Distribution of Taenia saginata cysticerci in tissues of experimentally infected cattle

摘要

Bovine cysticercosis caused by Taenia saginata is a zoonotic disease warranting routine inspection measures for the postmortem detection of cysticerci (cysts) in beef destined for human consumption. Detection is based on gross examination of traditional carcass predilection sites, although there is evidence to suggest that examination of other sites may offer improvements in sensitivity. In order to evaluate the efficacy of current inspection protocols, this study determined the distribution and number of cysticerci in the tissues of experimentally infected cattle. Forty-two commercial beef cattle were divided into five groups of 5-12 animals each and inoculated with either 10,000, 5000, 1000, 100 or 10 T. saginata eggs. At time points ranging from 47 to 376 days post-inoculation (DPI), 10 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 an additional 20 individual muscles or muscle groups. After performing the Canadian Food inspection Agency's (CFIA) routine inspection protocol for cysticerci on traditional tissue sites, tissues from all sites were cut into approximately 0.5cm thick slices and the total number of parasitic cysts and cyst density (number of cysts/g of tissue) determined for each site. Traditional sites were similarly evaluated for the remaining 32 animals killed between 117 and 466 DPI. Sites were ranked based on cyst density. Infection was confirmed in 37 animals, of which only 20 were detected by routine inspection, and of which 7 harboured no cysts in traditional sites. For the animals in which additional non-traditional sites were evaluated, none yielded higher cyst densities than those traditionally inspected. When only traditional sites (for all animals) were compared, the heart ranked highest overall, although it was not significantly different from the masseter muscle, and was the most frequently affected site. The traditional site of oesophagus was one of the least rewarding of all sites for detection of cysticerci. The heart was confirmed as the preferred site for detection of bovine cysticercosis based on high cyst density and frequency of infection, and greater visibility of gross lesions due to the early inflammatory response in cardiac muscle. More extensive examination of the heart is recommended to improve detection of infected animals.