In Finland, every third wild predator carries Trichinella
Trichinellae, or trichinae, continue to thrive in Finnish wildlife: multi-annual follow-up studies show that approximately one in three of the animals tested carry trichinellae. The majority of trichinellae are still found in raccoon dogs, but the trichinellae species have changed. When cooking meat from bears, badgers or other carnivores for food, remember that all Trichinella species infect humans easily if they consume undercooked meat.
The frequency of trichinellae is among the highest in the world in Finland. Trichinellae, formerly called trichinae, were last studied between 2011 and 2013 and the results were compared with the results obtained in previous years, 1993 - 1997 and 1999 - 2005. The results prove that the Trichinella species have changed.
"The so-called sylvatic cycle of trichinellae in wild animals must have been very common in Finland ever since raccoon dogs settled in this country, but for the last 30 years at least. In Lapland, where raccoon dogs are not yet common, trichinellae are rarer", says Research Professor Antti Oksanen of the Finnish Food Safety AuthorityEvira.
Four species are found in Finland: Trichinella nativa, Trichinella spiralis, Trichinella pseudospiralis and Trichinella britovi. They each have their position and play a role in the ecosystem, but they also partially compete for living space with each other.
The Arctic species does not usually infect pigs
Currently, the Arctic T. nativa is the predominant species in Finland.
"Climate change could be expected to undermine the living opportunities of the northern species, but the relative share of the species in the identified trichinella larvae has risen from the 1990s to 2010s, from about 60 % to 90 %. As the prevalence of all Trichinella infections has not changed, the Arctic species has become even more widespread while the climate has become warmer", says Oksanen.
Some cases of T. nativa have been diagnosed in Finnish wild boar, but usually this species does not infect swine. The great loser among trichinella species is T. spiralis, known as a cultural trichinella, synanthropic, as it is particularly adapted to the life cycle of domestic animals and rats.
The dramatic decline in the share of the species from 15 % to 1 % between 1993 and 2013 is explained by the modernisation of Finnish pig farming due to EU membership. In the early 2000s, trichinella infections disappeared practically completely from swine and T. spiralis no longer spread from farms to the forest cycle.
Another loser is the only species infectious to birds, T. pseudospiralis, whose share of trichinellae has dropped from 10 % to two and then to 0.5 %.
"The fate of this species puzzles me. Is it really disappearing and if so, why on earth? Perhaps the storage of larvae samples weakened especially the identification of this non-encapsulating species. Of the total of 206 Finnish larvae samples collected in 2017 and examined relatively fresh, the EU Reference Laboratory in Rome still identified T. pseudospiralis in 4 %. The preservability of this species larvae must be investigated further", says Oksanen.
The share of the European forest trichinella, Trichinella britovi, has remained fairly constant of the total, at just under 10 %.
Trichinella species are identified in muscle samples, from which the trichinella larvae are collected and identified using the multiplex PCR method. In Finnish studies, species identification has been performed by University of Helsinki, Finnish Food Safety Authority Evira and the EU reference Laboratory in Rome.
A joint study by Finnish Food Safety Authority Evira and the EU Reference Laboratory has been published in a peer-reviewed scientifical journal:
Oksanen, A., Interisano, M., Isomursu, M., Heikkinen, P., Tonanzi, D., Oivanen, L., Pozio, E. Trichinella spiralis prevalence among wildlife of a boreal region rapidly reduced in the absence of spillover from the domestic cycle. Veterinary Parasitology 2018: 262, pp. 1 - 5.
For further information, please contact:
Research Professor Antti Oksanen, tel. +358 (0)44 561 6491
The Finnish Food Safety Authority, the Finnish Agency for Rural Affairs and a part of the National Land Survey of Finland's Centre for ICT Services become the Finnish Food Authority on 1 January 2019.