The Life Cycle of Trichinella Spiralis

Trichinella spiralis is a parasitic infection caused by a microscopic organism known as a nematode.  This type of parasite will infect both humans and other animals who consume raw meat that is already infected with this nematode.  The types of meat commonly associated with Trichinella spiralis are pork and wild game.  The medical term used for this specific type of parasitic infection is known as trichinellosis or trichinosis and can also be caused by other species of Trichinella.

The life cycle of Trichinella spiralis is well known and documented.  The first phase of infection begins when a person or animal eats raw meat from another animal that was infected with the parasite.  The meat contains what are known as nurse cells.  These nurse cells are muscle cells of the host organism that the larva of Trichinella have invaded and programmed to support the growth of the nematode.  The nurse cells hatch when they enter a new host’s stomach and the nematodes then mature in the small intestine.  Adult nematodes mate and the female sheds newborn larva which enter lymph fluid and blood.  The newborns are then carried to other parts of the host’s body where they find muscle tissue.  It is here that the nematodes complete their life cycle and invade the muscle cells to create the nurse cells ready to invade the next host.

Trichinella spiralis was first discovered by a young medical student of the London Hospital Medical School named James Paget in 1835 who was curious about the strange toughness of the diaphram in a cadaver that was being autotopsied.  He noticed that there seemed to be very small worms coiled up in the tissues of the diaphram muscle which led to the discovery of this nematode.  Robert Owen, the assistant curator of the Royal College of Surgeons, took notice of Paget’s findings and wrote up and presented the findings to the Royal Society where he was given all of the credit for the discovery of this nematode.

The lifecycle of this nematode was observed by the German pathologist Rudolf Virchow from 1850 through 1870.  Virchow experimented by feeding a dog a piece of infected human flesh that had the same appearance as the diaphram tissue described earlier.  He then noted how the dog became infected a few days later and found adult nematodes in the dog’s small intestine when he performed an autotopsy.  Virchow was the first to realize that the nematodes would die when the infected flesh was cooked and became an advocate for getting the public of Germany to stop eating raw or lightly cooked pork.

The symptoms of a trichinellosis infection include diarrhea, fever, swelling around the eyes, profuse sweating, weakness, and muscular pain.  Thiabendazole is used to kill the adult nematodes in the small intestine while drugs such as mebendazole are used to kill the larva that are present in the muscle tissues.  Most infections of trichinellosis that occur in modern times are very minor unlike the infections found in the cadavers during the 1800s.  To keep from getting infected, always cook meats thouroughly.