Ovine listerial encephalitis: analysis, hypothesis and synthesis

Area of Science:

• Veterinary Neurology
• Microbiology
• Sheep Pathology

Background:

• Listerial encephalitis is a significant neurological disease in sheep.
• Field data indicated a seasonal and age-related prevalence, particularly in sheep experiencing dental changes.
• The trigeminal nerve's role in potential infection pathways was previously unconfirmed.

Purpose of the Study:

• To investigate the hypothesis that dental pulp infection by Listeria monocytogenes can cause encephalitis in sheep.
• To determine the feasibility of the dental pulp as a route for Listeria monocytogenes to reach the trigeminal nerve.
• To establish the incubation period for clinical neurological disease following experimental infection.

Main Methods:

• Analysis of field data on listerial encephalitis incidence in sheep.
• Experimental inoculation of Listeria monocytogenes directly into the dental pulp of sheep.
• Histopathological examination to confirm encephalitis.
• Clinical observation to determine the onset of neurological signs.

Main Results:

• Field data showed listerial encephalitis was most prevalent in winter/early spring in sheep with deciduous teeth.
• Experimental inoculation into dental pulp successfully demonstrated a feasible route for Listeria monocytogenes infection.
• Histological evidence of encephalitis was observed as early as six days post-inoculation.

Conclusions:

• Ingestion of Listeria monocytogenes by sheep with dental issues (cutting, changing, or losing teeth) may lead to encephalitis via the trigeminal nerve.
• The dental pulp serves as a viable entry point for Listeria monocytogenes to cause ascending neuritis and encephalitis.
• The incubation period from dental pulp infection to clinical neurological signs in sheep is at least three weeks.