Quantitative comparison of the intensity of Schistosoma mansoni infections in man and experimental animals

Abstract

In man and mice infected with S. mansoni, a state of near equilibrium (steady state) develops in which the rates of deposition and destruction of S. mansoni eggs in the tissues are approximately equal. Infections in man and experimental animals result in roughly comparable numbers of eggs per WP (worm pair) in the tissues; however, the concentration of eggs per gramme of tissue is much higher in mice infected with a single worm pair than it is in the most heavily infected human subjects. The number of eggs per gramme of tissue of human subjects and experimental animals is roughly proportional to the number of WP per kg. BW (body weight). The intensity of infection in experimental animals is frequently greater than 50 WP per kg. BW and in mice it can never be substantially lower than this. In man, worm burdens greater than 5 WP per kg. BW have seldom been reported. Quantitative comparison of schistosome infections between species will be more meaningful if the numbers of eggs in the tissues are considered in terms of both total number and concentration. The number of eggs in the faeces of different host species can be compared only if the number of eggs passed in the faeces per day is known and related to the intensity of infection.