Food Animal Production: Poultry: Mareks

What western provinces are you more likely to see vx used in broilers?

- BC, not so much in Alberta because MD not common - US → risk factor → don't clean out barns very commonly, up to 5 years, so more likely to use vx with strain 1 or 2

What can tumors due to Mareks in organs such as the liver be confused with?

- E coli granulomas

What might be seen on tissue sent for histo?

- Pleomorphic lymphocytes - T cell → 60-90%, lack IgM marker - B cells → 3- 25%

How can MD vx be given?

- SQ - In ovo ST 1 Rispens ST 2 SB - 1 ST 3 HVT

What form of MD is the most oncogenic form?

- Serotype 1 → gallid herpesvirus 2 ***this is the one you will see if see any of them*** - he has seen this one due to vx breaks or challeng from a strong strain

What birds does Mareks primarily affect?

- chickens - quail, turkey, and pheasants mildly ( he has never seen)

Due to the mode of transmission, what seems to be a very important part of dz control?

- controlling feather dander → need to focus on cleanliness - because this is hard to do, Vx has become very important

How is mareks transmitted?

- direct or indirect contact → airborne

What lesion might be seen on the iris?

- discolouration

What might be seen with feather follicles?

- enlargement → skin leukosis

Where does the virus replicate?

- epithelial cells of the feather follicle

Why did today's commercial broilers result from the previous economic problems with Mareks dz?

- found that commercial broilers were less susceptible

Describe the etiology of Mereks Dz?

- herpesvirus → induces neoplastic dz

What is the number one way to dx Mareks?

- histopathology

How long do infected chickens shed the virus for?

- indefinetly

Describe the pathogenesis of MD?

- lymphocytic herpesvirus → causing immunosupression - cytolytic infection → immunosuppression - changes in cytokine expression - genetic resistance → this has become key for prevention

What might be included in your biosecurity plan?

- multiage flocks - resused litter

What CS is more commonly seen in todays poultry industry?

- neoplasms

Does vertical trasmission occur with Mareks?

- no

What is the mortality rate with Marek's Dz today? Why is there this difference?

- not nearly as much because of vaccnination

Why is vx against MD considered very important?

- represents an example of successful dz control in vet. medicine - first effective vx against cancer in any spp

In what age of chickens is Mereks dz commonly seen in?

- sexually immature 2-7 months - can occur in any age after 3 weeks

What abnormality might you see at a processing plant with broilers that should have you worried about Mareks?

- torn skin, with holes in it, look like multiple tears

Describe the classical form?

• ataxia • flaccid paralysis → neck and limbs • progression of the dz → neoplasms

Describe the acute form of Mareks?

• death within 24 - 72 hours following onset of paralytic signs

What are the 3 serotypes of Mareks? Which types have a vx associated with it?

1. Sertotype 1 → gallid herpesvirus 2 → ubiquitous in chickens (oncogenic) → mild, virulent, very virulent, very virulent plus 2. Serotype 2 → Gallid herpesvirus 3 → common in chickens, not oncogenic 3. Serotype 3 → Meleagrid herpesvirus 1 → turkeys, non oncogenic - all have a vx → can use a combo or single

What are the types of Vx available?

1. Turkey Herpesvirus (serotype 3) 2. Serotype 2 3. Sertotype 1 MDV, attenuated 4. combo of serotype 1, 2, 3

How is MD best controlled?

1. Vx 2. Genetic resistance 3. Biosecurity

What are two forms of clinical dz associated with Mareks>

1. classical 2. Acute form

How is MD dx?

1. hx 2. age of birds old → but could occur in onset of egg producton 3. location of neoplasm → bursa?? 4. Histo *****

What might be seen on gross pathology associated with Mareks: - nerves: which nerve is almost always abnormal? - visceral organs

1. nerves • loss of cross striations • gray or yellow discolouration • nerve tract enlargement • sciatic ****enlarged**** 2. visceral tumors → ovary, lungs, heart, kidney, liver (early enlarged), skeletal muscle, intestines, iris,skin

What are CS associated with Mareks?

1. paralysis 2. neoplasms plus 3. wgt loss/anorexia 4. paleness 5. starvation/dehydration → birds will waste away

What has the mortality in layer flocks been historically with mareks?

60%

SLIDE on Imune Responses??

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