title: Fatal pulmonary hemorrhage associated with RTX toxin producing Actinobacillus equuli subspecies haemolyticus infection in an adult horse.
abstract: A case of fatal pulmonary hemorrhage in a 6-year-old American Paint mare with a 2-week history of intermittent coughing, fever, and epistaxis is described. Significant macroscopic abnormalities at postmortem examination were restricted to the respiratory system, and microscopically, severe pulmonary hemorrhage with suppurative bronchopneumonia was found. Actinobacillus equuli subsp. haemolyticus was cultured from a transtracheal wash performed antemortem as well as from the lungs at necropsy. The presence of airway-associated hemorrhage in conjunction with bacterial bronchopneumonia suggested endothelial damage caused by a locally elaborated bacterial toxin, possibly produced by the A. equuli strain isolated from the lungs. The objective of this report was to indirectly document the presence of hemolysin repeat in structural toxin (RTX) in the lungs of the reported mare. A real-time polymerase chain reaction (PCR) assay targeting the recently described aqx gene of A. equuli subsp. haemolyticus was established and validated. Transcriptional activity of the aqx gene was used as a surrogate method to document toxin production. Real-time PCR analysis of the transtracheal fluid and lung tissue of the affected mare confirmed the presence and the transcriptional activity of the aqx gene at the genomic (gDNA) and complementary DNA (cDNA) levels, respectively. The presence of pneumonia associated with hemorrhagic pulmonary fluid and the culture of large numbers of hemolytic A. equuli should prompt the clinician to consider endothelial damage caused by bacterial toxins.
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. npusterla@ucdavis.edu
authors.forename: Nicola
authors.initials: N
authors.lastname: Pusterla
authors.forename: Megan E B
authors.initials: ME
authors.lastname: Jones
authors.forename: F Charles
authors.initials: FC
authors.lastname: Mohr
authors.forename: Jamie K
authors.initials: JK
authors.lastname: Higgins
authors.forename: Samantha
authors.initials: S
authors.lastname: Mapes
authors.forename: Spencer S
authors.initials: SS
authors.lastname: Jang
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Samitz
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Byrne
mesh_terms: D000189:Actinobacillus Infections / Q000382:microbiology / Q000662:veterinary*; D044131:Actinobacillus equuli / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D017809:Fatal Outcome; D005260:Female; D006651:Histocytochemistry / Q000662:veterinary; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses; D008171:Lung Diseases / Q000382:microbiology / Q000662:veterinary*; D016133:Polymerase Chain Reaction / Q000662:veterinary; D011247:Pregnancy
chemical_list: C079721:ApxIII toxin protein, Actinobacillus; D001426:Bacterial Proteins; D004269:DNA, Bacterial