Virology

Question 1

Virus unique characteristics

Answer 1

Are smallest infectious particles
Range from 18 - 300 nm in size 100 nm
Consist of either DNA or RNA (but not both) and proteins with or without a lipid membrane coat
Lack an independent metabolic system
Require host cells for replication: true parasites
Consist of an intracellular reproductive cycle, and an extracellular transmissive cycle

Question 2

Unicellular organisms

Answer 2

Protozoa, fungi, bacteria, rickettsiae, mycoplasmas, chlamydiae
Unicellular, both DNA and RNA, binary fission

Question 3

Viruses

Answer 3

Obligate intracellular, either DNA or RNA (not both)
Two life cycles: extracellular (transmissive, inert), intracellular (reproductive)

Question 4

Prions

Answer 4

Proteins only, a small proteinaceous infectious particle (no nucleic acid genome). Prion diseases–Spongiform encephalitides
High resistance to heat, UV, irradiation, chemicals

Prion proteins:
Present in normal cells (PrPc)
Abnormal, conformational aberration: amyloid formation (PrPsc)

Question 5

Non-enveloped viruses

Answer 5

Protein subunit
Structure unit
Capsomer
Capsid (coat or shell)

Nucleocapsid
Only nucleocapsid protein (“naked”, no envelope)
More resistant: longer survival in environment, not seasonal disease, difficult to inactivate
Pathogenesis: lytic cell infection: often associated with acute disease, less chronic

Question 6

Enveloped viruses

Answer 6

Building blocks of non-enveloped viruses plus
Envelope: peplomer/spike, matrix proteins, lipids
Epidemiology: short survival in environment, labile, “easier” to inactivate, often associated with seasonal diseases
Pathogenesis: budding through infected cells, chronic/persistent infections
Immunology: Glycoprotein antigens: VN, CMI, vaccine immunity

Question 7

prevalence

Answer 7

photograph/snapshot
Insidious onset with unknown initial date
Chronic, long duration diseases
No time parameters only number of cases in defined number of subjects

Question 8

Incidence

Answer 8

Number of cases over number of subjects over a period of time (case:population ratio).
Acute, short duration diseases.
Denominator: population in a time frame: thus person- years or subject-weeks

Question 9

Enzootic

Answer 9

Multiple, continuous transmissions, disease presence in a defined population/region/time

Question 10

Epizootic

Answer 10

Peaks in incidence exceeding the endemic baseline. Nature and degree of expected damage defines whether it is called epidemic (high damage) or not (low damage)

Question 11

Panzootic

Answer 11

Worldwide outbreak

Question 12

incubation period

Answer 12

Moment of infection to onset of clinical signs
Short? long? variable?

Question 13

generation time

Answer 13

From moment of infection to first day virus shedding
Mostly shorter than incubation period. Influence in spreading disease

Question 14

period of infectivity

Answer 14

From first day to last day of virus shedding
May or may not be longer than clinical signs
Great influence in spreading disease

Question 15

Horizontal transmission

Answer 15

viruses are transmitted among individuals of the same generation

Question 16

Vertical transmission

Answer 16

occurs from mothers to their offspring

Question 17

Zoonotic transmission

Answer 17

an infectious disease that has jumped from a non-human animal to humans

Viral diseases transmissible under natural conditions from vertebrate animals to humans

Question 18

Vector-borne transmission

Answer 18

one in which transmission of infection in a population (the host population) occurs only via a second population (vectors). Vectors are usually haematophagous (blood-feeding) arthropods such as mosquitoes, sandflies or ticks

Question 19

Iatrogenic transmission

Answer 19

refers to the spread of a pathogen, (bacteria or virus) through a medical procedure or treatment such as a blood transfusion, reuse of needles or IV sets, or by touching a wound on an infected horse and then handling another horse

Question 20

Nosocomial transmission

Answer 20

an infection that is acquired in a hospital or other health care facility????

Question 21

Arbovirus transmission

Answer 21

Biological vector: virus replicate, magnify in vectors,
efficient transmission
Mechanical vector: no virus replication in vectors,
not efficient for transmission
Transmitted by mosquitoes, ticks, and sandflies

Question 21

Arbovirus transmission

Answer 21

Biological vector: virus replicate, magnify in vectors,
efficient transmission
Mechanical vector: no virus replication in vectors,
not efficient for transmission
Transmitted by mosquitoes, ticks, and sandflies

Question 22

acute virus infections

Answer 22

Rapid production of infectious viruses
Rapid resolution and elimination of the infection (virus clearance) by the host
Acute infections do not always produce disease

Question 23

Persistent virus infections

Answer 23

Infection not cleared efficiently
Virus particles are produced for a long period of time either continuously or intermittently for months or years

Question 24

Latent virus infections

Answer 24

Viral genomes integrated into cellular genomes, not expressed
no infectious progeny

Question 25

Host Range

Answer 25

receptors on animal tissues/cells; susceptible for wide range of infections or restricted infections

Question 26

Susceptibility

Answer 26

ability to become infected

Question 27

Permissivity

Answer 27

ability to replicate and produce progeny viruses

Question 28

Skin (routes of virus shedding)

Answer 28

Not a major route
Contact, abrasions, wounds

Question 29

Respiratory Secretions (routes of virus shedding)

Answer 29

Very important
Numerous diseases, local, systemic
Shedding occur before, during, after clinical signs

Question 30

Saliva (routes of virus shedding)

Answer 30

Salivary gland, oral cavity
Rabies, FIV

Question 31

Genital secretions (routes of virus shedding)

Answer 31

Sexual activity, semen, mucus

Question 32

Urine (routes of virus shedding)

Answer 32

Rinderpest, FMD, canine hepatitis in kidneys
Hantaviruses: mice to humans

Question 33

Milk: Not an important route
(routes of virus shedding)

Answer 33

Mammary gland replication, caprine arthritis-encephalitis