Sexing schistosome larvae.

Biological and immunological factors may influence changes in sex ratios at different points of the schistosome life cycle, resulting in the fact that female schistosomes are significantly outnumbered by males in chronic infections of snails and mammalian hosts. Analysis of this phenomenon has long been hampered by shortcomings in the methods used to determine sex ratios. Here, Robin Gasser describes recently developed molecular methods for sexing schistosome larvae. These have opened the way towards understanding why sex ratios become male biased and allow a proper assessment of its consequences in the epidemiology, diagnosis and pathology of infection.