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Improving the Safety of Pork: Preliminary Steps to Reduce Contamination of Pig Farms with Toxoplasma, a Common Parasite Transmitted From Pork to People


In Illinois, approximately 21% of sows and 3 % of market hogs are infected with the microscopic parasite, Toxoplasma, which is a zoonotic pathogen that can be transmitted to humans from pork. Human infection with this parasite is the 3rd leading cause of food-related deaths in the U.S., ranking higher than E. coli O157. Pork is the most consistently implicated food source of human infection with Toxoplasma in this country. Pigs become infected with Toxoplasma by ingesting the organism's microscopic eggs, which contaminate soil and feedstuffs. These eggs are shed in the feces of cats; thus, contamination of farm premises and animal feeds is the major cause of contaminated pork. A helpful solution would be a vaccine for cats to prevent them from shedding the Toxoplasma eggs that infect pigs. An ideal vaccine should be administered orally in baits, treats, or mixed into a pan of milk, and it should be inexpensive enough to administer frequently (whenever new cats and kittens may arrive). That is precisely the type of vaccine that we can develop. The ultimate objective of this research is to develop an oral vaccine that can be delivered using baits placed on and around pig farms, for the purpose of preventing cats from contaminating farm premises and swine feeds with the Toxoplasma parasite, and thereby reducing the prevalence of Toxoplasma contamination of pork. The immediate objective of this proposal is to find a dosage of gamma irradiation to apply to Toxoplasma eggs that will: a) render the eggs harmless if accidentally ingested by pigs (i.e. they will not cause Toxoplasma contamination of pork); and b) block parasite transmission by cats.

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NON-TECHNICAL SUMMARY: A microscopic parasite, Toxoplasma, is the most common zoonotic infection of pork. Toxoplasma is the third leading cause of food-borne deaths in the U.S., and pork is the major food source for transmitting this disease to humans in this country. Toxoplasma is transmitted to pigs from cats, thus we propose to develop a vaccine that will prevent farm cats from infecting pigs. The current project proposes development of a new, practical method to reduce the prevalence of Toxoplasma infection of pork. The major reasons to address this problem are to protect and improve public health, to preserve the wholesome reputation that the pork industry has worked so hard to develop, and to pro-actively avoid the possibility of recalls of retail pork similar to what has occurred in retail beef regarding contamination (post-slaughter) with E. coli O157.<P>APPROACH: We have identified and adapted a promising new vaccine strain of Toxoplasma that can be transmitted to cats in oral baits or treats, without the need for refrigeration or handling of individual cats. This vaccine strain will be attenuated (weakened) by exposure of the organism's eggs to gamma irradiation. The proper dose of irradiation will be determined by testing in cats for efficacy, and by testing in pigs which should not become infected as a prerequisite of any vaccine to be administered in baits on farms.

McAllister, Milton
University of Illinois - Urbana-Champaign
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