Survival of Taenia saginata eggs under different environmental conditions

This study aimed to assess in vitro the transmission potential of T. saginata eggs stored in different media at various temperatures, and to optimize recovery, hatching and activation methods. A total of 42 freshwater and 42 silt samples were spiked with 100 μl of a T. saginata egg suspension, of which half were stored at 5 °C and the other half at 20 °C. Additionally, 5 silt and 35 tap water control samples were included. Eggs were obtained from gravid proglottids passed by a human carrier following treatment. The duration of the experiment was 6 months, with three sampling time points at 2, 4 and 6 months, respectively (Study 1). In addition, two pilot studies were carried out. One included 8 samples kept in a freshwater stream for a period of 2 and 4 months, respectively, from December 2016 until February 2017 (Study 2). Another study used 6 water samples which were stored for one week in the freezer at -18 °C, and 6 samples that were stored outdoor from 7 to 14 February, at temperatures ranging from - 6 °C to 5 °C (Study 3). To assess survival of T. saginata eggs, recovery, hatching and activation methods were optimized. Taenia saginata eggs could be activated after 6 months of storage in water and silt at 5 °C. Storage at 20 °C significantly decreased activation of the eggs, to 4 months when stored in water and 2 months when stored in silt. Furthermore, degenerative changes in oncospheres were observed when eggs were stored at 20 °C, which were associated with an increased loss of oncospheres during activation. Eggs could be activated after 4 months of storage in the stream at temperatures ranging from - 10 °C to 17 °C, as well as after one week of constant freezing at - 18 °C, or repeated freezing and thawing from - 6 °C to 5 °C. This study indicates that T. saginata eggs can survive a Northern European winter, and thus pose a significant risk of transmission, and that in vitro activation is a more accurate method for assessing the transmission potential of T. saginata eggs, than recovery, integrity and hatching. Studies will be needed to assess how accurate the in vitro activation correlates to in vivo infectivity to ensure an accurate assessment of the transmission potential at a larger scale for surveillance purposes.