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

Abstract

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.

Population-specific toxicity of six insecticides to the trematode Echinoparyphium sp.

“…Indeed, for both populations of Echinoparyphium, we detected a hormetic-like curve when cercariae were exposed to carbaryl and thiamethoxam. An increasing number of studies have reported hormetic responses to environmental toxins challenging the traditional dose-dependent paradigm used in environmental toxicology (Calabrese and Baldwin, 2003;Morley et al 2003;Calabrese, 2005;Costantini et al 2010). This is the first evidence of hormesis in trematode responses to pesticides and this discovery corroborates the evidence suggesting that hormesis is a common phenomenon across a diversity of taxa.…”

“…While a diversity of factors can drive disease dynamics, there is growing awareness that human actions may be a significant contributor. Human activities have dramatically altered the environment through climate change, habitat fragmentation, and introduced species, which can directly or indirectly influence disease dynamics (Blaustein and Kiesecker, 2002;Morley et al 2003Morley et al , 2005Daszak et al 2003;Jones et al 2008;Blaustein et al 2011). Recently, the influence of agrochemicals on disease dynamics has garnered attention.…”

Parasites and hystopathology of <i>Mullus barbatus</i> and <i>Citharus linguatula</i> (Pisces) from two sites in the NW Mediterranean with different degrees of pollution

“…In our study, digenean increase with pollution in M. barbatus, and specifically that of O. furcatus, might indicate that environmental impact could affect the host response to the parasite but would not affect the survival and infectivity of the larvae, as pointed out by Morley et al (2003). This result suggests that some larval parasite stages may not be as fragile as has been previously suggested.…”

The role of the invasive snail Potamopyrgus antipodarum in the transmission of trematode parasites in Europe and its implications for ecotoxicological studies

“…Pollutant toxicity to molluscan-trematode communities: implications for Potamopyrgus antipodarum ecotoxicological studies There is a growing amount of information from both field and laboratory studies on the interactions between trematodes and molluscs in polluted conditions (Morley et al, 2003a;. In laboratory studies, primary trematode infections are largely detrimental to molluscan life history traits compared to uninfected controls exposed to acute concentrations of xenobiotics with a differential host survival dependent on the specific species of parasite they are infected with (Guth et al, 1977;Morley et al, 2003b).…”

“…It is also common for molluscs to act as second intermediate hosts for trematode metacercariae, which are typically less host specific, and can cause increased mortality (Schneck and Fried, 2004), reduced growth (Thieltges, 2006), and altered behaviour (Babirat et al, 2004) in infected individuals. The extensive effects trematode parasitism can cause to their molluscan hosts makes them an important natural stressor that can impact molluscan communities, especially those exposed to polluted conditions (Morley et al, 2003a). As such, their status in field populations needs to be properly assessed so that ecotoxicological laboratory studies on molluscan model species may more accurately reflect natural conditions.…”