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06 December 2016

Establishment of the Scottish Schistosomiasis National Advice, Investigation and Liaison Group (SNAIL).

Background to Scottish context

Schistosomiasis is the most frequently reported parasitic disease in Scottish travellers. Infection occurs following contact with fresh water where free-swimming cercariae released from snail hosts penetrate human skin and migrate to reproduce in the liver portal system. The adult worms then migrate to the venules surrounding the bowel and bladder where they release eggs into the lumen of the bowel and bladder. Human infection can result in acute symptoms (Katayama fever); early signs of chronic infection such as haematuria, dysuria, abdominal pain; or genital lesions due to egg migration and granuloma formation; or remain asymptomatic. In endemic regions, untreated infection following years of exposure results in late complications with significant morbidity and mortality such as portal hypertension, bladder calcification and squamous cell carcinoma of the bladder. These complications are rarely seen in travellers who tend to have low burdens following isolated exposures. The long term sequelae of chronic low level infection in travellers are largely unknown.

Affordable air travel and continuing partnerships between Scotland and Malawi/Uganda ensure a steady flow of travellers, often school or university groups, to these regions to participate in water-based activities. This has led to an increase in exposure to the infective cercariae over recent years. The number of imported cases in Scotland is higher than the rest of Europe with an average of 155 cases since 2011. Due to the predominantly asymptomatic nature and the lack of awareness of the disease, it is likely that the number of cases is significantly underestimated (Data extracted from ECOSS).

Diagnosis and Management

Diagnostic testing for schistosomiasis relies largely on serology testing which provides a robust, reliable and cost-effective method to screen individuals with a history of exposure in high-risk areas. Blood samples should be taken 8-12 weeks post exposure as earlier serology can provide a false negative result. In addition to serological testing, microscopy can also be performed on stool and urine specimens, looking for ova and viability testing any ova present.

No standardised procedure currently exists in Scotland for the testing of patients for schistosomiasis. Variation exists between Scottish NHS boards regarding the timing of sampling, follow-up testing and treatment protocols, and no surveillance data is available. Limited data from Lothian cases where follow-up testing is performed more frequently than in other NHS boards has highlighted the existence of late sero-conversion resulting in positive cases being mis-diagnosed as negative during preliminary screening. Without follow-up testing, these patients would not have received any treatment despite having the disease, and would therefore have been potentially at risk of associated detrimental long term conditions.

In addition, testing and treatment protocols vary depending on local infectious diseases (ID) clinic and there is an enthusiasm to standardise this.

The Liaison Group

The group has formed, chaired by Claire Alexander from the Scottish Parasite Diagnostic Reference Laboratory (SPDRL), and comprising representation from across the relevant fields (including ID, Public Health, Diagnostics, HPS, Parasitology, Primary Care).

During the inaugural meeting of the group in May 2016, aims/outputs and governance were discussed.

In summary:

Aims of the Group

  • to raise awareness of schistosomiasis, particularly amongst higher risk groups;
  • to create a single national testing algorithm to ensure standardisation across Scotland;
  • to draft clinical guidance on best practice in screening, diagnosis and management for use by clinicians (and others) across NHS Scotland;
  • to explore the possibility of an enhanced surveillance system for schistosomiasis cases.

First Steps

As part of the work of this group, and to help inform clinical guidance development, a service evaluation audit is being progressed in a collaboration between Lothian Regional ID Unit, SPDRL and HPS. This involves assessing the benefit and timing of repeat schistosomiasis serology post treatment in returned travellers to establish a) if a reduction in antibody level is seen, and b) the time point at which repeat serology may show any meaningful reduction.

This information will help guide the follow-up of treated patients and may help identify those who require further treatment, for example if some antibody levels fall, and some do not, future evaluation could determine whether this correlates with treatment failure.

Cases will be identified and the data on antibody levels will be supplied to HPS (with patient identifiers removed) by SPDRL. The approximate date of treatment will be determined by examination of the clinical records by clinical staff in Lothian. The data will be stored, collated and analysed on computer (with no patient identifiable information) in HPS.

Governance and Reporting

Oversight of development of the algorithm and clinical guidance will fall under the newly formed ID Clinical Network. Regular updates on progress and outputs will be brought to the Scottish Immunisation Programme Implementation Group, part of the Scottish Health Protection Network, as appropriate and/or requested.

Further information on the work of the group can be obtained from the Travel and International Health Team at HPS (Tel: 0141 300 1137 or email:

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Vol: 50 No: 49 Year: 2016 Page:


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