What is Newcastle disease (ND) and How to Prevent and Treat of New Castle (ND)?

★Overview

Newcastle disease (ND) is an acute, highly contagious disease of chickens and turkeys caused by a strong strain of Newcastle disease virus (NDV). It often presents as septicemia. Newcastle disease is a Class A infectious disease stipulated by the 0IE. my country classifies Newcastle disease as a Class I animal disease. At present, Newcastle disease is still the main viral disease in the poultry industry.

*Pathogen

Newcastle disease virus belongs to the genus Mumps virus of the family Paramyxoviridae. The NDV nucleic acid type is single-stranded negative-stranded non-segmented RNA. The shape of complete virus particles varies. Most of them are spherical with a diameter of 100~500nm. The nucleocapsid is spirally symmetrical and has an envelope. The NDV serotype is APMV-1. NDV can agglutinate red blood cells of many animals.

★Epidemiology

Source of infection: Sick chickens and infected chickens are the main sources of infection.

Route of transmission: Respiratory and digestive tract transmission is the main route of transmission, followed by eye knots, infected eggs, trauma and mating. Non-susceptible wild birds, external parasites, and humans and livestock can mechanically spread Newcastle disease virus.

Susceptible animals: Chickens of different ages have different susceptibility. Chickens under 70 days old are most susceptible. Chickens aged 15-32 days, 40-60 days, and laying period have a high incidence rate.

Transmission media: Water, feed, equipment contaminated by NDV, and wild birds, external parasites, and factory workers with the virus are the main transmission media.

This disease can occur in all seasons, with more in spring and winter. The onset depends on the number of new chickens in different seasons and the conditions suitable for the survival and spread of the virus. The polluted environment and the infected chickens are the common causes of the epidemic.

The onset age of the disease is getting earlier and earlier. The earliest can develop the disease at 3 days old. The mortality rate depends on the level of the body. Chickens with low antibody levels or no immunization have a mortality rate of up to 75%~100%: immune chickens can still develop the disease, and the mortality rate varies greatly, ranging from 3% to 40%.

In recent years, the incidence of atypical Newcastle disease has been on the rise. It is rare to have a single disease. It is often mixed with one or more diseases such as Escherichia coli, infectious bursal disease, chronic respiratory disease, coccidiosis, etc., resulting in a significant increase in mortality.

★Clinical symptoms

The incubation period is 3~5 days for natural infection and 2~5 days for artificial infection.

1. The initial body temperature of typical Newcastle disease is as high as 43~44℃. The sick chickens are depressed, their eyes are half closed like a drowsy state, their feed intake is reduced and their water intake is increased. There is a large amount of sour and smelly liquid in the crop, they are unwilling to move, their wings are drooping, their combs and wattles are bluish-purple, they have difficulty breathing with a "snoring" sound, green liquid flows out of their mouths, and they excrete yellow-green feces; in the middle and late stages, sick chickens have symptoms such as leg and wing paralysis, movement disorders, turning in circles, and stargazing, accompanied by a drop in body temperature, and finally die in a coma. The egg production rate dropped by 20% to 70%, and the number of soft-shelled eggs, sandy-shelled eggs, faded eggs, white-shelled eggs, and small eggs increased significantly, and the fertilization rate of breeder chickens decreased significantly.

Commercial broiler flocks are mostly concentrated around 18 days and 30 days of age. They first have difficulty breathing and fever, and then neurological symptoms appear in the later stage, and eventually die of emaciation.

2. Atypical Newcastle disease

The initial stage is similar to typical Newcastle disease. The chickens are more common after vaccination, and the incidence and mortality rate are relatively low. The duration of death is long. The clinical symptoms are mainly respiratory symptoms, neurological symptoms and decreased egg production rate, and other symptoms are not obvious.

After the onset of the disease, the spirit and feed intake of laying hens are basically normal, and some have diarrhea; 5-7 days after the onset of the disease, symptoms such as paralysis, twisted neck, stargazing, shaking head, and head nodding appear; generally 7-10 days after the onset of the disease, the egg production rate decreases, white shell eggs, deformed eggs, sand shell eggs, and broken shell eggs increase, and the fertilization rate, hatching rate, and healthy chick rate of breeder chickens are all lower than normal levels, or they may eventually cause yolk membrane inflammation due to secondary infection of Escherichia coli disease, Salmonella disease, and other diseases, and egg production is not easy to return to normal levels.

Chicks and young laying hens may have respiratory symptoms of varying degrees, such as shaking head, coughing, and light "snoring", and some open mouth breathing.

★Pathological changes

The main pathological features are systemic mucosal and serosal bleeding, swelling, bleeding and necrosis of lymphoid tissue, and digestive and respiratory bleeding.

