Viruses and neoplasia

Question 1

Give examples of some viruses that can cause neoplasia

Answer 1

RNA: Avian leukosis (lymphoid, myeloid, sarcomas)
Feline retroviruses (lymphoid)
DNA: Herpesviridae (Marek’s disease virus– lymphoid)

Question 2

What is a proto-oncogene

Answer 2

A gene that tends to be involved in a growth of cells, but if a mutation or increased expression occurs then it can become an oncogene

Question 3

How can viral transduction results in oncogenes?

Answer 3

Integration of a recombinant retrovirus carrying a c-onc gene into host genome
(Virus can pick up an
oncogene and change it slightly and then introduce it into other cells.)

Question 4

What is different about RSV virus?

Answer 4

-Most viruses that acquire a c-onc lose essential genes of their own so become defective and need help to replicate. RSV is different as it have a v-src which has a C terminal deletion that makes it permanently active. This active v-src is passed onto other cells promoting the growth of very rapid tumours. This is called an ACUTE TRANSORMING RETROVIRUS

Question 5

What is the main mechanism for oncogenesis for feline leukaemia and avian leukosis viruses?

Answer 5

Insertional activation

Question 6

Which part of the virus determines the kinetics of the cancer (how fast it grows)

Answer 6

The LTR (long terminal repeat)

Question 7

Describe avian leukosis

Answer 7

• It is a retrovirus
  -Transmitted from hen to egg
  -Get persistently infected chicks
  -Immunotolerant to viral antigens (develop tumours)
  Tumours form quickly (from about 4 months) because the chicks were infected before being immunocompentant so don’t recognise virus as a foreign threat.
  -B cell tumours
  -Control by eradication in breeder flocks

Question 8

How does gene inactivation help as a mechanism of retroviral oncogenesis?

Answer 8

If a retrovirus gene is inserted into the middle of a tumour suppressor gene e.g. p53 then it can turn that gene off.

Question 9

Describe Bovine Leukaemia virus

Answer 9

• Causes enzoootic bovine leukosis
• Infects B lymphocytes and become latent
• NO FREE VIRUS IN BLOOD
• Antiviral antibodies in PI cattle
• Products of transactivated cellular genes may be oncogenic

Question 10

What is TAX transactivation?

Answer 10

Can switch LTRs on and off–> meaning it can become latent to avoid detection by the host response. Activated cytokines (growth promoters)

Question 11

Describe JSRV virus

Answer 11

-Replicates in type 2 pneumocytes and Clara cells (in teh lung)

Question 12

Describe JSRV virus

Answer 12

• Replicates in type 2 pneumocytes and Clara cells (in the lung)
• Viral Env protein switches on signals for cell division
• The respiratory secretions are VERY infectious, eradication by rapid isolation and culling of infected animals.

Question 13

What is a clinical sign of JSRV in sheep?

Answer 13

• If you wheelbarrow the sheep you get lots of surfactant fluid draining out the nostrils

Question 14

What plant is linked with bladder cancers?

Answer 14

Bracken as it is immunosuppressive and mutagenic= quercetin and ptaquiloside

Question 15

What species does Marek disease virus affect?

Answer 15

• Poultry
• Tumours from T lymphocytes
• Classical form is bird going off legs due to nerve routes being invaded
• Commonly affects birds aged 12-24 weeks

Question 16

Describe the pathogenesis of Mareks Disease

Answer 16

• Enveloped virus from feather follicle cells
• Enters respiratory tract
• Migrates to bursa, thymus, spleen
• Kills B and M cells causing immunosuppresion
• Becomes latent in T cells causing tumours

Question 17

How does Marek disease cause neoplasia?

Answer 17

The Meq gene is involved in transformation of the lymphocytes