“THE MOSQUITO
HAS A HIGHLY
SOPHISTICATED
SENSE OF SMELL”
JAMES LOGAN, APOPO TRAINING AND RESEARCH CENTER /APOPO.ORG, SCIENCE PHOTO LIBRARY2 detec t when ou r odou r is d if ferent f rom
usual. This is vital, because scientists
suspect t hat when we’re u nwell, ou r
unique aroma changes; each diseases
could even have its own signature pong.
“If we can figure out these chemical
signatures and mimic the animals’ smell-
power, then we can use them to achieve
earlier diagnosis and perhaps save lives,”
says Prof James Logan, head of disease
control at the London School of Hygiene
and Tropical Medicine. And that’s exactly
what he and his colleagues have been
doing for one killer disease: malaria.
GETTING BUGGED
The sea rch begins with the mosquito.
Although unpopular, it has one important
asset: a highly sophisticated sense of smell,
which it uses to hunt us down. It’s this
efficiency that makes it a threat to human life in those parts
of the world where it carries the malaria parasite, Plasmodium.
Progress in t he fight against mala ria has stalled, pa rtly
because some people don’t realise they have the infection, and
can pass it on when they’re bitten again. But Logan and his
team of researchers discovered that when someone is infected
by a malaria-carrying mosquito, they produce chemicals that
change their smell, making them evenmoreattractive to other
mosquitoes. “So the malaria parasite is manipulating the human
body to boost its chances of being transmitted,” says Logan.
In a double-whammy, malaria also supercharges a mosquito’s
sense of smell – all the better for sniffing
out its human victims.
The researchers resolved to find out
exactly what chemicals were attracting the
mosquitoes. They collected odour samples
from the feet of children with malaria,
and separated these odours out into their
component parts. Tiny electrodes were
attached to mosquitoes’ antennae, which
they use for detecting smells. They then
exposed the mosquitoes to the different
components, and measured the electrical
responses of the smell receptors in the
antennae. The culprits that triggered the
highest response turned out to be mainly
chemicals called aldehydes. These could
be synthesised in the laboratory and kept
in a bottle. More on that later.
But how do we turn a mosquito into
a diagnostic tool? “It would be lovely if
we could put a leash on a mosquito and
take it round a community to find people
infected with malaria. Not possible. But
there is an animal we can do that with,”
says Logan. Enter the dog – arguably theRed blood cells infected
with the malaria parasite
(yellow). Generally,
symptoms appear
once the red blood cells
are aected