7 - Evolution and emergence of new viruses

Question 1

What is meant by quasi species?

Answer 1

within a single infected person, they will have viral genomes that are slightly different because they evolve whilst they are in the host

Question 2

How can drug resistance be prevented?

Answer 2

use a combination of antiviral drugs

Question 3

What does HAART stand for?

Answer 3

Highly Active Anti-Retroviral Therapy

Question 4

What is antigenic drift?

Answer 4

when antigens gradually change over a period of time due to pressure exerted by antibodies

Question 5

How do new viruses emerge?

Answer 5

• zoonosis
• genetic variation
• increased exposure - travel or world population
• increased exposure - spread of vector
• new discoveries

Question 6

Define arboviruses

Answer 6

a class of viruses transmitted to humans by arthropods such as mosquitoes and ticks

Question 7

Give some examples of arboviruses

Answer 7

yellow fever
dengue
west nile

NOTE: many of these are flaviviruses

Question 8

What are flaviviruses?

Answer 8

have single stranded positive-sense RNA genomes

Question 9

What is meant by Antibody Dependent Enhancement of the Infection with reference to dengue fever?

Answer 9

4 serotypes of the dengue virus

• the first time you get dengue, you are ill, but not severely
• the second time, you will be infected with a different serotype - and the antibodies that you develop the first time will make you more ill

Question 10

What is meant by host range?

Answer 10

refers to an organism’s ability to infect and reproduce in wide range of organisms.

The spectrum of strains of bacterial species that a given strain of phage can infect. The range of cells that can act as a host to a virus or bacteriophage.

Question 11

Dengue antibodies can neutralise or. enhance infections. What is the mechanism by which they enhance it?

Answer 11

• the virus binds to the wrong anti-dengue antibodies, and this gives it another way of getting into cells
• dengue virus usually gets into the cells by binding to specific receptors
• if you have homogenous antibodies (all the same), viral antigens will bind them tightly and stop it from entering the cell
• if infected by a different viral serotype, the antibodies will bind the antigens loosely but won’t block it
• then the antibodies will bind to Fc receptors on immune cells, thus carrying the virus into immune cells
• this leads to a cytokine storm and dengue haemorrhagic fever

Question 12

What is meant by zoonosis?

Answer 12

a disease that can be transmitted from animals to humans

more specifically, a disease that normally exists in animals but that can infect humans

Question 13

Which zoonoses have the potential to start a pandemic but do not transmit efficiently?

Answer 13

SARS
ebola
Hendra
nipah

Question 14

What does SARS stand for?

How it is transmitted?

Answer 14

Severe Acute Respiratory Syndrome

transmitted via respiratory droplets

Question 15

What is the time relationship between becoming symptomatic and contagious of SARS?

Answer 15

does not become contagious until late into infection once it has become symptomatic
therefore, the virus is containable

NOTE: flu is the opposite

Question 16

Swine flu and antigenic drift

Answer 16

• as the virus circulated in humans, it changed gradually and so it has antigenic subtypes
• you do not get antigenic drift in pigs because they do not live long enough to be re-infected
• humans live long enough to be re-infected so their antibodies drive evolution of the virus
• Now, the H1 virus in totally different to that in humans