Equine Health Update EHU Vol 19 Issue 4 - Page 21

EQUINE | CPD Article In adult horses Actinobacillosis is rare and usually acts as a secondary bacterial infection complicating some other primary condition, usually some other concur- rent pathogenic bacterial or viral infection, but under the right circumstances Actinobacillus sp can be pri- mary pathogens. Infection in adult horses is gener- ally more localised and include cutaneous abscesses, guttural pouch infections, endometritis, pericarditis, endocarditis, peritonitis, encephalitis, arthritis, orchi- tis and abortion. The syndromes of acute peritonitis, encephalitis and fatal pulmonary hemorrhage with pneumonia due to endothelial damage caused by bac- terial toxins, have been more recently described. In addition, it has been documented that the same mare may abort in successive pregnancies. Rare cases of septicemia associated with both Actinobacillus equuli subsp equuli and Actinobacillus equuli subsp hemo- lyticus, have been documented. Figure 4: Foal liver histopathology – note the hepatic sinusoidal bacterial emboli (arrows) with associated micro-abcessation. Diagnosis Definitive diagnosis of Actinobacillus equuli relies on the isolation of the bacteria by culture. • In live foals the preferred sample is blood for blood culture collected directly into blood culture bottles. • In dead foals at postmortem kidney and lung are the preferred tissues, either fresh biopsies or char- coal swabs. • In adult horses the primary target organ of the dis- ease syndrome is sampled. Histopathology is also an extremely useful diagnostic procedure as the presence of large embolic bacterial colonies plugging the capillary’s of various visceral or- gans, are a common and consistent histological find- ing and easily visible in H&E stained sections (Figure 4 and Figure 5). Figure 5: Foal kidney histopathology – note the plugging of glomerular and periglomerular bloodvessels by large bacterial emboli (arrows). Prevention and Control Infected horses may be treated with various antibiotics including streptomycin, tetracycline, ampicillin and • Volume 19 no 4 • December 2017 • 21