Duck Viral Enteritis

(Duck plague) Duck viral enteritis is an acute, highly contagious disease of ducks, geese, and swans of all ages, characterized by sudden death, high mortality (particularly among older ducks), and hemorrhages and necrosis in internal organs. It has been reported in domestic and wild waterfowl in Europe, Asia, North America, and Africa. Economic losses on domestic duck farms have been limited to serious, and sporadic die-offs in wild waterfowl have been limited to massive. Etiology: Field strains of the causative herpesvirus are similar antigenically but vary considerably in pathogenicity. The virus is relatively sensitive to heat and pH and is inactivated by lipid solvents, trypsin, and chymotrypsin. It causes intranuclear inclusion bodies in infected tissues and in inoculated cell cultures. In nature, the virus is mainly transmitted from infected to susceptible ducks by direct contact or water and is acquired mainly by the oral route. Parenteral, intranasal, or oral administration of infected tissues can establish experimental infection. Recovered birds may remain carriers and serve as uncontrolled sources of the virus for susceptible ducks. Clinical Findings: The incubation period is 3-7 days. Sudden high and persistent mortality is often the first sign of the disease. Mortality may vary from 5 to 100% depending on the virulence of the infecting viral strain. Photophobia, inappetence, extreme thirst, droopiness, ataxia, nasal discharge, soiled vents, and watery or bloody diarrhea may be seen. Dead males may have prolapse of the penis. Adult ducks may die in good flesh. In contrast, ducklings frequently show dehydration and weight loss, as well as blue beaks and blood-stained vents. Adult ducks usually die in higher proportions than young ones, which increases the economic significance of the disease. In laying flocks, egg production may drop sharply. Lesions: Lesions indicate serious damage to blood vessels throughout the body. There are hemorrhages in various tissues and free blood in body cavities. Petechial and ecchymotic hemorrhages on the heart (“paintbrush” appearance), liver, pancreas, mesentery, and other organs are characteristic. Specific mucosal eruptions, found in the oral cavity, esophagus, ceca, rectum, and cloaca, undergo progressive alterations during the course of the disease. Initially, macular hemorrhages develop into elevated, yellowish, crusted plaques and organize into green, superficial scabs, which may coalesce into large, patchy, diphtheritic membranes. The mucosal lesions align parallel with the longitudinal folds in the esophagus and with the annular bands in the intestines. All lymphoid organs are affected; necrosis and hemorrhages are apparent. A clear, yellow fluid infiltrates and discolors the subcutaneous tissues from the thoracic inlet to the upper third of the neck. Ruptured yolk and free blood may be found in the abdominal cavity of laying ducks

A presumptive diagnosis is based on disease history and lesions. Isolation of a virus that fails to propagate in embryonating chickens, on chorioallantoic membrane of susceptible embryonating duck eggs, or in duck-embryo fibroblast cell culture, and that produces mortality and characteristic lesions when inoculated into day-old ducklings is highly suggestive. Neutralization with specific antiserum confirms the identity of the virus. Differential diagnoses include duck viral hepatitis, pasteurellosis, necrotic and hemorrhagic enteritis, trauma, drake damage, and various toxicoses. Newcastle disease, avian influenza, and fowl pox may cause similar lesions, but they are rarely reported in ducks. Established cases should be reported to the appropriate regulatory agency.

Prevention, Treatment, and Control:

There is no treatment. Prevention is based on maintaining susceptible birds in a disease-free environment. Contact with wild, free-flying waterfowl and direct or indirect contact with contaminated birds or material (free-flowing water) should be avoided. Control is effected by depopulation, removal of birds from the infected environment, sanitation, and disinfection. A chicken-embryo-adapted, modified live virus vaccine has been approved for use in domestic ducks, in zoological aviaries, and by private aviculturists. A 0.5 mL dose is administered SC or IM to domestic ducklings >2 wk old, with a booster inoculation 1 yr later. The vaccine is not approved for use in wild ducks.