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 •
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