Effect of rodent control on Toxoplasma gondii infections in animal friendly pig farms with a rodent problem.

Summary

Livestock farming can be prone to rodent infestations as it provides unlimited amounts of shelter, water and food to commensal rodents. Besides economic losses and structural damages, these rodents may transmit pathogens directly to farmers or via livestock to consumers of livestock products. Hygienic standards in intensive pig production systems have largely eliminated the contact between rodents and livestock. The introduction of animal-friendly production sytems may however lead to an increased contact between livestock and small mammals (both rodents & insectivores). This has led to a demand for rodent control methods that are in line with ecologic principles. To underline the necessity of appropriate rodent control in animal-friendly farming systems we used the tranfer of an important food-borne pathogen, Toxoplasma gondii, as an example. Using lightcycler PCR methods we showed that rodents on animal-friendly farms indeed harbored Toxoplasma gondii. Subsequently three farms with a rodent problem were chosen to investigate the effect of an intense rodent control campaign on the seroprevalence of Toxoplasma infection of slaughtered pigs.
During the time period July 2006 to January 2007 rodent control campaigns were started on these three farms and all consecutive slaughtered pigs were tested for the presence of Toxoplasma antibodies. Toxoplasma seroprevalence on all three farms dropped during the rodent control campaign. Further research is needed to exactly find out which rodent or insectivore species form the largest risk for transfer of Toxoplasma infection and which control method is most appropriate to target these species.
This project thus shows that rodent control needs extensive attention in animal friendly farming systems. Although extermination of rodents is possible using methods that are in line with organic principles we would like to stress the importance of prevention. Rodent prevention includes measures such as making the direct environment of the barns unattractive for rodents, closing cracks and openings of the barn to limit access of rodents, closing feed storage and using natural predators in the vicinity of the farm (predatory birds).
Inappropriate rodent control is not only a problem that concerns organic farming, but should be addressed in any livestock system where increased contact between wildlife and farm animals is possible.