Pollution toxicity to the transmission of larval digeneans through their molluscan hosts

The increased occurrence of pollutants in ecosystems is a continuing area of concern. It is known that numerous diseases of wild aquatic animals can Occur with decreased or increased prevalences in areas associated with high or chronic levels of pollution. This may have serious implications for environmental health. There has consequently been an increasing number of laboratory and field Studies on disease transmission under polluted conditions, especially focusing on digeneans of medical or economic importance. The effect of pollutants to the transmission of larval digeneans (miracidia, cercariae, metacercariae) and snail-digenean interactions is therefore considered. An overview and interpretation of the published literature on laboratory and field studies is provided. It is apparent from these studies that the influence of pollutants on digenean transmission is highly complex with much of the observed effects in the laboratory often masked by a complexity of other factors in the field. Future studies would benefit from a standardisation of experimental procedures, increasing the number of combined laboratory and field studies, and increasing the complexity of the experiments undertaken.