Salmonella Abortusovis experimental infection induced by the conjunctival route: clinical, serological and bacteriological study of the dose effect in female lambs.

The aim of this work was to explore the first stages of infection with Salmonella Abortusovis after a mucosal inoculation, and to establish an experimental model limiting the bacteriological investigations to the inoculation site. Four groups of 6 ewe-lambs were infected by the conjunctival route with decreasing doses of Salmonella Abortusovis. The clinical and serological survey was completed by a daily bacteriological examination of nasal swabs and faeces. Enumeration of viable bacteria was performed on liver, spleen, lungs and lymph nodes harvested 1, 8, and 22 d after inoculation. A rapid colonization of the cephalic lymph nodes was observed, associated with a transient spreading to prescapular and subiliac lymph nodes without dissemination to the liver and spleen. An irregular and low level faecal excretion was associated with the colonization of mesenteric lymph nodes. The infection by the conjunctival route may either systemically propagated or be locally restricted by the lymphoid system in relation to doses administered. This model uses low infective doses similar to those occurring in field conditions and offers the possibility of limiting the bacteriological control to the regional lymph nodes. It confirms that live attenuated Salmonella strains may be used as vaccinal vectors by the mucosal route.