Perinatal lamb mortality in Western Australia. 6. Listeric infection.

Listeric abortion was diagnosed in sheep on 14 occasions between 1963-65, and 4 of these were associated with other major abortion pathogens. Except for infection in one district, the outbreaks were scattered sporadically over the southern agricultural area. The diagnosis in 1963 was the first time listeriosis had been found in animals or man in Western Australia. L. monocytogenes was readily recovered in pure culture from all organs and sites cultured. All the strains were serotype 5 Ivanov, with a distinctive double zone of haemolysis. The time-of-death of the 40 infected lambs was: ante-parturient death 50%, parturient death 10% and post-parturient death 40%. Three-quarters of the lambs had gross lesions, the most consistent being small necrotic foci in the liver. Typically, lambs with congenital listeriosis had subcutaneous oedema, hydrothorax, hydroperitoneum, distended abdomen, enlarged pale bronze-red friable livers with small necrotic foci, small abomasal erosions, increased yellow-orange mucoid meconium and enlarged mesenteric lymph nodes. The finding of small yellowish, necrotic foci in the liver, small abomasal erosions and yellow-orange meconium in an aborted lamb was considered to be almost pathognomonic for listeriosis. The origin of these outbreaks was unknown. No evidence of Listeria was found in 61 specimens from 7 species of native fauna caught in the infected areas. Epizootiological observations are reported. No cases of neuro-listeriosis were observed.