Freeze-tolerance of Trichinella muscle larvae in experimentally infected wild boars.

Freeze-tolerance of encapsulated Trichinella muscle larvae (ML) is mainly determined by Trichinella species, but is also influenced by host species, the age of the infection and the storage time and temperature of the infected meat. Moreover, the freeze-tolerance of the encapsulated species appears to be correlated to the development of thick capsule walls which increases with age. An extended infection period and the muscle composition in some hosts (e.g. herbivores) may provide freeze-avoiding matrices due to high carbohydrate contents. The present experiment compares freeze-tolerance of Trichinella spiralis and Trichinella britovi ML in wild boar meat 24 weeks post inoculation (wpi). Three groups of four wild boars were infected with 200, 2000 or 20,000 ML of T. britovi (ISS 1575), respectively. Additionally, three wild boars were inoculated with 20,000 ML of T. spiralis (ISS 004) and two animals served as negative controls. All wild boars were sacrificed 24 wpi. Muscle samples of 70 g were stored at -21°C for 19, 30 and 56 h, and for 1-8 weeks. Larvae were recovered by artificial digestion. Their mobilities were recorded using Saisam(®) image analysis software and their infectivities were evaluated using mouse bioassays. Samples frozen for 19, 30 and 56 h allowed recovery of mobile ML, but samples frozen for 1 or 2 weeks did not. Correspondingly, only T. spiralis and T. britovi larvae isolated from wild boar meat frozen for 19, 30 and 56 h established in mice. This study showed that freezing at -21°C for 1 week inactivated T. spiralis and T. britovi ML encapsulated in wild boar meat for 24 weeks.