Sheep abortions in Southland caused by an as-yet unidentified Gram-negative rod

Several, often large, abortion outbreaks, with lesions in the liver of fetal lambs resembling those seen in abortions due to Campylobacter spp., have been seen in sheep flocks in Canterbury, Otago and Southland since 1992. In spite of extensive investigations, a causative agent had not been identified.
This season, a large abortion outbreak in a flock of sheep in Southland was investigated. Gross liver lesions resembling those seen in abortions due to Campylobacter spp. were seen in the aborted lambs but no Campylobacter spp. were isolated, and the ewes had been previously vaccinated against this bacterium. Histopathological examination of fixed livers from a number of aborted lambs showed variable numbers of silver-positive curved rods along the sinusoidal margins of intact hepatocytes. These bacteria failed to stain with Gram and Giemsa stains. Although similar, faintly staining, Gram-negative rods were seen in fresh stomach contents of some of these lambs, nothing of significance was cultured despite using a variety of methods.
Electron microscopy of sections from blocks taken from an affected, formalised, fetal liver identified, within the biliary cananiculi, moderate numbers of slightly curved rods with a spiral periplasmic membrane. Flagella were not seen but this may have been due to ageing of the sample.
From its ultrastructure this organism resembled ‘Flexispira rappini’, a bacterium that belongs to the Helicobacter group. This organism has been previously reported as causing a small number of abortions in sheep flocks in the USA and UK.