Trichinella spiralis : Epidemiology, Laboratory Diagnosis & Treatment

Trichinella spiralis commonly known as Trichina worm causing Trichinosis, trichinellosis is found worldwide, with the exception of the tropics, where it is only rarely reported, and is most common in meat-eating people. This organism has been discovered in a variety of animals, including the pig, deer, bear, walrus, and rat. The fact that these animals live in such a wide range of temperature zones suggests that Trichinella spiralis is more resistant to colder regions of the world than most parasites studied thus far.

The feeding of contaminated pork scraps to hogs is thought to be a major mode of Trichinella spiralis transmission in developed areas. Similarly, other animals become infected with this parasite after eating contaminated meat.

Morphology of Trichinella spiralis

Encysted Larvae

The average size of a juvenile encysted larvae is 75 to 120 m by 4 to 7 m. A fully developed larva can grow to be 1 mm long. These larvae settle by coiling up and becoming encysted in muscle fibers. Biopsies of these larvae frequently reveal a distinct inflammatory infiltrate in response to the larvae’s presence. A nurse cell, a striated muscle cell, surrounds the coiled larva.

Adults

Although adult Trichinella spiralis worms are rarely seen, they have been described. The female is 4 by 0.5 mm in size, while the male is significantly smaller at 2 by 0.04 mm. A typical male adult has a thin anterior end with a small mouth, a long and slender digestive tract, and a curved posterior end with two somewhat rounded appendages. In two ways, the female differs from the male. The female has a blunt, rounded back end and a single ovary with a vulva in the anterior fifth of the body

Life Cycle of Trichinella spiralis

Trichinella spiralis infection in humans is the result of an unintentional human infection with a parasite whose natural host is an animal (zoonosis). Consumption of undercooked contaminated meat, primarily striated muscle, causes infection. Trichinella spiralis larvae enter the intestine as a result of human digestion. Maturation into adult worms happens quickly. Because there is no egg stage in this life cycle, mating occurs and the gravid adult female migrates to the intestinal submucosa to lay her live larvae. The infant larvae then enter the bloodstream and make their way to striated muscle, where they encyst nurse cells. A granuloma forms over time, which becomes calcified around these cells. Because humans are not the traditional hosts for Trichinella spiralis, the life cycle is not completed, and the cycle ends with the encystation of the larvae.

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