Progress 10/15/05 to 09/30/07
Outputs
We have completed the Year 1 project and a manuscript has been submitted with an abstract that reads: A prospective cohort study was used to determine if Salmonella shedding in feedlot cattle treated for respiratory disease was associated with treatment failure or case fatality. Genotypic and phenotypic characteristics of Salmonella strains in the population were also determined. Feces were collected per rectum from cattle that were examined for apparent respiratory disease, had a rectal temperature at or above 40 Celsius, and subsequently received antimicrobial treatment. Salmonella were recovered from 918 (73.7 percent) of 1,245 fecal samples and weekly prevalence estimates ranged from 49 to 100 percent over the 3-month study. Serogroup E Salmonella were most common (73.3 percent), followed by C1 (11.0 percent), C3 (8.6 percent), and B (1.1 percent). Predominant serotypes were Orion (46.5 percent), Anatum (19.8 percent), Kentucky (8.7 percent), Montevideo (7.5
percent), and Senftenberg (4.9 percent). All Salmonella had virulence genes invA and pagC, but few (3.9 percent) were positive for antimicrobial resistance-associated integron gene intI1. Retreatment and case fatality rates were numerically higher, but not statistically different for individuals that were Salmonella-positive versus -negative at initial treatment. However, the case fatality rate was higher for cattle shedding Group B Salmonella than for cattle shedding other serogroups. Pens with a higher Salmonella prevalence at first treatment had a higher proportion of mortalities occur in a hospital pen, higher overall retreatment rates, and were more likely to be sampled later in the study. Results indicate a high prevalence of Salmonella in cattle treated for respiratory disease, and that effects associated with clinical outcomes may depend on the Salmonella strain and lot-level risk factors. Year 2 goals were to assess prevalence and bacterial characteristics of Salmonella in
feedlot cattle at arrival and pre-slaughter, determine if the Salmonella status was associated with cattle performance and health, and determine if strains recovered at arrival and at slaughter were similar. We studied 30 lots of feedlot cattle that arrived between October 2006 and January 2007, and were slaughtered between April and August 2007. Approximately 1,800 fecal samples (30 per lot/time) were cultured for Salmonella. We have completed all sample culture and isolation, and currently are characterizing Salmonella isolates and interpreting data. Cattle health and performance data have been received from the participating feedlot and linked to corresponding Salmonella results. Within-lot prevalence of Salmonella averaged 65 percent (range: 16.7 - 100) at arrival to the feedlot and averaged 73.1 percent (range: 0 - 100) for samples collected pre-slaughter. Some serotyping and genotyping data are still pending, but preliminary data indicate tremendous diversity among strains that
were recovered from cattle at arrival and pre-slaughter with little evidence at this point that strains present in arrival cattle spread and persist through to slaughter.
Impacts
Many types of Salmonella can cause disease in animals and people. The presence of Salmonella in cattle production systems could result in adverse health effects in both cattle and humans. In cattle, Salmonella can affect both health and production, but effects are largely undocumented for cattle in commercial feedlot production systems. In humans, Salmonella is one of the most common causes of foodborne illness and has been associated with the consumption of many different foods. We have evaluated the frequency and strains of Salmonella present in both clinically ill (Year 1) and clinically normal (Year 2) feedlot cattle. Most of the cattle that were clinically ill and treated with antimicrobials were shedding Salmonella in their feces. However, during the following year, the prevalence for clinically normal cattle, both at arrival and pre-slaughter, was also high. We found little evidence that Salmonella shedding in general was associated with clinical or subclinical
disease in the cattle. It appears that any effects associated with clinical outcomes depend on the Salmonella strain and lot-level risk factors. Although the high prevalence of Salmonella in cattle feces may have public health implications, the frequency distribution of serotypes in this study is not similar to the distribution of serotypes reported in national human disease surveillance programs. The project contributes to our long-term goal, which is to identify and reduce the impacts on cattle health, cattle production and human health associated with Salmonella in beef cattle production systems.
Publications
- Renter D.G., Oberst R.D., Sanderson M.W., Drouillard J., Thomson D.U., L. Zurek, Nagaraja T.G. 2007. Ecology of E. coli O157:H7, non-O157 Shigatoxigenic E. coli, and Salmonella in beef cattle production systems (Poster). Proceedings of the Association of Schools of Public Health/Association of American Veterinary Medical Colleges Joint Symposium on Veterinary Public Health: 22.
