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Risk-based examples and approach for control of Trichinella spp. and Taenia saginata in meat

Revised edition











FAO and WHO. 2020. Risk-based examples and approach for control of Trichinella spp. and Taenia saginata in meat, Revised edition. Microbiological Risk Assessment Series no. 25. Rome.




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    Summary Risk Profile on Cysticercus bovis in meat from domestic cattle 2013
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    Bovine cysticercosis is a parasitic disease of cattle caused by the larval stage (Cysticercus bovis) of the human tapeworm Taenia saginata. The indirect life cycle of this taeniid involves only humans as the primary host and bovines as the intermediate host. Infection of humans with the adult tapeworm, known as taeniosis, occurs via the consumption of beef which has been insufficiently cooked or frozen to kill the cysticerci. Although multiple infections in humans can occur, most cases of taenio sis involve a single tapeworm, which can persist for years. The adult tapeworm develops to reproductive maturity as early as 10-12 weeks after infection. The adult tapeworm regularly sheds its most posterior and mature segments, called gravid proglottids, which are discharged from infected humans spontaneously or with defecation. Upon release, these proglottids contain thousands of infective eggs that can remain in the proglottid or be expelled into the surrounding fecal matrix or environment. E ggs can remain infective for several months under cool and moist environmental conditions, and can be disseminated by water and other fomites. Upon ingestion of contaminated feed or water by a bovine intermediate host, a hexacanth embryo, or oncosphere, hatches from the egg and penetrates the intestinal mucosa within a few hours to enter the cardiovascular or lymphatic system. Once it reaches a suitable muscle or other tissue site it develops into a cysticercus and becomes infective for a human host after about 10-12 weeks. In cattle, cysticerci are found predominantly in cardiac and skeletal musculature, and occasionally in other sites including liver, lungs, kidneys and lymph nodes. Cysticerci remain infective for several months to a year or more
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    Proper targets for public health attention: the New Zealand experience with Taenia saginata
    Conference Room Document proposed by New Zealand
    2002
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    Cattle can be a host for the Taenia saginata infection which presents as a tapeworm in humans. It is not of large public health significance in New Zealand, nor in its beef production. A range of treatments - including proper cooking - is possible for meat which might carry undetected cysts. Medical treatment is also readily available in New Zealand for any humans infected. Studies have shown that a (theoretical) suspension of post-mortem inspection for the parasite would make little impact on p ublic health outcomes. Many importing country requirements still require this check to be part of the processing procedures. There are grounds for reassessing the reasons for this inspection in New Zealand's case, and for considering better use of scarce resources. Other countries may wish to consider the New Zealand modelling as they rank their public health priorities. As the Codex Alimentarius Commission considers its work on food safety objectives (and the Codex Committee on Meat and Poultry Hygiene recommences work), there may be lessons with wider relevance than just their application to the New Zealand situation
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    Summary Risk Profile on Trichinella in meat 2013
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    Trichinellosis is a parasitic disease of humans caused by eating raw or inadequately treated meat from domestic or game animals infected by Trichinella spp. Infective first stage larvae live in muscle cells of a wide range of meat-eating mammals, and some birds and reptiles (OIE, 2012). Human trichinellosis contracted from commercial supplies of meat have been most often linked to infected pigs, wild boar, or horses. Human cases have been also linked to the consumption of infected meat from game animals including bears and walruses. The parasite is a nematode which has an atypical direct life cycle that does not involve stages developing outside of the host. Muscle larvae are released from infected meat in the stomach of suitable host species, develop to adult worms in the intestine, and produce pre-encapsulated larvae which migrate preferentially to certain muscle sites in the host to complete the life cycle within several weeks. Within the muscle cells the larvae of some Trichinella species are encapsulated in a thick collagen layer. Within the host muscle larvae remain infective for up to several years. All genotypes of Trichinella are pathogenic for humans, but in animals the infection appears clinically unapparent. Some animal species serve as reservoir hosts. Domestic pigs and rats have been reported to harbour T. spiralis within the domestic cycle mostly in temperate regions of the world (

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