1. Introduction
Hirudo nipponia, commonly known as the leech, belongs to the Hirudinidae and Hirudo families, is widely distributed in Northeast, North and Southwest China (Michalak et al., 2009) and is the main representative species of leeches. Leeches were used to promote blood circulation and eliminate blood stasis. In addition to being an anticoagulant, leeches also showed anti-inflammatory, anti-tumor and anti-fibrosis effects, playing an important role in the prevention and treatment of a variety of diseases(Ahmad, 2006; Rowghani et al., 2007). For example, Hirudin extracted from leech saliva can inhibit blood coagulation and was known as the strongest natural anticoagulant in the world. The effects of Hirudin were stronger than heparin and showed a significant effect on cardiovascular and cerebrovascular diseases(El-Husseiny et al., 2008). There are 10 types of Chinese patent medicines where leeches as the main raw material, that are used to treat many diseases(Mo et al., 2003). In recent years, the living environment of leeches was severely damaged and the number of wild leech population was sharply reduced due to an increase in overhunting(Yu et al., 2020).
To protect wild resources and meet the needs of clinical and scientific research, leeches were artificially bred and cultured. Presently, Russia, the United Kingdom, France and Turkey have large leech breeding industries(Zhang et al., 2010). Leech breeding technology research in China is less prominent, resulting in only a few large-scale breeding enterprises. At the same time, there was low leech reproduction technology, wild leech sources were reduced and the quality of leech seedlings was declining, leading to leech diseases. However, sick leeches may reduce clinical treatment effects and may even bring disease to patients. Yet, there have been few reports on leech disease research in China and abroad. Only some experiments reported diseases related pathogens and conducted drug screenings (Gouda et al., 2006; Hamilton et al., 2005; Zhang et al., 2009; Zhang et al., 2006), but have not evaluated the possibility that leeches may be used as a vector to spread certain pathogens to cause further harm to humans.
From 2016 to 2018, Hirudo nipponia died on farms in the Hubei Province in China. These leeches showed reduced food intake, poor swimming ability, edematous bodies and hyperemia. Dissections revealed that H. nipponia bodies were full of water and eroded, but a parasite infection was not found. Based on a bacteriological study, a number of bacteria was isolated from diseasedH. nipponia , which were collected in different batches and times. Many of the dominant bacteria were identified as the same based on their morphology and dominance. Here, the pathogenicity of the bacteria isolated from H. nipponia was studied. Our results confirmed that pathogenic bacteria caused the disease in H. nipponia and also caused diseases in humans. This provided important methods for the diagnosis and control of this emerging disease from leeches and suggested there may be a risk in Traditional Chinese medicine such as Hirudin.