Most literature on APV infection describes case-reports or outbreak studies. By contrast, we focus on the prevalence of endemic disease in a single wild bird host. This is the first large-scale study of APV prevalence in house sparrows; previous studies have used more limited samples sizes [8,13,20,23,32–35]. We found a moderate prevalence (around 3%) of pox-like lesions in several areas in Spain. Similarly, in a study on 81 house sparrows captured in Hawaii authors found prevalences of 2.5% and 4.9% of active and inactive avian pox lesions, respectively . Conversely, in closely related Spanish sparrows (P. hispanolensis), Smits and co-workers  did not find APV affected birds in the Canary Islands (n = 128). The prevalence reported here is similar to that found in blackcaps (3.7%) from the Czech Republic .