Bovine cysticercosis is a zoonotic disease for which cattle are the intermediate hosts of the human tapeworm <i>Taenia saginata</i>. Routine inspection measures are implemented in Canada by the Canadian Food Inspection Agency (CFIA), and similarly elsewhere, for the postmortem detection of larval parasite cysts (cysticerci) in beef destined for human consumption. Detection is based on the gross examination of traditional carcass predilection sites, although it is recognized that the parasite has no true predilection for a particular tissue or site. In order to evaluate the efficacy of the inspection protocol currently implemented in Canada, a study was undertaken to determine the distribution of <i>T. saginata</i> cysticerci in tissues of experimentally infected cattle. Forty-two cross-bred beef cattle were divided into five groups of 5-12 animals each and inoculated orally with either 10000, 5000, 1000, 100 or 10 <i>T. saginata</i> eggs obtained from cases of human taeniosis in Thailand. From 47 to 376 days post-inoculation (DPI), ten animals inoculated with 5000 eggs were killed and the carcasses partitioned into 31 tissue sites. These consisted of the traditionally inspected tissue sites of heart, masseter and pterygoid muscles, tongue, oesophagus, and diaphragm (membranous and crura); as well as non-traditional sites of lung, liver and 20 additional muscles or muscle groups. After the routine inspection for cysticerci of traditional tissue sites, tissues from all sites were each cut into approximately 0.5 cm thick slices and the total number of parasitic cysts and cyst density (cysts/g of tissue) were determined for each site. Traditional sites were similarly evaluated for the remaining 32 animals that were killed between 117 and 466 DPI. Sites were ranked based on cyst density. In the animals for which non-traditional sites were also evaluated, no sites had higher cyst densities than those traditionally inspected. When only traditional sites for all animals were compared, the heart ranked highest overall, although not significantly different from masseter, and was the most frequently affected site. The traditional site of oesophagus was among the poorest of all sites for detection of cysticerci. The heart was confirmed as the site of choice for detection of bovine cysticercosis based on high cyst density and frequency of infection. There was also enhanced visibility of parasite lesions in the heart due to the relatively early degeneration and resultant gross pathology that occurs in cardiac muscle. More thorough examination of the heart is recommended during post-mortem inspection for this parasite, particularly when examining animals from an infected herd. <p>Currently, confirmation by CFIA of suspect cysticerci recovered during meat inspection relies on gross, stereomicroscopic, or standard histological examination. Although degenerating cysticerci are more likely to be detected and submitted for diagnosis, they often cannot be definitively identified by these methods. A recently developed monoclonal antibody-based immunohistochemical (IHC) assay for post-mortem diagnosis of this parasite was optimized and standardized. The IHC method was compared to the currently used histological assay using 169 degenerated known-positive <i>T. saginata</i> cysticerci collected from the experimental infections in the first study and from field submissions, and known-negative specimens and lesions of various etiologies from non-infected cattle. The use of the IHC assay identified significantly more known-positive bovine cysticerci (91.7%) than the histological method (38.5%), and non-specifically reacted only with the other cestode species examined. Since <i>T. saginata</i> is the only larval cestode typically found in the muscle of cattle, this cross-reactivity is not significant and the IHC assay will be a useful tool for the identification of lesions caused by degenerated bovine cysticerci.<p>This research provided evidence to support changes to the current post-mortem inspection, detection and diagnostic procedures and will contribute to more effective and efficient control of bovine cysticercosis.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-08082007-101817 |
| Date | 15 August 2007 |
| Creators | Scandrett, William Bradley |
| Contributors | Haines, Deborah |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-08082007-101817/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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