Tenacity of mammalian viruses in the gut of leeches fed with porcine blood.

Leech therapy is currently considered to be of high therapeutic value in medicine. However, feeding leeches with fresh animal blood during the maintenance and reproduction phase bears the risk of transmission of zoonotic viruses to the patient. We hypothesize that this would be abolished by subjecting leeches to quarantine measures prior to use. The required duration of quarantine would depend on the maximum survival time of pathogens in contaminated leeches. In order to be able to estimate this survival time reliably, experiments were conducted with enveloped and non-enveloped mammalian viruses possessing either RNA or DNA. Leeches were fed porcine blood contaminated with bovine parvovirus (BPV), feline calicivirus (FCV), equine arteritis virus (EAV) and equine herpesvirus type 1 (EHV-1) and kept in aquaria at 10 °C. From week 6 after feeding onwards, some leeches were held at 30 °C. Before feeding and at different time points thereafter, blood samples were taken from the leeches to determine residual virus infectivity. Prototype mammalian viruses were able to survive in inoculated leeches for considerable periods of time. When leeches were kept at 10 °C throughout, reisolation of infectious virus from the leeches' abdominal cavity blood was no longer possible at 23 (FCV), 23 (EAV), 27 (EHV-1) and 29 (BPV) weeks after inoculation. Shifting the temperature to 30 °C in week 6 slightly reduced the duration of detection of infectious viruses to 15 (EAV and EHV-1), 21 (FCV) and 27 (BPV) weeks. These data indicate that the ability of mammalian viruses to survive in leeches theoretically poses a possible risk for patients unless adequate precautionary measures are adopted. Application of a quarantine period, e.g. 31 weeks (i.e. including an additional safety period) at 10 °C, may be a suitable measure to significantly decrease this risk.