Longevity of the Tapeworm, Hymenolepis diminuta

Abstract

Hymenolepis diminuta adults were maintained in rat hosts for 14 years by 13 successive surgical transplantations, showing that this worm has a life-span potential far exceeding those of its usual rodent hosts. Over a period of some years, it has been observed that the egg production and apparent growth of the strobilate phase of the rat tapeworm, Hymenolepis diminuta, seems to continue in an unabated fashion for the life-span of its rat host in the laboratory. The present report documents the fact that this worm may live for at least 14 years, a period far exceeding the life of its usual host. MATERIALS AND METHODS For the initiating infection, cysticercoids of H. diminuta were reared in the beetle, Tenebrio molitor, and administered to young male rats per os with a pipette. At about 1-year intervals, transplants of these worms were made from rat to rat using the following procedure: Donor rats were killed by a blow on the head and the small gut was flushed with warm Ringer's solution. The worms were recovered and the anterior 2 cm of each worm was cut off with sharp scissors. The recipient host was placed under Nembutal anesthesia and the midventural body wall opened. The surgically shortened worms were introduced through the gut wall into the lumen of the recipient's small intestine through a 16-gauge hypodermic needle. The body wall of the recipient was Received for publication 21 July 1967. * This work was supported in part by a grant from the NIH, U. S. Public Health Service (AI01384). closed and the animal maintained in the general animal colony for subsequent months. At each transplantation, the available worms were divided as evenly as possible among the recipient animals. RESULTS AND DISCUSSION In the initial infection in February 1949, each of four young male Wistar rats were given 25 cysticercoids of H. diminuta. These animals were maintained at the Rice Institute for about 16 months. In August of 1950, worms from these animals were transplanted to three new hosts which were immediately shipped to the University of California, Los Angeles. During the next 4 years, three successive additional transplants were made, in each case to two young male Long-Evans rats. In 1954, two infected animals were carried by automobile to Johns Hopkins University, Baltimore, Maryland. During the next 5 years, six successive transplants were made, in each case to two Sprague-Dawley rats. In 1959, two infected animals were carried by air to Rice University. Three successive transplants, in each case to one Sprague-Dawley rat, were made at Rice. The experiment was terminated by the accidental death of the single remaining host in November 1963. The pertinent data from this experiment are TABLE I. Schedule for transplantations of Hymenolepis diminuta in successive hosts for a 14-year period. Date of Total worms Donor Strain and number transplant recovered strain of recipients Feb. 1949 (Initial)-Wistar (4) Aug. 1950 78 Wistar Wistar (3) July 1951 62 Wistar Long-Evans (2) Aug. 1952 56 Long-Evans Long-Evans (2) Sept. 1953 38 Long-Evans Long-Evans (2) Oct. 1954 31 Long-Evans Sprague-Dawley (2) Dec. 1955 28 Sprague-Dawley Sprague-Dawley (2) Sept. 1956 20 Sprague-Dawley Sprague-Dawley (2) Oct. 1958 18 Sprague-Dawley Sprague-Dawley (2) May 1959 17 Sprague-Dawley Sprague-Dawley (2) May 1960 15 Sprague-Dawley Sprague-Dawley (1) Oct. 1961 9 Sprague-Dawley Sprague-Dawley (1) Sept. 1962 8 Sprague-Dawley Sprague-Dawley (1) Nov. 1963 2 (Terminal)