Effects of experimental immunosuppression in cattle with persistently high antibody levels to Salmonella Dublin lipopolysaccharide O-antigens

This study examined nine adult cattle with persistently high antibody responses to S. Dublin O-antigen based lipopolysaccharide for cultivable bacteria in faeces, milk and internal organs before and after transportation, isolation and experimental immunosuppression with dexamethasone sodium phosphate over a period of 7–14 days.Clear signs of immunosuppression were seen as expression of leucocytosis and neutrophilia in all animals on day 3–5 after the first injections with dexamethasone sodium phosphate. No clinical signs or necropsy findings indicating salmonellosis were observed in any of the animals. No shedding of S. Dublin was found in faeces (collected four times daily) or milk (collected twice daily) at any point in time during the 7–14 day period. S. Dublin was recovered by a conventional culture method from tissue samples from mammary lymph nodes, spleen and liver collected from three animals at necropsy.In this study, immunosuppression by transportation stress or dexamethasone treatment did not lead to excretion of S. Dublin in milk or faeces from infected animals. The study questions the general conception that cattle with persistently high antibody levels against S. Dublin O-antigens in naturally infected herds should be considered high risk for transmission and therefore culled as part of effective intervention strategies. It is suggested that the location of S. Dublin infected foci in the animal plays a major role for the risk of excreting bacteria.Salmonella enterica subsp. enterica serovar Dublin (S. Dublin) is a zoonotic bacterium which is host adapted to cattle. Although it infects cattle at all ages, severe clinical disease is mostly seen in calves [1]. The bacterium occasionally infects humans where it causes severe illness and high case mortality due to septicaemia [2].An epidemiologically important feature of S. Dublin is its ability to cause subclinical persistent infection in cattle (carriers) [3]. Such carriers probably harbour the bacterium