A sour and turbid liquid accumulates in the crop (currently not common in large-scale farms, but more common in free-range chickens).

The laryngeal and tracheal mucosa are congested and bleeding, with a large amount of yellow-white mucus or yellow cheese-like substances. There are bleeding spots or bleeding bands at the junction of the crop and glandular stomach, and at the junction of the glandular stomach and muscular stomach; the gastric mucosa is swollen and bleeding, and there is bleeding between the glandular stomach papilla and papilla; there are bleeding spots under the stratum corneum of the muscular stomach, or granular ulcers: there is gelatinous exudate at the junction of the glandular stomach and muscular stomach.

The intestinal mucosa has bleeding spots of varying sizes or diffuse bleeding, and the rectal mucosal folds have strip bleeding or punctate bleeding, or there are yellow fibrous necrotic foci. The lymphoid tissue and cecal tonsils are enlarged, bleeding, necrotic and ulcerated, and the surface of the intestinal mucosa has a fibrinous necrotic pseudomembrane, which is slightly higher than the mucosal surface, and the serosal surface is red like a date pit. Abdominal fat and coronary fat are bleeding; the thymus and spleen are enlarged and bleeding; the kidneys are congested and edematous, and there are urate deposits in the ureters.

The oviduct mucosa is congested, the follicles are congested, bleeding, degenerated, and even necrotic, and the yolk ruptures and falls into the abdominal cavity, forming yolk peritonitis.

★ Differential diagnosis of avian influenza and Newcastle disease

1. Epidemiological differentiation

(1) Highly pathogenic avian influenza is characterized by rapid onset, short course, rapid death, and large-scale death in a short period of time, and may even show no clinical symptoms. Atypical Newcastle disease is more common, with gradual death, low mortality and a long course of disease, mostly more than 4 days.

(2) Poultry (chickens, ducks, geese) may also become ill in and near the epidemic sites of highly pathogenic avian influenza, while Newcastle disease generally only causes illness in chickens.

2. Differentiation of clinical symptoms

(1) The typical symptoms of chickens infected with highly pathogenic avian influenza are purple and swollen combs and wattles, swollen heads and faces, and bleeding under the scales, while chickens infected with Newcastle disease rarely have swollen heads, swollen faces, and bleeding under the scales.

(2) Newcastle disease chickens often stand still with their eyes closed and their necks shrunk, appearing sleepy. They often make snoring sounds and shake their heads. Some sick chickens have green loose feces. However, avian influenza chickens, except for being mentally exhausted and having ruffled feathers, are similar to Newcastle disease chickens, but most of the above symptoms are absent.

3 Identification of pathological changes

Both avian influenza and Newcastle disease have bleeding characteristics in subcutaneous muscles and most organs and serous and mucous membranes, but there are many differences between the two.

(1) Most typical Newcastle disease chickens have bloated crops filled with sour and smelly liquid or paste, while avian influenza chickens generally do not have this condition.

(2) Respiratory symptoms include congestion and bleeding of the larynx and trachea, which contain mucous secretions. However, due to the long course of the disease, Newcastle disease chickens often have lobar pneumonia on one or both sides of the lungs. In many cases, adhesions between the lungs and the pleura can be seen.

(3) Both have swollen glandular stomach papillae or bleeding spots on the papillae. The muscular stomach of Newcastle disease chickens has bleeding under the stratum corneum, and the stomach contents are mostly green.

(4) The course of disease of chickens with lesions in the cecal tonsils and air sacs is mostly more than 5 days. These two lesions are completely different from Newcastle disease and avian influenza. Newcastle disease is characterized by severe swelling of the cecal tonsils, which swell into round lumps as big as soybeans. After cutting, they are severely hyperplastic and bleeding; second, the thoracic and abdominal air sacs of most Newcastle disease chickens show severe suppurative necrotizing air sacitis. Once highly pathogenic avian influenza occurs, almost the entire flock will die within 1~2 days. At present, the mortality rate of Newcastle disease in most cases is less than 20%.

(5) There is a coagulable and non-coagulable secretion in the oviduct of chickens that died of avian influenza, but not in the oviduct of chickens that died of Newcastle disease.

★Prevention and treatment

1. Prevention

Vaccination is the key measure to prevent Newcastle disease. Strengthen feeding management at ordinary times, appropriately increase vitamins and Chinese medicine to enhance the body's immunity to enhance the chicken's physique and improve disease resistance; strictly implement the disinfection system, combine temporary disinfection with regular disinfection, and cut off the transmission route of pathogens.

2. Use medication according to recommendations