Susceptibility Studies in Schistosomiasis. II. Susceptibility of Wild Mammals to Infection by Schistosoma Mansoni in Egypt, with Emphasis on Rodents

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  • Parasitology Department, U. S. Naval Medical Research Unit No. 3, Cairo, Egypt

Summary

Nine species of wild rodents, three carnivores and an insectivore from Lower Egypt have been subjected to experimental infection by Schistosoma mansoni. The rodents, as a group, are the most acceptable hosts for S. mansoni, whereas the carnivores at their best show only negligible susceptibility to infection. The hedgehog, an insectivore, is a poor host occupying an intermediate position between the rodents and the carnivores.

As expected, the recovery of schistosomes and the conditions attendant to infection in all hosts, including the species with the most favorable host-parasite relationships, show a considerable range of variability. Egg production by the parasites is also quite variable. Schistosomes in poor hosts tend to produce fewer eggs than parasites in satisfactory hosts. Apparently the relationship between egg production and host-parasite compatibility is not absolute and does not apply to the individual worms. Some individuals of a group of schistosomes in a poor host produce eggs, while others do not. Furthermore, the degree and incidence of splenic enlargement in small mammals infected with S. mansoni follows no definite pattern in the various hosts examined.

Arvicanthis niloticus, the Nile rat, is the best of the rodents studied from the standpoint of general parasitological relationships and requirements, and gives satisfactory yields of well-developed schistosomes which deposit numerous eggs in the wall of the lower intestine as well as in other organs of the body. Arvicanthis has not yet been found naturally infected although it is a satisfactory host for S. mansoni and is frequently found near or even in the water of irrigation systems in areas where schistosome infection is common in snails and in man.

Author Notes

Present address: Parasitology Department, Naval Medical School, National Naval Medical Center, Bethesda 14, Maryland.

Parasitology Department, Naval Medical Research Institute, National Naval Medical Center, Bethesda 14, Maryland.

The authors are indebted to Harry Hoogstraal, Head of the Department of Medical Zoology, Naval Medical Research Unit No. 3, who gave assistance in obtaining the many wild rodents used. He also has provided the authors with the host identifications. We also wish to thank LT(j.g.) W. H. Wells of NAMRU-3, who took part in the earlier stages of this investigation.

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