Mouse models for evaluation of virulence of Chlamydia psittaci isolated from ruminants.

Intestinal strains of Chlamydia psittaci isolated from faeces of clinically healthy sheep or goats were differentiated from pathogenic strains isolated from animals affected with chlamydial diseases by their virulence in mice. The invasiveness of strains after footpad inoculation was estimated in non-pregnant mice by recording the colonisation and the enlargement of the spleen on days 6 and 9 after inoculation. The abortifacient effect was judged by measuring the colonisation of placenta and fetuses of pregnant mice inoculated intravenously on day 11 +/- 1 of pregnancy. While 25 of 27 pathogenic strains were invasive and able to colonise placenta and fetuses, eight of 10 intestinal strains were not. The model permits graded differentiation between virulent and non-virulent strains and suggests that in propitious circumstances intestinal chlamydia could reach and colonise the placenta and disturb the pregnancy.