![]() Ĭompetition between co-infecting strains may affect the dynamics of one or more serovars. Salmonella Mbandaka has not been associated with any egg related outbreaks in Australia, although this serovar has been associated with egg product related Salmonella outbreaks in the US. Field epidemiological investigations suggested that Salmonella Mbandaka was commonly isolated along with Salmonella Typhimurium in layer flocks without any clinical signs in chickens. The poultry farm environment is often contaminated with multiple serovars. In the Australian egg industry, Salmonella Typhimurium is frequently isolated from eggshell surfaces but it is not the only serovar isolated from egg farms. The host immune response to Salmonella infection may also contribute to increased corticosterone levels however, relationship between persistent Salmonella colonisation and stress in birds is unclear. Stress has also been linked with impaired immunity which may increase intestinal colonization by enteric pathogens such as Salmonella. The productive lifetime of a layer hen, however, can extend beyond 50 weeks of age and few studies have investigated extended bacterial shedding dynamics, egg contamination and host responses to infection.During productive lifespan, layer hens may also experience many physiological and environmental stressors, such as overcrowding, extreme temperature variation and the onset of lay that may lead to increased fecal shedding of Salmonella. Moreover, the data obtained from these investigations was collected for 3–4 weeks pi. These studies, however, have infected birds at different ages, using a variety of inoculation methods limiting the degree to which the data can be directly compared. Previous experimental infection trials have examined egg contamination and internal organ colonization of layer hens. ĭue to the public health importance of contaminated eggs, understanding the dynamics of Salmonella Typhimurium shedding patterns and associated host responses to infection is of critical importance. Despite improvements of on-farm control strategies, Salmonella Typhimurium remains a significant problem within the Australian layer industry. Over the same period, the number of cases linked directly with eggs increased from 20.8 to 44.8%. In 2011, the total number of food related disease outbreaks had increased to over 150 and 38.4% were attributed to Salmonella. Over the past several years, the incidence of human cases of salmonellosis in Australia has been increasing. Strains of Salmonella Typhimurium, however, are most frequently identified during Australian outbreaks of egg-related cases of salmonellosis. In North America and Europe, the most common serovar isolated during egg-related outbreaks is Salmonella Enteritidis followed by Salmonella Typhimurium. ![]() Thus, the zoonotic potential of Salmonella represents a significant global public health concern. Eggs and raw egg based food products are often identified as the source of Salmonella during outbreaks of human gastrointestinal disease. Spleen, liver and caecal tonsils were positive for bacteria in both groups, indicating that Salmonella was not cleared from the birds and internal organ colonization could serve as a reservoir for continued bacterial shedding.Ĭommercial poultry are often persistently infected with non-typhoidal serovars of Salmonella enterica. Bacterial loads in internal organs were characterised to determine persistence. Salmonella Typhimurium specific antibody was lower in co-infected animals than monoinfected animals. Antibody responses to infection were monitored in both serum and yolk samples. The onset of lay occurred between weeks 6–8 post-infection (pi) and Fecal corticosterone metabolite (FCM) concentrations increased in both control and co-infected birds. On day 1, fecal corticosterone metabolites in birds infected with Salmonella Typhimurium (674.2 ± 109.3 pg/mg) were significantly higher than control (238.0 ± 12.62 pg/mg) or co-infected (175.4 ± 8.58 pg/mg) birds. Salmonella shedding was quantified using the most probable number and qPCR methods and was highly variable over the course of the experiment. ![]() The present study sought to characterise bacterial shedding and host responses to infection in hens infected with only Salmonella Typhimurium or co-infected with both Salmonella Typhimurium and Salmonella Mbandaka over a 16 week period. While a number of studies have investigated Salmonella shedding and host responses to infection, they have been conducted over a short time period. In Australia, Salmonella Typhimurium is the most common serovar identified in egg product related foodborne outbreaks. Salmonella Enteriditis and Salmonella Typhimurium are commonly isolated during egg-related outbreaks of salmonellosis and represent a significant international public health issue.
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