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Salmonella is a prominent foodborne pathogen in the US and dairy cattle have frequently been identified as reservoirs for this organism. Here we describe a long-term outbreak of Salmonella enterica subsp. enterica Cerro that was detected in a Pennsylvania dairy herd during routine monitoring as part of a longitudinal study of several dairy herds. An initial analysis of individual fecal grab samples from the milking herd indicated a very low prevalence of Salmonella (1/102) and Salmonella was not detected in 10 environmental samples. In a subsequent sampling 6 mo later, Salmonella was isolated from 43.5% (47/108) of the cows and 40% of collected environmental samples (10/25). The Salmonella isolated in the first sampling was serovar Typhimurium var. Copenhagen, however isolates from the second herd sampling were serovars Cerro (91.5%) and Kentucky (8.5%). Sporadic environmental sampling between these initial complete milking herd samplings yielded serotypes Kentucky, Typhimurium var. Copenhagen, and Cerro and clinical salmonellosis was observed in several cows shedding Typhimurium var. Copenhagen. The herd was sampled nine additional times over the next 14 mo and fecal prevalence of Salmonella ranged from 8.4% to 89%. Prevalence remained high (58 to 69%) over the following 8 mo, showed evidence of decline over the next 3 mo, and then increased again to 89%. Cerro was the only serotype isolated during this period. Bulk milk was cultured weekly during this 22-mo period and Salmonella was isolated from 5.3% (5/94) of milk samples. For the last 14 mo of the study, milk filters were also cultured for Salmonella on a weekly basis and 65% (37/57) of the filters tested positive. There were no significant health or production concerns in the herd during this outbreak. Based on these observations we conclude that sub-clinical Salmonella enterica subsp. enterica Cerro infection can be persistent in a milking herd. [ABSTRACT FROM AUTHOR]

Environmental contamination with Mycobacterium avium subsp. paratuberculosis (MAP) is thought to be one of the primary sources of infection for dairy cattle. The exact link between fecal shedding of MAP by individual cows and environmental contamination levels at the herd level was explored with a cross-sectional analysis of longitudinally collected samples on 3 dairy farms. Composite samples from multiple environmental sites in 3 commercial dairy herds in the Northeast US were cultured quarterly for MAP, providing 1131 samples (133 (11.8%) were culture-positive), and all adult animals in the herds were tested biannually by fecal culture (FC), for 6 years. Of the environmental sites sampled, manure storage areas and shared alleyways were most likely to be culture-positive. Environmental sample results were compared to FC results from either the concurrent or previous sampling date at both the herd and the pen level. At the herd level, a 1 log unit increase in average fecal shedding increased the odds of a positive non-pen environmental sample by a factor of 6 and increased the average amount of MAP in non-pen samples by 2.9 cfu/g. At the pen level, a 1 log unit increase in average fecal shedding in the pen increased the odds of a positive environment by a factor of 2.4 and the average amount of MAP was increased by 3.5 cfu/g. We were not able to model the relationship between non-pen environmental sample status and the distance between shedding animals and the sample's location, and neighboring pens did not significantly affect the results of the pen-level analysis. The amount of MAP in pen-level samples and the probability of a pen testing positive for MAP were both positively but non-significantly correlated with the number of animals in the pen shedding >30 cfu/g of MAP. At least 6 environmental samples met the criteria for the U.S. Voluntary Bovine Johne's Disease Control Program on 47 of the 72 sampling dates; of these, 19 of the 47 FC-positive sampling dates were positive by the 6-sample environmental testing method, resulting in a herd sensitivity of 0.40 (95% CI: 0.26-0.54). None of the 3 FC-negative sampling dates produced positive environmental samples. Although environmental sampling can be used as a tool in understanding the level of MAP infection in a herd or pen, it did not appear to be a sensitive diagnostic method for herd positivity in these low prevalence herds, and its use may require caution., (Copyright © 2011 Elsevier B.V. All rights reserved.)

We developed a mathematical model of the transmission dynamics of salmonella to describe an outbreak of S. Cerro infection that occurred in a Pennsylvania dairy herd. The data were collected as part of a cooperative research project between the Regional Dairy Quality Management Alliance and the Agricultural Research Service. After the initial detection of a high prevalence of S. Cerro infection in the herd, a frequent and intensive sampling was conducted and the outbreak was followed for 1 year. The data showed a persistent presence of S. Cerro with a high prevalence of infection in the herd. The dynamics of host and pathogen were modelled using a set of nonlinear differential equations. A more realistically distributed (gamma-distributed) infectious period using multiple stages of infection was considered. The basic reproduction number was calculated and relevance to the intervention strategies is discussed.

Salmonellae are a major group of foodborne pathogens known to affect both humans and animals. Dairy cattle are a known reservoir of these bacteria and human Salmonella infections have been associated with the consumption of improperly processed or contaminated dairy products. Many of the over 2500 known serotypes of Salmonella are known to infect cattle, resulting in asymptomatic to fatal salmonellosis. This study describes the course of a Salmonella outbreak and subsequent endemic infection on a dairy farm in Pennsylvania. The outbreak was initially detected when a few cows with clinical symptoms and one fatality were found to be infected with Salmonella enterica subsp. enterica serovar Typhimurium var. Copenhagan. Based upon sampling of the farm environment, Salmonella Typhimurium var. Copenhagan was succeeded within 3 months by Salmonella enterica subsp. enterica serovar Kentucky. Salmonella enterica subsp. enterica serovar Cerro ultimately supplanted Typhimurium var. Copenhagan and Kentucky in individual animals and environmental samples and persisted in the herd at high prevalence for almost 2 years. Since there were no obvious clinical consequences of the Salmonella Cerro infection, these data suggest that some serotypes of S. enterica subsp. enterica can behave as commensal organisms in dairy cattle and illustrate the difficulties of controlling Salmonella in milk production systems. The consistent finding of Salmonella in the environment reinforces the potential for human exposure to this pathogen and the need to understand the dynamics and ecology of Salmonella in dairy production settings.