Protective assay in suckling mice. Protective effects of monovalent mouse antisera were evaluated in suckling mice. Suckling mice were intracerebrally inoculated with DENV1, 2, 3, or 4, and clinical signs of infection, mainly hind leg paralysis, alterations in spinal column and mortality, were monitored for 21 days. (A) survival curve; (B) mobidity curve. Different letters mean statistically significant differences by the Log-rank test. *indicates statistical significance (*P < 0.05; **P < 0.01).