[A] 1.73 Carcinogenesis (biological agents)

Question 1

Biological carcinogens: Fungi

Answer 1

Mycotoxins:

• Hepatotoxic & Hepatocarcinogenic effect
• Aspergillus flavus B1 aflatoxin
• Penicillum species:
  
  • Ochratoxin
  • Patulin
  • Trichotecen

Question 2

Biological carcinogens: Plants

Answer 2

Eagle fern

• Chronic bladder bleeding of cattle
• Chronic cases:
  
  • Papilloma
  • Carcinoma

Question 3

Biological carcinogens: Oncogenic viruses

Answer 3

• Dominant oncogenes in many viruses
• Rous (Chicken - Sarcoma)
• Shope (Rabbit - Fibroma)
• Bittner (Murine mammary gland tumour)
• Gross (Murine leukemia)

Question 4

Oncogenic virus: Mechanism of action

Answer 4

1. Uncontrolled oncoprotein production in virus
2. Cell proliferation
3. Viruses insert viral oncogenes into host genome
4. Activation of oncoprotein production

Question 5

RNA-viruses as carcinogens

Answer 5

• Typical example: Retroviruses
• Two groups:
  
  • Contains oncogens / transformation genes
  • Lack of v-onc

Question 6

RNA viruses as carcinogens: Mechanism of action

Answer 6

Long terminal repeat (LTR) sequences aid the gene’s activation:

1. ALV & FeLV: Integrate before proviral c-onc
2. LTR follows this → c-onc is expressed
3. Leukemia

Some viruses: c-conc instead of env, this is “v-onc”

Question 7

Oncogenic DNA viruses

Answer 7

• Direct: Primarily activates c-onc
• Indirect: Stops apoptosis, inactivating tumor supressor genes

E.g Marek’s disease, Herpes-, papilloma-, poxvirus

Question 8

Give the biological causes of carcinogenesis

Answer 8

• Fungi
• Plants
• Viruses - RNA & DNA
• Parasites

Question 9

Parasite-induced carcinogenesis

Answer 9

• Spiprocerca lupi - Distal part of oesophagus, dog
• Eimeria stiedae - Biliary coccidiosis; Biliary papillomatosis (Rabbit)