Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease. 2 Attempts to upgrade the reliability and the efficacy of xenodiagnosis in chronic Chagas' disease.

In order to upgrade the reliability of xenodiagnosis, attention has been directed towards population dynamics of the parasite, with particular interest for the following factors: 1. Parasite density which by itself is not a research objective, but by giving an accurate portrayal of parasite development and multiplication, has been incorporated in screening of bugs for xenodiagnosis. 2.

SCHISTOSOMIASIS: AGE OF SNAILS AND SUSCEPTIBILITY TO X-IRRADIATION.

Studies on sensitivity of Australorbis glabratus to x-rays have defined the chronological and physiological age at which the snail is most sensitive to radiation damage. Results showed that the dose producing 50percent mortality at 30 days after irradiation increased with age but that at 90 days it was practically constant from 2 to 210 days of age. In view of the available data on recovery from radiation damage caused by doses from 6000 to 9000 roentgens it is suggested that doses above those causing 50 percent lethality at 60 days but below those causing 50 percent lethality for 30 days should be considered in setting up "radiation barriers" to control snails in water-distribution systems.

Schistosoma mansoni: development of challenge infections in mice exposed to irradiated cercariae.

The principal effect of x-irradiated Schistosoma mansoni cercariae may be to slow the migration and development of the worms of a challenge infection. This would account for the smaller number of worms found in the portal system in the early weeks and the delayed accumulation of recoverable worms and eggs.