In ferrets, although the lymphopenia was moderate on most days after infection (e.g. ∼60% of pre-challenge levels on day 5), a marked lymphopenia was present 2 days post-infection, with lymphocytes as a whole dropping to ∼20% of pre-challenge levels and CD8+ T cells in some ferrets dropping to 5% of pre-challenge levels. This evidence concerns the gene CD8A and infection.