2.1. Parasite material

Faecal samples from companion animals were obtained from the University of Glasgow’s Veterinary Diagnostic Services (VDS). This comprised samples sent to the laboratory to investigate infectious causes of diarrhoea in animals attending a variety of veterinary clinics primarily in the UK between January 2018 and June 2021. DNA extracts of companion animal faecal samples, which were found to be Giardia-positive by a diagnostic RT-qPCR (Verweij et al., 2003), were retained for the present study and were stored at −80 ​°C. A total of 174 feline and canine samples with Ct-values ranging from 17 to 39 were collected.

Human faecal samples containing Giardia were obtained from the national Reference Laboratory collection within the Scottish Microbiology Reference Laboratories, Glasgow (SMiRL) which forms part of the National Health Service (NHS) in Scotland. Surplus samples were tested via Giardia lamblia antigen-based EIA (Catalogue number GL2-96, Launch Diagnostics, Kent, UK) that had been submitted for routine parasite investigations, therefore no additional samples were requested. Samples were fully anonymised, and no patient identifiers were released to protect patient confidentiality. A total of 79 human faecal samples submitted from Scottish cases between September 2019 and March 2020 were collected and stored in Faeces Stabilisation Buffer (Stratec, Birkenfeld, Germany) at −4 ​°C before DNA extraction for the present study.

Seven known positive DNA extracts were selected from VDS stock to optimise the newly designed primers. Four canine and three feline samples with Ct-values ranging from 17 to 33 were selected to span the range of Ct-values and represent the main species for which samples are processed by the VDS.