Strain and Family Differences in Susceptibility to Cysticercus Sarcoma

Abstract

Since Borrel (1) pointed out the relationship between Cysticercus fasciolaris and sarcoma of the rat liver, several investigators have reported one or more cases of Cysticercus sarcoma noting the presence of the parasite. McCoy (2) autopsied 100,000 American wild rats and observed 22 primary tumors of the liver, in thirteen of which he found the parasite. He says: “It is quite probable that these parasites were present even more frequently than is shown in the tablet as some of the tumors were quite large and the worm may have escaped the rather cursory search that, on account of lack of time, it was sometimes necessary to make.” Bridre” and Conseil (3) found 10 rats with Cysticercus sarcoma in 7770 North African wild rats which they autopsied. Of this number 2174 were found to be infested with Cysticercus fasciolaris , the infested animals nearly all belonging to the species Mus decumanus ; the other two species Mus rattus and Mus alexandrinus , which formed 2 to 3 per cent of their group, were almost never bearers of the parasite. In 23,000 American wild rats Woolley and Wherry (4) recorded 3 liver tumors, each a Cysticercus sarcoma with the worm included in the growth. In an earlier communication (5) from this laboratory, which dealt with the experimental production of sarcoma of the liver of rats by infestation with the Cysticercus of Taenia crassicolis , it was stated that previous to these experiments twenty cases of liver tumors observed at this laboratory in domestic rats were associated with Cysticercus fasciolaris . Only one other primary liver tumor has been observed here in rats not experimentally infested with the parasite. This tumor was a polymorphous-cell sarcoma resembling morphologically the Cysticercus tumors of this type and it may also have originated in a Cysticercus cyst since it showed extensive necrosis in the tumor which might have destroyed both cyst and parasite. These twenty-one tumors were observed in the thousands of rats of all ages which have been autopsied during the ten years existence of the laboratory, but the number and age of the rats in which tumors were not found is not in general recorded. However, three of the twenty-one cases (one of the animals having two apparently independent Cysticercus tumors) were found by Bullock and Rohdenburg (6) in a group of 4300 adult rats, all of which were autopsied. In the report (5) of the first 85 Cysticercus sarcomata which occurred in the present experiments the relation of the parasitic cyst to the tumor was discussed in some detail, and the 682 tumors which have since occurred have been in line with the cases there recorded. Of the total 767 tumors which have occurred in the experiments up to the present date (March 26, 1923) the parasites were found in 684; in each of 49 others there was a cyst-like space in the tumor and a free worm in the peritoneal cavity; in 16 the cysts were apparently obliterated, but a free worm was present in the body cavity of each host; 12 showed considerable tumor necrosis which had probably destroyed both cysts and parasites; the hosts of the remaining 6 had been partly eviscerated by their cage mates and a part of their tumors were gone. There is a possibility that any tumor in which the cyst or parasite was not identified within the tumor arose in the liver outside a cyst, but so far no early extracystic sarcoma of the liver has been observed. Every small sound tumor arose in the walls of a cyst containing a parasite and in nearly every case the worm was alive. In the older tumors (i.e., larger and more necrotic) all stages in the obliteration of the cyst and the degeneration and disintegration of the parasite were observed. In each of several tumors the dead parasite was reduced to a few fragments imbedded in necrotic tumor tissue and in a few cases the worm fragments could only be identified microscopically. A complete histological examination of the large necrotic tumors in which the parasites were not found would have involved a prohibitive amount of labor. The sound areas of these tumors resemble morphologically the tumors in which the worms were found, and the extent of the necrosis was in all cases sufficient to account for the destruction and disappearance of both cyst and parasite. We believe that the fairest interpretation of the facts is that each liver tumor in these experiments arose in the wall of a Cysticercus cyst and that in the thousands of infested and uninfested rats autopsied in this laboratory no liver neoplasm of any other origin has been observed.