Viral population dynamics of very virulent infectious bursal disease virus (vvIBDV) field strains isolated in the Iberian Peninsula since the first outbreak in the 1990s have been analysed. Low levels of genetic variability and a global purification selection pattern were reported in 480 base pairs of the hypervariable region of the VP2 gene, indicating a lack of a selection-driven immune escape in the evolutive pathway of the virus. The viral population structure of vvIBDV strains in the Iberian Peninsula showed a strong relationship between geography and phylogeny, with two main groups observed. A global comparison among vvIBDV strains also showed an association with sequences from the same country. The low variability, the strong purifying selection and the geographical pattern observed point to a picture where the virus evolves slowly, occupying the same geographical niche for a long time. The scenario depicted fits well with the biological features of the virus: being able to remain viable for long periods of time due to a strong environmental resistance, and as an immunosuppressive agent, capable per se of annihilating temporally the immune system of the host. © 2012 Houghton Trust Ltd.