Anna Cichy

Symptoms of behavioural anapyrexia - reverse fever as a defence response of snails to fluke invasion.

The subject of the research was the thermal preferences of Planorbarius corneus individuals infected by larvae of digenetic trematodes. Snails were obtained over two consecutive years, 2009 and 2010, from 10 water bodies located in central Poland. The relationship between the seasons and the occurrence of patent invasions in hosts found in the shore-zone of lakes was observed. Behavioural experiments conducted on P. corneus individuals placed in a thermal gradient demonstrated that parasite infection had an impact on the thermal preferences of the snails. Individuals that shed cercariae of Bilharziella polonica, Cotylurus sp., Notocotylus ephemera, Rubenstrema exasperatum/Neoglyphe locellus, Rubenstrema opisthovitellinum, or Tylodelphys excavata displayed symptoms of behavioural anapyrexia, similarly to experimentally injured snails. This response increased the survival of infected individuals while simultaneously prolonging the period of shedding of dispersive forms of parasites. This point of view was upheld by the observation that infected snails bred at 19°C lived longer than at 26°C and the shedding rate of cercariae at a lower temperature was lower than at a higher one.

Factors affecting trematode infection rates in freshwater mussels

Abstract Mussels are intermediate hosts of digenean trematodes, but determinants of these infections remain unknown. To address this problem, we collected duck mussels Anodonta anatina in eighteen lakes from northeastern Poland and examined how mussel age, sex, and the encrustation with zebra mussels Dreissena polymorpha and environmental conditions in lakes influenced infection rates. We also assessed parasitic preferences to host gonads and hepatopancreas and the impact of parasites on female fertility. Mussels were infected with Rhipidocotyle campanula and Phyllodistomum sp. Infection rates were higher in older and female mussels but were unrelated to the biomass of encrusting D. polymorpha and the trophy, thermal conditions, and Ca2+ availability. Parasites occupied gonads more often than hepatopancreas. Infected females were less likely to carry glochidia and incubated fewer glochidia. We suggest that the risk of infection by digenean trematodes increases with the amount of water processed by filter-feeding hosts and/or that parasites actively seek hosts which can provide them with abundant resources. This mechanism explains why parasites more often occupied older and female mussels and targeted their gonads. Future research on trematode-mussel interactions should integrate knowledge on different elements of the complex trematode life cycles, including effects of higher-order hosts such as fish.

Potamopyrgus antipodarum as a potential defender against swimmer’s itch in European recreational water bodies—experimental study

Swimmer’s itch is a re-emerging human disease caused by bird schistosome cercariae, which can infect bathing or working people in water bodies. Even if cercariae fail after penetrating the human skin, they can cause dangerous symptoms in atypical mammal hosts. One of the natural methods to reduce the presence of cercariae in the environment could lie in the introduction of non–host snail species to the ecosystem, which is known as the “dilution” or “decoy” effect. The caenogastropod Potamopyrgus antipodarum—an alien in Europe—could be a good candidate against swimmer’s itch because of its apparent resistance to invasion by European bird schistosome species and its high population density. As a pilot study on this topic, we have carried out a laboratory experiment on how P. antipodarum influences the infestation of the intermediate host Radix balthica (a native lymnaeid) by the bird schistosome Trichobilharzia regenti. We found that the co–exposure of 200 P. antipodarum individuals per one R. balthica to the T. regenti miracidia under experimental conditions makes the infestation ineffective. Our results show that a non–host snail population has the potential to interfere with the transmission of a trematode via suitable snail hosts.

Agents of swimmer’s itch—dangerous minority in the Digenea invasion of Lymnaeidae in water bodies and the first report of Trichobilharzia regenti in Poland

Trichobilharzia spp. have been identified as a causative agent of swimmers’ itch, a skin disease provoked by contact with these digenean trematodes in water. These parasites have developed a number of strategies to invade vertebrates. Since we have little understanding of the behavior of these parasites inside the human body, the monitoring of their invasion in snail host populations is highly recommended. In our research, lymnaeid snails were collected from several Polish lakes for two vegetation seasons. The prevalence of bird schistosomes in snail host populations was significantly lower than that of other digenean species. We were the first to detect the presence of the snails emitted Trichobilharzia regenti (potentially the most dangerous nasal schistosome) in Poland. In addition, by sequencing partial rDNA genes, we confirmed the presence of the snails positive with Trichobilharzia szidati in Polish water bodies, showing that swimmer’s itch is more frequent during summer months and that large snails are more often infected with bird schistosomes than small ones.

Ketoprofen-induced inhibition of symptoms of behavioural fever observed in wintering Planorbarius corneus (L.) (Gastropoda: Planorbidae)

Research on behavioural fever in Planorbarius corneus was undertaken using a longitudinal thermal gradient. Before the experiment, snails were acclimated at 19 °C. Following injections of lipopolysaccharide (LPS, a pyrogenic agent), ketoprofen (an antipyretic) or saline solution (control), thermal behaviour of the animals was automatically recorded for 48 h. The results demonstrated that LPS-induced symptoms of behavioural fever were inhibited by ketoprofen. Additionally, it was observed that snails which, before the injection of LPS, were preinjected with ketoprofen showed symptoms of behavioural fever with a 20-h delay. This result shows the inhibitory effect of ketoprofen on the occurrence of behavioural fever symptoms in P. corneus. It may suggest some similarity in mechanism of enhanced thermal preference in snails to vertebrate fever— both effectively inhibited by aspirin-like anti-inflammatory compounds.

A morphological study of Diplodiscus subclavatus (Pallas, 1760) (Trematoda: Diplodiscidae) adults from the accidental host, Viviparus contectus (Millet, 1813) (Caenogastropoda: Viviparidae).

A phenomenon of switching of the parasite in the food chain to an accidental host is commonly observed in nature. However, there is little available data concerning the morphological descriptions of parasites that passively get into the atypical hosts and are capable, at least to some degree, of somatic growth and development of reproductive structures. A morphological survey of Diplodiscus subclavatus (Pallas, 1760) adults isolated from a digestive tract of an accidental host, Viviparus contectus (Millet, 1813), was carried out. Diplodiscus subclavatus individuals identified in prosobranch snails were morphologically similar to adult forms of the parasite described from amphibians, typical final hosts in the life cycle of this paramphistomid. The observed forms of D. subclavatus had a fully developed reproductive system, sperm in the seminal vesicle and oocytes in the ovary. The number of eggs in the uterus ranged from 3 to 17. Our research indicates that D. subclavatus individuals reach the sexual maturity in the accidental, invertebrate hosts.

Can Parasites Change Thermal Preferences of Hosts

Scientific literature provides many examples of parasite-induced changes in thermal preferences of animals. These alterations can be interpreted as a defense response of hosts, a by-product of parasitic invasion or host manipulation aimed at increasing chances of parasite transmission. In this chapter we present an overview of ectothermic host-parasite relationships using snail-parasite, insect-parasite, and fish-parasite interactions to provide an answer to the initial question. Interestingly, in all the above examples (regardless of the systematic position of hosts) the invasion of eukaryotic parasites is correlated with host thermal behavior, benefiting parasites. It should be emphasized that although numerous analysis of this phenomenon sound convincing, without thorough understanding of the molecular basis of thermal behavior of ectotherms they fail to provide sufficient explanation. We are convinced that research on the mechanism of thermal preferences of ectothermic animals in terms of physiology, metabolism, neuromodulation, and immunology will clarify the suggested impact of parasites on thermal behavior of their hosts.