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Researchers Develop Simoa-based Assay for Dengue Fever Host Immune Response

NEW YORK (GenomeWeb) – A team from Tufts University has published a proof of concept demonstrating that Quanterix's digital ELISA technology, Simoa, may allow more sensitive detection of the host immune response to dengue fever than other current methods.

In the study, published this week online as an accepted manuscript in the Journal of Clinical Microbiology, the Tufts group described their development of a Simoa-based assay to detect type 2 anti-dengue IgG and IgM and compared its sensitivity to two commercially available ELISA kits for the two antibodies.

The comparison showed that the Simoa approach was 1,000 times more sensitive than one of the kits, and 10,000 times more sensitive than the other.

According to the group, currently used ELISAs for anti-dengue antibody detection suffer from a lack of sensitivity in the first few days of illness, when antibodies against the disease may be present at too low a concentration to be detected.

RT-PCR tests are available for early dengue diagnosis, but serological methods are more cost effective and easily available making them attractive, especially in dengue endemic countries.

The Tufts team set out to develop and test a Simoa-based dengue test hoping that the digital platform might be able to more sensitively detect anti-dengue antibodies, opening up the possibility of detecting the disease earlier after infection.

Their group's indirect Simoa method relies on inactivated dengue virus type 2 antigen-coated magnetic beads for the capture of dengue-specific antibodies, the authors wrote.

The addition of biotinylated detector antibody specific to human IgG or IgM allows each captured antibody to be detected, and individual beads are then isolated and sealed in reaction wells in the presence of a fluorogenic substrate.

Measuring the concentration of the fluorescent product in the reaction wells allows the detection of single antibody molecules. By comparing the number of active wells to inactive wells, one is able to infer the concentration of the IgG or IgM molecules in the original sample.

In their study, the Tufts team first measured the Simoa assay's sensitivity, as well as those of two ELISA kits for dengue detection, using serial dilutions of dengue type 2-positive plasma.

According to the authors, the IgG ELISA was able to detect a plasma dilution down to 1:10,000. In contrast, the IgG Simoa was able to detect anti-dengue IgG at 1:10,000,000 dilution, making it 1,000 times more sensitive than the EuroImmun IgG ELISA kit.

Similarly, the IgM Simoa was able to detect anti-dengue IgM at 10,000 times higher dilution than the EuroImmun IgM ELISA kit.

Overall, the results suggest that Simoa may be able to detect dengue infection at a much earlier stage of infection as compared to ELISAs, the authors wrote.

With additional clinical validation, the method could provide a means to distinguish between primary and secondary infections and identify those at risk for developing dengue hemorrhagic fever or shock syndrome. 

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