As a graduate student at the University of South Carolina, one of my jobs was to care for the laboratory rats.  A small colony was kept for laboratory experiments in physiology and parasitology.  It was my job to infect rats with Trichinella spiralis and Hymenolepis diminuta for the parasitology labs (similar to lab exercises outlined in another part of this website).  I learned very quickly that one shouldn’t go overboard to insure an infection. 

    For the Trichinella infections, I would fast a rat for 24 hours and then give it a morsel of a drawn and sugar-cured but uncooked rat supplied by Carolina Biological Company.  The larvae of Trichinella are in the skeletal muscle but some muscles are more heavily infected than others.  It appears that muscles of higher metabolic activity such as jaw, eye, tongue, intercostals and especially diaphragm have heavy concentrations of larvae.  As a young, inexperienced student, I certainly didn’t want to disappoint my professor by inadequately infecting the rats.  So, I made sure by giving them ample portions of the above-mentioned muscles.  One rat was simply given the skull with attached muscles. 

    Not only did I successfully infect the necessary dozen rats, but three died during the first three days of acute intestinal distress.  It is during that period that the larvae have attained adulthood and are active burrowing through the mucosal lining.  Apparently, I had overdosed a few and they died of intestinal bleeding. 

    However, one of the most remarkable events that occurred during my rat care days was a bit of serendipity associated with the infection of rats with Hymenolepis diminuta .  When the parasitology students sacrificed their infected rats in the laboratory in preparation for slide making, one rat had a prominent, pearly-white nodule positioned on its liver.  We were all curious as to what it was, suspecting it to be a cancer of some sort.  Felix Lauter, my advisor carefully dissected it out and pronounced it to be a strobilocercous of Taenia taeniaformis, a tapeworm of cats.  In the life cycle of this worm, rats serve as the intermediate host, becoming infected with egg capsules in food contaminated by cat feces.  The curious nature of this infection was that these rats had not ever been out of their cages, nor had their parents, grandparents and so on for countless generations.  How then, did that rat become infected? 

    The beauty of parasitism is that though many hosts are likely to become infected because of their habits and habitats, a few infections appear under the most improbable situation.  This was one of them. The likely scenario which resulted in this infection probably involved rat chow contaminated at the factory by a infected cat.  Factories with ingredients for making animal chow are havens for rodents and where there are rodents, there are also cats, whether they are pets or feral animals.  One need only think about Philadelphia’s Veteran Stadium (which has since been demolished).  It had become a rat and cat haven with many of the ballplayers recognizing particular felines by their coats and calling them by name.