Adaptation of Trichinella spp. for survival in cold climates

Parasites of the genus Trichinella are a complex of at least 12 taxa with a broad geographic range, including, Africa, the Americas, Asia, Australasia and Europe, and a broad host spectrum encompassing mammals, birds and reptiles. These entozoic parasites complete their life cycle in only one host; however, there are several biological and epidemiological features, which suggest that the environmental temperature and moisture influence the circulation of these nematodes in nature. An important adaptation of these parasites, which facilitates their transmission, is the physiological mechanism utilized by muscle larvae to promote their survival in decaying carcasses. The greater the persistence of larval viability, the higher the probability of being ingested by a scavenging host. The larval metabolism is basically anaerobic favoring its survival in decaying tissues. The persistence of larvae in putrefying flesh is, of course, also determined by high humidity and low temperatures. This condition has been proposed as the environment of the “free-living” stage, resembling the egg stage of most of other nematode species. The importance of this stage in the natural cycle of these parasites is underscored by the survival of muscle larvae of Trichinella nativa, Trichinella T6 and, to a lesser degree, of Trichinella britovi in frozen muscles of carrions for months up to several years. Survival is greatest at temperatures between 0°C and −20°C. At lower temperatures, survival time is reduced rapidly, suggesting that the optimal temperature range for survival to freezing corresponds to the temperature under the snow. The subnivean climate is characterized by a stable temperature near freezing because heat released from the soil is trapped by the low thermal conductivity of snow. This adaptation for survival of Trichinella spp. in cold climates is under the influence of six intrinsic and extrinsic factors. The survival of larvae of the three Trichinella taxa to freezing in host muscles represents a concern for the food safety of humans consuming game meat. The climate change certainly will influence the natural cycle of Trichinella taxa circulating in cold climates, due to the increasing temperature, decreasing humidity and snow cover, and increasing exposure to heat stress. A reduction of the distribution area of T. nativa and Trichinella T6, and an advance toward the north of the distribution area of T. britovi can be expected. •Larvae of some Trichinella taxa in ca