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VIRAL HEPATITIS DUCK
Ducklings viral hepatitis (lat. - Hepatits viriosa anaticularum; Duck virus hepatitis; infectious ducklings hepatitis, ducklings hepatitis, HHV) is an acute ducklings disease characterized by liver damage and high mortality in adult ducks without symptoms.
Historical background, distribution, hazard and damage. In 1949, in the United States, among the bred ducklings of the Peking breed, a new disease was first registered. The disease was characterized by high mortality (up to 70 ... 80% of ducklings of each conclusion).
The disease quickly spread to all countries with developed leadership (England, Canada, Belgium, France, Germany, the Czech Republic, Poland, India, Brazil).
In the former USSR, the first outbreak of the Voronezh State University was recorded in Ukraine in 1960 by M. T. Prokofieva and I. N. Doroshko. The disease is also noted in the farms of the central zone of the Russian Federation.
VSU causes significant economic damage. Mortality ranges from 30 to 95%. Ill ducklings lag behind in growth and development, which leads to a partial loss of meat productivity, disruption of breeding work. The damage from the disease is exacerbated by the costs of restrictive measures that violate the economy of the economy, especially when the disease becomes stationary.
The causative agent of the disease. The virus belongs to the Picornaviridae family, has a spherical shape, does not have hemagglutinating properties, is easily cultivated on bird embryos, as well as duck embryo cell culture. In cell culture, the virus exerts a CPP.
Depending on the virulence of the virus and the age of the embryos, after 48 ... 96 hours after infection, 90% of their deaths with massive hemorrhages are noted.
In the external environment in the spring months, the virus remains viable for 25 days, in the winter - up to 105 days. The maximum shelf life of the pathogen in infected water was 74 days. The virus is sensitive to high temperatures - heating to 56 ° C causes it to inactivate for 60 minutes. Under the influence of ultraviolet rays, he dies within 10 minutes.
For disinfection of poultry facilities use a 1% solution of formaldehyde; 4% hot (40 ... 45 ° С) sodium hydroxide solution at 12 hours exposure; sodium hypochlorite solution with a content of 1.5% active chlorine, 1.2% free alkali and exposure of 6 hours, 5% chlorine solution of iodine chloride, exposure also 6 hours
Neutralization of the virus also occurs during aerosol disinfection of houses with 40% formaldehyde solution and exposure for 12 hours, as well as 20% aqueous formaldehyde solution and exposure for 24 hours. Feed containing hepatitis virus can be neutralized by steaming at a temperature of 65 ... 75 ° C for 1 hour
Epizootology. Ducklings, goslings are susceptible to the disease; insensitive birds from the order of chicken and laboratory animals. Wild ducks are susceptible to infection with the hepatitis virus, their clinical and pathological changes are the same as those of domestic ducks. Domestic goslings are susceptible to the virus by contact infection from sick ducklings.
Young birds are more susceptible to VSU. In adult ducks, after infection, clinical signs of the disease, as a rule, do not occur. In some households, ducklings older than 2 months of age are infected, which is associated with the presence of highly virulent strains of viruses in the external environment and unfavorable conditions for feeding and keeping.
Among the unfavorable factors affecting the course of the disease are the overcrowding of young animals, damp litter, drafts in the room, low temperature, and unsatisfactory conditions.
In many cases, it is not easy to establish the root cause of the introduction of the disease into the economy. The spread of infection occurs after the introduction of hatching eggs, daily young animals, adult virus-carrying ducks to safe farms. Possible infection on water walks in contact with poultry and wild.
In the future, the infected animals, water, litter, and bird care items serve as a reservoir of infection. It has been established that in some eggs infected during the formation of the virus the virus is contained in the yolk, the embryos in such eggs in 7 ... 50% of cases die at various stages of embryonic development. It was noted that sick ducks can remain virus carriers for 300 ... 650 days.
The hepatitis virus is released into the environment by sick ducklings and virus carriers in various ways: with droppings, nasal discharge and eye secretion. Methods of infection in vivo - oral and aerogenic.
Outbreaks of VSU are often observed in ducklings in the early days of life. Often the disease lasts several days and then stops. The epizootic curve of morbidity and mortality has a pronounced rise on the 5th day of life of young animals. If a disease occurs on the farm, then, as a rule, the entire batch of newly hatched ducklings is affected.
Pathogenesis. After the pathogen enters the body, it multiplies rapidly and causes viremia, is introduced with blood into all tissues, affects cells of the most vital organs (liver, spleen, brain).
The course and clinical manifestation. The incubation period with natural infection of ducklings lasts about 2 ... 5 days, sometimes longer. The disease often proceeds sharply, the appearance of clinical signs begins suddenly in apparently healthy birds externally: they refuse to feed, are motionless, possibly a disorder of the nervous system. In the future, narrowing of the palpebral fissure occurs and conjunctivitis develops. Ducklings lie with their legs wide apart. Then convulsive movements of the limbs occur, ducklings make swimming movements. When these signs appear, the duckling, as a rule, dies within a few hours. Before the death of the bird, they throw their head back on their backs, stretch their limbs (opistotonus) and remain in this position.
