Viral infection risks for patients using the finished product Hirudo verbana (medicinal leech)

The virological safety of medicinal leeches has to be ensured prior to their use on patients. While leeches can be kept and bred under standardized conditions, feeding them horse blood adds a non-standardized component, which poses some risk of infection of the treated patients. Here, we investigated the speed at which blood-borne viruses are degraded by the microbial flora in the leech intestine, in order to define the safety of the product and the length of the necessary quarantine period prior to its administration to patients. Feeding blood was spiked with bovine viral diarrhea virus (BVDV), reovirus, and murine parvovirus (10(7) ID₅₀ ml(-1)). The virus titer in the intestinal contents of the leeches was determined using permissive cell cultures and compared to that of the original virus titer at the following time points: immediately after feeding; after 3, 14, and 30 days; and monthly thereafter until the 7th month. The BVDV titer was below the detection limit of 10(1) TCID₅₀ ml(-1) after 3 months, while reovirus and murine parvovirus titers were undetectable after 4 months. No positive virus findings were obtained at later time points. Thus, when fed the blood of vertebrates, the finished product "Medicinal leech, Hirudo verbana" can be considered virologically safe if the animals are maintained at 20 °C, which corresponds to their natural habitat conditions and ensures a high metabolic rate. Therefore, after the last feeding, a quarantine period of 4-6 months and appropriate care at room temperature, which supports microbial degradation and digestive processes, are recommended.