Aquatic molluscs as auxiliary hosts for terrestrial nematode parasites: implications for pathogen transmission in a changing climate

Abstract

Nematodes are common parasites of molluscs but are often overlooked. Both metastrongyloid and rhabditoid species dominate the fauna within land snail and slug populations. Nevertheless, a key characteristic of many laboratory studies is the ability of these terrestrial nematodes to utilize aquatic molluscs as auxiliary hosts. The significance of this to the ecology of the parasite has never been evaluated. There is increasing concern as to the impact of climate change on the epidemiology of many parasitic diseases. In particular, it has been suggested that host switching may increase under the pressure of extreme climatic conditions. It is therefore timely to assess the role that aquatic molluscs may play in transmitting terrestrial nematodes, which include species of medical and veterinary importance such as Angiostrongylus cantonensis, A. vasorum, and Muellerius capillaris. The present review assesses the mechanisms of terrestrial nematode transmission through aquatic molluscs focusing on metastrongyloid and rhabditoid species, the importance of variable susceptibility of molluscan hosts, field studies on natural occurrence within aquatic habitats, and the impact of extreme climatic events (floods and droughts) that may increase in frequency under climate change.

Effect of temperature on activity of third-stage larvae of Angiostrongylus vasorum

“…This report is consistent with literature showing that climate and temperature play an important role in aspects of parasite transmission such as dynamics and the activity of the intermediate host and parasite development in the intermediary host (Jenkins et al 2006;Ferdushy et al 2010;Morgan et al 2010;Morley 2010). …”

“…Consequently, their survival is dependent on a range of environmental factors. These L1 infect several species of terrestrial and aquatic snails (intermediate hosts) by ingestion and/or penetration (Rosen et al 1970;Guilhon and Cens 1973;Thiengo 1996;Grewal et al 2003;Morley 2010). After two molts, the third (L3) infective stage remains in the tissues of the snail or can be actively released into the environment, especially under light and/or thermal stimulus (Barçante et al 2003).…”

“…Survival is related to declining energy reserves. Metabolic rates increase dramatically after a few weeks in water (Morley 2010). A. vasorum have free-living and intermediate host stages, the development and survival of which are strongly affected by temperature, water availability, and, consequently, local climate, and L3 may survive for many days or even months in fresh water (personal observation; Barçante et al 2003).…”

The complete mitochondrial genome of the rodent intra-arterial nematodes Angiostrongylus cantonensis and Angiostrongylus costaricensis

“…require intermediate hosts to complete their life cycle (Anderson 2000). Terrestrial mollusks, such as snails and slugs, normally play this role, but some freshwater snails have been found to be particularly important for the transmission of angiostrongyliasis (Yousif and Lammler 1975;Morley 2006;Lv et al 2008Lv et al , 2009a. Most of them are highly specific with regard to their definitive rodent host species and even intermediate mollusk hosts, althouth cross infections have been observed (Lv et al 2008).…”

The ecology, evolution, impacts and management of host–parasite interactions of marine molluscs

“…Due to the commercial value of cultivated species, much more attention has been given to their parasites and diseases than those of wild populations (Hine and Thorne, 2000;Carnegie, 2009;Morley, 2010a;Lafferty et al, 2015). Nevertheless, in instances where the diseases of cultivated molluscs have been compared to wild populations, often of the same species and growing alongside, the two groups often display very different patterns of infection (e.g., Wilkie et al, 2013;Lafferty et al, 2015).…”