Trichinella

The name describes the larva in the muscle: from the Greek trichos, a hair, with the diminutive ella, and the species name spiralis for the tight spiral it forms in its cyst. Its common name is the trichina worm. It is a nematode, a roundworm, with a direct lifecycle and no free-living stage. The adults live in the lining of the small intestine, and the larvae encyst in striated muscle, each coiled inside a modified muscle cell that acts as its nurse.

It was identified in the 1830s. In 1835 the medical student James Paget observed the encysted worm in the diaphragm of a cadaver at St Bartholomew's in London, and Richard Owen described and named it Trichina spiralis in the same year. Joseph Leidy found it in the muscle of a pig in Philadelphia in 1846, and Friedrich Zenker demonstrated transmission from pork to humans in 1860; Rudolf Virchow had described the lifecycle the year before. The genus was later renamed Trichinella, the name Trichina having already been used for an insect. This is the parasite that gave undercooked pork its dangerous reputation, and the reason that, for a long period, every dry-cured pork process had to be validated against it.

Its course through a person is direct. Live larvae eaten in raw or undercooked meat are released in the stomach, mature to adults in the gut, and the females produce larvae that travel in the blood to striated muscle and encyst, where they can persist for years. The disease, trichinosis, causes fever, muscle pain, swelling around the eyes, and a rise in eosinophils. The reservoir is pork, wild boar and bear, and more than a hundred other mammals, in domestic and wild cycles. Commercial pork in developed countries now carries it rarely, and wild game is the main current risk.

**How it endangers cured meat.** It is already present in the muscle of infected pork or game, and it does not grow in the product; the concern is that it survives a process that does not specifically kill it. Because dry-cured pork is eaten raw, a mild or hurried cure can leave live larvae in the finished sausage or ham, and a short fermentation on its own does not kill them: a recent study found encysted larvae still viable after five days of traditional sour-pork fermentation. This is why it sits at the Foundation, a matter of the right process held for the right time.

Three methods reliably kill it. Thorough cooking, to an internal 63 degrees C (145 F) for whole cuts with a three-minute rest, or 71 degrees C (160 F) for ground pork. Freezing to a defined schedule, for example about minus 15 degrees C held for twenty days for thin pieces, with the important exception that the freeze-resistant Arctic species, such as Trichinella nativa in bear and walrus, survive freezing. And a validated cure-and-dry, the salt, drying and holding schedule set in United States regulation as the prescribed treatment for pork to destroy trichinae. A dry-cured raw pork product is safe against it only through a process shown to kill it.