Mareks Disease

What serotype of MD is important? it is cancer causing

1

What age of chickens does MD affect?

ANY

TF - Mareks disease affects quail, turkey, pheasants and waterfowl

FALSE - not water fowl

Age of onset = 4 weeks peripheral nerve involvement PRESENT Bursa of Fab is either diffusely enlarged or atrophied Skin and muscle tumors may be present

Mareks Disease

What is one of the most common clinical signs of unilateral paralysis in birds due to MD?

One leg stretched forward and the other back

What is the most useful test to confirm MD?

PCR

_____ strain has been able to protect against Mareks but if there is any increase in virulence, it will not longer be protected by ____ strain

Rispens strain

When can birds be vaccinated for MD?

SQ at age 1 day In OVO (common in the US)

TF - Birds WILL be exposed to Mareks Disease Virus in the enviornment

TRUE TRUE TRUE

What birds does MD serotype 3 affect?

Turkeys - causes herpes no disease in chickens!

Is MD sensitive to the enviornment + disinfectants?

YES

What are the most common serological tests used for MD?

agar gel precipitin, IFA, ELISA, and virus neutralization

Ddx that is a problem in backyard chickens and is from Mycobacterium avium

avian tuberculosis

What is used most commonly to perform VI?

blood lymphocytes or splenocytes

What sample is best for virus isolation?

buffy coat

DDx - due to infection that is caused by coliform bacilus

coligranulomatosis

Besides lymphoid leukosis, what are other Ddx to MD?

coligranulomatosis Avian TB Reticuloendotheliosis

What is the key to diagnosing Mareks disease?

diagnose the disease (tumors) not the infection

what part of the body do infectious virus particles replicated

epithelial cells

What is serology most helpful for?

exclusion of other avian tumor viruses or the monitoring of SPF flocks

What sample is best for PCR?

feather pulp

Where is MD localized to anatomically?

feathers and dander

What is highly valuable in the ddx of MD?

immunohistochem - can differentiate from lymphoid leucosis and reticluendotheliosis bursal lymphoma which are B cell tumors

What do most cases of MD death result from?

inability to reach food and water due to paralysis - this is NOT a CNS disease!!!!

Age of onset = 16 weeks NO peripheral nerve involvement Nodular tumors in the Bursa of Fab skin and muscle tumors are ABSENT

lymphoid leukosis

highly contagious neoplastic disease of poultry characterized by *t cell lymphoma and enlarged peripheral nerves*

mareks disease

What accounts for global economic losses related to mareks disease?

mortality, condemation and slaughter and vaccination costs

CS of lesions in peripheral nerves

paralysis of extremities including wing and neck paralysis

where does initial infection of MDV occur?

respiratory route

DDx that results in tumors in the intestines and breast meat

reticuloendotheliosis

IF MD affects the thymus and bursa, what will be noted about them?

they will be atrophied

TF - 20 years ago when MDV was first reported it was a mild disease, but now it is extremely virulent

true

TF - If you are only vaccinating with a mild strain of MDV you are not protecting from the more virulent strains

true

TF - Once you have mareks disease, it is almost impossible to get rid of the virus since feathers are everywhere and the virus remains infectious for several months at room temp and up to years at 4C

true

TF - Real time quantitative PCR can also be valuable in making a Ddx

true

TF - Serotype 2 MD does NOT cause disease

true

TF - There are both oncogenic strains and low path strains of MD serotype 1

true

TF - Tumors from MD can occur in nearly ever organ, particularly spleen, heart, liver, gonads lungs, proventriculus and muscle

true

TF - Vaccines should be frozen and you should always verify the N2 level in the dewar

true

TF - When PCR'ing for MD, must take caution when birds have been vaccinated for serotype 1 as most primers do NOT distinguish bt virulent and vaccine strains

true

TF - demonstrating that the virus is present supports a dx of MD but alone is not a definitive diagnosis bc the virus is commonly detected in non-diseased birds. want tumors, clinical signs and THEN a molecular dx

true

TF - lymphoid leukosis is a retrovirus and is controlled by keeping breeders free of the virus

true

VI DOES not provide a ddx for MD but can be ____

useful for conformation of other methods for dx - used to CONFIRM based on other sx

What nerves may be enlarged with MD? Why are they enlarged?

vagus, Brachial, sciatic, sacral plexus - enlarged due to lymphocyte infiltration

Why do many MD outbreaks appear in vaccinated flocks?

very virulent strains of MD Interval vaccination is a challenge presence of immunosuppressive agents like CAV Inadequate vaccine programs Poor vaccine prep and admin

Where are skin tumors from MD most often visualized?

with feather follicles - can see mostly in broilers after defeathering

What are the steps of pathophys of MDV?

1. Virus enters birds via infection by respiratory tract (lives on dander, skin and dust) 2. Migrates from the lungs and infects *b cells* 3. After infecting B cells it then infects T cells 4. T cells are destroyed by virus and virus migrates to hair follicles skin etc OR *maintained latently in the T lymphs* -- when they are maintained leads to *T cell lymphoma* which leads to death

What are the most common MD gross lesions?

Enlarged nerves and tumors - can be diffuse or focal, unilateral or bilateral

what is the most effective vaccinatin program in commerical layers?

HVT + RISPENS + SB1 combo

What is most effect vaccination program against MD in meat birds (broilers and broiler breeders)?

HVT + Rispens

What is a huge differential diagnosis to MDV?

Lymphoid leukosis! - similar changes, cant differentiate the two just by looking HOWEVER peripheral nerves are not usually affected with LL