Retroviridae - Alpharetrovirus: Avian Leukosis

Question 1

How many subgroups of Alpharetroviruses are there and what are they based on?

Answer 1

Viruses are classified into 10 subgroups based on antigenic differences in viral envelop antigens.

Question 2

Which subgroup of alpharetrovirus is associated with most field outbreaks of leukosis?

Answer 2

Subgroup A and B

Question 3

Which subgroup of alpha viruses are genetically inherited and non-oncogenic?

Answer 3

Subgroup E

Question 4

Which subgroup of alpharetrovirus is associated with myeloid leukosis?

Answer 4

Subgroup J

Question 5

What species and where is avian leukosis endemic?

Answer 5

Endemic in all chicken populations worldwide.

Question 6

When chickens are infected horizontally, and are over 5 to 6 days old, will the infection be severe?

Answer 6

If chickens are infected horizontally when more than 5 to 6 days of age they are unlikely to develop leukemia

instead they develop a transient viremia and produce neutralizing antibody

Question 7

When chickens are infected congenitally, via the egg or within the first few days of life, will the infection be severe?

Answer 7

The chicken develops a viremia that persists for life because of the induction immunological tolerance.

Birds may appear to grow normally, but they subsequently can develop leukemia.

Question 8

What type of infection would you usually see with vertical transmission?

Answer 8

Usually latent infection

Vertical transmission through provirus integrated into the DNA of the host germ cells

No viremia

No leukemia

Question 9

What are the primary target cells of avian leukosis virus?

Answer 9

Lymphocytes with B lymphocyte markers in burse of fabricius

Question 10

What can prevent the development of lymphoid leukosis?

Answer 10

Bursectomy

Question 11

Which type of exogenous viruses can tumors only occur when infected congenitally with persistant viremia?

Answer 11

Exogenous non-defective (competent) viruses

Question 12

Would you expect to see tumors with exogenous replication of defective viruses?

Answer 12

Yes, some exogenous viruses acquire an oncogene (v-onc) from a cellular oncogene (c-onc) and then can induce malignant tumors rapidly.

Question 13

What conditions would you expect to see with exogenous replication of competent viruses?

Answer 13

Lymphoid leukosis (visceral lymphomatosis; big liver disease)

Osteoporosis (thick leg)

Renal tumors

Question 14

What conditions would you expect to see with exogenous replication of defective viruses?

Answer 14

Avian erythroblastosis, myelobastosis, myelocytomatosis

**Outcome of above: **anemia, leukemia

Also sarcoma