Immunosuppressive and respiratory poultry diseases Flashcards
Describe the anatomy of the lymphoid system in birds
- No lymph nodes in the bird
- They have lymphoid tissues which accumulate as patches
- Other important lymphoid tissues are the spleen, bone marrow, harderian gland (behind the eyeball), GI tract associated lymphoid tissues
Where are T and B cells matured in the bird?
T-cells = thymus B-cells = Bursa of Fabricius
What happens to the thymus and Bursa of Fabricius over a birds life?
These organs get larger over the first 3-5 weeks of a bird’s life, before they regress
Infectious bursal disease mostly affects which cells?
B-cells
Chicken anaemia virus mostly affects which cells?
T-cells
Why is infectious bursal disease important?
- Causes direct high mortality 40%+
- Causes immunosuppression’s resulting in secondary infections
What is the importance of a virus being unenveloped?
Harder to kill with disinfectant
Describe the 4 different pathotypes/strains of infectious bursal disease virus
- Mild strains: no clinical signs or mortality but may cause bursal lesions
- Classic strains: less than 20 mortality, cause bursal lesions
- Very virulent strains: severe mortality of more than 20%, causes bursal lesions
- Variant strains: causes infection and severe bursal lesions resulting in immunosuppression, mortality <5%
Describe clinical acute infectious bursal disease
- sudden onset
- depression, ruffled feathers, vent pecking
- mortality after 3 days of infection
- dehydration
- muscular haemorrhage
- variable size and bursal lesion depending on disease progress
How does very virulent compare to classical infectious bursal disease?
Similar to classical except:
- With much higher morbidity and mortality.
- More prominent haemorrhage on muscle, proventriculus and bursa.
- Others lymphoid organs are also affected, eg. Thymus, caecal tonsil, spleen etc)
How is infectious bursal disease transmitted?
Faeco-oral route
Describe how infectious bursal disease infection attacks the body
- IBDV infects and destroys B-cells
- Number of plasma cells decreases
- Decreased antibody production
- Increased susceptibility to other pathogenic agents
- Decreased immune response to vaccination
Describe subclinical infectious bursal disease
- Infection of chicks with MDA at young age (< two weeks) leads infection and replication of virulent IBD in the bursa [but protected against IBD clinical signs]
- No typical mortality pattern of clinical IBD
- Increased incidence of secondary infection
- Often decreased response to other vaccinations (eg. ND, IB, ILT and etc)
- Increased carcass condemnation (indirectly)
What pathological lesion is seen with subclinical infectious bursal disease?
Bursal atrophy (rather than size increase-normal-regress)
How is infectious bursal disease diagnosed?
- Necropsy
- Histopathology of the bursa
- ELISA
- Identification of virus in tissues
How is chicken anaemia virus transmitted?
- Faeco-oral
- Respiratory
- Feather follicles
- Vertically
Which birds are affected by chicken anaemia virus and why?
Problem of young birds as they thymus has regressed once they are older so there is no site of infection
Describe the clinical signs of chicken anaemia virus
Clinical signs about 12-17 days-old, anorexic, weak and depressed, pale, low PCV, anaemic on blood smears, leukopenia/pancytopenia. Mortality variable. Major problem – increased susceptibility to secondary infection and poor response to common vaccinations.
Describe the gross pathological lesions caused by chicken anaemia virus
- Thymus, pale and atrophy
- Bursa of Fabricius, small?
- Bone marrow: pale or yellow
- Haemorrhage: skin, muscle and organs
Describe the histological appearance of chicken anaemia virus
Histopathology – depletion of lymphoid cells in lymphoid organs; bone marrow – atrophic or hypoplastic
How is chicken anaemia virus diagnosed?
- History, clinical signs and lesions
- PCR detects viral DNA
How is chicken anaemia virus treated and prevented?
- No treatment available
- Live vaccines given via injection or drinking water
How is Marek’s disease characterised?
Nerve swellings and tumours
What is the cause of Marek’s disease?
An oncogenic herpes virus
How is Marek’s disease transmitted?
- Mature virus is excreted only by the feather follicles
- Inhaled by other birds
- High virus load in dander, dust
Describe some of the manifestations of Marek’s disease
- Neurological: infiltration of the CNS
- Visceral: Tumours in heart, ovary, tests, muscles, lungs
- Cutaneous: Tumours of feather follicles
- Ocular
- Immunosuppression
Marek’s disease causes floppy broiler syndrome, what it is?
infiltration of the CNS and nerves - transient paralysis of legs or wings and eye lesions
How is Marek’s disease diagnosed?
Clinical condition, lesions, histopathology, PCR
How is Marek’s disease controlled?
Live vaccines given by injection at day old only
How does Infectious bronchitis affect broilers and layers
- Respiratory disease
- Reduced body weight
- Egg drop
- Poor egg quality
What are the effects of infectious bronchitis on the female reproductive tract?
- oviduct is small and not functional
- ovary function slows and eventually stops
Infectious bronchitis can also cause problems in which other part of the body?
Kidneys - nephritis
