Size and Shape Analysis of Schistosome Egg-Counts in Egyptian Autopsy Data

Abstract

We study egg-counts from a series of Egyptian autopsy cases with active schistosomiasis at death (Kamel, Cheever, Elwi, Mosimann and Danner 1977). The data are unique, and enable us to study the proportional distribution of eggs among various organs in relation to infection intensity for two species of schistosome worms. We develop a model for the distribution of eggs in three organs of the mesenteric circulation. Under a lognormal distribution assumption, several exact statistical procedures are presented and used to examine model consistency as well as isometry with respect to geometric means. Mesenteric egg counts for both Schistosoma mansoni and S. haematobium behave consistently with the model, and show little or no departure from isometry in cases without Symmers' fibrosis of the liver. We show that cases with Symmers' fibrosis have relatively more S. mansoni eggs in the small, as opposed to large, intestine. In the genito-urinary organs we show that the proportion of S. haematobium eggs in the bladder is high for low-intensity infections. This is consistent with the conclusion of Smith, Elwi, Kamel and Lichtenberg (1975), based on egg/gram data, that such infections may be initiated in the bladder. The correspondingly high proportion of eggs in the ureters with high-intensity infections indicates that increased intensity may have a disproportionately large pathologic effect on the infected individual.