Marek's disease and avian leukosis

Question 1

What is marek’s disease?

Answer 1

a herpesvirus-induced neoplastic disease of chickens. characterized by infiltration of various nerve trunks/organs by pleomorphic lymphoid cells

Question 2

Who does marek’s disease occur in? (species)

Answer 2

chickens (sometimes quail, rarely turkey, pheasants, jungle fowl).

Question 3

What age does marek’s disease occur in

Answer 3

sexually IMMATURE chickens 2-7 months (>3 weeks)

Question 4

What are the three serotypes of alpha herpes virus?

Answer 4

serotype 1--ubiquitous, the oncogenic type is serotype 1
serotype 2--common in chickens, nononcogenic
serotype 3 (turkey) is ubiquitous in turkes and nononcogenic

Question 5

Is there cross-reactivity between the isotypes of alpha herpes virus?

Answer 5

yes

Question 6

What is the epidemiology of mareks?

Answer 6

infected chickens shed virus in feather follicle dander, other birds inhale it. Carriers may or may not be sick and shed throughout life.

Question 7

Does vertical transmission occur in marek’s?

Answer 7

no

Question 8

What are the clinical signs of Marek’s disease?

Answer 8

1. death

2. paralysis

Question 9

What are the lesions of marek’s disease?

Answer 9

1. gross enlargement/yellowing/loss of cross-striations of peripheral nerves
2. discoloration of iris (rare)
3. enlargement of feather follicles
4. visceral tumors (most common)

Question 10

What is skin leukosis

Answer 10

A lesion of Marek’s disease. enlargement of feather follicles with reddening

Question 11

What is seen microscopically with Marek’s disease?

Answer 11

lymphomas characterized by PLEOMORPHIC LYMPHOCYTES (T and B cells)

Question 12

How is Marek’s disease diagnosed?

Answer 12

1. history
2. clinical signs
3. distribution of lesions
4. age–2-5mo or after egg production (late mareks)
5. histopathology

Question 13

What are ddx for Marek’s?

Answer 13

1. lymphoid leukosis
2. botulism
3. deficiency of thiamine

Question 14

Why is serology and virology not useful for diagnosis of Marek’s disease?

Answer 14

the Marek’s disease virus is ubiuitous

Question 15

How is Marek’s disease controlled

Answer 15

Immunization

Minimize early exposure before immunity develops (7-10d). only need to vaccinate once

Question 16

How long can MD virus survive in the environment?

Answer 16

1 month?

Question 17

What is the most common vaccine for Marek’s disease?

Answer 17

serotype 3 (turkey herpes virus) or serotype 2 and 3

Question 18

What is avian leukosis?

Answer 18

retrovirus-caused neoplastic diseases of chickens with lymphoid leukosis being most common

Question 19

What are the characteristics of lymphoid leukosis in a flock?

Answer 19

1. persistent low mortality

2. neoplasia of bursa of fabricius with metastasis

Question 20

avian leukosis J causes what?

Answer 20

Primarily causes myeloid leukosis

Question 21

What age of birds does avian leukosis occur in?

Answer 21

birds 16 weeks or older

Question 22

Avian leukosis viruses (alpha retroviruses) are classified into what?

Answer 22

10 subgroups

Question 23

What subgroup of avian leukosis viruses most commonly causes lymphoid leukosis?

Answer 23

A

Question 24

Which subgroup of avian leukosis viruses is endogenous?

Answer 24

E

Question 25

Does vertical transmission (egg transmission) occur with avian leukosis virus?

Answer 25

yes! important mechanism of spread

Question 26

What is the epidemiology of avian leukosis virus

Answer 26

vertical transmission. infected chicks are permanently viremic, don't develop antibody and have increased risk of death from lymphoid leukemia, have fewer eggs (maybe) and likely shed virus to own eggs

Question 27

What are clinical signs of birds with lymphoid leukosis?

Answer 27

1. non specific or no signs 2. unthrifty or emaciated, pale combs and wattles 3. enlargement of liver 4. enlarged and lumpy bursa of fabricius 5. birds with skeletal myelocyomatosis may have observable masses on shanks, head, thorax 6. depressed egg production in affected flocks

Question 28

What are the lesions of avian leukosis?

Answer 28

lymphomas seen in many organs in chickens >16 weeks esp liver, kidney, ovary, bursa

Question 29

What are the microsopic characteristics of avian leukosis lesions?

Answer 29

UNIFORMLY LYMPHOBLASTIC neoplastic cells in lymphoid tumors. Originate from B cells?

Question 30

How is lymphoid leukosis diagnosed?

Answer 30

1. age 2. course of disease 3. pattern of mortality 4. location of gross lesions--bursa of Fabricius nearly always involved

Question 31

Why is virology and serology not that helpful for diagnosing avian leukosis?

Answer 31

because ALV is very widespread in chickens

Question 32

How is lymphoid leukosis controlled?

Answer 32

by eradication, focused at the level of primary breeding companies--test prior to egg production and remove.

Question 33

Is there a vaccine for avian leukosis? what is it used for?

Answer 33

yes, the vaccine is used to immunize parent stock where ALV has been eradicated and they pass their maternal immunity to progeny. Does NOT work for tumor mortality protection as congenitally infected chicks are immunologically tolerant and cannot be immunized.

Question 34

What is the treatment for lymphoid leukosis?

Answer 34

none