Evidence for a permanent presence of schistosomiasis in Corsica, France, 2015

ECDC comment

​The study of Berry et al. reports a single case of acute infection of urinary schistomiasis probably acquired through bathing in the Cavu River in Corsica in summer 2015. It is the first reported case in Corsica with exposure in 2015.

Berry A, Fillaux J, Martin-Blondel G, Boissier J, Iriart X, Marchou B, Magnaval F, Delobel P. Euro Surveill. 2016;21(1):pii=30100.

The study of Berry et al. reports a single case of acute infection of urinary schistomiasis probably acquired through bathing in the Cavu River in Corsica in summer 2015. It is the first reported case in Corsica with exposure in 2015.

The patient presented with a 15-day history of diffuse abdominal pain, headache and asthenia late August-early September 2015. He reported bathing twice in the Cavu River on 30 July and 11 August 2015 and had no history of bathing in other rivers in Corsica or staying in or travelling to known endemic areas of schistosomiasis. At the first consultation on 11 September in the University Hospital Center of Toulouse (France), the patient had a blood eosinophilia (3.2 × 109 cells/L, normal range:  0.5 × 109 cells/L) and a negative serodiagnosis of schistosomiasis. The serological follow-up during further medical consultations in September and October 2015 demonstrated an increase of Schistosoma antibodies consistent with a seroconversion. Detection for eggs in the urine remained negative on 15 and 26 October 2015.
 
The compatible timing between potential exposure and clinical symptoms, the transient blood eosinophilia, the positive results from three immunodiagnostic tests (ELISA, IHA and Western blot), and the negative results of serodiagnosis for other helminthiases support the diagnostic of an acute schistosomiasis infection. The patient was treated by a single dose of praziquantel (40 mg/ kg).
 
The patient’s family members (four persons) sharing the same exposure in the Cavu River were investigated. Three of them had unremarkable results and one child had discrepant immunodiagnostic results for schistosomiasis. Despites inconclusive serodiagnosis, the child was treated with a single dose of praziquantel (40 mg/kg) and serological follow-up is on-going.
 

ECDC comment: 

This article reports a case of human schistosomiasis probably acquired through bathing in the Cavu River in Corsica in summer 2015.  From the screening program lead by the French health authorities and launched in the aftermath of the local schistosamiasis transmission in 2013 linked to exposure to Cavu River, almost 37 000 individuals were investigated and around 120 cases of autochthonous schistosomiasis were diagnosed in France [1].
 
Possible transmission linked to Cavu River has also been reported before 2013, and in 2014 – despite there being a swimming ban in place in 2014 – and surrounding rivers in southern Corsica (see last ECDC Rapid Risk Assessment on Local transmission of Schistosoma haematobium in Corsica, July 2015). However, the diagnostic confirmation of schistosomiasis infection was questioned by experts taking into account that the standard for confirmation of urinary schistosomiasis is identification of eggs by microscopic examination of urine samples. Applying this criterion, only one case with exposure in 2013 in the Cavu River can be classified as confirmed [2-4].
 
The occurrence of Schistosoma haematobium infection in the Cavu River in 2015 is not unexpected as Bulinus snails, which can serve as intermediate hosts for S. haematobium, were found there in 2014 and because the river was the focus of an outbreak in 2013. However, the risk in Corsica would need to be re-evaluated in the light of further investigations and research findings ahead of the summer season 2016 for the Cavu River and other receptive areas where the intermediate host has been found during the malacological surveys [5,6].
 
The origin of the parasite remains unclear and more molecular investigations are needed to understand the epidemiological observations. Molecular information is limited  to a single publication based on one early case showing that the 2013 schistosomiasis cluster in Corsica was due to a genetic variant of S. haematobium having genes from S. bovis through introgression which is shown to be related to African strains [7].
 
The introduction of the parasite into a receptive area could have been caused by travellers, personnel returning from deployments or immigrants from endemic areas, who have acquired the infection while in endemic areas.
 
Recurrent seasonal foci of transmission of S. haematobium or S. haematobium/S. bovis could occur through the persistence of the parasite in the environment within intermediate hosts during the winter, but this is unlikely due to the weather conditions. In addition, there is a theoretical possibility that the hybrid parasite S. haematobium/S. bovis identified in Corsica could be reintroduced from an animal reservoir, although ongoing investigations have not substantiated this hypothesis to date [5 ]. The re-introduction in receptive areas from an individual either infected abroad or infected locally in a previous season is suggested as a likely hypothesis by the authors of the case report [1]. This hypothesis cannot be assessed through molecular assay as no parasite eggs where retrieved during medical consultations.
 
The study of Berry et al. confirms the need to maintain awareness among clinicians of the possibility of schistosomiasis among travellers presenting with unexplained chronic urinary symptoms or blood eosinophilia that have engaged in previous years in recreational water activities in receptive areas of southern Europe and particularly in the Cavu River since 2013 [1]. This case report highlights the importance of multiple serological tests to follow up a potential urinary schistosomiasis sero-conversion in the absence of identifying eggs in urine and negative results of serodiagnosis for other helminthiases. The conclusions and options for prevention and control from the Rapid Risk Assessment on Local transmission of S. haematobium in Corsica, France 24 July 2015 remain valid.
 
Thorough investigation of cases remains of primary importance to confirm the diagnosis. This includes sending samples to reference laboratories for, especially, serological assessment, documenting time and location of bathing exposure and informing the relevant national and regional health authorities and ECDC about the findings of the investigation of the cases to facilitate risk assessment and implementation of public health prevention and control measures.
 
Comments or questions on this Scientific Advance are welcome and should be addressed to: evd@ecdc.europa.eu.