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Although human infections caused by Trichinella sp. have not been reported in Finland for several decades and Trichinella sp. infection in pork has become virtually extinct in the last decade, sylvatic Trichinella spp. infection is still highly prevalent in Finland. Muscle digestion of 2,483 carnivorous wild animals from 9 host species during 1999-2005 showed 617 positive animals (24.8%). Molecular identification from 328 larval isolates revealed 4 different endemic Trichinella species, i.e., T. nativa, T. spiralis, T. britovi, and T. pseudospiralis. Seven percent of the infected animals carried mixed infections. Trichinella nativa was the most common species (74%), but T. spiralis was identified in 12%, T. britovi in 6%, and T. pseudospiralis in 1% of the animals. Host species showed different sample prevalence and Trichinella species distribution. Geographical distribution also varied, with the southern part of the country having significantly higher percentages than the northern part. Infection density was dependent on both the infecting Trichinella species and the host species. Trichinella spiralis was discovered in areas with no known domestic infection cases, indicating that it can also occur in the sylvatic cycle. Raccoon dogs and red foxes are the most important reservoir animals for T. spiralis , as well as for the sylvatic Trichinella species in Finland.

Examination of 627 wild animals--raccoon dogs (Nyctereutes procyonoides), red foxes (Vulpes vulpes), European lynxes (Lynx lynx), brown bears (Ursus arctos), wolves (Canis lupus), and badgers (Meles meles)--revealed Trichinella spp. The prevalence varied according to geographical region of Finland (north; southwest, SW; and southeast, SE) and was the highest among lynxes (70%, SW). The risk of trichinellosis was higher in the SE (odds ratio, OR, 19.4) and SW regions (OR 14.3), as compared with the northern region (OR 1), with no difference between the former 2 regions. Foxes (OR 2.1) and lynxes (OR 1.9) had a higher risk than raccoon dogs (OR 1) of being infected. The distribution of different Trichinella species was evaluated in 87 wild and domestic mammals by multiplex polymerase chain reaction. Trichinella spiralis was detected more often in domestic and synanthropic animals than in sylvatic hosts. Trichinella nativa was detected only in wildlife. Trichinella pseudospiralis was found both in sylvatic and synanthropic hosts. Trichinella britovi was detected only in mixed infections with other Trichinella species. The raccoon dog was the sole host for all 4 Trichinella species and also carried the most intense infections.

A reflection of highly prevalent endemic wildlife trichinellosis is seen in wild boar farming in Finland. During the last five years, 0.7% (15/2265) of wild boars undergoing official meat inspection have been determined to be Trichinella-positive. These findings originate from six different farms. In Finland, T. spiralis and T. pseudospiralis have been discovered in meat inspection of wild boars. ELISA showed 11 out of 99 serum samples (11%) as having specific antibodies for T. spiralis crude antigen. Positive samples were from three out of the thirteen farms from which the sera were available. Most of the positive serum samples (8/11) originated from a farm where trichinellosis was also revealed in meat inspection, the other two seropositive farms were without previous Trichinella records. Over the last few decades, no reports have been made of human trichinellosis acquired in Finland. This indicates both efficient meat inspection as well as public awareness of high-risk foodstuff.

Trichinella larvae collected from wildlife, domestic and synanthropic animals in Finland were identified to species by two molecular techniques: Random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) and the recently described multiplex PCR. The RAPD-PCR was very sensitive to the sub-optimal preservation muscle larvae and resulting in weak and smeared bands on the gels for such material. However, the same samples yielded easily recognizable bands in the multiplex PCR; this latter technique is then recommended for epidemiological studies, especially when the preservation of the samples is sub-optimal. For larvae in good condition the unequivocal bands obtained by multiplex was the easiest identifiable. Four species of Trichinella were identified in the material: T. spiralis, T. nativa, T. britovi, and T. pseudospiralis. Trichinella britovi is a new record for Finland, and T. pseudospiralis is a new record for Northern Europe. Mixed infections between T. britovi and T. spiralis, T. nativa and T. spiralis, and between T. britovi and T. nativa were detected; this is the first record of a mixed infection between T. spiralis and T. nativa in a naturally infected host. Raccoon dogs were the only host species from which all of the four Trichinella species were detected. Trichinella spiralis was found in both domestic animals and wildlife, but none of the sylvatic Trichinella species were detected in domestic pig.