Immunosuppressive and respiratory poultry diseases

Question 1

Describe the anatomy of the lymphoid system in birds

Answer 1

• 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

Question 2

Where are T and B cells matured in the bird?

Answer 2

T-cells = thymus
B-cells = Bursa of Fabricius

Question 3

What happens to the thymus and Bursa of Fabricius over a birds life?

Answer 3

These organs get larger over the first 3-5 weeks of a bird’s life, before they regress

Question 4

Infectious bursal disease mostly affects which cells?

Answer 4

B-cells

Question 5

Chicken anaemia virus mostly affects which cells?

Answer 5

T-cells

Question 6

Why is infectious bursal disease important?

Answer 6

• Causes direct high mortality 40%+

- Causes immunosuppression’s resulting in secondary infections

Question 7

What is the importance of a virus being unenveloped?

Answer 7

Harder to kill with disinfectant

Question 8

Describe the 4 different pathotypes/strains of infectious bursal disease virus

Answer 8

1. Mild strains: no clinical signs or mortality but may cause bursal lesions
2. Classic strains: less than 20 mortality, cause bursal lesions
3. Very virulent strains: severe mortality of more than 20%, causes bursal lesions
4. Variant strains: causes infection and severe bursal lesions resulting in immunosuppression, mortality <5%

Question 9

Describe clinical acute infectious bursal disease

Answer 9

• 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

Question 10

How does very virulent compare to classical infectious bursal disease?

Answer 10

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)

Question 11

How is infectious bursal disease transmitted?

Answer 11

Faeco-oral route

Question 12

Describe how infectious bursal disease infection attacks the body

Answer 12

• 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

Question 13

Describe subclinical infectious bursal disease

Answer 13

• 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)

Question 14

What pathological lesion is seen with subclinical infectious bursal disease?

Answer 14

Bursal atrophy (rather than size increase-normal-regress)

Question 15

How is infectious bursal disease diagnosed?

Answer 15

• Necropsy
• Histopathology of the bursa
• ELISA
• Identification of virus in tissues

Question 16

How is chicken anaemia virus transmitted?

Answer 16

• Faeco-oral
• Respiratory
• Feather follicles
• Vertically

Question 17

Which birds are affected by chicken anaemia virus and why?

Answer 17

Problem of young birds as they thymus has regressed once they are older so there is no site of infection

Question 18

Describe the clinical signs of chicken anaemia virus

Answer 18

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.

Question 19

Describe the gross pathological lesions caused by chicken anaemia virus

Answer 19

• Thymus, pale and atrophy
• Bursa of Fabricius, small?
• Bone marrow: pale or yellow
• Haemorrhage: skin, muscle and organs

Question 20

Describe the histological appearance of chicken anaemia virus

Answer 20

Histopathology – depletion of lymphoid cells in lymphoid organs; bone marrow – atrophic or hypoplastic

Question 21

How is chicken anaemia virus diagnosed?

Answer 21

• History, clinical signs and lesions

- PCR detects viral DNA

Question 22

How is chicken anaemia virus treated and prevented?

Answer 22

• No treatment available

- Live vaccines given via injection or drinking water

Question 23

How is Marek’s disease characterised?

Answer 23

Nerve swellings and tumours

Question 24

What is the cause of Marek’s disease?

Answer 24

An oncogenic herpes virus

Question 25

How is Marek’s disease transmitted?

Answer 25

• Mature virus is excreted only by the feather follicles
• Inhaled by other birds
• High virus load in dander, dust

Question 26

Describe some of the manifestations of Marek’s disease

Answer 26

• Neurological: infiltration of the CNS
• Visceral: Tumours in heart, ovary, tests, muscles, lungs
• Cutaneous: Tumours of feather follicles
• Ocular
• Immunosuppression

Question 27

Marek’s disease causes floppy broiler syndrome, what it is?

Answer 27

infiltration of the CNS and nerves - transient paralysis of legs or wings and eye lesions

Question 28

How is Marek’s disease diagnosed?

Answer 28

Clinical condition, lesions, histopathology, PCR

Question 29

How is Marek’s disease controlled?

Answer 29

Live vaccines given by injection at day old only

Question 30

How does Infectious bronchitis affect broilers and layers

Answer 30

• Respiratory disease
• Reduced body weight
• Egg drop
• Poor egg quality

Question 31

What are the effects of infectious bronchitis on the female reproductive tract?

Answer 31

• oviduct is small and not functional

- ovary function slows and eventually stops

Question 32

Infectious bronchitis can also cause problems in which other part of the body?

Answer 32

Kidneys - nephritis