**2.1 Life cycle**

The life cycle of *Trichinella* plays an important role in its establishment in domestic as well as wildlife settings. **Figure 1** represents the diagrammatic life cycle of the parasite. In many aspects, the life cycle is peculiar. To begin with, only one host serves as both the definitive and intermediate host. There are two types of cycles: domestic and sylvatic. The infection is transferred to humans in the domestic cycle by eating undercooked meat infected with the encysted larvae. The only ones who develop clinical symptoms are humans, also forming the dead end in the parasite's life cycle. The larva is released in the intestine after the digestion of the cyst, where they disrupt the columnar epithelium and moult four times before growing into male and female worms within 30 hours. After fertilising the female, the male dies, but the viviparous female continues to produce thousands of larvae. The larvae will only encyst in striated muscles, where they will modify muscle cells to ensure their own survival, establishing a nurse cell complex. A collagen capsule is produced around the nurse cell as a result of the host immune cell reaction, with a capillary network around it for nutrition. The larva experiences a developmental halt at this point, before this it becomes infective within five weeks and calcifying after months or years according to the *Trichinella* species and host species. The parasite is passed on to domestic pigs, rats and boars through cannibalism and the ingestion of meat scraps. Predation and scavenging habits among wildlife species, such as those of carnivores and omnivores, are pronounced in the sylvatic cycle. Humans become infected after consuming raw undercooked meat (**Table 1**) [1, 9, 10].

*Non-Encapsulated Trichinella Species:* T. pseudo spiralis*,* T. papuae *and* T. zimbawensis *DOI: http://dx.doi.org/10.5772/intechopen.105680*

#### **Figure 1.**

*Life cycle of* Trichinella *species [10–13]. Image from the Centers for Disease Control and Prevention Image Library.*


#### **Table 1.**

*Geographical distribution and general characteristics of the non-encapsulated species.*
