaten
by locking the nutrients it contains
behind an impenetrable barrier.
Spider silk is made of proteins that
ought to be attractive to microbes. More-
over, because webs are often built in
environments, like forests and bogs, that
are rife with these bugs, there should be
ample opportunities for bacteria to settle
on the strands and feast. Remarkably,thisdoesnotseemtohappen.
Dr Wang and Dr Tso were curious
about how spiders manage this. They
began their investigation by putting
bacteria and spider silks together in
laboratory conditions perfect for bacteri-
al growth. They worked with silk strands
collected from three species of spider
that build their webs in different envi-
ronments, and set these down on nutri-
ent-rich plates. Each plate had one of
four bacterial species growing on it. The
team then used microscopes to monitor
the behaviour of the bacteria over the
course of 24 hours.
After repeating the experiment three
times, they found that the bacteria never
fed on the silks. They also found, how-
ever, that the strands were not immune
to having bacteria grow over and around
them—suggesting that those strands
were not laced with antibiotics.
The two researchers then tried grow-
ing their bacteria directly on silk strands,
by providing them with a range of nutri-
ent supplements. Only one of these
supplements, nitrogen, encouraged
consumption of the silk. When the
strands were lathered in a nitrogen-rich
solution, bacteria ate them. Without
nitrogen, they were held at bay. This is
odd, because proteins (of which silk is
made) are, themselves, rich in nitrogen.
That led Dr Wang and Dr Tso to con-
clude that the antibacterial properties of
spider silk are caused not by any sort of
antibiotic but, rather, the structure of the
silk itself. Natural selection, it seems,
has driven spider silk to store the pro-
teins it is composed of behind a layer
made impenetrable by its physical rather
than its chemical structure.
What, exactly, that structure is the
two researchers have yet to determine.
Once it has been elucidated, though, the
discovery should pave the way for artifi-
cial antibacterial materials that do not
use antibiotics to keep the bugs away.Protect and survive
Natural materialsHow spider silk avoids the attention of hungry bacteriaA materials scientist at work