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Physicists Discover New Way to Spot Malaria Using Light and Magnets
Place an infected sample of blood in a powerful magnetic field and crystals produced by malaria parasites line up like toy soldiers, allowing them to be easily identified
Malaria is one of the world’s most insidious diseases. It infects some 200 million people every year and kills 1 million of them.
But malaria is treatable so many of these deaths are avoidable. So the race is on to find a cheap and simple way to identify the disease.
Today, Adam Butykai at the Budapest University of Technology and Economics in Hungary and a few pals say they’ve discovered a promising new technique for spotting malaria parasites in blood that is as good as today’s best methods but with the potential to be significantly cheaper.
At the moment, the best way to diagnose malaria is by using a microscope to physically spot the malaria parasites in a drop of blood.
The personnel and equipment for this are expensive but the technique is reliable and can identify the disease at levels as low as 5-10 parasites per microlitre of blood. That’s important for early diagnosis.
The visual technique also allows medics to distinguish newly infected individuals from those who have had the disease in the past and have been treated but still have parasites in their blood. That’s an important feature since most people in areas where the disease is endemic will have been infected at some point.
There are other ways to spot the disease. For example, a new generation of rapid diagnostic tests are being developed that use malaria antigens to bind with parasites and produce a visual signal, perhaps on a test strip for example. These are particularly cheap and quick.
But they work only at levels above 100 parasites per microlitre of blood. That’s of limited use for early diagnosis What’s more, the technique cannot distinguish between new and old cases of the disease and can also be fooled by genetic changes in the parasite as it evolves.
The new technique from the Bulgarian team detects a byproduct that malaria parasites produce in the blood when they break down molecules of the blood pigment, haemoglobin.
This process creates tiny cylindrical crystals of a substance called hemozoin, which turns out to have remarkable properties. The most significant of these is its iron content makes hemozoin magnetic.
Various research groups have noted that placing infected blood in a magnetic field causes the crystals to line up. However, this effect is countered by the constant buffeting of thermal forces which tend to disorder the sample.
That gave Butykai and co an idea. Instead of a static field, these guys put their sample in a rotating field which causes the crystals to spin, like tiny magnetic spinning tops. Since their magnetic axis is along the length of the cylinder, they spin around this long axis, making the crystals stand up in the field like toy soldiers.
This alignment is much more stable against thermal forces and gives the blood unusual optical properties since it allows polarised light to travel more easily along one direction than in the perpendicular direction.
In addition, Butykai and co have found that the hemozoin soldiers interact more readily with some frequencies than others, producing a unique optical signature. It’s this that can be used to spot malaria parasites in blood, serum or plasma.
Butykai and co say the technique is currently sensitive down to 50 parasites per microlitre of blood. In blood plasma, however, it can detect the disease at levels below 1 parasite per microlitre.
“The sensitivity achieved in our test measurements on hemozoin in blood plasma exceeds that of the most reliable diagnostic methods used presently,” they say.
That’s impressive and has the potential to be optimised further by filtering the blood, for example. The test is also immune to genetic variations in the parasite, which can stymie antigen-based tests.
The big question,of course, is whether the test can easily be developed into a cost effective device for use in developing countries.
That’s a big ask. The light diagnostics should be straightforward to make but the required magnetic field is large–about 0.5 Tesla or so. That’s not so easy.
There have been great strides in producing lab-on-a-chip type devices in recent years so it’s not beyond the realms of possibility that a cheap and robust device could emerge. Much will depend on the willingness and ability of engineers to take this bull by the horns.
That’s not beyond the realms of possibility. The world’s biggest funder of malaria research is the US military, which has an obvious interest in preventing and treating the disease for its troops. If there’s any organisation with the resources to develop such a device, perhaps that’s it.
Ref: arxiv.org/abs/1210.5920: Malaria Pigment Crystals As Magnetic Micro-Rotors: Key For High-Sensitivity Diagnosis
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