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Background: A series of unusual abortions occurred in Thoroughbred and Quarterhorse mares in the Hunter Valley region of New South Wales from mid-March to November 2004. The initial link between early cases was the microbiological culture of atypical environmental coryneforms from the stomach contents and/or lungs of fetuses aborted on different properties., Methods: The unique pathologic lesions were described with a case definition and the term 'equine amnionitis and fetal loss' (EAFL) was established., Results: The causal factor was the ingestion of the processionary caterpillar (Ochrogaster lunifer). Bacteria from the Actinomycetales order were isolated from 40% of the combined suspect and confirmed EAFL cases and included Microbacterium arborescens, Cellulomonas sp., Arthrobacter spp. and Cellulosimicrobium sp. Other bacteria isolated included various Gram-negative bacilli and Gram-positive cocci., Conclusions: Although the predominant type of bacteria isolated from EAFL was environmental coryneforms, it is important to note that a variety of bacteria were associated with the characteristic histopathological changes outlined by the case definition. This highlights the importance of histopathology on both fetal membranes and fetuses, as well as culture to confirm EAFL and to exclude other possible causes of abortion., (© 2013 The Authors. Australian Veterinary Journal © 2013 Australian Veterinary Association.)

Pulsed-field gel electrophoresis of restriction endonuclease-digested genomic DNA from a large collection of clinical isolates of Rhodococcus equi, an important pathogen of foals, was used to compare strain distribution between farms and over time. Forty-four strains were found among 209 isolates, with 5 of these accounting for over half the isolates and the 22 strains isolated more than once accounting for 90% of the isolates. The average genotypic diversity on each farm and in each year was found to be less than the genotypic diversity of the isolates taken as a whole, with 5.2% of the total diversity being due to differences between farms and 5.5% to differences between years. A small number of strains on each farm were found to have caused at least half the clinical cases of disease, and these varied between farms and, to a lesser extent, years. Most strains were found on more than one farm, and some very similar restriction patterns were found among isolates from different continents, indicating that strains can be very widespread. Multiple strains were isolated in five of the six cases in which more than one isolate from a single foal was examined, indicating that disease may commonly be caused by simultaneous infection with multiple strains. It was concluded that there are a number of different strains of R. equi which carry the vapA gene, and these strains tend to be widespread, but individual farms tend to have particular strains associated with them.

A trial was conducted on a Thoroughbred stud to determine whether or not the administration of anti-Rhodococcus equi hyperimmune plasma would reduce the prevalence of R equi pneumonia (rattles) in foals born in the 1992 horse breeding season. Hyperimmune plasma was administered to 34 foals; another 57 foals were untreated. There was no significant difference in the number of transfused foals developing R equi pneumonia compared with the untreated foals. The time required for recovery from pneumonia between the 2 groups was not significantly different.