Observations on the distribution of Trichinella spiralis in muscles of rats and mice and its number in capsule

In order to observe the distribution of T.spiralis larvae in muscles of rats and mice and its number in capsule,30 male Kunming mice and 30 male Sprague Dawley(SD)rats were randomly divided into 3 groups(10 animals for each group):i.e.light,moderate and heavy infection groups.Each group was orally inoculated with 1,5 or 20 T.spiralis muscle larvae per gram of body weight,respectively.All infected animals were slaughtered at 42 days post-infection.The muscles were compressed between two slides to examine under microscope for the larval burden(larvae per gram,lpg)and the number in capsule(nurse cell).In rats with light infection,the larval burden in masseter muscle was the highest;in rats with moderate and heavy infection,the muscles contained the highest larval burden was diaphragmatic and lingual muscle,respectively.In mice with light infection,the larval burden in masseter muscle was also the highest;In both groups of mice with moderate and heavy infection,the larval burden in diaphragms was the highest.The frequency of capsules contained 1,2 and 3 larvae among 8028 capsules in infected rat muscles was 97.91%,1.95% and 0.14%,respectively.Out of 7559 capsules in infected mouse muscles,the capsules contained 1,2 and 3 larvae accounted for 97.33%,2.54% and 0.13%,respectively.The detection rate of capsules contained multiple(2-3)larvae in infected mouse muscles was obviously higher than that in infected rat muscles(χ2=5.644,P0.05).The detection rate of capsules contained multiple larvae in rats and mice has the elevating trend with the increase of infective dose(χ2rat=42.656,P0.05;χ2mouse=45.713,P0.05).The muscles of rats and mice with heavy infection accounted for 81.82%(9/11)and 100%(10/10)of the muscles contained the capsules with 3 larvae.The capsules contained more than 4 larvae(4 or more)were not observed.These results indicate that when the epidemiological investigation on murine Trichinella infection was carried out,masseter muscles are preferred for pathogen examination,the next is diaphragm or masseter muscles;the detection of the capsules contained 3 larvae during muscle biopsy or meat quarantine suggests the presence of heavy Trichinella infection.