Muscovy duck parvovirus disease

Muscovy duck parvovirus disease commonly known as "three weeks disease" is a new disease caused by Muscovy duck parvovirus with diarrhea, asthma and soft foot as the main symptoms. It mainly invades young ducks from 1 week to 3 weeks of age and is highly contagious. Its incidence and mortality are high.

pathogen

The pathogen of this disease is the parvovirus of the family Parvoviridae and Parvovirus. The virus has two kinds of solid and hollow particles under the electron microscope. It is a icosahedron with a circular, equiaxed and three-dimensional symmetry. It has no capsule membrane and has a diameter of 20 nm to 25 nm.

Muscovy duck parvovirus is a single-stranded DNA virus and has three structural proteins: VP1, VP2, and VP3, of which VP3 is the major structural protein. The virus does not agglutinate with the red blood cells of birds, mammals and humans. This is a difference from the mammalian parvoviruses. Muscovy duck parvoviruses can reproduce in Muscovy duck embryos and goose embryos and cause embryonic death. They can also multiply on Muscovy duck embryo fibroblasts and cause cytopathy. Fluorescent antibody staining shows bright yellow-green fluorescence in the nucleus. The virus was replicated in the nucleus.

The virus is very resistant to the action of inactivated factors such as ether, trypsin, acid and heat, but the virus is sensitive to ultraviolet radiation.

Popular features

Muscovy ducklings are the only animals with natural infections. Morbidity and mortality are closely related to age. The smaller the age, the higher the incidence and mortality. In general, onset of onset occurs at 4 days of age and 5 days of age, peaks at about 10 days of age, and then gradually decreases. Sporadic occurrence occurs around 20 days of age, and adult ducks do not develop. Ducks, mules, Beijing ducks, Cherry Valley ducks, geese, and chickens do not present clinical symptoms even if they are polycultured or artificially inoculated with sick ducks.

Sick ducks excrete large amounts of virus through secretions and excreta, especially through faeces. These excreta contaminate feed, water sources, feeding tools, transportation vehicles, breeders, and immunization personnel. Susceptible Muscovy ducks cause the spread of the disease through contact with these media. The excrement of sick ducks contaminates the egg shells and transmits the virus to newly hatched ducklings, causing an outbreak of the disease.

The occurrence of this disease has no obvious seasonality. However, due to low temperatures in winter and spring, the air in the brooding room is poor, the concentration of ammonia and carbon dioxide in the air is high, and the incidence and mortality are high.

Clinical symptoms and pathological changes

The incubation period of this disease is 4 days to 9 days, and the duration of disease is 2 days to 7 days. The length of the disease is closely related to the age of onset. According to the length of the disease can be divided into the most acute type, acute type and subacute type.

Most acute type

It occurs in about 6 days of ducklings. The disease is ferocious and the course of the disease is short, only a few hours. Often die without sudden signs of aura. There were neurological symptoms at the time of his death. The head and neck were twisted to one side and the feet were scratched. Mortality 4% to 6%. The necropsy was insignificant, with only acute catarrhal enteritis or intestinal mucosal bleeding.

Acute type

Mainly seen in 7 days old -21 days old young duck. Diseased larvae mainly manifested in different degrees of diarrhea, excreted pale or light green dilute feces, purulent in the feces, and adhered to the anus. Difficulty in breathing, cyanosis, phlegm, late phlegm, mouth breathing. The course of the disease is generally 2 days to 4 days. The diseased ducks are weighed down and paralyzed before their death. They fall to the ground and die of failure. The necropsy lesions were obvious, and all organs of the body had bleeding. There were characteristic lesions. In some cases, the small intestine had 1 segment to 2 segments of intestine, which resembled “sausage”. The pale white pseudomembrane consisting of fibrinous exudates and detached intestinal mucosa wraps the feces, and the other intestinal mucosa also shows edema and hyperemia.

Subacute

It is rare, and often it is the transformation of acute cases. Mainly manifested as mental fatigue, luxuriant, weak feet, walking slowly, yellowish green or grayish excrement, and adhere to the anus. The mortality rate was low and most of the affected ducks were hindered from growing and becoming frozen ducks.

diagnosis

Based on the epidemiology, clinical symptoms and pathological changes of the disease, a preliminary diagnosis can be made. In clinical practice, this disease is often mixed with duck viral hepatitis and R. anatipestifer disease, which can easily lead to misdiagnosis and missed diagnosis. Therefore, the definite diagnosis of this disease must rely on etiology and serological methods.

Virus isolation and identification

The internal organs of liver, spleen, kidney, and intestine of diseased ducks were collected and ground into a suspension after grinding and freezing and thawing. The allantoic cavity was inoculated with 10-days old and 12-day-old non-immunized duck embryos or geese. Embryos were set to 37% hatch for 5 days to 10 days. Discard dead embryos within 24 hours. Normally, the embryos die 3 days to 10 days after inoculation, and allantoic fluid is collected for virus passage and serological tests.

Inoculated young duck

The treated supernatant or the toxic allantoic fluid was subcutaneously or intramuscularly inoculated with susceptible young muscovy ducks from 5 days old to 10 days old and observed for 10 days. The dead ducklings were tested for the same pathological changes as the natural case.

Duck body neutralization test

Disease supernatant or toxic allantoic fluid was divided into two groups, one group was added with 4 times the amount of anti-parasitic duck parvovirus positive serum, the other group was added with 4 times the amount of sterile saline as a control, and mixed after 37 °C for 1 hour and then inoculated with ducklings. After inoculation of ducklings, they were isolated and observed for 10 days. The serogroup was active and the control group died of onset. The clinical symptoms and lesions were the same as those of natural cases, and the duck was diagnosed as Muscovy duck parvovirus.

Duck (goose) embryo neutralization test

There are two methods: fixed virus dilution serum method and fixed serum dilution virus method. The former is used to detect the neutralization titer of the test sera, and the latter is used to determine the neutralizing index of the virus to be detected. Practice the same as conventional. Latex agglutination test, enzyme-linked immunosorbent assay (ELISA), agar diffusion precipitation test (AGP) and nucleic acid probes can be used for the diagnosis of the disease.

Prevention

Feeding and management factors play an important role in the prevention and control of the disease. Strictly sterilizing eggs, hatchery and brooding room, improving ventilation conditions in the brooding room, combined with vaccination, can prevent the occurrence and prevalence of this disease.

In the contaminated area of ​​the disease, female ducks are vaccinated with the inactivated vaccine of the disease 2 weeks before the start of production, which protects the offspring. One day old ducklings can also be vaccinated with attenuated vaccines, and the protection rate is also high.

At present, there is no specific treatment for the disease. Once an outbreak occurs, the diseased young is immediately quarantined. The site is completely sterilized. Each muscle is injected with 1 ml of highly immuno-conjugated egg yolk antibodies, and the cure rate is more than 80%. In order to prevent and reduce secondary bacterial and fungal infections, proper application of antibiotics and sulfonamides is also necessary.