A mouse model to compare virulence of abortive and intestinal ovine strains of Chlamydia psittaci: influence of the route of inoculation.

Strains of Chlamydia psittaci isolated from faeces of a clinically healthy ewe (intestinal strain IB1) and from the foetus of an aborted ewe (abortive strain AB7) were injected into pregnant mice via the intraperitoneal route and into non-pregnant mice via the footpad route. In pregnant mice the response to inoculation was followed by recording the performance and viability of infant mice, and in the non-pregnant mice by an enlargement of the spleen and colonization of both the spleen and popliteal lymph node. The intestinal Chlamydia strain was less virulent than the abortive strain, but the actual difference of virulence depends upon the route of inoculation. Thus the intestinal strain was at least 500 times less virulent than the abortive strain and was rapidly ruled out when injected subcutaneously into the footpad, whereas it was even less than 100 times less virulent than the abortive strain, and able to induce death of some infant mice, when given intraperitoneally in pregnant mice. The mouse model of experimental subcutaneous infection via the footpad route could be used to easily test the differences of virulence between different strains of C. psittaci.