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December 2007 Issue

Swine Salmonella: The Disease and European Regulation

Salmonella bacteria are widespread in human and animal populations. Some of them cause food poisoning in humans or disease in animals. Salmonellosis is mainly a problem in the growing pig. The organisms are found in the intestine of the animals and they are excreted for long periods of time with little or no disease. Salmonella in the gut of the pig can contaminate carcasses during the slaughter process and their presence creates potential public health risks.

Regulation (EC) No. 2160/2003 on the control of Salmonella provides for the setting of community targets for reducing the prevalence in pig herds of Salmonella serovars with public health significance. According to this regulation, the targets must include:
• the deadline by which the targets must be reached
• the definition of epidemiological units to be tested
• the definition of the Salmonella serovars with public health significance, where relevant
• the definition of the testing schemes necessary to verify achievement of the targets

The regulation states that before proposing such rules on specific control methods, the Commission shall consult the European Food Safety Authority (EFSA) in accordance with the operative aspects of the longitudinal and integrated food safety assurance (LISA) concept, shown below in Figure 1.

The timetable for setting targets for pig production is March/April 2008 for herds of slaughter pigs and March/April 2009 for breeding herds of pigs.

Three key concepts for successful swine Salmonella control

1. Producers must become actively involved in disease control.
   In some EU member states, such as Denmark, Great Britain, Germany, and the Netherlands, Salmonella control programs already exist that require measurable and significant reductions in Salmonella prevalence among herds of slaughter pigs. Participating producers must ensure that they possess a valid certificate of categorization for their herd and make it available on request at pig slaughter plants.
    
Learn the factors that affect the type of test used for Salmonella surveillance. Intervention programs depend upon the results.
2. Pork consumption: Salmonella-free pork will drive the future of swine production
   The changing demands of consumers and the main pork-importing countries inside and outside the EU will have decisive impacts on the organization and production goals of the swine industry and the implementation of Salmonella monitoring and control programs. These measures will have a significant positive effect on the acceptance of pork among consumers, and the competitiveness of EU-produced pork in the global marketplace.
   
   
3. Appropriate methods for Salmonella surveillance: serology and bacteriology.
   Two main options exist for the implementation of monitoring schemes aimed at detecting and evaluating Salmonella prevalence or previous exposure to Salmonella in pig production. The combination between serology and bacteriology will depend on the actual situation and the questions that have to be answered. In particular, available serological testing such as the IDEXX HerdChek* Swine Salmonella enzyme-linked immunoassay (ELISA) is both economical and useful in a variety of situations:
   • An initial monitoring is required in order to establish a base point for a herd
   • As a focused intervention for the control and elimination of all serovars associated with a specific swine Salmonella infection
   • In medium and high prevalence countries, as a periodic screening tool to demonstrate changes in Salmonella prevalence
   • To evaluate interventions at regularly controlled intervals, in order to ensure compliance and efficacy, and plan any necessary intervention modifications
   • To track clinically health/swine that may be carriers of Salmonella. Such carrier animals are the major source of infection in slaughterhouses, a significant food contamination risk, and a major concern for the food industry
   • The use of antibiotics may limit the sensitivity of bacteriological testing
   • The correlation between serum and meat juice ELISA results is important to corroborate the results of field and slaughterhouse testing during a disease control program (see Figure 2)

In addition, ELISA serology has distinct quality advantages over bacteriology in many circumstances, as shown in Table 1 below.

Serological testing of Salmonella in swine: The HerdChek* Swine Salmonella ELISA

The IDEXX HerdChek* Swine Salmonella Antibody Test Kit was developed in collaboration with the Dutch Animal Health Service Institute in Deventer, the Netherlands. The test was evaluated using several negative populations from different geographical areas in Europe and in the US. The herds in the study were kept under strict management and the serum and meat juice samples were collected carefully to ensure high quality samples. Reference sera provided by different European Reference Laboratories were used to measure serotype detectability (groups B, C and D). These reference sera are listed in Table 2.

The next sections describe three different test result sets in Germany, Austria and Italy showing the versatility of HerdChek Swine Salmonella ELISA in identifying positive samples in blood and meat juice, and its usefulness in monitoring progress toward disease control.

