Magnesium emitted by snails alters swimming behaviour of Schistosoma mansoni miracidia

Abstract

Schistosoma mansoni is a parasitic flatworm transmitted by snails which infects millions of people in tropical countries with poor sanitation, where new irrigation schemes, population growth and continued poverty have increased the prevalence of infection. Larval worms, emerging from freshwater snails, penetrate human skin and mature in intestinal veins where they lay eggs. Many eggs remain in and damage tissues while others pass out in excreta and hatch in water, releasing embryos called miracidia. These short lived, multicellular, ciliated, free-swimming miracidia must find, penetrate and reproduce within certain snails whence emerge the larvae infective for man. Snails emit substances (“miraxones”) which alter the swimming behaviour of miracidia and may help them to locate and attack the snails^1–3. Miracidial behaviour is reportedly affected by snail-elaborated amino acids^4,5 and by various other agents, including fatty acids^6,7. We now report that magnesium appears in water in which uninfected Biomphalaria glabrata (a snail host of Schistosoma mansoni) is confined, and that magnesium ions alter miracidial swimming patterns.