6. Olds (Finals 2)

Question 1

What is the most important step for the successful infection of the cell?

Give 3 ways on how this can be blocked or prevented?

Answer 1

Most critical step is ATTACHMENT

3 ways to block/prevent:
1. Block the viral ligands (e.g. antibodies)
2. Change in receptor specificity (e.g. lapinized strain of hog cholera virus)
3. Breed species without the receptor? (BUT receptors serve normal physiologic functions, and viruses merely misuse these receptors)

Question 2

Define viremia. Explain it in the dead end host and reservoir host (?)

Answer 2

Viremia - presence of virus in the bloodstream

● Dead-end host - has limited ability to transmit virus to other host because it is incapable of high levels of replication, thus, virus is just transient in blood until killed.

● Reservoir host - species that can harbor high levels of replication (even subclinal) thus, it can be transmitted to other host.

Question 3

Give 5 examples of virus families with segmented genome.

Answer 3

1. Birnaviridae
2. Orthomyxoviridae
3. Arenaviridae
4. Reoviridae
5. Bunyaviridae

Question 4

Illustrate the genomic organization of the L segment of the Arenavirus and explain how it is expressed into proteins

Answer 4

Illustration

**S segment **- encodes viral nucleoprotein (NP) and glycoprotein precursor (GPC)

L segment - encodes viral RdRp (L) and matrix protein (Z)

Question 5

Give 5 methods of controlling vectors to prevent spread of arthropod-borne diseases.

Answer 5

1. Habitat control - reducing areas where vectors easily breed or live
2. Reducing contact - limiting exposure to arthropod vectors (nets or protective clothing)
3. Chemical control - insecticides, larvicides, repellents
4. Biological control - use of natural vector predators
5. Kill breeding area :D (gumana to sa vpar na ans)

Question 6

Give the 3 major disadvantages of live vaccines over killed vaccines

Answer 6

1. Stronger vaccine
2. Shorter shelf-life
3. Contains live pathogens (from virus) that could infect host upon administration
4. Longer immunity
5. Can’t be used to immunocompromised animals (under attenuated - virulence and disease)

Question 7

Give three major ways on how antibodies can protect the body from cell-free viruses.

Answer 7

1. Neutralization - binding to virus spikes so they don’t bind to healthy cells
2. Opsonization and Phagocytosis - Abs bind to Ag. Phagocytes have Fc receptors for Fc region of antibodies then attaches to it for phagocytosis
3. Complement System - utilizes proteins that produce membrane attack complexes
   (MACs) that destroys envelope/surface tubules of virus.

Question 8

Give 5 reasons why ASF is difficult to control

Answer 8

1. No treatment
2. No vaccine
3. Virus transmission via fresh meat and some cured meat products, can live for up to months or years in frozen meat.
4. Persistent infection in some pigs
5. Confusion with other disease like CSF, misdiagnosis
6. Persistent Tick transmission

Question 9

Give one major reason why PCR is more sensitive than viral isolation

Answer 9

• “n amount of PCR cycles = 2n amplicons”
• Important term: amplified (makes it easier to find the desired nucleotide sequences)

Question 10

Give three factors that contribute to the emergence of new viral diseases or resurgence of old viral diseases.

Answer 10

1. Constant change in ecological and anthropogenic factors
2. Virological determinants
3. Host and environmental factors

Question 11

Draw circovirus and influenza (orthomyxo?) virus.

Write 5 differences between the viruses in terms of structure, morphology, or chemical composition.

Answer 11

DRAWING

1. **Nucleic Acid Conformation **- Circo (ssDNA), Influenza (ssRNA)
2. **Presence of Envelope **- Circo (nonenveloped), Influenza (enveloped)
3. Proteins - Circo (2 major ORFs on opposite sides: replicase and capsid proteins), Influenza (proteins making up ribonucleotide: NP, PA, PB1, PB2) and in lipid envelope (HA, NA, M1, M2)
4. Shape of virions - Circo (spherical), Influenza (pleomorphic, filamentous)