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Mereks disease is seen in what species mostly? What other species are susceptible?
- Quail, turkey, pheasents
What causes mereks disease
What age group of chickens is mereks common in?
2-7 months but anything over 3 weeks
What are the 3 serotypes of mereks disease and which one is most important
- Gallid herpesvirus 2 - oncogenic and virulent
- Gallid herpesvirus 3
- meleagrid herpesvirus 1
How is mereks transfered
Virus replicates in the epithelial cells of the feather follicle. INfected chcikens shed virus indefinietly
Does mereks transfer vertically
What are the 2 main signs of mereks disease
2 forms of mereks?
- Classical form - ataxia, flaccid paralysis, neoplasms
- acute form - death within 24-72hr following onset of paralytic signs
3 gross pathological changes seen in the nerves of mereks affected birds?
- Loss of cross striations
- gray or yellow discoloration
- nerve tract enlargement
Where do mereks birds typically develope neoplasia
- Visceral organs
- ovary, lungs, heart, kidney, liver, intestins, iris
4 pathological lesions seen on necropsy of mereks birds
- 3 nerve lesions
- Visceral tumors
- enlargment of feather follicles
- discoloration of the iris
What do we see on the skin of mereks birds?
Enlarged feather follicles
What do we see on histopathology of mereks birds?
- Pleomorphic lymphocytes
- mainly t cells but some b cells
4 points to getting a mereks diagnoses
- age of birds
- location of neoplastic lesion
What serotypes do we vaccinate against mereks with?
2 and 3
3 ways to control mereks?
- genetic resistance
2 WAYS TO VACCINATE FOR MEREKS?
HAs the virus changed over time?
Yes the lesions and clinical presentations have greatly changed
What is the mortality of a flock that is vaccinated and gets mareks
- Layers <5%
- Broilers 0.1-0.5%
Do non oncogenic strains of mereks protect against the oncogenic?
What kind of virus is avian leukosis/sarcoma virus
When do we see leukosis virus?
Leukosis virus shows what pattern of neoplastic emergence?
Persistantly low mortality with neoplasia in the bursa, liver, and other visceral organs
Differentiate the kind of cancer that we see with mereks and with leukosis virus
Mereks is always a lymphocytic line of neoplasia and leukosis can be lymphoid, erythroid, or myeloid
What are 3 lines of leukosis virus
Mortality with leukosis?
1-2% but could be up to 20%
Leukosis virus does not occur prior to?
14 bweeks of age
How is leukosis virus transmitted primarily?
Vertically for the most part. Only exogenous virus is important in maintain the infection not endogenous
Why is endogenous virus not important to infection
avirulent and genetically defective
See marked pages in handout #1 for important diagrams
Horizontal transmission of leukosis only occurs when?
WHen birds are very young
Are all birds with virus and carrying virus ab+?
No many are negative
3 major clinical signs of leukosis?
- Enlargment of abdomen
- Enlarged and lumpy bursa of fabricius
- Depressed egg production
How can you control avian leukosis?
As soon as mass neoplasisa is not of leukosis origin it is cause by?
2 hints microscopically that it is leukosis virus?
- Uniformly lymphoblastic
- B cells have surface IgM markers
- Where as T cells in mereks lack IgM markers
3 parts of leukosis diagnosis
- Age of affected chickens
- Pattern of mortality
- Bursal lesions
2 forms of erythroblastosis with avian leukosis
- Proliferative form -liver, spleen etc enlargement
- Anemic form
What do we see with myeloblastosis leukosis
Liver is greatly enlatrged
Who is more susceptible to myeloid leukosis?
Meat type birds
What subgroup of leukosis causes myeloid leukosis (myelocytic myeloid leukosis)?
ALV - J
What are the clinical signs of myelocytomatosis
Leukosis comes from where on the production chain
How does leukosis cause osteopetrosis
Virus interferes with growth and differentiation fo osteoblasts, sweeling the diaphyses of nlong bones
Do birds develop active immunity against ALV?
Yes as long as they are older. If infected at a young age they will likely be permanently viremic. if older they will likely become tolerant to infection
The birds body uses what type of immunity to protect against ALV?
Cell mediated immunity.
What is the only way to control ALV?
Why do you have to test multiple ways to know if an animal is postive
- Due to endogenous virus that does not produce disease, and antibodies cannot be trusted
4 parts to ALV eradication
- Negative egg albumin or vaginal swab test
- Hatching of chicks in isloation in small groups
- Avoid manual vent sxing and vaccination with common needle
- Cleaning and disinfection of incubators brooding houses and all equipment
If you see endemic fibrosarcomas you know you have a what infection?