Retroviridae

Question 1

Genomic properties

Answer 1

Enveloped, positive sense, single stranded RNA

• reverse transcriptase: RNA dependent DNA polymerase
• diploid: 2 copies of RNA!

Question 2

Replication

Answer 2

• virus enters host via receptor
• reverse transcriptase copies the viral genome into DNA
• DNA integrates into the host genome
• provirus becomes transcribed and translated for assembly of new viral progeny

Question 3

Retrovirus induced oncogenesis

Answer 3

Insertional mutagenesis

• capture and unregulated expression of a host cell proto-oncogene
• includes genes that encode protein products directly oncogenic to infected cells

Question 4

Exogenous retrovirus

Answer 4

Replication defective

• transmission: infectious particles
• expression: yes
• genome: defective
• oncogene: present
• tumorigenicity: sarcoma, leukemia, or carcinoma after short incubation
• in vitro transformation: yes

Question 5

Avian leukosis/Sarcoma virus

Answer 5

Alpharetrovirus

• endemic in all flocks, affected within a few months of hatching
• A - E, J: chicken, oncogenic except E

Question 6

How is neoplasia spread with AL?

Answer 6

Congenital transmission, with exogenous replication defective virus

Question 7

What are 3 disease that cause neoplasms in poultry?

Answer 7

• Avian leukosis virus (chickens)
• Reticuloendotheliosis virus (chickens, turkeys, other avians)
• Marek’s disease virus

Question 8

What kind of neoplasms does ALV cause?

Answer 8

• mesenchymal
• renal
• osteopetrosis

Question 9

Diagnosis of ALV

Answer 9

• replication competent: FFA and interference assay in cell culture
• replication defective: FFA, ELISA, RT-PCR
• differentiate from tumors caused by REV and Marek’s!

Question 10

Bovine leukemia

Answer 10

Deltaretrovirus

• no oncogene
• dairy cattle has highest infection rates
• persistent, lifelong infection that progresses to multicentric lymphosarcoma
• less genetic variation among strains (97% relatedness)
• low overall incidence

Question 11

Transmission of bovine leukemia

Answer 11

• horizontally: close and prolonged contact with bodily fluids, trauma, reuse contaminated rectal examination gloves, needles, fomites, insect bites
• vertically: milk, colostrum, utero

Question 12

What are the 4 possible outcomes of bovine leukemia infection?

Answer 12

• genetic resistance: no infection
• asymptomatic infection: antibodies, seropositive 4-12 weeks later
• permanent infection: persistent lymphocytosis with benign proliferation of B lymphocytes
• infected, seropositive animals: lymphosarcoma <5% in ages 4-8 yrs

Question 13

Control of bovine leukemia

Answer 13

Repeated testing of animals over 6 months of age at 2-3 month intervals

• remove positive animals immediately
• isolated calves from infected dams, tested, allowed to enter seronegative herd only if they remain seronegative at 6 months

Question 14

Felive leukemia virus

Answer 14

Gammaretrovirus

• contagiously transmitted, associated with neoplastic and non-neoplastic disease
• exogenous FeLV: debilitating disease in domestic cats
• endogenous FeLV: not transmitted horizontally

Question 15

FeLV neoplasia

Answer 15

30% of feline tumors are associated with lymphosarcoma, 60-fold increase risk for lymphoma in FeLV + cats

• alimentary
• multicentric (multiple lymph nodes)
• thymic (mediastinal)
• unclassified (skin, eyes, CNS)

Question 16

Equine infectious anemia

Answer 16

Lentivirus

• blood borne infection
• lifelong, cell associated viremia
• transmission via flies, blood contaminated equipment
• transplacental infection, or horizontal infection

Question 17

EIA infection

Answer 17

• acute: fever, weight loss, anemia, edema, weakness, die 2-3 weeks, EIA test may be negative
• chronic: intermediated fever, lethargy, anorexia
• inapparent: EIA test is positive, no clinical signs

Question 18

Diagnosis of EIA

Answer 18

• Coggins test, ELISA60-100/day: false neg, false positive
• PCR amplification of provirus DNA: false neg, sequence variation
• PCR based diagnostic assays

Question 19

Control of EIA

Answer 19

• ID infected horses by serological testing
• euthanization
• iatrogenic: hygiene to preclude transfer of infective blood

Question 20

Accurate testing of EIA is done at _______

Answer 20

6 months of age

Question 21

Mississippi regulation of EIA

Answer 21

• equines except nursing foals entering MS must have an official copy of EIA test negative within 12 months
• all equidae, except nursing foals participate training, breeding, exhibition, moving require original copy of a current negative EIA test
• sale requires a valid negative EIA test

Question 22

Stages of FeLV

Answer 22

• acute: high-titer viremia, transit fever, peripheral lymph node enlargement, leukopenia
• prolonged chronic asymptomatic stage: lasts for years
• terminal stage: immunodeficiency, opportunistic infections, neurologic disease, neoplastic