They do be in a "Near Threatened" state due to medicinal uses.
"Manchester Royal Infirmary used 50,000 leeches a year in 1831. The price of leeches varied between one penny and threepence halfpenny each. In 1832 leeches accounted for 4.4% of the total hospital expenditure. The hospital maintained an aquarium for leeches until the 1930s.[15] The use of leeches began to become less widespread towards the end of the 19th century."