Blood gas analysis was performed as previously described [13, 41] . Three mice were anesthetized with Zoletil (tiletamine-zolazepam; Virbac; 20 mg/g) on days 4, 6, 8, 10 and 14 p.i. Arterial blood samples were withdrawn into a heparinized syringe by percutaneous left ventricular sampling of lightly anesthetized mice that were spontaneously breathing room air. Blood gas analysis was immediately performed using a Vetstat Electrolyte and Blood Gas Analyzer (Idexx laboratories, Westbrook, MA, USA).