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Domestic and sylvatic Trichinella genotypes were evaluated for infectivity, muscle larvae persistence, and host antibody responses in rats. Groups of rats were inoculated with T. spiralis, T. nativa, T. britovi, three genotypes of T. pseudospiralis (from USSR, USA, and Australia), T. murrelli, Trichinella T6, and T. nelsoni, respectively. The muscle larvae intensity (larvae per gram), total larval burden (Ipg x rat weight), and the antibody levels were determined at necropsy 5, 10, 20, and 40 weeks post inoculation. All Trichinella genotypes were established in the rats, but infectivity and persistence differed significantly: T. spiralis established and persisted in high numbers, the three T. pseudospiralis genotypes were also highly infective but differed significantly in persistence, T. britovi and T. nativa had limited infectivity and persistence, Trichinella T6 had low infectivity and very low persistence, and T. murrelli and T. nelsoni were almost non-infective. Except for T. spiralis, initial total muscle larval burdens declined significantly for other genotypes during the experiment. A high initial serological response was detected for all genotypes, but the antibody levels decreased rapidly in relation to decreasing larval burdens. After 20 w.p.i. the antibody levels I remained high only in T. spiralis and T. pseudospiralis infected rats. The high infectivity and persistence of T. pseudospiralis in rats, suggests that in addition to T. spiralis, this species might be of significant importance in the domestic cycle of trichinellosis.

The susceptibility of seals to infection with Trichinella nativa and the cold tolerant characteristics of muscle larvae in seal meat were evaluated. Two grey seals, Halichoerus grypus, were inoculated with 5,000 (100 larvae/kg) T. nativa larvae and two grey seals with 50,000 (1,000 larvae/kg). One seal from each dose group and two control seals were killed at 5 and 10 weeks post-inoculation (p.i.). At 5 weeks p.i., infection was established in both low and high dose seals with mean larval densities of 68 and 472 larvae per gram (lpg), respectively, using eight different muscles for analyses. At 10 weeks p.i., mean larval densities were 531 and 2,649 lpg, respectively, suggesting an extended persistence of intestinal worms. In seals with high larval density infections, the distribution of larvae in various muscles was uniform, but in one seal with a low larval density infection, predilection sites of larvae included muscle groups with a relative high blood flow, i.e. diaphragm, intercostal and rear flipper muscles. Trichinella-specific antibody levels, as measured by ELISA, increased during the 10 week experimental period. Infected seal muscle was stored at 5, −5 and −18 °C for 1, 4 and 8 weeks. Muscle larvae released from stored seal muscle by artificial digestion were inoculated into mice to assess viability and infectivity. Larvae from seal muscle 10 weeks p.i. tolerated −18 °C for 8 weeks but larvae from seal muscle 5 weeks p.i. tolerated only 1 week at −18 °C, supporting the hypothesis that freeze tolerance increases with the age of the host–parasite tissue complex. The expressed susceptibility to infection, extended production of larvae, antibody response and freeze tolerance of T. nativa in seals are new findings from the first experimental Trichinella infection in any marine mammal and suggest that pinnipeds (phocids, otariiids or walrus) may acquire Trichinella infection by scavenging even small amounts of infected tissue left by hunters or predators. [Copyright &y& Elsevier]

To evaluate infectivity for carnivores as well as other biological characteristics of the newly described Trichinella papuae, eight red foxes were experimentally infected with the parasite. Five weeks after inoculation, T. papuae larvae were recovered from nine different muscle types. The larvae recovered from muscle tissue were shown to be infective to mice, to have a very low tolerance to freezing, and to survive longer than the other Trichinella genotypes in decaying tissue up to 5 weeks after infection. [Copyright &y& Elsevier]