Simple Affordable Diagnostic Kit Developed for Chikungunya

Chikungunya (CHIKV), a mosquito-borne illness that while not often deadly causes severe, incapacitating and often chronic joint pain, is spreading globally and it can be difficult to diagnose and most tests available now are expensive and challenging to develop.

An innovative approach has been developed for the production of alphavirus antigens for use in diagnostic assays that results in reduced production complexity as well as improved sensitivity in application. The insect-specific nature of these chimeric viruses yields an advantageous safety profile and allows for safe handling of the antigen at the bench top.

Scientists at the University of Texas Medical Branch (Galveston, TX, USA) and their colleagues were able to use another mosquito-borne virus that had remained largely unknown and unstudied to create the new test that could help doctors and investigators diagnose and track the spread of chikungunya. The formerly unknown virus, now named Eilat virus (EILV), is related to chikungunya and other mosquito-borne viruses and was collected in Israel's Negev Desert about three decades ago. The virus will only replicate in mosquitoes, which makes it harmless to humans and other vertebrates.

The team worked with the private commercial laboratory InBios International (Seattle, WA, USA), and used the Eilat virus-based chimera to create a safe and simple-to-use diagnostic test. Health care professionals are able to take the serum of those suspected of being infected with chikungunya and, using the diagnostic test kit created in conjunction with InBios, have a result in less than two hours. To test the assay for immunoglobulin (IgM) enzyme-linked immunosorbent assay (ELISA) positive controls, a panel of five IgM/ELISA and plaque reduction neutralization test (PRNT)-positive convalescent sera obtained from patients diagnosed by reverse transcriptase-PCR with CHIKV infection was used. Eight human serum samples positive for either Dengue virus (DENV) or Venezuelan equine encephalitis virus (VEEV) but negative for CHIKV by hemagglutination inhibition (HI) were used as negative controls. Absorbance values for ELISAs were read at 450 nm on a VERSAmax tunable microplate reader (Molecular Devices; Sunnyvale, CA, USA).

Anti-CHIKV IgM was readily detected with OD values ranging from 0.23 to 3.0, whereas the negative controls yielded a mean OD value of 0.09. The scientists were able to demonstrate that EILV/CHIKV replicates to high titers in insect cells and can be applied directly in enzyme-linked immunosorbent assays without inactivation, resulting in highly sensitive detection of recent and past CHIKV infection, and outperforming traditional antigen preparations. They were also able to show that that their anti-CHIKV IgM and IgG ELISAs can distinguish between human infections caused by CHIKV and VEEV or DENV with a high degree of signal separation. The study was published on October 22, 2015, in the journal Public Library of Science Neglected Tropical Diseases.

Related Links:
University of Texas Medical Branch 
InBios International
Molecular Devices