Germany and Austria

Samples from different slaughterhouses in Germany (from 2003 to 2005) and in Austria (in 2003) were evaluated for Salmonella during a regular control program. Until 2003 these slaughterhouses used other methods for Salmonella detection, including culture. After 2003, these slaughterhouses started using the HerdChek* Swine Salmonella ELISA test kit. Use of this new monitoring tool led to more precise intervention measures in specific farms, causing an overall reduction in the percent of positive animals at the slaughterhouses in Germany (see Figure 3). In Austria, the HerdChek ELISA generated realistic and reliable results that correlated well with the presumed Salmonella prevalence of 1.81%, unlike other monitoring methods that generated an unrealistic prevalence of 4.92%, reported in 2002 (see Figure 4).

Italy

The IZSLE Institute supported by the Italian Health Ministry conducted a longitudinal study of Salmonella enterica infection on four Italian farrow-to-finish swine herds. In each herd, researchers ear-tagged six randomly selected piglets from each of five randomly selected litters (30 pigs on each of four farms).

Blood samples were taken from each piglet and sow at weaning. More blood samples were taken from the piglets at approximately 60, 90, 150, 210 and 270 days of life, and at slaughter. Five pooled fecal samples for bacteriological investigation were collected from each herd on the same schedule as the blood samples. The sample schedule and parameters are shown in Tables 3 and 4.

The blood samples were analyzed using a cutoff value of S/P ratio ≥ 0.25 (OD = 10%). Across the herds, sero prevalence among piglets emerged in a common pattern: the presence of maternal antibodies completely declined by day 60, seroconversion occurred between day 90 and day 150, and peak sero-prevalence was observed between day 210 and day 270. Assuming an interval of 30 days between the peak of fecal excretion and the greatest incidence of seroconversion, it can be inferred that the highest number of infections occurred approximately between day 60 and day 90 of life. In contrast with serological results obtained with the HerdChek ELISA, bacteriological examination of all fecal pools collected during that time period were negative. A possible contributing factor for lowered sensitivity in fecal samples is that these herds consumed feed containing antibiotic medication during most of the study time period.

Summary

The HerdChek* Swine Salmonella Antibody ELISA Test Kit is a valuable tool for monitoring Salmonella presence in herds before and after slaughter. While bacteriological evaluation of fecal samples may have a lower sensitivity when feed contains antibiotics, the serological testing clearly indicates the presence of infection. Serology testing is a practical solution for field monitoring and provides useful information about infection dynamics in herds, starting with the breeding animals (where the infection is diffuse), through the early fattening period recognized to be a period of massive spread of infection, and into the long fattening period.

Good monitoring tools and techniques help herd owners control and mitigate infections before they spread, and before slaughter. Using a successful testing protocol such as the HerdChek Swine Salmonella ELISA both on the farm and as follow-up monitoring at the slaughterhouse is a key component to an effective disease control program.

HerdChek* Swine Salmonella ELISA Test Kit
• High specificity and sensitivity
• Detects the most common serotypes (B, C1 and D)
• Serum, plasma or meat juice samples
• Broadly validated
• Robust ELISA kit
• Scientific cutoff (10%)
• Applied screening cutoff (20%; 40%)
• Results available as S/P and OD% values
• Two protocols—short (<2 hours) and overnight protocols
• Ready-to-use reagents
• Kit contains 5 plates (strips) / 30 plates (solid)
• Compatible with xChek* software

