FIGURE 1.

Usutu virus antibody response of reciprocal serum dilutions from captive birds at Zoological Society of London (ZSL) London Zoo. Antibody response is measured by proxy as a percentage of plaque reduction in Vero cell tissue culture when compared to a control (PRNT₉₀ titre range: 10⁻¹–10⁻⁶). Sampling date is detailed in the legend and serum samples that relate to the same bird have been given a unique alphabetized identifier for each species. Both 90% and 50% plaque reduction thresholds are denoted using a dashed line. Samples were considered to contain USUV‐specific neutralizing antibodies if ≥90% of plaques were reduced.