[Mosquito buzzing sound]
Malaria is an infectious disease caused by a parasite called Plasmodium.
It is spread from person to person by infected Anopheles mosquitoes.
The parasite’s lifecycle is complex.
When an infected mosquito feeds on a human it injects parasites, known as sporozoites, into the blood.
These parasites travel to the liver where they develop into merozoites.
These are released into the blood where they invade red blood cells and multiply many times.
They then burst out, destroying the red blood cells, leading to the symptoms of malaria
such as anaemia and fever.
Inside some red blood cells the parasite develops into male and female gametocytes.
These are taken up by another mosquito when it feeds on the blood.
The gametocytes mature in the mosquito gut and then fuse together to produce a new parasite.
This develops into thousands of sporozoites that are injected into a human
when the mosquito feeds and so the cycle starts again.
Malaria affects millions of people around the world. Today malaria infections are restricted
to some of the world’s poorest countries, in tropical regions such as Southern Asia,
Africa and South America. However, if you go back just one hundred years malaria was
found in most parts of the world including Europe and the United States of America.
“Malaria used to be a big problem in Europe, all the way up into England. It used to be
a problem in the United States, Washington DC was a terribly malarious area and even
up into New England, New York, Massachusetts, there was a lot of malaria. It’s now completely
gone so we can eliminate malaria.”
A simple way to reduce the transmission of malaria is with the use of insecticide-treated
bed nets. These act as a barrier and protect people from mosquito bites at night as they
sleep.
Nets can be supplied to communities and training can be given to make sure that people know
how to use them properly. However distribution can be a problem and many people still get
infected with malaria.There are over 200 million cases of malaria reported every year.
The main symptoms of the disease are a high fever and anaemia but severe cases can lead to life
threatening complications.
Over 780,000 lives are lost each year because of malaria. Children under the age of five
are most at risk and on average a child dies of malaria every 30 seconds.
The disease can also cause extreme complications in pregnant women, leading to the death of
200,000 newborn babies each year.
“So pregnant women can get massive malaria infections, specifically in their placenta
and that causes reduced oxygen and nutrient uptake to the developing foetus, which can
result in premature birth, so you get babies delivered early with a low birth rate, or
even still birth and abortion can be caused by these placental malarial infections.”
Despite the potential severity of malaria it can be easily treated with drugs that kill
the parasite. The use of simple blood tests enables the early detection and diagnosis
of the disease. Antimalarial drugs can then be given to shorten the duration of the disease
and prevent further complications and death. A continual challenge to treating malaria
is the emergence of drug resistant parasites. This happened with the drug chloroquine developed
in the 1940s.
“In the case of chloroquine historically we knew that resistance had first come up
in South East Asia, right on the Thailand-Cambodian border in the late 1950s. Right around the
same time it was reported in the Brazilian Amazon and then once we figured out what was
the genetic mutation that caused that resistance we were able to determine that, in fact, those
had been independent events. The form that came up in South East Asia then spread throughout
the rest of Asia and by 1978 it had arrived in Africa and then spread over the next 10
or 15 years through Africa.”
In the 1990s a new drug called artemisinin was developed, but within 10 years parasites
resistant to this drug emerged in South East Asia. To minimize the chances of resistance
developing in the parasite malaria drugs are now used in combinations rather than as single
drug treatments.
“So there’s a lot of anxiety in the malaria world right now about our current first line
class of drugs called the artemisinins because a sort of a mild form of resistance has emerged
in the last few years and looking at what happened with chloroquine, looking at what
happened with the anti-folate drugs, the fear is that it’s also going to spread from South
East Asia eventually to Africa and right now there’s really nothing in the drug development
pipeline that would be able to replace it. So if we lose the artemisinins we’re in
big trouble.”
By looking at the different stages of the parasite’s lifecycle it is hoped that targets
for new drugs and vaccines can be identified. Genome research is at the forefront of these investigations.
“A genome, when it comes down to it, is a list of all the genes that are present in
an organism, so the human genome gives us the list of everything that it takes to make
a human. In the same way, a parasite genome sequence, gives us a list of all the genes
it takes to make a parasite. So to a malaria researcher that genome sequence is a list
of targets, it’s a list of things that we can develop drugs against, a list of things
that we can develop vaccines against and if you have many hundreds of different genomes
you can see which of those genes are variable, which of those genes are conserved, which
of them are essential, which of them some parasites have and some parasites don’t.
All of that information is hugely beneficial to our efforts to develop new drugs or vaccines
against malaria.”
There is lots of research taking place around the world to improve our understanding of
the biology of malaria. This research is looking at the parasite, the mosquito vector and the
human host. It is hoped that this will lead to new interventions for the prevention, treatment
and ultimately the eradication of malaria, saving millions of lives worldwide.