Newcastle disease is an highly contagious viral disease caused by paramyxovirus. It mainly manifests as dyspnea, diarrhea, disordered nervous system, bleeding mucous membrane and serous membrane in sick chicken. And once chicken are affected, the mortality will be as high as 90%. With a high mortality rate and the severe economic consequences of its outbreaks in commercial poultry, the disease is reportable to the World Organization for Animal Health. Therefore, it is essential for chicken farmers to do a good job in the prevention and treatment of Newcastle disease, because a small error in it will lead to heavy losses. Next, let us to learn about the Newcastle disease.
Symptoms of Newcastle disease in poultry
- Sudden death and high mortality
- Sharp decreased egg production. Eggs may be abnormal in color, shape, or surface, and have watery albumen.
- Difficult breathing, sneezing, coughing, gasping
- Twisting of neck, circling, trembling, stiffness, spasms, depression, nervous manifestations
- Drooping wings, ruffled feathers
- Reduced feed consumption
- Decreased activity
- Swelling around the eyes and neck
- Watery diarrhea
If you find any of the above signs in your chicken flock, maybe the virulent Newcastle disease is attacking your chickens. You could check postmortem lesions as follows for primary diagnosis:
- Larynx edema or pointy petechiae;
- Adenogastric papillomedema, bleeding or ulceration;
- Swelling or slight bleeding of the descending duodenum, 2-3cm at the front and back of the yolk stalk and lleum lymphatic follicles;
- Brush rectal bleeding.
Of course, the diagnosis must be confirmed by virus isolation, virus detection by RT-PCR or immunohistochemical staining assays, and serology.
Newcastle Disease Infected Objects
- Newcastle disease infects chickens of all ages and breeds. While young birds have markedly higher morbidity and mortality than older chickens. And pure breed chickens are more susceptible and have a higher mortality.
- The disease is likely to occur all year around, especially with high incidence in spring and winter.
- It spreads so rapidly that many poultry die without showing any signs. And virtually all the birds will be infected within two to six days.
Newcastle disease transmission pathway
The main sources of infection for the disease are sick chickens, the faeces and oral mucus of carrier chickens. And there are also some potential pathways for the spread of the virus that need to get enough attention.
Direct contact transmission
Respiratory secretions
Infected birds spread the virus into the air by coughing and sneezing, etc. Healthy birds can be infected by inhaling droplets containing the virus.
Feces
The feces of infected birds contain a lot of viruses, and healthy birds can be infected through contact with contaminated bedding, feed and water.
Direct contact with infected birds
Direct contact between healthy birds and infected birds, such as pecking and mating, can also lead to infection.
Indirect contact transmission
Pollutant transmission
Feed, drinking water, bedding, cages, vehicles, tools, etc. contaminated by the virus may become vectors.
Personnel’s clothing, shoes, hands, etc. may also carry the virus and cause transmission.
Airborne
The virus can be spread over long distances through the air, especially in closed poultry houses.
Vector borne
Wild birds, rodents, insects, etc. may carry the virus and act as vectors.
Contaminated eggs may also spread the disease.
Vertical transmission
Infected females can transmit the virus to their chicks through their eggs.
Figure 1 Route of transmission of Newcastle disease
The transmission pathways of Newcastle Disease are complex and varied, making prevention and control difficult. Therefore, strengthening biosecurity measures, such as strict disinfection, isolation and immunization, is the key to preventing and controlling Newcastle disease.
As the saying goes, “prevention is better than cure”, through learning to understand the genotypes of Newcastle Disease and the main strains prevalent in the local area, paying attention to the early symptoms of the disease in chickens, strengthening the daily management, and injecting vaccines at an early stage, the resistance of chickens can be effectively improved, and contribute to the prevention and treatment of Newcastle Disease in chickens.
In 1995, Ballagi-Pordang et al. used restriction enzyme digestion analysis to genetically group more than 200 ND strains, which were mainly divided into 6 genetic groups, namely genetic groups Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, and Ⅵ. In 1997, lomnjczj and others reported genetic group Ⅶ, and genetic group Ⅷ was found in the progeny of recognized strains isolated in the 1960s in South Africa. Cao Dianjun divided the epidemic NDV genotype Ⅶ into 5 genotypes, namely Ⅶa, Ⅶb, Ⅶc, Ⅶd and Ⅶe. Since the first report of NDV infection in geese in 1997, the Key Laboratory for veterinary vaccine creation of the Ministry of agriculture has been committed to the epidemiological investigation of NDV in South China. Since 2005, 210 strong strains have been isolated, of which 86.2% (181/210) are subtype VII d（Fig. 1).
Successful construction of vaccine rGM-VII (Figs. 2 and 3)
To generate authentic 5’ ends of full-length viral antigenomic RNA transcripts, we introduced an overhanging hammerhead ribozyme (HamRz) sequence instead of two or three additional guanidine residues (Gs) at the 5’ terminal into the cDNA clone of GM. To establish a biomarker, an Asc I restriction enzyme site was generated by specific mutagenesis. The schematic cloning strategy is shown in Fig. 2 [1]
To attenuate rGM, the nucleotide sequences of the cleavage site of the TVT-rGM plasmid were modifified from 5’-AGGAGACAAAAACGCTTT-3’ to 5’-GGGAGACAGGGGCGCCTT-3’by PCR mutagenesis, which correspondingly change the motif from 112RRQKRF117 to 112GRQGRL117.
As the circulating NDV of genotype VII is virulent, most strains are not good candidates for vaccine strains. Only those of natural low virulence or those artificially created attenuated strains can be used for the development of vaccines. So to obtain low virulent strains is a key to vaccine development.
It can be seen that no obvious cytopathic changes occurred after 4 hours of inoculation of the virus to DF-1 cells, indicating that the virulence of rGM-VII was significantly weakened compared with that of the parent strain GM, which laid the foundation for the next step of vaccine development.
The immune effect of vaccine prepared by rGM-Ⅶ strain (0.02mL)
It can be seen that there is little difference in immune effect between single vaccine and combined vaccine prepared by rGM strain. rGM-VII is of good immunogenicity and high antibody titer [significantly higher than the national standard (4.0log2)]
Protective effect of rGM -VII vaccine against GM strain (0.02 ml)
Conclusion: the existing genotype II vaccine can not completely protect the genotype VII epidemic strain. And rGM -VII vaccine strain can provide full protection.
Newcastle Disease Vaccine Recommendations
Reference
Minhua Sun, Bin Xiang, et al. Generation and evaluation of a genetically attenuated Newcastle disease virus rGM-VIIm as a genotype-matched vaccine. Virus Genes (2017) 53:35–43
