Trichinella is a relatively small round worm: the length of adult females ranges from 2.5 to 3.5 mm; male - from 1.2 to 1.8 mm; body diameter - 36 microns. The form of Trichinella Spiralis (as the name suggests) is spiral, and worms can twist and unwind, especially active in the anterior part of the body, which is conical and round.
The skin-muscular body of the worm is covered with a thin hypodermis, and on top is a strong cuticle consisting of the fibrillar collagen protein, which is a buffer against the host's immune response. In the head part of the adult nematode there is a mouth cavity with a protruding acute process (stiletto), which passes into the esophagus (and then into the three-stage intestine with digestive glands in the muscular walls).
Nematodes of Trichinella spiralis have sensory organs: motion detecting bristles (mechanoreceptors) and amphides of chemical detection (chemoreceptors).
Larvae of Trichinellae (0.08 mm long and up to 7 μm in diameter) are covered with a two-layered membrane, the inner layer has a large number of very thin fibrils located parallel to the larval circumference. Outside there is a pointed ledge.
The trichinella reproduces sexually in the small intestine, in the wall of which adult individuals live about 4-6 weeks. During this time, one female worm produces up to 1-1.5 thousand larvae. Then adult Trichinella perishes and is excreted from the body with feces.
The egg in the body of the female is fertilized by the sperm of the male. Each fertilized egg develops into a whole celluloid, which in the course of morphogenetic changes is transformed into a larval-fetus (trophocyte). Larvae of Trichinella fill the uterus of the female worm and after 5-6 days they leave it. Further they penetrate into the mucous membrane of the small intestine, and from it into the lymph and blood, spreading throughout the body. So the migratory phase of the larval invasion begins.
It should be noted that only larvae survive to the striated muscles, since only cells of skeletal muscle tissue can support the existence of the parasite. The larva not only hides in such cells from the host's immune system, forming a collagen capsule, but also stimulates the development of blood vessels around the affected cell in order to obtain the necessary nutrients.
In the protective cyst passes the first larval - infectious stage Trichinella; here the anaerobic larva can be from 15 days to several months or dozens of years, preserving viability in capsules that become calcified and acquire the appearance of intramuscular cysts.