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.