3.3. Pathogenicity
In the pathogenicity study, the different experimental groups ofH. nipponia showed different degrees of death (Figure 4). In groups A and B, the mortality rate of H. nipponia was 100% and the dead leeches showed similar symptoms in accordance with natural diseases. However, there were no diseases or death observed in the control group. K. pneumoniae was isolated from the body of dyingH. nipponia again. Therefore, this experiment abided by Koch’s rule, which showed that K. pneumoniae was the pathogen of this disease in H. nipponia .