Europe parasite outbreak source traced using Museum specimens
Genetic analysis involving Museum scientists reveals that an outbreak of the neglected tropical disease schistosomiasis in Corsica was caused by parasites introduced from West Africa.
In research led by the University of Perpignan in France, Schistosoma parasite eggs and larvae were collected from urine samples of the infected patients.
DNA from these samples was then compared with that of Schistosoma parasite material stored in the Museum's SCAN collection. As a result, researcher Dr Bonnie Webster showed that the species present in Corsica were typical of an area of Senegal, West Africa.
The research, which appears in the Lancet Infectious Diseases journal, suggests that schistosomiasis was introduced to Corsica via infected individuals from Senegal.
Dr Webster says, 'The vast majority of schistosomiasis cases occur in Africa. However, this recent outbreak in Corsica demonstrates the potential for forms of this debilitating and potentially deadly infectious disease to become rapidly established in Europe.
'Our findings clarify how this outbreak happened and highlight freshwater areas that should be monitored closely for further transmission. They also point to the need for increased awareness among medical professionals of the potential presence of infection in Europe.'
Schistosomiasis is caused by parasitic flatworms (schistosomes) that live in the blood vessels of a vertebrate host. More than 200 million people worldwide are infected, 85% of whom live in Africa.
Schistosomiasis has an extremely high death rate. Aside from more immediate symptoms such as bloody urine and fever, patients with the disease often suffer severe organ damage later in life.
There are many different species of schistosome. However all of their complex life cycles require a body of fresh water and a vertebrate host, with aquatic snails as an intermediate host. One such snail species is found in lakes, rivers and reservoirs across the southern Mediterranean.
'The presence of this snail in Corsica, along with introduction of the parasite via human transport, made it possible for schistosomiasis to spread into a previously uninfected area,' says Dr Webster.
The Corsican schistosomiasis outbreak first occurred in 2013. An awareness campaign to diagnose infections and eliminate transmission followed, but the disease was still present in 2015. The island is a popular holiday destination, and many of the infected patients were tourists or summer workers.
Drafted in to determine the source of the outbreak, specialists from the University of Perpignan called on Museum experts to help identify the schistosome species.
An invaluable collection
The Museum's SCAN collection is one of the largest and most comprehensive collections of schistosomiasis material in the world. It contains snails, larvae and schistosome worms from a range of species and locations, over a time period spanning the last 30 years.
Museum researchers like Dr Webster have developed unique expertise in identifying and characterising schistosome parasites. This expertise is particularly important in determining the cause and effects of infection and transmission in the case of an outbreak.
Dr Webster says, 'SCAN acts as a reference collection. It allows us to match up the genetic fingerprint of schistosome species to areas where it is typically found, as well as to emerging areas of transmission.
'Each species is found in particular geographical areas, and some exhibit specific genetic differences that can help us to trace where they came from.'
The schistosome species found in Corsica was found to have an extremely close genetic link with species from Senegal. Dr Webster and colleagues have genetically characterised these African schistosomes in the past.
Species and hybrids
There are three main species of schistosome known to infect humans and other vertebrates. One - Schistosoma haematobium - is only found in humans and causes urogenital schistosomiasis, which affects the urinary tract and genitals. Many of the patients in Corsica were infected with this species.
Schistosomiasis disease transmission is most easily achieved through the transport of livestock. Since S. haematobium doesn’t appear to infect livestock, it was considered unlikely that urogenital schistosomiasis would spread beyond established populations in Africa and the Middle East.
The outbreak in Corsica shows that schistosome species considered low-risk in Europe are actually very capable of being transported by humans and thriving there.
Dr Webster and her colleagues found another surprising form of schistosome in Corsica - a hybrid.
The hybrids are a cross between S. haematobium, which uses humans as a host, and another species that uses cattle. The implications of this are very important in terms of disease transmission risk.
'Some patients were infected with a combination of the human and bovine species of schistosome that had bred together to form a viable hybrid,' explains Dr Webster. The hybrid can infect a wider range of intermediate snail hosts, increasing the potential for schistosomiasis transmission.
Treatment and raising awareness
The drug Praziquantel is an effective treatment for schistosomiasis, and is used widely in severely affected areas around the world. But people infected with schistosomiasis may have mild symptoms, or indeed none at all. This makes it difficult to trace the onward transmission of the disease, and puts those infected at risk of more serious complications.
If left untreated, urogenital schistosomiasis can cause liver disease, female infertility, kidney failure and bladder cancer later in life. It can also cause neurological problems.
In Corsica, patients who came forward with symptoms are being treated with Praziquantel, but it is likely that there are many who have not been diagnosed. Researchers hope to inform health professionals across Europe of the presence of schistosomiasis on the continent. They want to encourage them to look for symptoms of the disease and check where patients have travelled.