Interactive effects of infectious diseases and pollution in aquatic molluscs

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.

https://repository.royalholloway.ac.uk/file/4ca1608e-eb78-bae9-0298-abad440e5f0d/1/Morley%20review.pdf

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

The creation of large freshwater reservoirs is one of the most dramatic anthropogenic impacts on the natural environment. With worldwide rising demand for water, the construction of more reservoirs is inevitable. Although the effects of reservoir construction on many medically important parasites are well known and appreciated, changes to aquatic wildlife host–parasite interactions have been largely undervalued even though a large body of literature exists. The present review examines changes in the wildlife parasite fauna during the impoundment of reservoirs, focusing on the parasites of invertebrates, fish, and birds, the effects both upstream and downstream of the reservoir, parasitic zoonoses, the associated pollution generated, and assesses the impact of the recently completed Three Gorges Dam in China on the Yangtze River’s parasite fauna.

Anthropogenic Effects of Reservoir Construction on the Parasite Fauna of Aquatic Wildlife

Four families of trematodes were observed in histological sections during a 1992–1997 investigation of the parasites of zebra mussels Dreissena polymorpha. These included Aspidogastridae, i.e., Aspidogaster, Echinostomatidae, Bucephalidae, i.e., Bucephalus polymorphus, and Gorgoderidae, i.e., Phyllodistomum folium. This article describes the precise location of these trematodes in the tissues of D. polymorpha, provides graphic evidence of their effect on the organs they inhabit, and highlights the distinguishing morphological characteristics. Evidence of defense reaction of host to trematode infection, i.e., encapsulation of Aspidogaster and nacrezation of B. polymorphus, is also presented and is the first such report for zebra mussels. The histological photomicrographs included represent the first comprehensive series published on trematode infection of zebra mussels. These images, in conjunction with the morphological descriptions presented, should assist researchers in identifying the 4 major trematode...

Histological analysis of trematodes in Dreissena polymorpha: their location, pathogenicity, and distinguishing morphological characteristics.

Research on the infection of snails by trematodes has been conducted in Europe for over a hundred years. The initial poor knowledge of the intra-molluscan stages of these parasites together with the difficulty of classifying them constituted a serious obstacle to the undertaking of integrated parasitological and malacological efforts to gain a better understanding of the phenomenon. The compilation of morphological and anatomical results of research on trematode larvae resulted in the publication of keys to designate species of parasites, but was not sufficient to encourage malacologists to collaborate with parasitologists. This paper undertakes to collect data published over the last hundred years on the natural infection of European populations of freshwater snails by trematode larvae. The aim of this undertaking is to make researchers of malacofauna and, above all, experts on freshwater snails aware of the scale of the problem of molluscs being exploited as intermediate hosts of trematodes and, consequently, to encourage parasitologists and malacologists to collaborate on this phenomenon that is crucial for both parasites and hosts.

One hundred years of research on the natural infection of freshwater snails by trematode larvae in Europe

The freshwater snail, Bithynia tentaculata (Gastropoda: Prosobranchia), is frequently found in gravel pits and its role in the transmission of larval digeneans was assessed in one of these unstable water bodies from the Lower Thames Valley (UK) from June 1982 to December 1984. Eight species of cercarial and five species of metacercarial infections were reported from B. tentaculata, with up to 7.7% and 4.7% prevalence of infections, respectively, occurring in the snail, making it the most important host at this site. Seasonal peaks in cercarial infections occurred in late autumn/early winter but little seasonality was apparent in the occurrence of metacercarial infections. The life history characteristics of both hosts and parasites, which can affect intramolluscan digenean dynamics, are discussed.

The role of Bithynia tentaculata in the transmission of larval digeneans from a gravel pit in the Lower Thames Valley

Utilization of a single-species molluscan community of Lymnaea peregra by metacercariae of Echinoparyphium recurvatum over a summer (July-September) period in south-east England showed an increase in the mean number of cysts per host with host size and time of exposure. Aggregation resulting from host and habitat-related factors increased with host size and time of exposure. Encystment within the host was restricted to the peripheral organs in smaller juvenile snails but as snails increased in size, metacercariae were distributed throughout the tissues.

https://repository.royalholloway.ac.uk/items/b7236323-2b57-7790-6439-13863904292e/1/echinometa.pdf

Metacercarial utilization of a naturally infected single species (Lymnaea peregra) snail community by Echinoparyphium recurvatum.

Experimental infection of Echinoparyphium recurvatum von Linstow (Digenea: Echinostomatidae) cercariae in the snail second intermediate host Lymnaea peregra Muller shows that metacercarial encystment takes place on the lining of the mantle cavity, pericardial cavity and kidney lumen, with the mantle cavity the most preferred site. All three sites are accessible via the body openings. The metacercariae appear to be more susceptible to encapsulation in the visceral mass than in the cavity of the mantle, pericardium and the lumen of the kidney.

Sites of encystment by the metacercariae of Echinoparyphium recurvatum in Lymnaea peregra.

The purpose of this study was to create and verify a simple and accurate UV-Spectrophotometric technique for determining Folic acid in bulk and tablet dosage form. The approach was based on the measurement of folic acid solution absorbance at 255nm in 0.01M NaOH. In the concentration range of 10-50 g/ml, the constructed calibration curve was found to be linear (R2 = 0.9996). Limits of detection and quantification were 2.73 µg/ml, and 8.27 µg/ml, respectively. The precision of the developed method was confirmed by the obtained low RSD% values. Recoveries percentages were found 98.46%±1.42, 100.0%±0.20, 98.92%±1.12; n=3 for 50%, 100% and 150% levels, respectively indicating the method accuracy and freedom of interference from excipients. Folic acid content percent in the two analyzed brands were found to be equal 96.59%±0.005; n=3, and 97.28%±0.003; n=3 which complies with the official range (90-110%). 

M.E. Adam

Papers

The role of Bithynia tentaculata in the transmission of larval digeneans from a gravel pit in the Lower Thames Valley

Metacercarial utilization of a naturally infected single species (Lymnaea peregra) snail community by Echinoparyphium recurvatum.

Sites of encystment by the metacercariae of Echinoparyphium recurvatum in Lymnaea peregra.

Development and validation of UV-spectrophotometric method for the determination of folic acid in bulk and tablet dosage forms