To Mosquitoes, People with Malaria Smell Like Dinner
- From: "georgia" <jwissmille@xxxxxxx>
- Date: 12 Sep 2005 14:07:16 -0700
http://www.rxpgnews.com/research/infectiousdiseases/malaria/article_2023.sh
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Latest Research : Infectious Diseases : Malaria
To Mosquitoes, People with Malaria Smell Like Dinner
Aug 10, 2005, 21:14
Research determined that mosquitoes are more attracted to people
infected
with transmittable malaria than to either people infected with
non-transmittable
forms of the disease or uninfected people. To measure the attraction
of the
mosquitoes, the researchers set up a chamber of infected mosquitoes
surrounded
by tents containing the study participants.
By PLoS Biology, Malaria is a misnomer. People used to believe that
poisoned
or ³bad air,² the translation of the Italian phrase ³mal aria,²
caused
disease. In the 19th century, when parasitologists figured out that
single-celled
parasites cause malaria, they didn¹t bother to change the disease¹s
name.
Experimenters proved that these parasites need a host organism to
survive?so
they
can¹t be transmitted through air?and that the hosts, mosquitoes,
carry the
parasite to humans.
Researchers were optimistic that if they could find a disease¹s
cause, they
could also find the cure. Kill the mosquitoes and eradicate malaria.
And with
the advent of DDT and less environmentally harmful insecticides,
potent
anti-malarial drugs, and international funding in the late 20th
century,
eradication
of malaria seemed imminent.
But that expectation underestimated the flexibility of living
creatures.
Mosquitoes acquired resistance to insecticides while the parasites
acquired
resistance to anti-malarial drugs. Worse, the aggressive eradication
campaign
skipped over vast regions of the globe, especially sub-Saharan Africa.
Malaria remains a devastating problem in Africa for several reasons.
Environmental conditions provide an amenable atmosphere for both
Plasmodium
falciparum, the most dangerous form of the parasite, and the Anopheles
gambiae
mosquito,
the most effective vector. Also, many countries in sub-Saharan Africa
lack
the infrastructure to protect their citizens from malaria. Given the
overwhelming scope of malarial infection in Africa, new understanding
of the
disease will
help epidemiologists devise targeted anti-malarial strategies.
A new study conducted in Western Kenya by Jacob Koella and colleagues
analyzed mosquito behavior to discover how it facilitates the
transmission of
malaria. The research determined that mosquitoes are more attracted to
people
infected with transmittable malaria than to either people infected
with
non-transmittable forms of the disease or uninfected people. To
measure the
attraction of
the mosquitoes, the researchers set up a chamber of infected
mosquitoes
surrounded by tents containing the study participants. A device called
an
olfactometer wafted the odors of each participant toward the
mosquitoes.
Researchers
measured which smell most attracted the hungry bugs.
This question had long stalled scientists because of contradictory and
indirect evidence. Sweat, breath odor, and high body temperature all
increase
mosquitoes¹ blood lust, and no previous study had isolated the
variable of
malarial
infection.
To control for the natural variation in how attractive mosquitoes
found each
participant, Koella et al. compared the number of mosquitoes that were
attracted to infected people to the number of mosquitoes that were
attracted
to those
same people after they were no longer infected. The researchers found
that in
general, an individual attracted more mosquitoes when infected with
transmittable malaria. This demonstrates that malaria, in addition to
causing
fever,
vomiting, headache, and sometimes death, causes more mosquito bites.
The
biting
mosquitoes will then pick up the parasite and spread it to other
people.
As another control, the researchers compared infection with a
non-transmittable form of the parasite to infection with the
transmittable
form and to no
infection. A mosquito can pick up the malaria parasite only when in
its
sexually
reproductive stage. The transmittable parasite, known as a gametocyte,
multiplies in the mosquito¹s belly before traveling to the
mosquito¹s salivary
glands and, eventually, to the blood of the next human victim. But the
malaria
parasite has a complicated life cycle that also includes
non-transmittable
asexual
stages. Koella and colleagues found that these parasitic forms, unlike
the
sexually reproductive form, did not make humans more attractive to
mosquitoes.
Previous to the recent study, malaria researchers had proved that
mosquito
biting rates greatly influence the spread of malaria. Koella and
colleagues
showed that the parasite itself increases these biting rates when it
is ready
for
a new host.
References
1. (2005) To Mosquitoes, People with Malaria Smell Like Dinner. PLoS
Biol
3(9): e306
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