Freezing Resistance of a Trichinella spiralis nativa Isolate from a Gray Wolf, Canis lupus, in Montana, with Observations on Genetic and Biological Characteristics of the Biotype

A Trichinella spiralis isolate obtained from a gray wolf (Canis lupus) in northwestern Montana in 1987 was evaluated for infectivity and resistance to freezing and its DNA restriction fragment length polymorphisms (RFLP's) compared to that from other sylvatic and domestic isolates. Infectivity indices in albino mice were low (<2.6) and correlated well with mouse infectivity data from other sylvatic isolates. Larvae did not survive freezing after storage at —20 to — 30°C in wolf musculature for 1and 2-mo periods. Analysis of DNA extracted from the wolf isolate by RFLP's and DNA dot blots using a Trichinella spiralis spiralis-specific probe indicated that this isolate belongs to the Trichinella spiralis nativa group. Inability of the Montana wolf isolate to survive subfreezing temperatures contrasts with published data indicating long-term survival (>18 mo at — 10°C) of a Canadian wolf isolate. This disparity in cold-hardiness of T. spiralis isolates from wolves in neighboring zoogeographic regions as well as variations in RFLP banding patterns between the Montana wolf isolate and other freeze-resistant isolates (e.g., polar bear) indicates the coexistence of dissimilar sylvatic strains at higher latitudes where Arctic or freeze-resistant biotypes predominate.