Canine MDCKII (ref. 26 (link)), porcine NSK and NPTr cells30 (link) and human A549 (ref. 31 (link)) and HEK293T cells32 (link) were maintained in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal calf serum (FCS), 2 mM L-glutamine, 100 U penicillin per ml and 100 μg streptomycin per ml. Chicken hepatocellular epithelial cell line (LMH)33 (link) and chicken fibrolast cells (DF-1)34 (link) were grown in DMEM supplemented with 8% (v/v) FCS, 2% (v/v) chicken serum, 2 mM L-glutamine, 100 U penicillin per ml and 100 μg streptomycin per ml. Bat cells EpoNi/22.1 (ref. 35 (link)) and CarperAEC.B-3 (ref. 36 (link)) were maintained in DMEM supplemented with 10% (v/v) FCS, 2 mM L-glutamine, 100 U penicillin per ml, 100 μg streptomycin per ml, 1 mM sodium pyruvate and 0.1 mM non-essential amino acids (NEAAs, Cyagen catalogue number NEAA-10201-100). Primary HBAE cells (MucilAir, Epithelix Sàrl) reconstituted in Transwells of 6.5 mm of diameter with a pore size of 0.4 μm (Costar 3470, Corning) were maintained in MucilAir Culture Medium.