Lampreys play no role as an intermediate host for diseases, which may infect humans. Although, the mucus produced by the lamprey s skin is poisonous. One of the best known parasites on fish is the Argulus or fish louse. This is found on some species of eels. This parasite injects a poison, which irritates the tissues, causing inflammation.
Some small fish can t handle even a couple of Argulus and loose consciousness and die.
Most Lampreys have a parasitic relationship between other fish species. In most cases the lamprey doesn t kill the fish which it has latched onto. If the fish dies then the lamprey would have to locate another food source. Generally the fish a lamprey preys on are salmon and trout which are also a popular fish species for humans. Provided below are two phylogenetic trees.