General characteristics of the animals used in the study.

aFisher's exact probability test;bWith 1–3 (oligosymptomatic) or more than 3 (polysymptomatic) of the following clinical signs: emaciation, anemia, dermatitis, alopecia, conjunctivitis, onychogriphosis, increased lymph node size, splenomegaly and apathy. Detail are given in the text;cQuantitative PCR estimative only available for eight more recently collected animals of each group; Quantitative PCR was not available for 5 animals with organized and for 3 animals with disorganized splenic lymphoid tissue;dMann-Whitney test.eNot tested.