EXPERIMENTAL CONJUNCTIVAL-ROUTE INFECTION WITH MYCOPLASMA-AGALACTIAE IN LAMBS

Contagious agalactia caused by Mycoplasma agalactiae is a major cause of mastitis in ewes and goats. To explore the first stages of infectio n, an experimental infection in lambs has been developed, using the st rain P89 of M. agalactiae. Lambs were inoculated by the conjunctival r oute with various doses of viable bacteria. Following necropsy at regu lar intervals, enumeration of viable bacteria was performed on various organs including the lymph nodes (LNs) draining the conjunctiva. A ra pid colonization of LNs from Day 7 (Group 10(9) colony-forming units [ CFU]) or from Day 14 (Group 10(7) CFU) post-inoculation (p.i.) was obs erved and was associated with a transient infection of the spleen sugg esting a bacteriemic phase. In a second experiment, lambs were inocula ted with the 10(7) dose which had induced a regular infection on Day 1 4 p.i. in the first experiment. The lambs were necropsied on Days 14 o r 56 p.i. The bacteriological examinations of the group necropsied on Day 14 p.i. confirmed the previous results. On Day 56 p.i., the infect ion decreased but all head LNs remained infected and M. agalactiae was still present at the inoculation site in one lamb, suggesting that M. agalactiae can persist for a long time in its host. This experimental model, using lambs inoculated by the conjunctival route and slaughter ed 14 days after inoculation, was simple and easily reproducible, in c omparison with a model using lactating ewes. This model can be used to compare virulence of field strains and to test protection following i mmunization of lambs with attenuated strains of M. agalactiae or with antigens. (C) 1998 Elsevier Science B.V.