Oral Inoculation of Point-of-Lay Hens with the New South Wales Outbreak Strain of Salmonella Enteritidis Phage Type 12 Causes Infection, but Minimal Histopathology.

Abstract

An outbreak of food poisoning in New South Wales (NSW) Australia in 2018, caused by Salmonella enterica serovar Enteritidis phage type 12 (PT12), was traced to eggs consumed from a NSW layer flock. This was the first report of Salmonella Enteritidis infection in NSW layer flocks, despite ongoing environmental monitoring. Clinical signs and mortalities were minimal in most flocks, although seroconversion and infection were demonstrated in some flocks. An oral dose-response challenge study with Salmonella Enteritidis PT12 was undertaken in commercial point-of-lay hens. Cloacal swabs collected at 3, 7, 10, and 14 days postinoculation and caeca, liver, spleen, ovary, magnum, and isthmus tissues collected at necropsy at either 7 or 14 days were processed for Salmonella isolation (AS 5013.10-2009 from ISO6579:2002). Histopathology was performed on the above tissues, as well as lung, pancreas, kidney, heart, and additional intestinal and reproductive tract tissues. Salmonella Enteritidis was consistently detected in cloacal swabs between 7 and 14 days postchallenge. The Salmonella Enteritidis PT12 isolate successfully colonized the gastrointestinal tract, liver, and spleen of all hens orally challenged with 10⁷, 10⁸, and 10⁹ Salmonella Enteritidis, and less consistently colonized their reproductive tracts. On histopathology, mild lymphoid hyperplasia in the liver and spleen, along with hepatitis, typhlitis, serositis, and salpingitis, was observed at 7 and 14 days postchallenge, with a greater proportion of affected birds in the two higher dose groups. Diarrhea and culture of Salmonella Enteritidis from heart blood were not detected in challenged layers. The NSW isolate of Salmonella Enteritidis PT12 was able to invade and colonize the birds' reproductive tracts as well as a wide range of other tissues, indicating the potential for these naive commercial hens to contaminate their eggs.