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Slave trade brought deadly parasite to the Caribbean

Schistosoma mansoni, a water-borne parasite that affects millions of people worldwide, was carried to the Americas by the slave trade, researchers have found.

A genomic analysis of specimens from the Museum's schistosomiasis collection shows that S. mansoni flatworms in the Caribbean split from their counterparts in West Africa between 250 and 900 years ago.

'This overlaps with the time of the sixteenth to nineteenth-century Atlantic slave trade,' says Professor Joanne Webster from Imperial College London, who collaborated on the research.

'During this period more than 22,000 African people were transported from West Africa to Guadeloupe by French slave ships, and the parasite was carried with them.'

Deadly parasite

Infection with S. mansoni causes a disease called schistosomiasis, also known as bilharzia, which can lead to irreversible organ damage and kills more than 11,000 people each year.

With the right treatment programme, however, the disease is both curable and preventable.

In the current study, published in Nature's Scientific Reports, a team from the Wellcome Trust Sanger Institute, Imperial College London and the Royal Veterinary College compared the genetic sequence of S. mansoni parasite specimens in the Museum's collection gathered from across Africa and the Americas.

By looking for genetic changes in schistosome populations, such as those caused by the parasites' move to the Caribbean, researchers can better understand how to diagnose and control the disease.

'If we can track the genetic diversity of parasite populations through time, we can monitor how the parasites respond to various treatment strategies,' says Museum researcher Dr Aidan Emery, who manages the schistosome collection.

The Museum is continuing to develop the collection to create a global repository of schistosomiasis-related specimens to support this work.

The drug praziquantel is currently the only treatment for schistosomiasis, so monitoring the potential spread of drug resistance genes is one crucial application of research using the collection.

Genetic adaptations

As well as discovering the parasites' link to the slave trade, the new research found genetic variations that may have helped schistosomes infect humans.

By comparing the genome of S. mansoni to the genome of its closest relative, S. rodhani, which infects rats, the team found important differences in two genes - VAL21, and an elastase gene.

'VAL genes produce proteins that cause allergic responses, so it is possible that the variation in VAL21 helps the parasite to hide from our immune systems,' says Dr James Cotton from the Sanger Institute, senior author of the study.

'The elastase gene helps the parasite to burrow in to the body, by breaking down elastin - a major component of human skin.'

A better knowledge of the schistosomes' genetic makeup could lead to new treatments that target these adaptations, and help eradicate schistosomiasis around the world.

'This project illustrates the strength of our collections in enabling research,' adds Dr Emery. 

'Schistosomes cause a disease with a major impact, and collecting them is really challenging. It is vital that we continue to acquire and provide specimens that allow us to address new questions that are emerging as we learn more about the parasite.'