Exam 2 - Lecture 3

Question 1

Know what is meant by “direct” contact and be prepared to give some examples.

Answer 1

direct contact requires physical touching (i.e. handshake, kiss, sexual contact, or wound-wound)

Question 2

What types of viruses usually use this mode (direct contact)?

Answer 2

Usually viruses that use this mode are fragile in some way, and they must stay warm/moist
– these are often enveloped viruses

Question 3

Know what is meant by “indirect” contact and be prepared to give some examples.

Answer 3

Indirect contact is viral transmission via inanimate objects called fomites

Question 4

What types of viruses usually use this mode (indirect contact)?

Answer 4

These viruses are usually naked viruses (non-enveloped)

Question 5

What are fomites?

Answer 5

fomites are inanimate objects that bacteria and viruses can be dispersed onto by one host and then picked up by other hosts

Question 6

Droplet transmission - what is meant by this?

Answer 6

droplet transmission requires close contact but not physical touching
– incl. sneezing, coughing, and normal respiratory secretions

Question 7

What types of viruses are spread via droplet transmission?

Answer 7

respiratory viruses

Question 8

Droplet transmission - who is most susceptible to this mode (in which environments), how is it affected by humidity?

Answer 8

People in densely populated areas are at a higher risk of exposure to viruses via droplet transmission. Air humidity also affects how droplets travel, and lower humidity tends to lead to better spread

Question 9

Food/water/soil
- How do viruses make it into these environments and how do individuals get exposed to them?

Answer 9

Some viruses get excreted into the environment, and also food products can be exposed to contaminated water or soil
– individuals get infected by touching the contaminated soil, or by consuming contaminated food or water (and also bathing in said water)

Question 10

Food/water/soil
- How does this mode influence the virus’ ability to spread?

Answer 10

These viruses are very hardy, and they have the ability to spread long distances

Question 11

Food/water/soil
- What are properties of viruses that are spread via food/water/soil?

Answer 11

• most don’t have envelopes
• have capsids that are unusually stable and resistant to protein denaturation
• often embedded in occlusion bodies

Question 12

Food/water/soil
- How can plants get infected via soil viruses?

Answer 12

Plants can get infected from soil viruses if the plant is damaged and wind or rain transports contaminated soil into the wound, and they also often become infected by vectors

Question 13

Food/water/soil
- What factors influence virus’ ability to survive in soil?

Answer 13

Virus survivability in soil depends on moisture, soil type, temperature, and on other soil microbes

Question 14

What is a vector and what types of organisms serve as vectors?

Answer 14

Vectors are organisms that serve to transmit a virus between hosts
– common vectors include arthropods and fungi

Question 15

What are the 2 types of vectors?

Answer 15

• biological vector : the virus actually has to infect the vector
• mechanical vector : the vector picks up the virus and transmits it to a new host without the vector itself becoming infected

Question 16

What is a reservoir?

Answer 16

an intermediate between hosts, harboring a virus but the virus it isn’t harming it

Question 17

How does the vector get the virus?

Answer 17

Viruses are usually picked up after the vector “feeds” on a host

Question 18

How is the virus delivered from vector to host?

Answer 18

• Some viruses stay attached to vector mouthparts and quickly move from vector to new host
• Some viruses move into gut of vector and enter into its circulatory system -> salivary glands

Question 19

Know how vectors deliver virus to plant hosts.

Answer 19

• aphids will pierce the cell walls of plants to feed and end up ingesting the plant contents, and they will transmit virions as they feed
• nematodes transmit virions through plant roots
• some parasitic fungi transmit virions b/t plants

Question 20

Know how vectors deliver virus to vertebrate hosts.

Answer 20

a vector bites a host and internalizes blood that contained the virus, and then go on to bite a new host and excrete the virus via defamation, saliva, or regurgitation

Question 21

What is vertical transmission?

Answer 21

Vertical transmission of viruses is the spread from a host to its offspring

Question 22

What are three modes of vertical transmission in vertebrates?

Answer 22

1) transplacental : virus crosses the placenta and infects the fetus in utero
2) childbirth (baby moving down an infected birth canal, or mix of mom/baby blood)
3) breast feeding (the virus is transmitted via breast milk)

Question 23

How can viruses be transmitted vertically in plants?

Answer 23

The virus makes it into an ovule or pollen. The infected seed becomes an embryo, and finally a plant that is infected with the virus

Question 24

How can viruses be transmitted vertically in invertebrates?

Answer 24

The virus infects the eggs, or become bound to the surface of the eggs. This is called transovarial transmission

Question 25

What is meant by epidemiology?

Answer 25

Epidemiology explores what happens when viruses move in a population, and the impact of that

Question 26

What are the five outcomes of a virus entering into a population?

Answer 26

1) virus doesn’t spread well b/t humans and “dies out”
2) herd immunity is developed and virus “dies out”
3) virus becomes endemic
4) virus enters a highly susceptible population and destroys it
5) virus enters/exits population in waves

Question 27

What is meant by herd immunity?

Answer 27

Individuals who survive a virus usually can’t be reinfected, so if too many people become immune to the virus, the virus runs out of hosts. This results in a form of protection called herd immunity for the individuals left who have not been infected by the virus

Question 28

What does it mean to be endemic?

Answer 28

The virus enters a population and it never leaves; it just keeps finding new hosts.

Question 29

How do viruses sometimes come into populations in waves (e.g. what ability do they usually have?)

Answer 29

Viruses that are influenced by seasonal changes, have vectors that change, or mutate often come into populations in waves. This can also produce new epidemics