Scientists
know that humans infected with malaria are more likely to be bitten
again by disease-carrying mosquitoes - and now they think they know why.
Malaria may alter the way people smell to make them more alluring to mosquitoes, a new study has revealed.
Experiments
with mice suggest that the malaria parasite acts like a perfumier in
the body by mixing fragrances to produce an irresistible cocktail of
odours.
Scientists believe it is likely to have the same effect on humans and are studying volunteers in Africa to test the theory.
As
well as aiding the search for new treatments, the work could lead to a
method of screening symptom-free malaria carriers at risk of spreading
the infection.
In order to
complete its complex life cycle, the malaria parasite - the
single-celled organism Plasmodium - must both be transmitted and
ingested by the Anopheles mosquito via blood hosts.
Plasmodium
in the blood is able to alter the host’s odour profile to attract the
hungry insects and it even times the changes to coincide with when the
host is highly infectious.
‘There
appears to be an overall elevation of several compounds that are
attractive to mosquitoes,’ said Professor Consuelo De Moraes, one of the
scientists from the Swiss research institute ETH Zurich.
Tests
showed that mosquitoes were most drawn to mice with large numbers of
gametocytes - the parasite’s reproductive cells - in their blood.
WHAT IS MALARIA?
Malaria is a serious tropical disease spread by mosquitoes.
If malaria is not diagnosed and treated promptly, it can be fatal.
The World Health Organisation (WHO) said that there were 207 million documented cases of malaria in 2010 and it killed between around 627,000 people.
Symptoms of malaria include: a high temperature, sweats and chills, headaches, vomiting, muscle pains and diarrhoea.
They usually appear between seven and 18 days after becoming infected - but in some cases may not appear for a year.
Malaria is caused by the plasmodium parasite, which is mainly spread by female Anopheles mosquitoes.
When an infected mosquito bites a human, it passes the parasites into the bloodstream;
Malaria is found in more than 100 countries, mainly in the tropical regions of the world.
If malaria is not diagnosed and treated promptly, it can be fatal.
The World Health Organisation (WHO) said that there were 207 million documented cases of malaria in 2010 and it killed between around 627,000 people.
Symptoms of malaria include: a high temperature, sweats and chills, headaches, vomiting, muscle pains and diarrhoea.
They usually appear between seven and 18 days after becoming infected - but in some cases may not appear for a year.
Malaria is caused by the plasmodium parasite, which is mainly spread by female Anopheles mosquitoes.
When an infected mosquito bites a human, it passes the parasites into the bloodstream;
Malaria is found in more than 100 countries, mainly in the tropical regions of the world.
When the mosquito consumes these cells along with the host’s blood, a new development cycle starts in the insect’s gut.
The scientists used a technique called gas chromatography to analyse Plasmodium’s effect on body odour.
They
found no evidence that it generated unique odour components in the
host. Instead, the parasite altered levels of compounds already
naturally present, increasing most of them and raising concentrations of
several more than others.
The resulting blend of odours was especially tempting to Anopheles mosquitoes.
Dr
Mark Mescher, the lead author of the study who is also from ETH Zurich,
said: ‘Since mosquitoes probably don’t benefit from feeding on infected
people, it may make sense for the pathogen to exaggerate existing odour
cues that the insects are already using for host location.’
Malaria
infection appeared to leave its mark on body odour for life. Even when
infected mice no longer displayed any symptoms, their smell showed that
they still carried the parasite.
Not all stages of the disease smelled the same, however. Early and late stages of infection had different odour profiles.
Writing
in the journal Proceedings of the National Academy of Sciences, the
scientists concluded: ‘These findings...provide an important proof of
concept regarding the identification of volatile biomarkers of malarial
infection and the specific compounds identified should be viewed as
promising candidates for further investigation, with work on
malaria-induced changes in the odours of human subjects being an obvious
priority for further research.’
Source: NHS Choices
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