General Overview about Trichinella and Trichinellosis

Background: Trichinella had infected humans long before its discovery in the 1800's. In ancient Egypt, trichinellosis was highly prevalent and was found in many mummies as one of the earliest human infections documented around 1300 Before Christ (BC). Human trichinellosis is one of the most common parasitic zoonosis worldwide caused by nematodes infection of genus Trichinella. After the consumption of pork from a domestic pig in 1975, a human trichinellosis outbreak occurred among French tourists. A prevalence of 4.5% in domestic pigs slaughtered at the Cairo abattoir was observed at that time. In addition, several cases were reported in various Egyptian localities including Tanta. After consumption of infected meat, the enzymes pepsin and hydrochloric acid act in the stomach and lead to the release of the first stage larvae (L1). These larvae penetrate the small intestine. Invasion may be asymptomatic or may be associated with abdominal pain, diarrhea, nausea and vomiting. Larvae then become adults and mate. Larvae are produced by female Trichinella which complete the gastrointestinal or enteric stage. Larvae join the lymphatic circulation and then enter the blood to reach organs with high oxygen content, skeletal muscles, myocardium and brain. This phase results in systemic symptoms as fever, myalgias, myositis, periorbital edema and may cause myocarditis and encephalitis up to death. The larvae cause significant eosinophilia, especially in patients with cardiac and CNS dysfunction. The severity of the clinical course depends mainly on parasitic factors, such as the type of species involved and the number of infective larvae consumed as well as host factors, such as age, sex and immune status. In humans, T. spiralis infection may remain asymptomatic if it involves a few number of larvae ingested, but in case of ingestion of hundreds of larvae, gastrointestinal symptoms appear as soon as 2 days post ingestion (p.i). subsequently a sever, rarely fatal, disease develops. Trichinellosis usually has a benign and self-limiting course. Complete recovery of patients is expected within 2 to 6 months of infection. Some cases may be severe, and even death may occur. However, death is unlikely if the heart and CNS are uninvolved. Many people with CNS involvement may have residual long standing deficits. Trichinellosis prognosis correlates proportionately to the parasite load. Some complications may occur in untreated cases such as chronic diarrhea myocarditis, pneum