Some aspects of the epidemiology of Salmonella abortus-equi infection in equines

Development and application of a competitive ELISA for the detection of antibodies against Salmonella Abortusequi in equids

The high abortion rate associated with Salmonella Abortusequi (S. Abortusequi) infection in equids has re-emerged over the past 10 years and has caused serious economic losses to China. Our previous studies showed that the flagellin FljB gene could distinguish S. Abortusequi from most Salmonella serotypes. In this study, the flagellin antigen was used to develop a competitive enzyme-linked immunosorbent assay (cELISA) that could be used to detect both horse and donkey serum samples using a monoclonal antibody (MAb) that was found to bind to FljB. A cELISA was established using the purified MAb coating of the plate and incubation of the mixture of horseradish peroxidase (HRP)-conjugated FljB antigen with the undiluted serum sample. The performance of the cELISA and the tube agglutination test (TAT) assay was compared with respect to sensitivity and specificity, by testing a panel containing 660 S. Abortusequi-positive and 515 S. Abortusequi-negative serum samples, all of which had been characterized by Western blotting. Receiver operator characteristic (ROC) analyses were performed to determine the cutoff value and estimate the detection specificity (Sp) and sensitivity (Se). ROC analysis showed that the area under the ROC curve (AUC) values of cELISA [AUC = 0.9941; 95% confidence interval (CI), 0.9898-0.9984] were higher than those of TAT (AUC = 0.7705; 95% Cl, 0.7437-0.7972). A cutoff value of 39.5% was selected with Sp and Se values of 100 (95% Cl, 99.26-100.00) and 97.58 (95% Cl, 96.10-98.50), respectively. The cELISA has excellent futures compared with TAT, such as shortened detection time, no need for pre-treatment of sera, and easy interpretation of the results, and is more suitable for disease surveillance.

Aneurysm of the cranial mesenteric artery as a site of carriage of Salmonella enterica subsp. enterica serovar Abortusequi in the horse

Salmonella enterica subsp. enterica serovar Abortusequi is a pathogen restricted to horses. Our investigation targeted 4 draft horses (9-10 months old) kept on a Japanese farm that had suffered an outbreak of S. Abortusequi abortion. The 4 horses were suspected to be carriers of the bacterium owing to their high agglutination titers (≥1:2,560) in tube agglutination testing. The owners' on-farm observations confirmed that the horses had no apparent abnormalities, and S. Abortusequi was not isolated from their blood, rectal swabs, or sternal bone marrow fluid at antemortem investigation. However, at autopsy, all horses displayed the following: suppurative aneurysm of the cranial mesenteric artery with heavy infection with Strongylus vulgaris larvae; heavy intestinal parasitic infection with Gasterophilus intestinalis, Parascaris equorum, Anoplocephala perfoliata, and S. vulgaris; and enlargement of the systemic lymph nodes. In each case, large numbers of S. Abortusequi were isolated from the anterior mesenteric artery thrombus. The thrombus isolates harbored a single virulence plasmid, and the pulsed-field gel electrophoresis profiles of the isolates were identical not only to each other but also to those of Japanese enzootic strains of S. Abortusequi. These results reveal that parasitic aneurysms of the cranial mesenteric artery should be considered an important possible site of carriage of S. Abortusequi in horses. The results also suggest high clonality of the isolated serovar in the horse population in Japan.