Proactive wildlife disease surveillance and associated reactive contingency planning are fundamental to detect and respond to pathogenic infection. In North Wales, red squirrels ( Sciurus vulgaris ) are present on either side of the Menai Strait. The mainland element of this single population is sympatric with the non-native grey squirrel ( Sciurus carolinensis ). The latter species carries squirrelpox virus (SQPV) as an asymptomatic infection, while in the native red squirrel SQPV is invariably pathogenic and can lead to high mortality.1 Squirrelpox was first confirmed in these …