The Life Cycle of Trichinella spiralis

    Trichinella spiralis infects, perhaps, a wider range of hosts than any other parasite.  In recent years, "splitter" taxonomists have subsequently named other species, largely dependent on the geographic range of this nematode.  Many vertebrates are susceptible and even invertebrates are believed to be involved as paratenic hosts.  The object of this exercise is to demonstrate the life cycle of this worm in the laboratory rat by feeding it skeletal muscle laden with larvae.

PROCEDURE

1.  Starve a suitable number of rats for 12 hours (allow them water ad libidum), and feed a piece of Trichinella-infected skeletal muscle to the rat.  Sucrose-preserved, infected rat muscle can be obtained from Carolina Biological Supply Company.  This muscle contains live larvae and should be treated with great caution since Trichinella is a human pathogen.  Gloves should be worn at all time when handling the meat and all contaminated glassware and dissecting tools should be boiled or autoclaved afterward.  The muscles with heaviest concentrations of larvae are the intercostals, diaphragm, eye muscles, tongue and facial muscles.  The muscles of the axis are also infected but usually to a lesser degree.
2.  Place the infected meat in a clean cage with the rat until it has been devoured.  Then, return the rat to its regular cage and provide rat chow.
3.  Some rats which have been given an unusually high dose of larvae, may bleed from the anus and may die.
4.  Sacrifice a few rats after 5 days and place the upper third of the small intestine in mammalian Ringer's solution.
5.  Slit open the small intestine and scrape the lining with the edge of a scalpel or razor blade to free the adults burrowed into the mucosa.
6.  Collect the adults and free them of intestinal debris by washing them with fresh Ringer's solution. Determine the ratio of females to male worms.
7.  Mount a male and female on a glass slide using the 10% glycerine-glycerine jelly technique as described in various parasitology lab manuals.
8.  Sacrifice a few other rats after 8-10 days and examine the blood drawn from the hepatic portal vein, the lungs, liver and muscle for larvae.  Stain the blood with the Giemsa stain technique and examine the tissues for larvae by pressing a piece of tissue between two glass slides and examining it at 30X with a dissecting microscope. 
9.  Sacrifice a few rats at 15 days and a few more at 35 days.  Examine the skeletal muscles for the presence of larvae, pressing some tissue between two glass slides.
10.  Fix and embed in paraffin in preparation for microtomy. 
10.  Make prepared slides of skeletal muscle using the Hematoxylin-Eosin Technique.
 

    Trichinella spiralis infection occur as the result of the ingestion of infected meat.  The larvae are freed from the meat during the host's digestion and soon enter the mucosa of the small intestine where further development and copulation of the adults occurs. The female delivers live (ovoviviparous) larvae to the mucosa over the course of 4 to 16 weeks.  As the larvae are delivered they make their way via the hepatic-portal vein to the venous return, appearing in the lungs and numerous other tissues.  The larvae eventually take up residence in the skeletal muscles, most notably those of highest activity such as the muscles of breathing, diaphragm, intercostals, masticatory muscles, and the muscles of the eyes and tongue.