Herd Health Principles in Backyard Poultry

Question 1

What is Marek’s Disease?

Answer 1

a common lymphoproliferative disease of chickens, caused by an alphaherpesvirus, usually characterized by infiltrates in peripheral nerves and various other organs and tissues including iris and skin

Question 2

Describe the epidemiology of Marek’s Disease

Answer 2

Natural hosts: Chicken, turkey, quail

MD Virus is ubiquitous among commercial flocks but the disease is not

Dander, litter, feathers infectious for 4-8 months at room temperature

Horizontal transmission

Infection spreads quickly within the flock

Question 3

What are the 3 serotypes of Marek’s Disease?

Answer 3

MDV-1 (oncogenic & causes Marek’s disease in chickens, pathogenic)

MDV-2 (non-oncogenic & affects chickens, non-pathogenic)

MDV-3 (non-oncogenic & affects turkeys, non-pathogenic)

Question 4

Describe the process of Marek’s Disease Infection

Answer 4

1. Birds inhale poultry dust containing MDV
2. Cytolytic phase - Virus enters B-cells & activated T-cells, causing cell death & severe immunosuppression (esp. with very virulent MDV)
3. Rapid replication occurs in first week, making birds vulnerable to secondary infections
4. MDV establishes latency in T-cells
5. 3-4 weeks later, infected T-cells transform into lymphomas –> tumour formation in nerves & organs

Question 5

How does MDV spread and persist in the environment?

Answer 5

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

Question 6

What key lesions are found in post-mortem examinations of MDV-infected birds?

Answer 6

Spleen Enlargement → Correlates with increasing MDV virulence

Bursa of Fabricius Atrophy → Progressive shrinkage with more pathogenic MDV strains

Question 7

What are the non-neoplastic syndromes of MD?

Answer 7

Immunosuppression → Destruction of bursa & thymus

Transient paralysis (esp. in broilers) → Vasogenic brain oedema, with recovery in 24-48h

Question 8

What are the neoplastic-related syndromes of MD?

Answer 8

Tumour formation in multiple organs

Nervous signs → Spastic paralysis

Stunting, depression, paleness

Increased mortality & carcass condemnation

Question 9

What diagnostic tools are used for MD?

Answer 9

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

Question 10

Describe the features of MD vaccines

Answer 10

in-ovo vaccine
live attenuated MDV strain
early onset of protection
low maternal antibody interference
protect against clinical MD
Do not protect against:
- MDV infection
- MDV shedding
- MDV transmission

Question 11

What makes PREVEXXION® RN1250 different from other MD vaccines?

Answer 11

Genetically distinct from existing MD vaccines

First hybrid vaccine, combining traits from 3 different Serotype 1 strains

LTR (long terminal repeat) insertion allows attenuation without losing efficacy, bypassing traditional cell passage

Balances high efficacy without compromising performance

Question 12

What is the most common vaccination regime against Marek’s Disease?

Answer 12

Rispens vaccine (MDV-1) in combination with HVT vaccine (MDV-3) - occasionally SB-1 vaccine (MDV-2)