Comprehensive Analysis of Newcastle Disease Vaccine: A Key Line of Defense for Poultry Health
Newcastle Disease (ND) is one of the "top killers" in the global poultry industry, causing substantial economic losses to farmers over the long term. Scientific selection and application of Newcastle Disease vaccines are the core measures for preventing and controlling this disease. This article will comprehensively popularize knowledge related to Newcastle Disease vaccines from aspects such as the nature of the disease, vaccine classification, and prevention and control schemes.
I. Understanding Newcastle Disease: An Unignorable Threat to Poultry Farming
The culprit of Newcastle Disease is Newcastle Disease Virus (NDV), which belongs to Avian Paramyxovirus Type 1 of the Paramyxoviridae family. The virus exists in all tissues, organs, and secretions of infected poultry, with the highest viral load in the brain, spleen, and lungs, and the longest survival time in the bone marrow.
The virus has extremely strong low-temperature resistance: it can survive for 12 years at 4℃, more than 10 years at -20℃, and vacuum freeze-dried virus can be preserved for 230 days at 15℃. The genotype VII subtype strains prevalent in recent years are highly transmissible and pathogenic, with limited prevention and control effects of traditional vaccines. Infected poultry will show symptoms such as dyspnea, diarrhea, and neurological disorders, with extremely high mortality in chicks and a significant drop in egg production in laying hens.
II. Classification of Newcastle Disease Vaccines: Different Strains with Distinct Focuses
The virulence of vaccine strains is mainly evaluated by Mean Death Time (MDT), Intracerebral Pathogenicity Index (ICPI), and Intravenous Pathogenicity Index (IVPI), among which ICPI is the most critical virulence indicator. According to the viral replication and colonization sites, vaccines can be divided into enterotropic and respiratory tropic types, with obvious differences in applicable scenarios among different strains:
Enterotropic strains
- The VG/GA strain has extremely low virulence, suitable for spray and drinking water immunization of 1-day-old chicks.
- The V4 (VH) strain has mild and stable virulence, applicable to poultry of all ages, especially suitable for drinking water vaccination, with almost unaffected effectiveness.
Respiratory tropic strains
- The Lasota strain has strong immunogenicity, can overcome maternal antibodies, and can be inoculated via eye drop/nasal drop after 7 days of age.
- Both Clone30 and N79 strains are derived from the Lasota strain, with mild virulence, not interfered by maternal antibodies, and suitable for young chicks.
- The CS2 strain is only used for booster immunization of 30-day-old chickens, requiring subcutaneous or intramuscular injection.
- The HB1 strain has weak immunogenicity and has been basically eliminated.
In response to the currently prevalent genotype VII subtype strains, WollVac has launched targeted inactivated vaccines, which have excellent immunogenic effects against both Lasota strains and genotype VII subtype strains.
III. Scientific Prevention and Control Scheme: Core Guidelines for Vaccine Use
Newcastle Disease prevention and control need to consider six key links including breeding management, disinfection, and immunization, and cannot rely solely on vaccines. The following are the key immunization points:
(I) Vaccine combination strategy
The combined use of live vaccines and inactivated vaccines can achieve complementary advantages and produce strong protection:
- Live vaccines can induce local mucosal antibodies and humoral antibodies, activate immune responses, and reduce differences in antibody levels among flocks.
- Inactivated vaccines with oil adjuvants have significantly enhanced immunogenicity, less interference from maternal antibodies, produce immunity in 10-14 days, and have higher antibody levels and longer duration.
Chicks need to receive combined "live vaccine + inactivated vaccine" immunization during the brooding and rearing period and before laying, covering the brooding period and the entire laying cycle respectively.
(II) Vaccination methods and vaccine selection
- 1-day-old chicks can be immunized by spray. WollVac series live vaccines contain heat-resistant stabilizers, dissolve immediately in water, and have high safety.
- Drinking water immunization is recommended during the laying period. Priority should be given to vaccines containing genotype VII subtype strains and enterotropic strains, avoiding respiratory tropic strains such as Lasota (the effect of drinking water immunization decreases by more than 50%).
- Corresponding vaccination methods such as eye drop/nasal drop and subcutaneous injection should be matched according to different ages and immunization purposes.
(III) Key supporting measures
- Formulate scientific immunization procedures, and adjust vaccination time and dosage according to maternal antibody levels, poultry breeds, and vaccine types.
- Conduct regular antibody testing: timely immunization is required when HI titer is lower than 1:2⁸, and immunization protection is reliable when HI titer is higher than 1:2⁹.
- In case of epidemic outbreaks, high-dose live vaccines can be used for emergency vaccination, combined with antibiotics to prevent secondary bacterial infections.
IV. Core Advantages of High-Quality Vaccines: Taking WollVac Series as an Example
The production process and components of high-quality vaccines are the guarantee of immunogenic effect. Taking WollVac Newcastle Disease vaccines as an example:
- Live vaccines are produced using SPF chicken embryos with purified antigens, containing core strains such as genotype VII subtype, VG/GA, and V4, with a viral titer of no less than 10⁶.⁰ EID₅₀ per dose.
- Inactivated vaccines use imported adjuvants and inactivators, and adopt ultrafiltration concentration technology to remove impurities, resulting in minimal immune side effects. They can be stably preserved at 40℃, and their titer is not affected after 5-7 days of long-distance transportation. The titer of genotype VII subtype strains reaches 3×10⁹.⁰ EID₅₀/0.1ml before inactivation.
The core of Newcastle Disease prevention and control lies in "targeted vaccine selection + scientific immunization + comprehensive management". Choosing vaccines that are compatible with prevalent strains and have advanced processes, combined with standardized immunization procedures, can minimize the risk of disease occurrence.