Eel hemorrhagic open-mouth disease is a viral disease.

[Pathogen] The pathogen of eel hemorrhagic open-mouth disease is a DNA-type virus.

[Symptoms and pathological changes] Diseased eels show severe hemorrhage, mainly in the cranial cavity, followed by hemorrhage in the oral cavity and head muscles. The diseased fish have osteoporosis and are prone to bone fragmentation, with an "open skylight" appearing in the cranial cavity; the connection between the dentary and the articular bone becomes loose, and the mouth often remains open and cannot close. The liver, spleen, and kidney are enlarged, with extreme anemia. Observation of ultrathin sections of the blood of diseased eels reveals virus particles within the blood cells.

[Epidemiology] Cases of eel hemorrhagic open-mouth disease have been reported in Fujian and Guangdong, China. It mainly affects eels over 1 year of age. The disease season is from May to October, with the peak incidence in July and August, and the mortality rate can reach 90%.

[Prevention and control methods] There is currently no effective prevention or treatment method for this disease. The main approach is, on the basis of comprehensive prevention, to spread bactericidal drugs throughout the pond to prevent bacterial infection from worsening the condition.