The Viability of Paramecia and Euglenae in the Digestive Tract of Cockroaches

Abstract

Experimental studies of the relations between cockroaches and protozoa have a bearing on two important problems, (1) the origin of the enteroparasitic habit of certain protozoa and (2) the possible transmission of human protozoa by cockroaches. Porter (1919) reports that the cysts of Giardia lamblia from man may pass unharmed through the alimentary canal of cockroaches and are then infective to white rats, but her work needs confirmation. Pessoa and Correa (1927) find that cysts of Giardia lamblia may be ingested by cockroaches and later may either be regurgitated or deposited in their feces in a living condition. It thus seems possible that cockroaches may aid in the distribution of the cysts of human protozoa, not only those of intestinal flagellates, but probably also those of intestinal amoebae. That the trophozoites of Trichomonas hominis do not succeed in passing through the cockroach alive seems to have been definitely proved by the experiments of the writer (Hegner, 1928). Fecal material containing these organisms was readily ingested, but most of the trichomonads were killed before they reached the stomach, within from two to five and one-half hours. Movement of material through the digestive tract of the cockroach is so slow that the chances of trichomonads being passed in a viable condition in the feces are very slight. The problem of the origin of the enteroparasitic habit of certain protozoa is a difficult one, but data of interest may be obtained by feeding free-living protozoa to various laboratory animals and determining their viability during their progress through the alimentary canal. So far as I am aware the cockroach has been used in experiments of this type only by Cleveland (1927). He discovered living, active paramecia in the stomach (crop?) of 3 cockroaches about 2 hours after the insects had been collected, but could find only the remains of paramecia in 2 specimens about 5 or 6 hours later. Cockroaches were starved, then given a rich culture of paramecia and killed and dissected at intervals. Few, if any, of the paramecia were killed during the first 2 hours after ingestion but all were destroyed by the end of 5 hours except in one specimen in which 3 paramecia were still alive at the end of 6 hours. Cleveland concludes that the cockroaches in which the