Trichinella spiralis

INTRODUCTION Trichinella spiralis is a nematode parasite, occurring in rats, pigs, bears and humans, and is responsible for the disease trichinosis. It is sometimes referred to as the "pork worm" due to it being found commonly in undercooked pork products.

Introd……. First observed in 1821 in the muscles of a patient at autopsy by James Paget who was a first year medical students at St Bartholomew’s Hospital London. Owen in 1835 describe the encysted larva form in the muscle and named it Trichina spiralis. Leuckart, Virchow and Zenker (1853-60) independently proved the infectivity of the encysted larvae when fed to experimental animals. They traced the life cycle of the worms from the encysted larvae in muscles, to adult in the duodenum and then again encystement in muscles. Trichinella derived from minute size of adult (Gr.trichos-hair ella spiralis refers to spirally coiled appearance of larva in muscles.

Morphology T. spiralis is white roundworm with an un- segmented body and is visible to naked eye and inhabit small intestinal. The adult male has a body size of 1.5mm by 0.04 mm, and adult females are 3mm by 0.06 mm with muscle larvae measuring about 1mm.

Trichinella spiralis larvae in muscle tissue

Scientific classification Kingdom:Animalia Phylum:Nematoda Class:Adenophorea Order:Trichurida Family:Trichinellidae Genus:Trichinella Species: spiralis Name: Trichinella spiralis

EPIDEMIOLOGY About 11 million individuals are infected with Trichinella; Trichinella spiralis is the species responsible for most of these infections. The number of cases has decreased because of increased public awareness of the danger of eating raw or undercooked pork products

LIFE CYCLE The infective stage is the encysted larva found in the muscle of pigs and other animals. After humans ingest the cysts from infected undercooked meat, pepsin and hydrochloric acid help free the larvae in the cysts in the stomach. The larvae then migrate to the small intestine, where they molt four times before becoming adults.

LIFE CYCLE Thirty to 34 hours after the cysts were originally ingested, the adults mate, and within five days produce larvae. The larvae then use their piercing mouthpart, called the "stylet", to pass through the intestinal mucosa and enter the lymphatic vessels, and then enter the bloodstream.

LIFE CYCLE The larvae travel by capillaries to various organs, such as the retina, myocardium, or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst. 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.

LIFE CYCLE

Pathogenesis and Clinical features Stage of intestinal: the larvae encyst, invade the intestinal epithelium in the duodenum and jejunum and develop into adult. Symptoms: nausea, diarrhea, abdominal cramps and sometimes vomiting. This is diagnosed as food poisoning. The onset of illness may be from 2 to 30 hours of ingestion of infective food.

Pathogenesis and Clinical features conti…. Muscle phase: this occurs during the release of larvae, their migration, deposition and encapsulation in muscle. Typical presentation with fever, oedema of face, swelling and weakness affected muscles. Eosinophilia is constant feature Myocarditis and encephalitis are serious and potentially fatal complication. Respiratory symptoms may occur, This stage appears usually one to four weeks after infection.

Pathogenesis & clinical features conti… Encapsulation phase: lasting one to eight months after infection, the fever and other symptoms subside. After the stage the cyst begin to calcify.

SYMPTOMS 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. 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.

SYMPTOMS….. Splinter hemorrhage in the nails is also a common symptom. Most dangerous case is worms entering the central nervous system. Cannot survive there, but they may cause enough damage to produce serious neurological deficits (such as ataxia or respiratory paralysis), and even death.

SYMPTOMS….. 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.

Epidemiology The life cycle can be passed in one host stating with ingestion of infective encysted larvae to the development of adult in the upper intestine, larviposition, deposition of larva in muscle, and their development into infective cysts. Only a single cycle occurs in one host and for continuation of the cycle and maintenance of the species, it is necessary for the infection to be transmitted to another host of the same species or of different species.

T spiralis is maintained in nature in three cycles: i)Pig to Pig: this is facilitated by customer of feeding pigs with untreated household garbage. Such may contain bits of pork with infective cysts. ii) Rat to Rat; rat may get infection by eating household garbage or by cannibalistically eating one another. iii) Feral cycle: involve wild animal such as boar, wild rodent and various carnivores. Human infection come mainly by eating undercooked pork or inadequately processed sausage or other meat product. Human infection is dead end as the cysts in human muscle are unlikely to be eaten by another host.

DIAGNOSIS Muscle biopsy is used for trichinosis detection. Several immunodiagnostic tests are also available; -Immunoassays, such as ELISA. -Serological tests include a blood test for eosinophilia, increased levels of creatine phosphokinase, IgG, and antibodies against newly hatched larvae.

TREATMENT Patients are treated with either mebendazole or albendazole. Symptoms can be relieved by use of analgesics and corticosteroids

Education and training Food preparation Hygienic pig farming PREVENTION Legislation Education and training Food preparation Hygienic pig farming Legislation -there are laws that dictate how the pigs are taken care off and what they are fed and all

REFERENCES http://web.gideononline.com www.dec.ny.gov/permits http://www.aphis.usda.gov/vs/trichinae