Shining Light Through Skin To Diagnose Malaria
Researchers in the U.S. have come up with a way to rapidly diagnose malaria simply by shining brief pulses of light from a laser through the skin.
“This method is distinct from all previous diagnostic approaches, which all rely upon using a needle to obtain blood, require reagents to detect the infection, and are time- and labour-consuming,” noted the scientists in a paper published this week in the Proceedings of the National Academy of Sciences (PNAS).
Rugged and inexpensive microlasers exist that could be modified to create portable devices capable of operating in harsh conditions. Non-medical personnel would be able to operate these devices and obtain a diagnosis in seconds, according to their paper.
Such a device was under development, said Rice University’s Dimtri O. Lapotko, the senior author of the paper, in an email.
When a malaria parasite invades red blood cells, it gorges on the haemoglobin those cells contain. Haemoglobin is the molecule that helps carry oxygen to all parts of the body. The parasite turns the iron-containing haeme component, which can be toxic for the organism, into an insoluble pigment, haemozoin.
The technique developed by Dr. Lapotko and his colleagues relies on detecting the haemozoin in red blood cells. They achieve this by using a narrow band of near-infrared light that is strongly absorbed by haemozoin but not haemoglobin.
A brief pulse of light in this band from a low-power laser heated up the tiny particles of haemozoin, causing a “vapour nanobubble” to form in the fluid around each particle. These bubbles expand explosively and then collapse with a characteristic sound that could be picked up with an ultrasound sensor.
The scientists demonstrated the technique in animal trials using malaria-infected mice.
A probe that carried an optical fibre as well as an ultrasound sensor was clamped to the ear of the mice so that laser light could be shone at a surface blood vessel and the resulting sounds recorded.
The device was able to accurately pick out infected animals, even when only about one in a million red blood cells carried the parasite, their paper reported.
The first trials of the technology in humans was expected to begin in early 2014 at Houston where Rice University is based, according to a University press release quoting Dr. Lapotko.
“It is a fantastic technique” but has an important limitation, observed Vinod Prakash Sharma, who was founder director of the National Institute of Malaria Research in New Delhi.
The method would be unable to distinguish between two species of the parasite, Plasmodium falciparum and Plasmodium vivax, that cause malaria in India. Treatment depended on which parasite was infecting a patient.
The technique described in the PNAS paper would therefore have to be combined with ways of discriminating between the two, Dr. Sharma told this correspondent.
Moreover, haemozoin may persist in the blood even after the parasite has been cleared, remarked V. Arun Nagaraj, Ramanunjan Fellow at the Indian Institute of Science in Bangalore. With this technique, a previously-infected individual who had another bout of fever from some other cause might potentially be misdiagnosed as having malaria.
