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Marek’s Disease (MD) is a serious threat to the poultry industry and its control depends largely on effective vaccination. When an MD outbreak occurs, most companies conduct an audit of hatchery vaccination protocols. Additionally, other critical aspects must be monitored in order to better understand the origin of the outbreak. This article analyzes an outbreak of MD progressively to highlight the main factors responsible for vaccination / protection failures.
Critical points for establishing adequate immunity to MD include:
- Proper handling of the vaccine during the vaccination procedure
- Correct administration of the vaccine
- Replication of the vaccine virus in chicken
- Stimulation of adequate immunity capable of providing protection against Marek’s disease virus (MDV)
Adequate vaccination monitoring can be carried out by measuring the replication of the vaccine virus in one-week-old chicks. This not only provides information on the protection of the flock against MD, but also serves to confirm that vaccination has been done correctly Protection against MD can be monitored by assessing the viral load of oncogenic MDVs in chicks from 3 weeks of age. In the event that more virulent viruses are suspected, the pathotype of the isolated strains can be determined to establish the appropriate vaccination program. Understanding all the above critical points is the only way to effectively improve MD control methods.
Knowing the problem
Marek’s disease is a lymphoproliferative disease caused by Marek’s Disease virus (MDV), a herpesvirus that affects chickens. MD has been successfully controlled since the late 1960s. However, outbreaks of MD occur sporadically in vaccinated flocks, causing significant economic losses and is of great concern to the sector. Once an outbreak of MD has been confirmed, it is important to assess all critical points that have led to a failure in immunization. This article reviews the steps to follow to investigate an outbreak of MD (Figure 1).
When an outbreak of MD occurs, companies should conduct a vaccination audit to verify that the vaccines are being handled correctly and that none of the steps mentioned above have been affected.
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