Helsingin yliopisto


Helsingin yliopiston verkkojulkaisut

University of Helsinki, Helsinki 2006

Experimental and immunological comparison of Trichinella spiralis and Trichinella nativa

Anu Näreaho

Doctoral dissertation, May 2006.
University of Helsinki, Faculty of Veterinary Medicine, Department of Basic Veterinary Sciences, Pathology.

Trichinella is a widely spread zoonotic nematode parasite. Human infection occurs after eating under-cooked meat, typically pork, wild boar or horse, containing infective Trichinella-larvae. Heavy infection may be fatal.

Eleven genotypes of Trichinella have been differentiated by PCR-based methods. In Finland, four species have been confirmed: Trichinella spiralis, T. nativa, T. britovi and T. pseudospiralis. Trichinella spiralis occurs in the domestic cycle, whereas T. nativa is the most common species infecting sylvatic animals in Finland. These two species have differences in their infectivity in different hosts and also in their resistance to freezing; T. spiralis does not survive at -20ºC, but in certain host species T. nativa does.

To learn more about the two most common Trichinella species in Finland, T. spiralis and T. nativa, these species were compared in this thesis both in vivo and in vitro. Raccoon dogs (Nyctereutes procyonoides), common Trichinella hosts in the Finnish fauna, and complement factor C6-deficient rats, in which the complement membrane attack complex was inactivated, were used as in vivo experimental models.

Raccoon dogs are favourable hosts for Trichinellae - they do not suffer from any clinical signs of trichinellosis even when the infection doses are fairly high. No significant differences in the course of infection were noted between T. spiralis and T. nativa. A peak of eosinophilic granulocytes was observed on the second week of infection, and weight loss and anaemia were more common in the infected group than in controls. Clear morphological differences between the species were observed in the tissue capsules. Trichinella spiralis capsules were lemon-shaped, whereas the capsules of T. nativa were more spherical and had more intense inflammation around them. Specific antibodies were recognized after two weeks of infection in both ELISA and Western blot analysis.

The role of the complement system in the host's defence against Trichinella was evaluated in an experimental infection of normal and complement factor C6-deficient rats with both T. spiralis and T. nativa. Trichinella nativa has a lower infectivity in rats. The survival of larvae in normal and C6-deficient serum was also observed in vitro. No effect of C6 deficiency was noted in either species in vivo or in vitro. When exposed to human serum, no binding of complement factors C1q, C3, C8 or C9 to the outermost layer of the cuticle of adults, newborn larvae or muscle larvae was observed. This suggests that Trichinellae have mechanisms for evasion of complement, and that membrane attack complex does not explain the different infectivity of these two species in rats.

To investigate differences between T. spiralis and T. nativa, soluble proteins of their crude larval extracts were analysed by two-dimensional electrophoresis. Clearly different protein patterns were seen. Freezing was also shown to cause some changes in protein patterns. After MALDI-TOF analysis, we were not, however, able to identify the different proteins in database searches. Immunological differences were observed in two-dimensional Western blot analysis.

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Last updated 25.04.2006

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