Causes and control methods of Newcastle disease in white-feathered broilers

Chicken Newcastle disease is also called Asian chicken plague. Newcastle disease is a highly contagious and acute septic infectious disease caused by virus. The main characteristics of Newcastle disease in chickens are dyspnea, dysentery, neurological disorders, mucosal and serosa bleeding. It mainly invades chickens and turkeys, but other birds can also be infected.

1. The pathogen of the disease is Newcastle disease virus, which is a paramyxovirus. It has strong resistance to heat, usually 100 ℃ 1 minute, 50 ℃ 5 ℃ 6 minutes, 37 ℃ hours to several days, but still has infectivity, immunogenicity and agglutination to red blood cells. It can adapt to a wide range of acids and bases, and is infectious in the range of pH2-10. At the same time, it is also resistant to low temperature. the lower the temperature, the longer the survival time. Weak resistance to disinfectants, infection with allantoic fluid virus, encounter 2% formalin or 3% Lysol, can lose infection in a few minutes.

2. Epidemic characteristics: chickens, turkeys, quails, pheasants and other birds are susceptible to the disease, of which chickens are the most sensitive, followed by pheasants, Laihang chickens are more sensitive than local chickens, and old chickens are less sensitive. The main infectious sources of the disease are diseased chickens, dead chickens and infected chickens. Some birds can spread the disease. Diseased chickens expel the virus from oral and nasal secretions and feces. After the epidemic, the infected chickens show a chronic process, which is one of the reasons for the epidemic of Newcastle disease. Newcastle disease is mainly infected through the respiratory tract and digestive tract, and eggs can also carry the virus. Wild birds, ectoparasites, humans and animals can transmit pathogens mechanically. Diseased chicken secretions and feces, blood, meat, viscera, chicken feathers and digestive tract contents are the main sources of infection.

3. The incubation period of clinical symptoms is generally 3 Mel 5 days. According to the virulence and duration of the virus, it can be divided into three types: the most acute, acute and subacute or chronic.

(1) chickens with the most acute disease often die suddenly without any symptoms.

(2) the body temperature of acute diseased chickens increased to 4312, and their intake decreased or did not eat at all. The spirit is not good, stand apart from the group, shrink neck and close eyes, chicken crown, flesh beard is purplish red or purple-black. Have difficulty breathing, stretch your neck, open your mouth, shake your head, make a "goo" or "cluck" sound, and sometimes sneeze. When lifting the chicken, a large amount of light white liquid flows from the mouth. The sac is filled with liquid or gas, diarrhea, and sometimes blood. The laying of laying hens decreases or stops. Sick chickens usually die within 1-2 days or 3-Mel within 5 days.

(3) subacute or chronic disease mostly changed from acute to acute, and the initial symptoms of diseased chickens were the same as acute type, showing obvious respiratory symptoms, while those with a longer course of disease appeared neurological symptoms, lameness and paralysis of one or both limbs. Wings droop, circle, back, head back or twist to one side. The course of the disease is about 10 days, and a few diseased chickens can heal themselves. In addition to mild general symptoms, adult chickens are mainly characterized by a sharp decline in egg production, a significant increase in soft eggs than usual, or diarrhea symptoms.

4. Pathological changes: the crop is full of acidic fluid with bubbles; glandular gastric mucosal edema, bleeding at the top of or between nipples, some bleeding spots under the myogastric corneal layer, and cecal tonsil swelling, bleeding and necrosis. There are jujube nucleus-like fibrinous necrotic foci in small intestinal mucosa and rectal mucosal bleeding.

5. Prevention and control measures through health management and vaccination comprehensive measures to prevent the occurrence of Newcastle disease. Health management is mainly to control the invasion of pathogens into chickens. Outsiders are not allowed to enter the chicken farm and prevent the invasion of birds and wild animals. Strict market quarantine and the sale of sick and dead chickens is prohibited. Once Newcastle disease occurs in chicken farms, comprehensive measures such as strict blockade, isolation, disinfection, culling of diseased chickens and emergency vaccination are required to extinguish the epidemic quickly. To guide immunization according to the results of antibody surveillance is the most effective means to prevent Newcastle disease. In a conditional chicken farm, it is best to determine the best time for chicken flock immunization according to the results of monitoring the antibody of the flock. At present, there are 4 strains of Newcastle disease vaccine produced in China, such as Ⅱ, Ⅲ and Ⅳ. The engineering vaccine (also known as Indian vaccine) is a moderately virulent vaccine, and the other three vaccines are attenuated vaccines. Among the attenuated vaccines, the virulence of Ⅳ strain (Lasota) was the strongest, the Ⅱ strain was the second, and the foot line was the weakest. Attenuated vaccine is suitable for chicks and adult chickens, generally after vaccination will not cause serious reactions. The engineering vaccine is only used for chickens for more than two months, and sometimes individual chickens react obviously after vaccination, but they produce antibodies quickly and have strong immunity after immunization, so they are suitable for use in areas with serious epidemic diseases.

However, for the sake of safety, attenuated vaccines should be used for basic immunization before using the vaccine. The antibody produced by oil emulsion inactivated vaccine is slow, but the antibody produced is high and neat, and lasts for a long time. When used in combination with attenuated vaccine, some chicken farms seriously polluted by Newcastle disease virus can be immunized with attenuated vaccine through nose, eye or fog before 10 days old, and half dose of oil emulsion inactivated vaccine at 10 days old. Since then, antibody monitoring has been carried out every 15 mi 20 days. When 20% of the chickens in the flock have antibody titers below 4Lg2, they will be immunized with attenuated vaccines. White-feathered broilers were injected with oil emulsion inactivated vaccine at the age of 18 Mel for 20 weeks. In the future, we should continue to monitor the antibody of chickens every month. When 20% of the chickens in the flock have antibody titers below 8Lg2, they should be immunized with Ⅳ vaccine aerosol or injected with oil emulsion inactivated vaccine at the same time, so as to keep the antibody level of chicken flock above 8Lg2 all the time. Only in this way can the egg production level of the flock be kept stable. In the event of an epidemic, chicken Newcastle disease high immune egg yolk antibody can be injected in time, or emergency injection with 4 times dose of Ⅳ vaccine.