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Horse of Troy: Virus’s own protein used to defeat it

Posted By Andrew Farrer On June 11, 2012 @ 3:20 pm In Science & Technology | No Comments

A new test uses the chikungunya virus’s (CHIKV) own protein to screen whether people have contracted the virus or not. Control of the disease, which can lead to brain disease and liver failure, will aid in reducing economic and social strains put on communities affected by the virus.

Just like malaria, CHIKV is transmitted to humans by mosquitoes (Aedes aegypti and albopictus). While the disease is generally non-fatal, characterised by fever, headaches, rashes, nausea, vomiting and joint and muscle pain, on rare occasions it can have complications resulting in brain disease and liver failure. There are no specific treatments or any licensed vaccines for CHIKV available for humans. Early and accurate diagnoses are vital to counteract the large social and economic pressures this virus puts on local communities.

Reverse Transcriptase PCR (RT-PCR) is an early and accurate diagnosis method. CHIKV’s genome is made of RNA; RT-PCR converts this to DNA, allowing accurate identification of the virus if present. Unfortunately, in primary clinical samples there may only be a very small amount of the virus present with concentrations too low for RT-PCR to pick up.

To tackle this problem, Magdline Sum and David Perera of the Institute of Health and Community Medicine at the Universiti Malaysia Sarawak have worked to develop an alternative method using Enzyme Linked Immunosorbant Assays (ELISA’s). ELISA is a biochemical technique that takes advantage of the antigen – antibody reactions that occur naturally in our bodies.

Antigens, unique proteins found on the outside of cells, are usí to identify a cell as a body cell or an invading cell. Antigens evoke the production of antibodies, large Y-shaped proteins and are used by the immune system to bind to the antigens of invading cells. By doing so they are marking the invader for destruction by white blood cells. E1 is an antigen present on the CHIKV.

The ELISA uses isolated antigens to see if the matching antibodies are present. If they are, this shows that the antigen and, hence, the invader cell are already present in the patient. Using E1 in an ELISA can accurately determine the presence of CHIKV when RT-PCR cannot.

CHIKV diagram

CHIKV was propagated in two cell lines. Infected and control C6/36 and Vero cells (A). Amplification of the E1 gene (B). Expression of recombinant protein in Sf9 insect cells (C).

However, extracting and purifying antigens from live viruses is high risk. Errors may infect the patient rather than help them. To remove this risk the team use recombinant E1. Recombinant proteins are made by placing the sequence coding for that protein into another type of cell. This allows the protein to be made by an organism which poses no health risks. The E1 gene was copied into a baculovirus, a virus which only targets insect cells. E1 is made inside the insect cell and is identical in structure to the normal protein. Large quantities of E1 can then be generated and are safe for medical use.

ELISA’s, using the recombinant E1, will aid in the detection of CHIKV in patients, maximizing time to provide aid to both the individual and the community.

For further information contact:

Dr Magdline S.H. Sum
Institute of Health and Community Medicine
Universiti Malaysia Sarawak
Email: shsmag@ihcm.unimas.my

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