Norovirus infection is the most common cause of acute gastroenteritis in
developed countries. Developing an assay based on a non-invasive biomarker for
detecting incident norovirus infections could improve disease surveillance and
epidemiological investigations. This project involved analysis of IgA and IgG
norovirus-specific antibody responses in saliva samples from a Norwalk virus
(Genogroup I, genotype 1 norovirus) challenge study involving infected and
symptomatic, and non-infected asymptomatic individuals. Saliva was collected at
the challenge, and two weeks and 40 days post-challenge. Samples were analyzed
using the Luminex fluorometric and Meso Scale Discovery (MSD)
electrochemiluminescence immunoassays. Recombinant P domains of Norwalk virus
capsid protein, as well as similar recombinant proteins of two genogroup II
noroviruses (VA387 and VA207) were used as antigens. Immunoconversions were
defined as >4-fold increase in antibody responses to the norovirus
antigens. Various sample pre-treatment options, buffers, saliva dilution ratios,
and data adjustment approaches to control for sample-to-sample variability in
saliva composition were compared using the Luminex assay. The results suggest
that adjusting responses to the norovirus antigens for responses to the protein
purification tag, glutathione-S-transferase (GST), significantly improved the
odds of producing a correct immunoconversion test result. IgG-based tests were
more accurate compared to IgA-based tests. At optimal conditions, both Luminex
and MSD assays for Norwalk-specific IgG antibodies correctly identified all
infected and non-infected individuals. There was no evidence of cross-reactivity
of anti-Norwalk virus antibodies with genogroup II noroviruses. These results
suggest that salivary antibody responses can be used for the detection of
incident infections with Norwalk virus in prospective surveys.