Causes and Prevention and Control Methods of Duck Hemorrhagic Disease

Duck hemorrhagic disease is an infectious disease caused by a novel herpesvirus (Duck herpesvirus type II) that can infect ducks of all breeds and all ages. Because the feather shafts of both wings, the tip of the upper beak, and the tips of the claws and webbed feet of affected ducks often bleed and appear purplish-black, it is commonly known as duck "black feather disease," duck "black shaft disease," and duck "purple beak and black foot disease"; based on the characteristic necropsy lesions of the disease, it is also called duck hemorrhagic disease. At present, the disease occurs in several southern provinces of China, including Fujian, Guangdong, and Zhejiang, and affected duck flocks are prone to concurrent or secondary bacterial infectious diseases (such as duck infectious serositis, duck colibacillosis, etc.) or viral infectious diseases (such as duckling viral hepatitis, duck influenza, etc.), and is therefore easily overlooked.

1. Epidemiological characteristics

Ducks of all breeds can be infected and develop the disease, but Muscovy ducks are the most susceptible. So far, no other poultry or mammals have been found to develop this disease. The disease mostly occurs in duck flocks aged 10 to 55 days, but ducks in other age groups can also develop the disease. The morbidity and mortality rates vary and are closely related to the age of affected ducks. Within 35 days of age, the younger the duck, the higher the morbidity and mortality rates, sometimes reaching as high as 80%; in duck flocks over 35 days of age with a single infection of this disease, the daily mortality rate is 1% to 1.7% as age increases. The occurrence of this disease has no obvious seasonality, but it occurs more frequently when temperatures drop suddenly or during rainy, cold weather.

2. Clinical symptoms

The characteristic clinical symptoms of this disease are hemorrhage or congestion within the feather shafts of both wings of sick or dead ducks, appearing purplish-black on the outside, and the hemorrhagic blackened feather shafts break and fall off easily. The tip of the upper beak, claw tips, and the peripheral edges of the webbed feet of dead ducks become cyanotic and also appear purplish-black. Yellow liquid flows from the mouth and nose of dead ducks, staining the front end of the upper beak and the feathers around the mouth, and some feathers are even dyed yellow.

3. Necropsy lesions

The characteristic necropsy lesions of this disease are hemorrhage within the feather shafts of both wings and hemorrhage or congestion of tissues and organs. Specifically, the liver is slightly enlarged, showing branch-like hemorrhage or congestion, with occasional individual white necrotic spots; the pancreas often hemorrhages, with petechiae or ecchymoses visible, or the entire pancreas hemorrhaging and appearing red. The small intestine, rectum, and cecum show obvious hemorrhage, and sometimes hemorrhagic rings are visible in the small intestine segment. The spleen, kidneys, brain, and bursa of Fabricius show mild hemorrhage or congestion.

4. Diagnosis

Based on the characteristic clinical symptoms and necropsy lesions of affected ducks, diagnosis is not difficult to make. Confirmation of the disease depends on laboratory methods. Clinically, this disease is easily confused with duckling viral hepatitis, duck plague, duck influenza, duck coccidiosis, breeder duck necrotic enteritis, and other diseases, and should be differentiated based on the clinical symptoms and characteristic necropsy lesions of each disease. Breeder duck necrotic enteritis is a disease that mostly occurs in breeder ducks, more frequently in autumn and winter, and is clinically characterized by weakness, loss of appetite, inability to stand, sudden death, and necrosis of the intestinal mucosa. However, this disease can occur in ducks of different ages, and when breeder ducks develop hemorrhagic disease, in addition to intestinal hemorrhage, the pancreas, liver, kidneys, etc. all show varying degrees of hemorrhage.

5. Prevention and control methods

Different preventive measures can be taken according to different disease onset characteristics. In meat ducks, in some duck farms the occurrence of this disease is mostly concentrated in a certain age range (such as 20 to 35 days of age), while it is rare or absent in other age groups; for this situation, it is only necessary to inject duck hemorrhagic disease hyperimmune yolk antibody (1 to 1.5 milliliters per bird) 2 to 3 days before the susceptible age; while in some duck farms, the disease occurs at a certain age (such as 20 days of age) and above; for this situation, intramuscular injection of duck hemorrhagic disease attenuated vaccine (0.2 to 0.5 milliliters per bird) within 10 days of age is required. For breeder ducks or laying ducks, in addition to immunization together with ducklings during the brooding stage, 10 to 12 days before the start of laying, duck hemorrhagic disease inactivated vaccine (0.5 to 1 milliliter per bird) should be injected subcutaneously on the dorsal side of the neck or subcutaneously in the femoral inguinal region, which can prevent the drop in egg production caused by this disease.

When this disease occurs in a duck flock, in addition to strengthening feeding management and disinfection, duck hemorrhagic disease hyperimmune yolk antibody (1.5 to 3 milliliters per bird) should be injected as early as possible, and broad-spectrum antibacterial drugs should be administered simultaneously to prevent secondary bacterial infectious diseases.