Detailed Explanation of the Harm Caused by Duck Influenza and Comprehensive Prevention and Control Methods

Duck influenza is a highly lethal infectious disease caused by type A influenza virus that can infect ducks of all breeds and all ages, and it is currently the most serious disease harming the @#@231@#@ industry.

1. Epidemiological characteristics

In the past, people generally believed that waterfowl were only carriers of influenza virus and did not become ill. However, since the mid-1990s, the fact that ducks infected with highly pathogenic influenza virus became ill and died broke the traditional understanding of duck influenza. Ducks are not only highly susceptible to influenza, but can also horizontally transmit it to terrestrial poultry and become a source of infection for their influenza. This is a trend that should be taken very seriously at present.

Sick poultry, dead poultry, and apparently healthy virus-carrying poultry with avian influenza are all sources of infection for the disease. This disease can be transmitted vertically and horizontally (through contaminated water sources, air, birds, duck traders, etc.). Ducks of all breeds can be infected and become ill, but Muscovy ducks are the most severely affected. Ducks of all ages can be infected and become ill, but clinically, disease is more commonly seen in duck flocks aged 20 days or older. The morbidity and mortality of affected duck flocks are related to the duck breed, age, virus subtype (virulence), and the presence or absence of concurrent or secondary infections. The morbidity of ducklings can be as high as 100%, while the mortality rate is 30%-95%. Infected ducks die within 1-3 days after the appearance of symptoms. Breeding ducks and layer ducks have relatively lower morbidity and virus rates, mainly manifesting as abnormal egg production.

The disease occurs throughout the year, but is more common from November of each year to April or May of the following year. Duck flocks affected by the disease are prone to concurrent or secondary infection with duck infectious serositis, duck colibacillosis, duck paratyphoid, duck cholera, and duck coccidiosis. In duck flocks with concurrent or secondary infection with other diseases, the virus rate is significantly increased.

Meat ducks, layer ducks, and breeding ducks under different rearing methods (floor or wire-floor rearing, confined or free-range rearing, single-species rearing or mixed chicken-duck rearing) all experience disease and death, only with differences in morbidity and mortality levels. Regular monitoring of the distribution of avian influenza virus in the bodies of ducks and other waterfowl and in their environment (water) is of great significance for preventing and controlling the occurrence and spread of avian influenza.

2. Clinical symptoms

In meat ducks, affected ducks show severe depression, mostly squatting with eyes closed; various neurological symptoms (twisted neck in an "S" shape, top of the head touching the ground, opisthotonus, lying on the side, reckless charging, ataxia, etc.); swollen head; tearing, with wet eye rings and red eyes; difficulty breathing (open-mouth breathing or gasping); in acutely dead sick ducks, cyanosis or hemorrhage can be seen in the upper beak and foot webs; diarrhea (white or greenish droppings). Sick ducks infected with moderately virulent influenza virus or partially immune ducks show emaciation and stunted growth.

In layer ducks and breeding ducks, among layer ducks or breeding ducks that have started laying affected by the disease, 15%-90% of ducks do not lay eggs, resulting in a sharp drop in the laying rate of the entire flock (for example, from 95% to about 10% or complete cessation of laying), abnormal eggs (soft-shelled eggs, rough-shelled eggs, thin-shelled eggs, shell-less eggs, deformed eggs, etc.), no laying peak or persistently low laying rate, and low mortality (daily mortality 0.1%-3% or no deaths).

3. Necropsy lesions

In meat ducks, dead ducks mainly show large amounts of caseous material or hemorrhage in the respiratory tract (trachea, bronchi), pulmonary hemorrhage or congestion; pancreatic hemorrhage, with large numbers of pinpoint white necrotic points (or necrotic patches) on the surface, or transparent-like (or liquefactive-like) necrotic points and necrotic foci; hemorrhage in the coronary fat and myocardium, with white striated necrosis in the myocardium, pericarditis, and pericardial effusion; focal ulcers in the proventricular mucosa; hemorrhage or hemorrhagic rings visible in the intestinal mucosa (duodenum, jejunum, rectum, etc.), and hemorrhage in the fat on the outer wall of the intestine. In addition, meningeal hemorrhage, focal necrosis of brain tissue, and swelling, hemorrhage, or congestion of the liver, spleen, and kidneys may also be seen. In sick ducks infected with moderately virulent influenza virus or partially immune ducks, the pectoral muscles and leg muscles are obviously underdeveloped, and the sternum becomes soft.

In layer ducks or breeding ducks that have started laying affected by the disease, in addition to the lesions seen in meat ducks, there are also severe congestion and hemorrhage of the follicular membrane, hemorrhage and edema of the oviduct mucosa with bean-dreg-like clots attached, and in some sick (dead) ducks, follicles may even rupture into the abdominal cavity.

4. Diagnosis

A preliminary diagnosis can be made based on the characteristic clinical symptoms and necropsy lesions of the disease.

Regarding differential diagnosis of the disease, in ducklings attention should be paid to distinguishing it from duck viral hepatitis, which is characterized by enlarged liver, punctate or petechial hemorrhage on the surface, and enlarged and hemorrhagic kidneys; for Muscovy ducklings, the disease is very easily confused with "three-week disease." Muscovy ducklings with "three-week disease" generally have no neurological symptoms and no characteristic lesions of the myocardium and pancreas seen in influenza sick (dead) ducks; for meat duck influenza cases with three inflammations (pericarditis, perihepatitis, airsacculitis) and influenza lesions, they should be distinguished from single duck infectious serositis, duck colibacillosis, etc. In breeding ducks and layer ducks, because influenza is very likely to be complicated by or secondary to colibacillosis, clinical diagnosis should also pay attention to distinguishing it from single colibacillosis.

5. Prevention and control methods

Controlling the introduction of the disease is key. Quarantine work for introduced breeding ducks and breeding eggs should be well carried out, the all-in-all-out rearing method should be adhered to, disinfection should be strengthened in ordinary times, and immunization against common diseases should be well performed to improve the resistance of ducks.

Inactivated duck influenza vaccine has good immunoprotective effects, and vaccination with it is the main measure for preventing the disease, but an inactivated vaccine with the same serum subtype as the locally prevalent duck influenza virus strain should be selected for immunization.

Once duck influenza caused by a highly pathogenic strain is found, it should be reported and eradicated in a timely manner. For duck influenza caused by moderately or low pathogenic strains, some antiviral drugs and broad-spectrum antibacterial drugs can be used to reduce deaths and control secondary infections.