In a significant part of ducklings, the disease can proceed easily and asymptomatically, after 72 ... 96 hours after infection, the young growth becomes lethargic, refuses to feed, in some cases, nervous phenomena occur, but these clinical signs gradually disappear, and the chicks recover.
In adult ducks, the disease proceeds without visible clinical signs; ovariosalpingitis is sometimes noted.
The most characteristic changes in dead ducklings are found in the liver: it is enlarged, its color varies from reddish-red to brown, the gall bladder is full of bile. In some cases, the area of the liver adjacent to the gallbladder acquires a dark greenish color. Small point and large focal hemorrhages penetrating the thickness of the parenchyma are found throughout the liver. In addition to changes in the liver, hemorrhagic ascites and pulmonary edema, pericarditis and fibrinous diphtheria overlays on the wall of the air sac are observed. In some cases, inflammation of the kidneys occurs. At the opening of the cranial cavity, a strong injection of the vessels of the meninges and small point hemorrhages are noted. In the chronic course of hepatitis, the characteristic pathological signs are an increase in the liver and spleen with foci of necrosis, periarthritis.
Histological changes in the liver are characterized by widespread necrobiosis and parenchyma necrosis, fatty metamorphosis of the cytoplasm of the liver cells with the decay of their nuclei, proliferation of RES and epithelium of the bile ducts. When histological sections of the liver tissue were stained using the Noble method with TatrazinFloxin, it was possible to detect oval or spherical inclusion bodies with a size of 1 to 8 μm.
Diagnostics and differential diagnostics. To make a diagnosis, it is necessary to take into account epizootological features, clinical and pathological changes. Laboratory studies are carried out in order to isolate the virus and its typification.
The laboratory examines the liver, spleen and brain from fallen ducklings.
The prepared material is used to infect chicken and duck 9 ... 12-day-old embryos.
For diagnosis of viral hepatitis, you can use a bioassay on susceptible ducklings. 48 ... 72 hours after intranasal infection, they develop clinical signs of hepatitis and typical pathological changes.
To typify the virus, you can use pH on chicken embryos with specific serum. This reaction may be useful for a retrospective diagnosis of viral hepatitis in sick ducks. RDP, RIF are also developed and can be applied.
With differential diagnosis, it is necessary to exclude paratyphoid, viral sinusitis, massive poisoning of ducklings.
Immunity, specific prevention. After the disease, the ducklings acquire a fairly stable immunity.
Vaccination of ducks of the parent herd in order to obtain immune offspring is widely practiced in many countries for the specific prevention of HHV. Virus vaccines from attenuated strains are often used to vaccinate ducklings. The most common is the intramuscular method of immunization. In this case, immunity is formed on the 4th ... 7th day after vaccination.
Also used are inactivated emulsified embryo vaccine UNIiP from strain ZM. A satisfactory immune response was observed with triple vaccination of ducks at the age of 8, 16 and 22 weeks.
Prevention The basis of VSU prophylaxis is the observance of the rules for the care, feeding and keeping of poultry, as well as the implementation of veterinary-sanitary rules to prevent the introduction of infection. It is forbidden to import hatching eggs from ducks from farms that are unsuccessful for this disease. In the system of veterinary sanitary measures
The separation of ducklings of different age groups when kept in poultry houses and in water bodies is of great importance.
The eggs of ducks entering the incubation must be disinfected twice on the 1st and 13th day after laying in the incubator.
Overexposure of ducklings in the hatchery is not allowed; after withdrawal, hatcher hatchers are dusted and disinfected after each batch of ducklings. Poultry houses should be carefully prepared to receive each batch of young animals. Floors before delivery of bedding material are sprinkled with fluff. Of great importance in the prevention of VSU, as well as other concomitant diseases, are the provision of ducklings with full-fledged feeding and the creation of the required animal health conditions.
When growing ducklings, the temperature in the house near the heater should not be lower than 28 ° C, relative humidity - 55 ... 60%. Planting density no more than 14 ducklings per 1 m2 of floor area.
Treatment. Of the specific treatments, serum and blood of convalescents, which is prepared after the slaughter of an adult bird, can be used.
Control measures. When a diagnosis is made, the farm is declared unsuccessful and the following restrictions are introduced: the export of hatching eggs, ducks and ducklings to safe farms, the use of ponds on which a sick bird was located, are prohibited; they are destroying sick ducklings, vaccinating daily young animals, and disinfecting houses and equipment. Before removing the restrictions, serological studies in the pH are performed.
Restrictions are removed from the farm after the cessation of the disease, the negative results of virological studies and the final disinfection.
Control questions and tasks. 1. Give a general definition of the disease and the value of the vertical path of transmission of the pathogen. 2. What clinical signs and pathological changes are noted with ducklings viral hepatitis? 3. List the features of laboratory diagnosis of the disease. 4. What are the specific measures for the prevention of infection in utilities with in-line technology.
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