The opportunistic nature of Trichinella--exploitation of new geographies and habitats.

For more than 100 years, Trichinella spiralis (former Trichina spiralis) was considered a zoonotic parasite of the domestic habitat involving pigs, synanthropic rats and humans. In the last 70 years, there has been increasing evidence that the biomass of nematodes of the genus Trichinella is greater in wild animals than in domestic animals. Omnivores and carnivores (mammals, birds and some reptiles), mainly those with cannibalistic and scavenger behaviour, act primarily as reservoirs for the 12 Trichinella taxa recognized to date. The distribution areas of Trichinella spp. hosts can help to identify the environmental suitability where the different Trichinella taxa can be detected. Both the survival of larvae in decaying muscles of their hosts, which is favoured by high humidity and low temperatures, and human behaviour in the domestic and wild habitats play roles in the transmission patterns of these nematodes. Although Trichinella taxa develop in different host species circulating in different geographical regions, there is a common denominator among the hosts, namely their scavenging behaviour.