Distribution of sylvatic species of Trichinella in Estonia according to climate zones

A survey on trichinellosis among sylvatic and domestic animals from Estonia revealed the presence of Trichinella nativa (Tn), Trichinella britovi (Tb), and Trichinella spiralis (Ts). Muscle samples were collected from 776 sylvatic and 1,086 domestic animals. Muscle larvae from 52 of the 74 positive samples were identified, using random-amplified polymorphic DNA analysis; 19 samples showed Tn, 27 samples Tb, and 4 samples Ts. A raccoon dog (Nyctereutes procyonoides) and a red fox (Vulpes vulpes) were infected with both Tn and Tb. Of the 19 animals infected with Tn, 16 (84%) were collected from the central-eastern regions of the country, east of the isotherm -5 C in January. Of the 27 animals infected with Tb, 22 (81%) were collected from the western regions of the country, west of the isotherm -4 C in January. Trichinella spiralis seemed to be present only in a focus (a fur-bearing animal farm) on Hiiumaa Island. These results can be used to support the hypothesis of a relationship between the distribution of Tn and Tb and the environmental temperature; they are also indicative of the importance of long-term survival of muscle larvae in host carcasses in the life cycle of these 2 species. In Estonia, the isotherms -4 and -6 C in January could be considered a thermic barrier for the distribution of Tn and Tb, respectively.