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Bacterial infection risk associated with outdoor organic pig production with special reference to Salmonella and Campylobacter infection

The modern consumers are becoming increasingly critical of the quality of meat and other types of products of animal origin. Focus is put on the animal husbandry and the way of production concerning animal welfare. This leads to increasing interest for organic, free-range or other kinds of animal-friendly production systems where the animals benefit from a low animal density and good possibilities for expressing normal behaviour. In general, consumers also expect products from these kinds of systems to be of a higher microbiological quality compared to products from conventional production systems. However, today there is no documentation for a lower level of the most common zoonotic bacterial infections (e.g. Salmonella, Campylobacter and Yersinia) in organic or other alternative production systems.

The objective of the proposed project is to improve the knowledge on the risk of outdoor pig production in relation to spread and persistence of Campylobacter and Salmonella infections. For Salmonella the specific objectives are to evaluate the survival of Salmonella Typhimurium in soil and grass of contaminated pastures used for outdoor pig production, measurement of the infectivity of naturally S. Typhimurium contaminated pastures in relation to time, and in the case of high infectivity, evaluation of the pathogen reducing effect of soil treatment. For thermophilic Campylobacter, the objectives are to describe the infection dynamics of natural Campylobacter infections over time in outdoor pigs, including time of colonisation, level of excretion in faeces, species distribution in the group and in the individuals, interaction with the environment, and to describe the possible changes in prevalence and species distribution in relation to time and environmental contamination.

Experimental pastures for production of outdoor organic piglets will be set up. Experimentally infected piglets will be grouped together with uninfected tracer piglets in order to monitor the transmission of infection. In addition, soil samples will be analysed to determine the level of contamination. After a period of two months, the pastures will be vacated, infected piglets slaughtered and tested. A new set of uninfected piglets will be introduced in each pasture to monitor if these animals become infected due to their habitation in the Salmonella contaminated pastures. The pastures and animals will be sampled and monitored (bacteriological (qualitatively and semi-quantitatively), serological and by necropsy examinations). Based on the results obtained in the second period, a third period of two months will be initiated for further monitoring of the infectivity of the Salmonella contaminated pasture environment, including the preventive effect of ploughing the pastures before new tracer animals are introduced.

A method will be developed and evaluated for determining the species composition (C. jejuni and C. coli) in faecal samples and subsequent isolation of the species in minority. The groups of pigs serving as controls in the experimental Salmonella infection study will also be used for studying the dynamics of natural Campylobacter infection in outdoor pigs. The piglets will be monitored for natural colonisation of thermophilic Campylobacter species, and the ratio between C. jejuni and C. coli. Likewise, environmental samples are analysed throughout the experimental periods. Isolates from animals and environment will be identified to the species level and serotyped to monitor the dynamics of the infection: number of different strains in each pig and persistence/exchange of strains over time.

The achievements obtained will be formulated in practical guidelines directly applicable for the organic pig producers in order to minimise the risk of zoonotic infection in organic pig herds. In addition, results will be available for the scientific community through publication in reviewed journals. The large amount of quantitative data obtained in this project will deliver the necessary information for use in quantitative risk assessment of zoonotic infection in organic pig production.

Publications

Project title
II.10 Bacterial infection risk associated with outdoor organic pig production with special reference to Salmonella and Campylobacter infection (SaCaFree)

Project leader
Senior research officer, DVM, ph.d. Dorte Lau Baggesen (DLB), Danish Veterinary Institute (formerly Danish Veterinary Laboratory), 27 Bülowsvej, DK-1790 Copenhagen V, Denmark. Phone +45 35 30 02 07, Fax +45 35 30 01 20,
E-mail: dlb@vetinst.dk

Project participants
Senior research officer, microbiologist, ph.d. Eva Møller Nielsen, Statens Serum Institut
Cand.scient Annette Nygård Jensen, Danish Institute for Food and Veterinary Research