Fig. 1.

Sialic acid and NS1 levels in serum of DENV-infected mice increase proportionally with infectious dose and are correlated with DENV-induced morbidity. Ifnar ^−/− mice were infected i.v. with increasing doses of DENV2 D220, and blood samples were collected on day 3 post-infection for serum testing by ELISA. Quantification of (a) Sia and (b) NS1 levels in serum from DENV-infected mice (mean±sd). Correlation analysis between DENV-induced (c) morbidity and Sia, (d) morbidity and NS1, and (e) Sia and NS1 levels in serum. Signs of morbidity were scored using a standardized scale, where 1=healthy; 2=mild signs of lethargy, some fur ruffling, no hunching; 3=fur ruffling, hunched, mild signs of lethargy; 4=ruffled, hunched and lethargic, limited morbidity; 5=moribund or dead. Data were combined from two experiments. ADE, antibody-dependent enhancement; p.f.u., plaque-forming units.