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“Trapping” RBCs to throw light on Malaria

Photo: Siddharth Kankaria / Research Matters

Malaria is a mosquito-borne disease that affects a large part of human population living in tropics and subtropics. Even though treatment for malaria is available, it continues to be a deadly disease causing an estimated 429,000 deaths worldwide in 2015 of which 24,000 were from India. Therefore, early and accurate diagnosis of malaria is essential to manage it. Currently, the gold standard for disease diagnosis is the microscopic identification of malarial parasite Plasmodium present inside red blood cells (RBCs). However, the diagnostic ability depends on the quality of the chemicals used for the test, microscope and the skill of technicians, making it inefficient and error-prone.

Now, in a recent study from researchers at the Indian Institute of Science, Bangalore, the group has devised a novel diagnostic technique using light rays. Prof. Vasant Natarajan and his team’s new method can detect even the early stages of malarial infection with a very small amount of blood sample. The researchers have devised a prototype based on the ‘optical tweezers trap technology’ in which a single RBC is trapped using laser light, as if the laser was a pair of tweezers.

The RBCs thus trapped show Brownian motion, i.e. they move around slightly but randomly in all directions. The researchers found that the Brownian motion of RBCs from a normal sample (nRBCs) differ from that of the RBCs from an infected sample (iRBCs). They quantified the Brownian fluctuations using a term called the ‘corner frequency’, and found that the corner frequency of the iRBCs was more than that of the nRBCs.

Prof. Natarajan explains that this difference in the corner frequency is due to differences in the mechanical properties of RBCs. The iRBCs are more rigid than the nRBCs, which prevents them from behaving normally, and is the main reason for the deadliness of the disease. This is because the rigid RBCs cannot squeeze through the tiny blood capillaries thus preventing oxygen from reaching many parts of the body supplied by these micro-tunnels. An important feature of this method is the use of the ‘bystander effect’, an effect where RBCs that do not host the parasite but are from the same blood sample also become rigid. Other studies have also found evidence of the bystander effect, but this is the first time that it is used for disease diagnosis.

Prof. Natarajan’s group had earlier shown similar results using samples obtained from laboratory cultures of the malaria parasite known as Plasmodium falciparum. However, they could not do so for the other parasite called Plasmodium vivax, which is responsible for majority of malaria cases in India. This was because Plasmodium vivax predominantly infects reticulocytes, a pre-mature form of RBCs, and it is quite difficult to maintain long-term cultures of such cells in the lab. By contrast, the current study utilised blood samples from hospital patients infected by both types of parasites to show that the corner frequency increased from nRBCs to iRBCs for both kinds of infections.

Among the many advantages of this new technique are easy automation and non-requirement of trained personnel because of the computer generated output, unlike conventional diagnosis. Additionally, it is independent of the stage of development of the parasite, and hence does not require the blood sample to be drawn at a particular time (for example, during the evening fever). Therefore, it can be used even during the earliest stages of the disease when the parasite count in blood is extremely low, and the only symptom is high fever.

But what makes the new method so accurate and sensitive? It is the bystander effect -- only a few cells, though not hosting the parasites, are sufficient for diagnosis. These characteristics make it a better method than others which primarily rely on visual identification of the parasite. Having so many advantages makes this invention an exciting choice for entrepreneurs and start-ups to develop it into a diagnostic tool. “Hopefully a hospital or an entrepreneur will take it up. We can help anyone who is interested in making it a commercial product”, signs off Prof. Natarajan.