avian viral diseases 1 - Aimee Flashcards
Marek’s disease is caused by what kind of virus?
Herpesvirus
Describe the pathogenesis of Marek’s Disease.
- Virus enters through respiratory tract then enters macrophages in the lungs = spread
- The virus curculates to secondary lymphoid organs then spreads through the lymphatic system (early cytolytic infection)
- The infectious form of the virus is produced in feather follicle epithelium & released in dandruff
- Late cytolytic infection causes visceral and neural lymphomas
Where does Marek’s disease develop latency?
CD4+ t cells
How is Marek’s disease transmitted?
Through the respiratory tract
Infectious form of the virus is produced in feather follicle epithelium and released in the feather dandruff
What effect does Marek’s disease have on lymphoid organs?
Causes atrophy of spleen, bursa of fabriculus, and thymus = immunosuppression.
What are the clinical signs of Marek’s disease?
- Neurologic signs (paralysis, tics, torticollis)
- Swollen feather follicles
- Irregular pupil
- Increased disease susceptibility
- Red leg
- Death
What lesions can be seen with Marek’s disease?
- Swollen sciatic nerve with discoloration and loss of striations (usually unilateral)
- Pale raised areas on liver due to lymphoid infiltration
- Lymphoid infiltration in muscle, kidneys, heart and lung, etc (most visceral organs)
What histological changes can be seen with Marek’s disease?
Lymphoid proliferation with heterogenous cells (different sizes)
How is latency with Marek’s disease different from other herpesviruses?
There is continuous replication in feather follicle epithelium (even when latent)
Describe the immune response to Marek’s disease.
Short strong innate response, adaptive starts approx 5 days post infection
What is the only way that a Marek’s disease diagnosis can be confirmed?
Need to demonstrate presence of viral genome or antigens to confirm diagosis.
History and exam can lead to suspect MD.
What is the main differential for Marek’s disease?
Avian leukosis tumors
How can you distinguish Marek’s disease from Avian Leukosis?
Marek’s disease has neurological signs but avian leukosis does not.
Marek’s disease is in younger birds.
Avian Leukosis can be transmitted vertically.
How is MD controlled?
Vaccination can reduce MD related losses but not infection.
Vaccination against non-pathogenic forms can create cross protection against MDV1. Or can use attenuated MD1 vaccines.
How did Marek’s disease develop virulence?
Vaccination induced jumps in virulence as the virus adapted against vaccine immunity.
What are the advantages of in ovo vaccination?
- Labour saving and convenient
- Shorter window of susceptibility
- As effective as D1 vaccination if given into the amniotic cavity
What type of virus causes infectious laryngotracheitis?
Herpesvirus
ILT is endemic in…
backyard flocks in Canada.
How is ILTV transmitted?
- Eye drop
- Contact
- Shared airspace
What are the gross lesions associated with ILTV?
Blood, mucus, and yellow caseous exudate or a hollow
caseous cast in the trachea.
When do lesions for ILTV and avian pox show up on the chorioallantoic membrane?
ILTV = 2 days
Avian pox = 6 days
How is ILTV controlled?
Modified live virus vaccines (two types = TCO tissue culture origin, CEO chicken embryo origin) or recombinant fowlpox/HVT vaccine with ILTV genes
Biosecurity is really important for control!
What are the limitations of ILT vaccines?
Modified live:
- Vaccine induced reaction
- Estabishment of latency and gaining virulence
- Involved in recombination leading to increased virulence
Recombinant:
- Partial protection
The majority of ILT in Alberta backyard flocks is caused by…
CEO vaccine revertants
Which ILTV vaccine is recommended for backyard flocks in Alberta?
TCO - tissue culture origin vaccine
How can ILTV be introduced to a flock?
- Other small flock owners
- Companion animals, wild birds
- Darkling beetles
- Contaminated coveralls, boots and equipment
- Improper dead bird disposal and handling of infected manure
Infectious bronchitis (IB) is caused by what kind of virus?
Coronavirus
Non-segmented, enveloped, +ssRNA
How is IB transmitted?
Respiratory droplets or fecal-oral
What is the host species for IB?
Mainly chickens
What system(s) are affected by IB?
It is multisystemic!!!
- Resp
- GIT
- Repro
- Urinary
What cells are infected by IB?
Macrophages and monocytes = can circulate through blood and lymph
How can the IB viral genome be visualized?
In situ hybridization
What are the main clinical signs of IB?
- Dyspnea
- Poor egg quality
- Shell-less egg syndrome
- False layer syndrome
What is the cause of shell-less egg syndrome?
IB infection causes the shell gland/uterus to become edematous and leads to eggs being laid without shells
What is the cause of false layer syndrome?
IB infection in young birds leads to a cystic oviduct (left)
What is common with FLS?
Egg laying stance and accumulation of egg yolk in the abdominal cavity
How is IB diagnosed?
Samples from nasal or tracheal tissue, kidney and intestinal swabs, caecal tonsils
Commercial serum antibody ELISA tests used for monitoring
Molecular techniques such as RT-PCR and sequencing differentiate vaccine and field strains
How is IBV controlled?
Mainly through vaccination - live attenuated (spray/water) and inactivated vaccines available.
What are the issues with IBV vaccines?
- Numerous strains, mutations
- Poor cross immunity across the variants
- Short lived protection-revaccination
- Live vaccines can cause mild infection
- Recombination of vaccine and field strains
How is IB vaccination different between broilers and layers?
Broilers - Spray vx on day of hatch and day 10-18 of age
Layers - Inactivated vaccine given every 4-6 weeks starting at hatchery until pre lay
