Lecture 18

Question 1

What 3 points of entry are there for viruses

Answer 1

1. Virus enters and circulates widely but can only infect cells in one location, where it replicates to cause disease e.g. Hep B with the liver
2. Virus infects cells at portal of entry and replicates by signs and symptoms, but physical barriers prevent spread elsewhere despite use of widely disributed cell receptors
3. Virus infects cells at portal of entry, replicates and breaches local barriers to spread systemically, gives variety of signs and symptoms e.g. measles with entry and exit via respiratory tract

Question 2

Infectious pathways

Answer 2

Contact: Bites, kisses, blood, injection, sex

Indirect: Faeces, urine, salvia -> Aerosol, environment, formites -> inhalation, ingestion

Question 3

Describe the yellow fever transmission cycle in S. America

Answer 3

Monkey transfer virus to Haemagogus spp

Haemagogus spp. Infects farmer

Farmer passes it to Aedes aegypti

Aedes aegypti infects humans in urban cycle

Question 4

Describe the yellow fever transmission cycle in Africa

Answer 4

Monkey passes virus to Aedes africanus and other Aedes spp.

Aedes spp. infect farmers and crop workers

Pass it to Aedes aegypti

Aedes aegypti infect people in urban cycle

Question 5

How is the sandfly fever virus passed

Answer 5

Cycle with sandfly and reservoir host exchanging virus

Sandfly infects humans and vice versa

Question 6

Yellow fever virus cycle

Answer 6

Virus is exchanged between monkeys and Mosquitos

Mosquitos infect humans and vice versa

Question 7

West Nile virus

Answer 7

Mosquito and bird can infect each other with the virus

Mosquito infects human

Question 8

Diagnosis of disease

Answer 8

• Symptoms
• PCR - detects viral genome

Immunological techniques - Detect viral proteins and host antibodies

Assays

Question 9

Plaque forming units

Answer 9

Quantifies presence of virus

Question 10

Haemagglutinin inhibition assay

Answer 10

Uses well plate where influenza virus is serially diluted

RBCs added at 0.5% v/v

RBCs settle to form button in absence of virus

RBCs agglutinate in presence of virus

Question 11

PCR

Answer 11

Nasopharyngeal swab - ~15 mins

Collected specimen - 0-72 hours

RNA extraction - ~45 mins

RT-PCR ~1 hour per primer set

Test results determined by fluorescence

Question 12

Serologic diagnostic test for COVID-19

Answer 12

1. Blood sample loaded into well
2. Buffer loaded into well
3. Sample incubation - Capillary action
4. Antigen-antibody recognition - Bind gold
5. COVID-19 antibody testing - At T, antibody-antigen complex binds immobilized anti-human igG/IgM antibodies
6. Control antibody detection
7. Interpreting results C and T show a line positive, C only is negative, T only or none is invalid

Question 13

ELISA

Answer 13

Typical ELISA test but uses chromogenic substrate for enzyme and colour intensity measured by spectrophotometry over time

Question 14

Neutralisation assay

Answer 14

Quantifies presence of functional antibodies to virus