Oncology: Viruses

Question 1

Name 4 retroviridae (RNA viruses) that cause cancer

Answer 1

Avian leukosis
Feline retroviruses
Jaagsiekte sheep retrovirus
Bovine leukosis

Question 2

What type of tumours does Avian leukosis cause?

Answer 2

Avian leukosis – lymphoid, myeloid tumours, sarcomas

Question 3

What type of tumours do Feline retroviruses cause?

Answer 3

Feline retroviruses – lymphoid tumours

Question 4

What type of tumours does Jaagsiekte sheep retrovirus cause?

Answer 4

Jaagsiekte sheep retrovirus – lung adenocarcinoma

Question 5

What type of tumours does Bovine leukosis cause?

Answer 5

Bovine leukosis – lymphoma

Question 6

Name a herpesviridae (DNA virus) that causes cancer

Answer 6

Marek’s disease virus – lymphoid tumours

Question 7

Name a papillomaviridae (DNA virus) that cause cancer

Answer 7

Bovine, equine, canine papilloma viruses - skin, mucosal

Question 8

Viral transduction can result in….

Answer 8

…overproduction of protein homologous to cellular oncogene (v-onc)

Question 9

Viral insertion can also….

Answer 9

….upregulate production of a cellular oncogene

Question 10

Where do chickens get avian leucosis form?

Answer 10

Transmitte d from the hen to the gee, leads to persistently infected chicks which are immunotolerant to viral antigens

Question 11

How long is the incubation period until tumour development for avian leucosis?

Answer 11

Over 4 months

Question 12

What are the three most important avian leucosis virus subgroups?

Answer 12

ALV subgroups A and B (‘conventional’) - B lymphocyte tumours in some birds
ALV subgroup J (emerging virus) - Myeloid tumours

Question 13

How is ALV controlled?

Answer 13

Control by eradication in breeder flocks: Select virus-free hens by screening eggs
Check eggs over 14-day period for ALV antigen in albumen by ELISA
Hatch chicks and rear in isolation
Test for ALV antigen in blood

Question 14

What type of retrovirus is bovine leukaemia virus and what does it cause?

Answer 14

(δ retrovirus)

Causes enzootic bovine leukosis

Question 15

Where does BLV infect?

Answer 15

Virus infects B lymphocytes and becomes latent so no free virus in blood
Antiviral antibodies in persistently infected cattle

Question 16

How is BLV transmitted?

Answer 16

Transmission via infected cells e.g. milk, blood.

Can be transmitted vertically or horizontally

Question 17

Is BLV notifiable?

Answer 17

Yes

Question 18

How does BLV cause tumours?

Answer 18

The viral Tax protein transactivates cellular genes
Products of transactivated cellular genes may be oncogenic
Lymphocytosis, lymphoma formation in older cattle

Question 19

What type of retroviridae is Jaagsiekte sheep retrovirus ?

Answer 19

(β retrovirus)

Question 20

How does JSRV cause tumours?

Answer 20

JSRV replicates only in type II pneumocytes and Clara cells
Replication leads to transformation of every cell
Viral Env protein switches on signals for cell division – activates cellular signalling pathways

Question 21

How does JSRV cause tumours?

Answer 21

JSRV replicates only in type II pneumocytes and Clara cells
Replication leads to transformation of every cell
Viral Env protein switches on signals for cell division – activates cellular signalling pathways

Question 22

What are the clinical signs of JSRV?

Answer 22

Wheelbarrow test- produces lots of surfactant fluid from lungs
Respiratory secretions are infectious

Question 23

How is JSRV transmitted and treated?

Answer 23

Requires close contact - More common in housed sheep

Can eliminate the disease by rapid isolation and culling of diseased animals

Question 24

How is JSRV diagnosed?

Answer 24

Diagnosis by histopathology/RT-PCR

Question 25

How do cows contract bovine papillomatosis?

Answer 25

When cows eat bracken they are exposed to a number of immunosupressive and mutagenic chemicals
e.g. quercetin and ptaquiloside and when exposed to the BPV they can develop tumours

Question 26

What are the types of bovine papillomatosis?

Answer 26

BPV-2: bladder carcinomas (enzootic haematuria)

BPV-4: alimentary carcinomas (oesophageal, rumen, reticulum)

Question 27

What is marek disease virus?

Answer 27

Oncogenic herpesvirus
Tumours derived from T lymphocytes
Field strains show variable virulence but commonly affects birds aged 12-24 wk.
Birds go off their legs due to neoplastic lymphoid cells blocking the nerve roots