Sources

Blaha T, et al.
Italy- Ring Trial for testing the comparability of the laboratory results of three commercial Salmonella antibody ELISA tests in Germany, Denmark and the Netherlands.
7th International Symposium on the epidemiology and control of foodborne pathogens in pork, SafePork 2007; May 9-11; 353-356. EFSA Journal.
Risk assessment and mitigation options of Salmonella in pig production. 2006; 341:1-131.
Kranker S, et al. Longitudinal study of Salmonella enterica Serotype Typhimurium in three Danish farrow-to-finish Swine Herds. Journal of clinical microbiology. 2003;41(6):2282-2288.
Merialdi G, et al. Longitudinal study of Salmonella infection in four Italian farrow to-finish swine herds. SafePork 2007, May 9-11;82-85.
Serum/meat juice correlation studies conducted by IDEXX Scandinavia AB, Sweden, 2002; data on file.
Voss, M. Control of Salmonella and other zoonotic agents in the European Community: current status of legislation. Lohmann Information 2007; 42(1):18- 28.
Wilhelm E, Rossmanith W, Gabler C, Hilbert F, and Smulders FJM. Salmonella Überwachung der Schlachtschweine. Fleischwirtschaft. 2005; 85(5):97-99.

Frequently asked questions about xChek* software

IDEXX provides xChek* software to assist you in the collection and management of the data from ELISA assays. Listed below are some commonly asked questions regarding the features found in xChek.

How do I change the placement of my controls from vertical to horizontal when creating a template?
To change the orientation of the controls on a template for a particular assay choose Database > Assay and select the specific test. In the Assay dialog box (shown here), choose Basic > Template and select the orientation from the dropdown list. This will now be the default orientation for the controls.

In an Analyze Case Report I would like to have calendar age shown on the printout along with the results. How is this accomplished?
When creating an Analyze Case Report, the final screen that appears before the report is generated (the “Analyze Report” dialog) allows you to choose your case and graph options. On the righthand side is the Variables button. Click the Variables button to see a list of variables that can be shown on the report. Check the box next to the variable you want to display on the report, such as “Calendar Age” near the bottom-left of the list of options. You will also see the Variables button in other screens when creating other reports and in Plate View after reading a plate.

Is there a place in xChek to enter our laboratory’s name so it appears on the reports?
xChek does allow the user to customize reports to show the laboratory name. Choose Options > System Settings. The Printing tab gives you three lines on which to place your laboratory’s name and address. Once you enter your laboratory’s information here, it will always be seen on saved and printed xChek reports.

How do I track the kit lot number and expiration date for each ELISA test kit that our laboratory is running?
Kit lot numbers and expiration dates can be entered in two places in the xChek software. This information can be entered each time an assay is run or – if you will be running the same lot number for several tests in a row – it can be entered into the database assay information. Lot number information can be entered in Plate View after reading your plate, by double-clicking the Kit or Expiration Date field. Entering the information this way will apply it only to this data set. By choosing Database > Assays and selecting the specific test, you can also enter the kit lot and expiration date information. If entered this way, this information will be applied to all testing until a new lot and expiration date are added.

Events Around the World

• Denver, Colorado, USA—January 12–27, 2008
  National Western Stock Show
• Atlanta, Georgia, USA—January 23–25, 2008
  International Poultry Exposition (IPE)
  www.ipe08.org
• Reno, Nevada, USA—February 6–9, 2008
  National Cattleman’s Beef Association (NCBA)
  www.beefusa.org
• Verona, Italy—February 8–9, 2008
  First European Congress of SIVAR at the 108th Fieragricola
  www.sivarnet.it

IDEXX welcomes Pablo Lopez—Worldwide Poultry Marketing Manager

IDEXX Laboratories is pleased to announce Pablo Lopez has joined Production Animal Services as Worldwide Poultry Marketing Manager. He brings more than twelve years of experience in the poultry industry. Most recently he served as Global Product Manager at Phibro Animal Health in New Jersey. He held earlier positions in Venezuela as Country Manager for Phibro, Poultry Technical Assistant for Pfizer and Veterinary Service Manager for Agropecuaria D'Stefano.

A native of Venezuela, Pablo completed his DVM at the Universidad Central de Venezuela and is currently pursuing an executive MBA at Cornell University. He recently relocated from New Jersey to Portland, Maine.

In his spare time, Pablo enjoys outdoor activities, including hiking, running and mountain biking.

Pablo’s contact information is:

Pablo Lopez
IDEXX Laboratories, Inc.
One IDEXX Drive
Westbrook, ME 04092
207-556-8668 (Direct)
E-mail: pablo-lopez@idexx.com

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