Herd health workshop Flashcards
What is Marek’s disease?
Lymphoproliferative disease of chickens caused by alphaherpesvirus, affecting peripheral nerves, organs, iris & skin
What are the 3 serotypes of Mardivirus?
MDV-1 (oncogenic & causes Marek’s disease in chickens)
MDV-2 (non-oncogenic & affects chickens)
MDV-3 (non-oncogenic & affects turkeys)
Describe the epidemiology of Marek’s disease
Exists in all poultry-producing countries
Natural hosts: Chicken, turkey, quail
MDV is ubiquitous among commercial flocks but disease is not
Transmitted via horizontal transmission (dander, litter, feathers) which remain infectious for 4-8 months at room temperature
Infection spreads quickly within flock
How does Marek’s Disease Virus (MDV) infect birds, and what happens in the first week?
- Birds inhale poultry dust containing MDV
- Virus enters B-cells & activated T-cells, causing cell death & severe immunosuppression (esp. with very virulent MDV)
- Rapid replication occurs in first week, making birds vulnerable to secondary infections
- MDV establishes latency in T-cells
- 3-4 weeks later, infected T-cells transform into lymphomas –> tumour formation in nerves & organs
How does MDV spread and persist in the environment?
Infected birds shed virus from feather follicle epithelium
Virus survives in dander, litter, and feathers for months
Naïve birds inhale infected dust, continuing transmission cycle
What key lesions are found in post-mortem examinations of MDV-infected birds?
Spleen Enlargement → Correlates with increasing MDV virulence
Bursa of Fabricius Atrophy → Progressive shrinkage with more pathogenic MDV strains
What are the non-neoplastic syndromes of MD?
Immunosuppression → Destruction of bursa & thymus
Transient paralysis (esp. in broilers) → Vasogenic brain oedema, with recovery in 24-48h
What are the neoplastic-related syndromes of MD?
Tumour formation in multiple organs
Nervous signs → Spastic paralysis
Stunting, depression, paleness
Increased mortality & carcass condemnation
What diagnostic tools are used for MD?
Histopathology → Confirms Marek’s in affected tissues
- samples collected include feather pulp, spleen, organs with tumours
PCR testing → Differentiates MDV serotypes, checks for vaccine uptake
What are key features of MD vaccines?
Early onset of protection
One-shot, lifelong tumour protection
Low maternal antibody interference
But they do not protect against:
- MDV infection
- MDV shedding
- MDV transmission
(Can have well vaccinated bird with good level of immunity against Marek’s disease without clinical signs, but it doesn’t stop bird carrying MDV & shedding it)
What is the goal of MD vaccines?
They prevent clinical disease (paralysis, lymphomas, death)
Birds still get infected but do not develop severe symptoms
Imperfect vaccine – reduces disease but doesn’t eliminate virus
What makes PREVEXXION® RN1250 different from other MD vaccines?
Genetically distinct from existing MD vaccines
First hybrid vaccine, combining traits from 3 different Serotype 1 strains
LTR insertion allows attenuation without losing efficacy, bypassing traditional cell passage
Balances high efficacy without compromising performance
