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.
Clinical Symptoms
Trichinosis, Trichinellosis
Trichinella spiralis is known as the great imitator because infected patients may exhibit a variety of symptoms that frequently resemble those of other diseases and conditions. Diarrhea and possibly a slight fever, suggestive of the flu, are common symptoms of a light infection. During the intestinal phase of infection, heavily infected patients experience symptoms such as vomiting, nausea, abdominal pain, diarrhea, headache, and possibly a fever. As the larvae begin to migrate through the body, infected people experience a variety of symptoms, including eosinophilia, pleural pain, fever, blurred vision, edema, and cough. During this stage, death is also possible. Muscular pain, edema, local inflammation, general fatigue, and weakness are common after the larvae settle into the striated muscle and begin the encystation process. The striated muscle of the face and limbs, as well as other parts of the body, can become infected.
Laboratory Diagnosis 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. T. 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 T. spiralis, the life cycle is not completed, and the cycle ends with the encystation of the larvae.
Treatment of Trichinosis, Trichinellosis
If the infected person has a non–life-threatening strain of the disease, no medications are recommended. These patients are advised to get plenty of rest, as well as drink plenty of fluids, take fever reducers, and pain relievers. Prednisone is typically used to treat patients who have severe infections that could be fatal. Thiabendazole may also be administered, despite the fact that research to date suggests that its efficacy is questionable. Steroids may also be administered under certain conditions.
Prevention and Control of Trichinosis, Trichinellosis
Thorough cooking of meats, especially those from animals known to harbor Trichinella spiralis, is critical to the parasite’s eradication. It has been determined that proper storage of these meats at subzero temperatures (i.e., 15° C [59° F] for 20 days or 30° C [86° F] for 6 days) will significantly reduce the organism’s viability. It is also necessary to avoid feeding pork scraps to hogs in order to break the Trichinella spiralis life cycle.
Reference
Clinical Parasitology: A PRACTICAL APPROACH. Elizabeth A. Gockel-Blessing (formerly Zeibig) P. 226 – 228
