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Identification and Characterization of Population(s) at Greatest Risk for Presences of Salmonella within Lymph Nodes


Salmonella continues to be a significant public health burden and is the causative agent of over 1
million cases of foodborne illness each year. As a result of such infections, it is believed that 19,000
hospitalizations and 400 deaths occur annually. Therefore, it is important to focus research efforts
on controlling this prominent microorganism in our food supply. It is well known that cattle harbor
Salmonella in their gastrointestinal tracts and the microorganism can then be transferred to beef
products, including ground beef. Science has proven that cattle feces present on their hides can
contaminate the animal and, ultimately, their subsequent meat products. However, Salmonella can
also be sequestered within the lymph nodes of cattle. These lymph nodes maybe present in the fat
that is incorporated into ground beef. It is for these reasons that research into this issue is necessary
if we are to protect our food supply. Needed are approaches to better understand the burden of
Salmonella in the lymph nodes of cattle presented for harvest as well as potential mitigation strategies.
1. Quantify prevalence of Salmonella in lymph nodes of fed and cull dairy cattle.<P>
2. Determine whether a commercially available Salmonella vaccine protects calves from lymph node
colonization following significant oral challenge with Salmonella

More information

Findings: <br/>
Study 1: Salmonella was readily recovered from subiliac lymph nodes, however regional and seasonal
differences were observed. Prevalence was found to be highest in fed cattle from the Southern High
Plains, averaging 15.9% and ranged from 29.5% positive in the fall of 2010 to 2.4% in the winter of
2011. Conversely, fed cattle from the Midwest showed a much lower prevalence rate, with only one
of four sample events resulting in the observation of a lymph node containing Salmonella. Prevalence
in lymph nodes of cull cattle from the High Southern Plains and the West Coast was generally low,
on average 0.65% and 2.0%, respectively. Salmonella prevalence in lymph nodes of cull cattle from
the Midwest was lowest, as none of the lymph nodes collected from cull cattle in this region were
found to be contaminated with Salmonella.
Study 2: No significant treatment differences were observed in the percentage of lymph nodes
positive for Salmonella Montevideo or Newport for Group 1. However at 21-d post- inoculation (i.e.
Group 2), there were fewer (P<0.05) right popliteal (0 versus 75%) and right pre-scapular nodes (0
versus 75%) that were Salmonella positive in the Vaccine - Newport compared to Control - Newport
treatments. The percentage of left popliteal and left pre-scapular nodes likewise tended (P=0.10) to
decrease in the Vaccine-Newport treatment compared to non-vaccinated controls. Post-inoculation
fecal samples were not affected by treatment for either strain. Initial and final body weights and
overall body weight change were not different among treatments.

Loneragan, Guy; Brashears, Mindy
Texas Tech University
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