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Progress 01/01/06 to 12/31/06
Outputs
Goals for Year 1 were to assess the prevalence and bacterial characteristics of Salmonella in feedlot cattle that were treated for respiratory disease and to determine if the Salmonella status of cattle was associated with subsequent health outcomes. We have completed field sampling and primary laboratory procedures to address the objectives of Year 1 as follows: Our feedlot cooperators collected 1,270 fecal samples from cattle in a large commercial feedyard during the fall of 2005. Cattle that were examined for apparent respiratory disease, had a rectal temperature >104 F, and received individual treatment with an injectable antibiotic were sampled with rectal sleeves. Samples were shipped by overnight courier to our laboratory and Salmonella were isolated from 946 of the samples (74.5 percent cumulative prevalence). Fecal samples were from 115 different incoming lots of cattle and the number sampled per lot ranged from 1 to 40 (reflected the number of cattle treated
for apparent respiratory disease). Prevalence within a lot ranged from 0 to 100 percent, but there were only 6 lots that had no Salmonella isolated and only one sample was collected from each of these lots. Over the 3-month sampling period, weekly prevalence estimates ranged from approximately 48 to 100 percent. Isolates have been serogrouped and 75 percent were in serogroup E, 11.2 percent in C1, 8.7 percent in C2/3, 1.1 percent in B, and 4.1 percent in other serogroups. Fifteen serotypes were detected, and predominant serotypes were Orion (41 percent), Anatum (25 percent), and Kentucky (10 percent). No Newport and only five Typhimurium isolates were recovered. The presence of virulence genes (invA and pagC) was demonstrated in all isolates by PCR analysis. Study cattle were monitored until slaughter for adverse health effects. Proportions of Salmonella positive and Salmonella negative cattle that were retreated for respiratory disease, repulled for treatment, culled for any cause,
or died from any cause were consistently higher numerically but not statistically different. Cattle shedding serogroup B isolates had a 40 percent (4/10) case fatality rate, but this was not statistically different than for cattle shedding other serogroups (approximately 14 percent). Cattle that were treated more times were more likely to shed Salmonella in their feces, yet this study was not able to evaluate a causal relationship. Overall, we found a high prevalence of Salmonella fecal shedding in these cattle that were clinically ill and treated with antibiotics for undifferentiated fever (assumed respiratory disease complex). However, we have not found evidence that Salmonella shedding was associated with clinical or subclinical disease in these cattle. Statistical analyses indicate no significant differences in subsequent health outcomes between Salmonella positive and negative cattle. Although the isolates are potentially pathogenic (possess invA and pagC genes), the frequency
distribution of serotypes in this study does not parallel the distribution of serotypes reported for human or cattle in U.S. national Salmonella surveillance systems.
Impacts
Many types of Salmonella can cause disease in animals and people. The presence of Salmonella in beef cattle production systems could result in adverse health effects in both cattle and humans. In cattle, Salmonella can affect both health and production, but the effects are largely undocumented for cattle in commercial feedlot production systems. In humans, Salmonella is one of the most common causes of foodborne illness and has been associated with the consumption of many different foods. We evaluated the frequency and types of Salmonella present in potentially high risk feedlot cattle. Most of these cattle that were clinically ill and treated with antibiotics were shedding Salmonella in their feces. However, we have not found evidence that Salmonella shedding was associated with clinical or subclinical disease in these cattle. Although the high prevalence of Salmonella in cattle feces may have public health implications, the frequency distribution of Salmonella
serotypes in this study is not similar to the distribution of serotypes reported in national human disease surveillance programs. We will continue to pursue our long-term research goal, which is to identify and reduce the impacts on cattle health, cattle production and human health associated with Salmonella in beef cattle production systems.
Publications
- Renter D.G., Alam M.J., Ives S.E., Hollis L.C., Thomson D.U., Sanderson M.W., Nagaraja T.G. Fecal shedding of Salmonella in feedlot cattle that were treated for apparent respiratory disease. Proceedings of the 87th Annual Conference of Research Workers in Animal Diseases, 2006: 57.
- Alam M.J., Renter D.G., Ives S.E., Nagaraja T.G. Salmonella in Clinically Ill Cattle in a Commercial Feedyard (Poster). Proceedings of the Annual General Meeting of the American Society of Microbiology, Florida. 2006: Z04.
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