FIG. 1. Comparison of the pathogenicity of the parental CDV strain A75/17 and its EGFP expression recombinant derivative A75eH. (A) Scheme of the A75eH genome with the EGFP open reading frame introduced as an additional transcription unit between the hemagglutinin (H) and polymerase (L) genes. The genome is shown as a white elongated box. The genes are indicated by the letters N (nucleocapsid), P (phosphoprotein), M (matrix), F (fusion), H, and L. The additional EGFP-containing transcription unit is represented by a black box and is marked "eGFP." (B) Time course of infection of groups of three animals. Each pair of symbols represents one animal. Squares indicate the onset of rash, and circles indicate the time of euthanasia for humane reasons . (C) Leukocyte number and (D) in vitro proliferation activity of lymphocytes from these animals. The group (n = 3) infected with A75/17 is represented by gray squares, and the group (n = 3) infected with A75eH is represented by black circles. Days postinfection are indicated on the x axis, and leukocyte number (leuko.) or proliferation activity is indicated on the y axis. Dotted lines or broad hatched gray lines indicate threshold levels used for the classification as moderate or severe immunosuppression, respectively.