Optical Technique Detects Malaria Early

Rapid detection of malaria, particularly in remote parts of the world, is not always possible because current methods are slow and require precise instrumentation and highly skilled microscopic analysis. Now, using a technique called secondary speckle sensing microscopy, malaria can be diagnosed with greater accuracy and in as little as 30 minutes.

“A new diagnostic tool is urgently needed,” said Dr. Dan Cojoc, a researcher at the Materials Technology Institute of the National Research Council. “With a fast, portable, low-cost and accurate diagnostic tool, physicians can confidently and quickly administer the correct therapy.”

Developed by Cojoc and his colleagues, including malaria experts from Israel and Spain, the new microscopy system uses “speckle imaging,” an optical sensing technique that measures the difference between how laser light bounces off the membranes of healthy and infected red blood cells. They compared the apparently random light scattering (speckling) as it built up from multiple images of 25 cell samples (12 healthy, 13 infected). They discovered that a clear statistical pattern emerged identifying cells that harbored the parasite responsible for malaria.

The difference between an infected red blood cell (top) and a healthy cell (bottom) is revealed by secondary speckle sensing microscopy (S3M), in part by considering the dynamics of the correlation value (CV). CV indicates the similarity between two patterns. One thousand CVs are calculated from pairs of consecutive speckles acquired in 1 s. As shown in the chart at right, the CV oscillation range for the infected cell (top, 0.36) is almost three times larger than that of the healthy red blood cell (bottom, 0.13). Indicated by the arrow in the top left image of the infected cell, a parasite life-cycle stage of malaria called “trophozoite” can be seen. (Image: Dan Cojoc, Materials Technology Institute, National Research Council, Italy.)

Malaria is most common in warm, wet climates where mosquitoes thrive. The deadly disease claims nearly 1 million lives a year, mostly those of African children.

By applying secondary speckle sensing microscopy to an automated high-throughput system, the researchers delivered results in as little as 30 minutes with a high rate of accuracy, and without the need for highly trained technicians or a well-equipped hospital laboratory. The current diagnostic gold standard for malaria, Giemsa-stained blood smear, requires skilled medical professionals trained to identify the signs of a parasite throughout its life cycle; diagnosis typically takes 8 to 10 hours.

The microscopy technique begins with illuminating red blood cells with a tilted laser beam to produce a time-varied speckle pattern field based on the cells’' thermal vibration and the movement of their membranes — traits that differ in healthy and diseased states. The speckle patterns are inspected under the microscope and recorded on a camera at a high frame rate. Using two automated analytical methods — "fuzzy logic" and "principal component analysis" — scientists scour a set of speckle parameters to extract statistical information about changes in red blood cells' membranes and their flickering movements. Then they can make a diagnosis based on statistical correlations in speckle patterns between healthy and diseased cells.

Timely diagnosis maximizes the likelihood of successful, life-saving treatment, according to the researchers. It also minimizes the chances that inappropriate therapy will be given, helping combat the growing problem of drug-resistant malaria.

Although preliminary results have proved encouraging, further study is needed to validate the results and refine the method. If the positive outcomes hold up, field studies or clinical trials of secondary speckle sensing microscopy may be deployed as early as 2013.

The research appears in the open-access, peer-reviewed journal Biomedical Optics Express.

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