The first whole genome analysis of a species of freshwater snail could help end chronic intestinal schistosomiasis in humans - a parasitic disease second only to malaria in its impact on global human health.
With significant input from teams at Brunel University London, more than 100 scientists across the world have sequenced and analysed the genome of Biomphalaria glabrata, with results published in Nature Communications.
This neotropical gastropod is commonly found in standing water or freshwater in South America, with related species responsible for parasite transmission in sub-Saharan Africa.
While we know the snails are instrumental in the transmission of the parasitic flatworms responsible for schistosomiasis infections in humans, the species’ complex molecular underpinnings had until now not been well understood.
Infected snails release the parasite as free-swimming larvae which penetrate human skin, mature into adult worms, reproduce in veins surrounding the intestines and then release eggs, resulting in diarrhoea, pain, vomiting, and often chronically debilitating damage to organs including the bladder, kidneys, liver and lungs.
Led by Professor Coen Adema from the University of New Mexico, researchers have uncovered vital information on Biomphalaria glabrata’s biology, which could contribute toward snail control and aid the World Health Organisation’s goal of eliminating schistosomiasis by the year 2025.
Their study explored aspects of immune function, pheromone perception, regulation of gene expression and stress responses in the snail, which may explain why and how the species is a suitable host for the Schistosoma mansoni parasite.
Analysis showed that the snails have a multi-faceted, complex, internal defence system which must be evaded or negated by parasites to successfully establish infection. But, surprisingly, the study found that the antimicrobial peptide arsenal of the snail was reduced compared to other invertebrate species.
Brunel’s research teams focused on identifying genes related to steroid production, identifying that Biomphalaria glabrata cannot process cholesterol to make vertebrate-like steroids, and the snail also appears to lack the aromatase enzyme required for the formation of estrogens.
Further, Brunel scientists were responsible for finally characterising all the snail's chromosomes making up its genome, an achievement that has not be completed before, after 50 years of trying.
These new biological insights will help researchers better understand how the snails modify their internal environment in the face of environmental and pathogenic challenges. Genetic information could also, for example, help with the development of tailored mollusc pesticides to selectively control reproduction or metabolism in Biomphalaria snails.
Researchers believe that the pheromone-based communication system that snails use to interact with each other, may have a ‘trade-off effect’ by potentially exposing the snail as a target for parasites.
Researchers suggest that by targeting aspects of this communication in Biomphalaria snails, mating dynamics could be changed, or the ability of parasitic flatworm larvae to find a host could be affected. Modification of identified ‘clock’ genes could also interrupt circadian rhythms, affecting feeding and egg-laying behaviour.
Information could also be applied to characterise and track various snail populations in related snail species from the Biomphalaria family, found in sub-Saharan Africa, which differ in their effectiveness of parasite transmission.
In 2015, some 250 million people were affected by schistosomiasis, with deaths estimated at between 4,400 to 200,000 people each year. In the absence of a vaccine, the WHO strategy recognises both targeting of snail hosts, and mass drug administration to human populations as crucial in eliminating the disease.
Work on ‘Whole genome analysis of a schistosomiasis-transmitting freshwater snail’ at Brunel University London was conducted by Dr Joanna Bridger, Dr Halime Arican-Goktas, Dr Anne Lockyer, Professor Susan Jobling, Dr Edwin Routledge and Dr Satwant Kaur from the Institute of Environment, Health & Societies, with Yusuf Mohammed from the University of Oxford and Emanuela Volpi at the University of Westminster.
Brunel research was funded by NC3Rs (a partnership with the University of Aberdeen) and National Institutes of Health (NIH) in collaboration with Professor Matty Knight, University of the District of Colombia.
Further UK research teams were based at the Universities of Aberdeen, Aberystwyth, Kingston, and the Natural History Museum.
Read more on BBC News
Sarah Cox, Media Relations