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Trichinella Trichinella spiralis : The adult worm of T.spiralis is the smallest nematodes which infects man. Trichinella spiralis is a nematode parasite of humans that is cosmopolitan in its geographical distribution. It is nearly unique among helminthic parasites in that all stages of development occur within a single host; over 100 species of mammals have been reported to be susceptible to infection. The infective encysted larvae may remain viable in the host’s musculature for many years; they may also survive long periods in decaying and putrefying muscle. Trichinella spiralis causes trichinellosis, a zoonotic infection in human. Humans are infected when parasite-infected meat (port in most instances) is ingested. The diseases that Trichinella spp. cause are collectively referred to as trichinellosis. This species is significantly higher in prevalence in people living in certain parts of Europe, Asia, and Southeast Asia than in the United States. It is now considered endemic in Japan and China. A large outbreak of trichinellosis occurred in Lebanon in 1997. Habitat: The adult worm inhabit the small intestine of pig , rat and man. Morphology: 1.Adult worm: It is minute, whitish, thread like ,both male and female worms are wider posteriorly than anteriorly. female worm is approximately twice as long as male,the female is ovoviviparous which producing eggs after fertilization that are immediately developed into larvae in the uterus and then passed in the stools. The male is shorter than female and the anterior end is delicate and filariform while posterior end bears two conspicuous conical papillae . Fig.(1): ♀of T.spiralis Fig.(2):♂ of T.spiralis 1 2.Larvae : These are released in the intestine,from where they are carried by systemic circulation and are deposite in various organs and tissues of the body. The larvae becomes encysted in the striated muscles, and are infective to other hosts. The larva in the cyst is coiled and hence the name spiralis in species. Figure(3): Infective first stage larva of Trichinella spiralis in its Nurse cell in muscle tissue. Life Cycle of T.spiralis : The typical life cycle for T. spiralis involves humans, pigs, and rodents. Pigs become infected when they eat infectious cysts in raw meat, often pork or rats (sylvatic cycle). Humans become infected when they eat raw or undercooked infected pork (domestic cycle). After humans ingest the cysts from infected undercooked meat, pepsin and hydrochloric acid help free the larvae in the cysts in the stomach. All stages of development occur within a single host such as humans, pigs, dogs, rats and cats. Adult worms reside in small intestine, and larvae reside in skeletal muscle. However, two different hosts are required to complete the life cycle. Primary host: The pig is the primary host. Natural host: rodents, carnivores and various other species of omnivorous animals are other natural hosts. Man is an accidental host and is the dead end for the parasite. When man consumes raw or rare flesh infected with cysts of Trichinella, the cysts are digested out of the muscle in the stomach; the larvae (first stage) are resistant to gastric juice. After passing to the small intestine, the larvae penetrate the villi of the small intestine, molt, and develop into mature adult within 48 hours. After fertilization, the gravid female burrow deep into the mucosa, discharging larvae beginning 5 to 46 days after infection and continuing for 2 to 4 weeks or occasionally longer. Widely disseminated via lymphatics and the bloodstream, larvae enter most organs, but persist only in individual skeletal muscle fibers. The larval host cell becomes a nurse cell in which the larvae will be encapsulated. The development of a capillary network around the nurse cell completes encystation of the larvae.Although the capsules calcify within six months to two years, the larvae within remain viable for months to years, rarely for decades. 2 Nurse cell formation This nematode is a multi-celular parasite that lives within a single muscle cell, which it modifies according to its own requirements. Trichinella spiralis larvae within the diaphragm muscle of a pig Nurse cell formation in skeletal muscle tissue is mediated by the hypoxic environment surrounding the new vessel formation.[4] The hypoxic environment stimulates cells in the surrounding tissue to regulate up and secrete angiogenic cytokines. 3 Clinical features: The great majority of trichinosis infections have either minor or no symptoms and no complications. There are two main phases for the infection: enteral (affecting the intestines) and parenteral (outside the intestines). The symptoms vary depending on the phase, species of Trichinella, amount of encysted larvae ingested, age, gender, and host immunity. Enteral phase : A large burden of adult worms in the intestines promote symptoms such as nausea, heartburn, dyspepsia, and diarrhea from two to seven days after infection, while small worm burdens generally are asymptomatic. Eosinophilia presents early and increases rapidly. Parenteral phase : The severity of symptoms caused by larval migration from the intestines depends on the number of larvae produced. As the larvae migrate through tissue and vessels, the body's inflammatory response results in edema, muscle pain, fever, and weakness. A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by vasculitis. Splinter hemorrhage in the nails is also a common symptom. The most dangerous case is worms entering the central nervous system (CNS). They cannot survive there, but they may cause enough damage to produce serious neurological deficits (such as ataxia or respiratory paralysis), and even death. The CNS is compromised by trichinosis in 1024% of reported cases of a rare form of stroke.[10] Trichinosis can be fatal depending on the severity of the infection; death can occur 4–6 weeks after the infection, and is usually caused by myocarditis, encephalitis, or pneumonia. Diagnosis : Muscle biopsy is used for trichinosis detection. Several immunodiagnostic tests are also available. In pigs, ELISA testing is possible as a method of diagnosis. Anthelmintics can treat and prevent Trichinella infections Acorrect diagnosis depend upon demonstration of Trichinella in the muscle either biopsy or autopsy.Various tests useful in diagnosis: 1.DLC:shows marked eosinophelia up to 50 . 2.X-Rays examination :may show the presence of calcified cysts in the muscles. 3.Increased levels of muscles enzymes:such as lactate dehydrogenase ,creatine phosphokinase due to muscles invasion . 4.muscles biopsy:This is the best way to demonstrate the presence 4 5