Abortion and calf septicemia associated with Salmonella Dublin infection in a Holstein herd
Margaret Stalker, Jamie Hobson, Cynthia Miltenburg, Andrew Brooks
Animal Health Laboratory, University of Guelph, Guelph, ON (Stalker, Brooks); Eldale Veterinary Clinic, Elmira, ON (Hobson); OMAFRA, Guelph, ON (Miltenburg)
AHL Newsletter 2020;24(4):7.
A near-term aborted Holstein fetus was presented to the AHL for postmortem examination. The herd had a history of two previous late term abortions in the last 2 months, and was also reporting losses of newborn to 2-week-old calves with apparent respiratory signs. The fetus was normally formed and autolysed. On histology, there were poorly preserved inflammatory cells within the lung. Bacterial culture of the lung grew 4+ Group D Salmonella spp., later serotyped as Salmonella Dublin. PCR tests for other infectious causes of abortion, including bovine herpesvirus 1, BVD, Neospora caninum and Leptospira spp. were negative.
Ten days later, a 5-week old calf that died following a clinical history of pneumonia was submitted for a follow-up postmortem. Gross lesions included an enlarged and meaty spleen and generalized pulmonary congestion. On histology, this calf had lesions of a fulminant bacterial septicemia, typified by multifocal areas of inflammation and necrosis with visible bacterial colonies in the spleen, kidney, liver and lung, as well as an enterocolitis. Primary bacterial cultures of lung and spleen again grew 4+ Salmonella Dublin, while Salmonella was isolated only on enrichment culture from the intestine.
Salmonella Dublin was first detected in Ontario in 2012, and continues to be an important emerging pathogen for the Ontario dairy industry. S. Dublin is a host-adapted strain for cattle, and transmission is typically via the fecal-oral route (1). The presence of infected but non-clinical carrier animals in the herd provides a source of environmental exposure, with intermittent shedding in manure, milk, saliva, and urine resulting in infection of susceptible animals. Colonization of the gastrointestinal tract is followed by bacteremia and spread to multiple organs including lung, liver, spleen and kidneys. Unlike most Salmonella infections which present clinically as diarrhea, common presenting signs of S. Dublin infection in calves are septicemia and pneumonia, often accompanied by fever, anorexia, and depression. Affected calves are usually 2-12 weeks of age; however, clinical disease can occur in calves up to 6 months old. Bloody diarrhea, arthritis or meningitis may also occur. While the initial infection is difficult to treat because most isolates are resistant to many antimicrobials, calves that survive the infection may become carriers for life. Identifying these carrier animals is very challenging, and improving biosecurity, sanitation, colostrum quality, and calf, heifer and mature cow management remain the mainstays of reducing the risk of disease transmission and limiting the cost of outbreaks.
As illustrated in this case, S. Dublin can become bacteremic, cross the placenta and cause abortion. This is the predominant clinical sign in some herds, particularly in Europe, where abortion may be the first indication of infection in a herd. However, this is the first case of abortion due to S. Dublin documented at the AHL in Ontario. AHL
Reference
1. Henderson K, Mason C. Diagnosis and control of Salmonella Dublin in dairy herds. In Practice 2017;39:158-168.