Helminth growth in vertebrate hosts: does host sex matter?

Helminth infections are usually more severe in male than in female vertebrate hosts. If parasite establishment is easier in male hosts, parasite growth may also be facilitated in males. This was tested with a meta-analysis of published between growth rates of worms in male and female vertebrate hosts. Two-thirds of the 48 comparisons found showed higher growth in male hosts than in females, but the average relative difference did not differ from zero. However, after controlling for sample size and for the variability in the original data, a small but significant effect of host sex was found. The meta-analysis suggests that male hosts harbour not only more helminths than females, but also slightly larger ones.