Listeriosis in sheep. Eperythrozoon ovis infection used as a model to study predisposing factors.

Three groups of 9 months old lambs, each group consisting of 5 animals, were infected experimentally with Eperythrozoon ovis (Eo), Listeria monocytogenes (Lm) and Eo/Lm, respectively. The animals infected with Eo developed haemolytic anaemia, but otherwise no clinical symptoms were seen. The animals infected with Lm had a period with fever and reduced appetite after infection. These symptoms lasted longer and were more pronounced in the group with the dual infection (Eo/Lm). None of the lambs developed clinical meningo-encephalitis during the experiment. Group Lm developed the highest reciprocal geometrical mean titres against Lm. No titer rise was found in group Eo, while group Eo/Lm had a slight rise towards the end of the experiment. Group Eo/Lm also had the strongest delayed hypersensitivity reaction against Lm. After Eo infection, a fall in packed cell volume, haemoglobin, number of red cells, and plasma glucose and an increase in serum iron were recorded. Serum iron dropped and serum copper increased after infection with Lm. In this experiment the blood changes induced by Eo, i.e. haemolytic anaemia and acidosis, led to a prolonged state of illness in animals infected with Lm, in addition to inhibited development of antibody titres, but not to clinical meningoencephalitis.