Elimination of Intestinal Helminths of Mice by Feeding Purified Diets

Abstract

Feeding a complete purified low-residue diet or powdered skim milk to mice infected with pinworms or with the tapeworm Hymenolepis nana resulted in loss of infection. It was demonstrated that loss of infection was due, at least in part, to the lack of residue which is present as crude fiber in natural diets. Intestinal mobility was found to be greatly decreased when the purified diet was fed, and was restored to normal when 20% powdered cellulose was incorporated in the diet. The addition of cellulose also diminished the curative effect of the purified diet. The effects of the low-residue diet on Nematospiroides dubius, a nematode that lives in the upper portion of the small intestine of mice, were less drastic than its effects on pinworms which localize in the cecum and large intestine. N. dubius infections were not completely eliminated from any of the mice studied; however, worm burden, the size of the worms, and the rate of egg deposition by the female worms were considerably reduced in mice given the purified diet. The tapeworm Hymenolepis nana and the pinworms Aspiculuris tetraptera and Syphacia obvelata are intestinal helminths that occur in laboratory mouse colonies unless rather drastic measures are taken to control the infections. These usually involve vigorous treatment with drugs to render the mice helminth-free, followed by maintenance of the animals in strict isolation with the use of sterilized cages, food, and bedding. Even when such measures are taken, recurrence of infection is common. In the course of conducting nutritional experiments it was observed that mice maintained on semisynthetic-type rations were seldom if ever found to be infected with intestinal helminths while those maintained on the usual stock commercial ration frequently harbored large numbers of parasites. This occurred even though all of the mice on both diets were derived from colonies known to be infected and subsequently maintained without special precautions to control transmission. The studies reported in the present paper were undertaken to elucidate the above observations and to obtain information on possible modes of action of the special diets in eliminating the infections. Received for publication 22 January 1964. MATERIALS AND METHODS White mice of the National Institutes of Health general purpose strain were used in these studies. For experiments with pinworm and tapeworm infections the mice were obtained as 12to 14-g weanlings from colonies known to be infected with Syphacia obvelata, Aspiculuris tetraptera, and Hymenolepis nana. The mice were held for several weeks in large plastic cages on sawdust bedding t allow the infections to become uniformly heavy. At the end of the holding period a group of mice, usually ten, was necropsied to determine infection rates and the remaining animals were randomly distributed into experimental groups and housed in plastic cages on sawdust. Worm counts were made on subgroups of mice on each diet at the various intervals indicated. In these initial studies no attempt was made to differentiate the species of pinworms present. Studies with Nematospiroides dubius were carried out with mice given a uniform number of infective larvae obtained from charcoal cultures. The stock N. dubius used was obtained from Dr. Ralph Thorson in 1956 and has been kept by passage in N.I.H. strain general purpose white mice maintained on a commercial pellet diet. Usually 100 larvae obtained by a dilution technique were administered by stomach tube. Mice were maintained in wire-mesh-bottom cages on assigned diets for several weeks before they were infected. Fecal egg counts were made on 24-hr specimens using a modification of the method of Stoll and Hausheer (1926), to which a digestion step was added. Such treatment was found to be necessary because the fecal pellets of mice on the