The use of a stereological method to estimate the volume of Schistosoma mansoni granulomas: the effect of zinc deficiency

Abstract

A quantitative, stereological method to assess the volume of Schistosoma mansoni granulomas is presented and its use demonstrated in a study of zinc-deficient animals. Twenty-six mice were divided into two groups, and given zinc-deficient or control food. After 4 weeks, the mean weight gain and thymus size were lower in the mice on the zinc-deficient diet. Eight mice in each group were then each infected with 60 S. mansoni cercariae and these mice were killed 12 weeks post-infection. There were then more eggs in the livers of the zinc-deficient mice than in those of the infected controls (7400/female worm v. 3300/female worm; P = 0.02), probably because of impaired intestinal egg expulsion and impaired resorption of eggs in the deficient mice. The median proportion of each liver occupied by granulomas was 0.11 among the zinc-deficient mice and 0.09 among the pair-fed, control mice (P = 0.08), and the median liver volumes were 1400 and 1450 microliters (P = 0.49), respectively. The computed median volume of all the granulomas in each liver was 160 microliters in zinc-deficient and 132 microliters in control mice (P = 0.32), while median granuloma volume per egg was 8.6 and 8.7 nl (P = 0.93), respectively. In contrast to conventional methods, modern stereological methods can provide estimates of granuloma volume or granuloma volume fractions without any assumptions about the size, shape, orientation or distribution of the granulomas in the liver.