Infection 4: How do viruses cause disease in humans?

Question 1

Incubation period

Answer 1

From infection to onset of symptoms in primary case

Question 2

Infectious period

Answer 2

Involves incubation period and symptoms

Question 3

What is a virus?

Answer 3

Particle made of nucleic acid and a protein coat

Small in size (100x smaller than our cells)

Obligate intracellular- only replicates inside living cells

Can infect wide range of organism

Question 4

Virus particles

Answer 4

Nucleic acid

• DNA or RNA
• ds or ss
• +/ve/-ve/ambisense

Protein coat

Enveloped/ unenveloped

Nucelocapsid

Question 5

Nucleocapsid

Answer 5

Nucleic acid and protein coat

Question 6

Virion

Answer 6

Complete intact virus particle

The physical particle in the extra-cellular phase which is able to spread to new host cells

Question 7

Viruses which cause encephalitis/ meningitis

Answer 7

JC virus

Measles

LCM virus

Arbovirus

Rabies

Question 8

Viruses which cause common cold

Answer 8

Rhinovirus

Parainfluenza virus

Respiratory syncytial virus

Question 9

Viruses which cause pharyngitis

Answer 9

Adenovirus

Epstein-Barr virus

Cytomegalovirus

Question 10

Viruses which cause gingivostomatitis

Answer 10

Herpes simples type 1

Question 11

Viruses which cause cardiovascular infection

Answer 11

Coxsackie B virus

Question 12

Viruses which cause hepatitis

Answer 12

Hepatitis A, B, C, D, E

Question 13

Viruses which cause skin infections

Answer 13

Varicella zoster virus

Human herpesvirus 6

Smallpox

Molluscum contagiosum

Human papillomavirus

Parvovirus B19

Rubella

Measles

Coxsackie A virus

Question 14

Viruses which cause eye infection

Answer 14

Herpes simplex virus

Adenovirus

Cytomegalovirus

Question 15

Viruses which cause parotitis

Answer 15

Mumps virus

Question 16

Viruses which cause pneumonia

Answer 16

Influenza virus A and B

Parainfluenza virus

Respiratory syncytial virus

Adenovirus

SARS cornoavirus

Question 17

Viruses which cause myelitis

Answer 17

Poliovirus

HTLC-I

Question 18

Viruses which cause gastroenteritis

Answer 18

Adenovirus

Rotavirus

Norovirus

Astrovirus

Conoavirus

Question 19

Viruses which cause pancreatitis

Answer 19

Coxsackie B virus

Question 20

Problems a virus must solve

Answer 20

Must know what cells to enter and how to enter them

How to replicate inside a cell

How to exit and move from one infected cell to a new cell

Develop mechanisms to evade host defences

Question 21

Viral pathogenesis

Answer 21

The process by which virus causes disease in a host

Two components of viral disease

• effects of viral replication on the host
• effects of host response on virus and the host

Question 22

Pathogenesis journey

Answer 22

Encounter

Entry

Multiplication

Spread

Damage

Outcome

Question 23

Encounter

Answer 23

Virus meets host

Question 24

Entry

Answer 24

Virus enters host

Question 25

Multiplication

Answer 25

Virus replicates in the host

Question 26

Spread

Answer 26

Virus spreads from the site of entry

Question 27

Damage

Answer 27

The virus, host response or both cause tissue damage

Question 28

Outcome

Answer 28

The virus or the host wins, or they coexist

Question 29

Skin

Answer 29

Abrasions Insect/ animal bites Needle punctures

Question 30

Alimentary tract

Answer 30

Gastroenteritis viruses Movement facilitate viral entry Hostile environment - extreme acidity/ alkalinity - digestive enzymes

Question 31

Urogenital tract

Answer 31

Mucus membranes; low pH Abrasions facilitate viral entry - HPV: local lesions - HIV: viral spread

Question 32

Eye

Answer 32

Localised infection- conjunctivitis Viral spread- eye blindness/ CNS

Question 33

Viral spread

Answer 33

After replication at site of infection - some remain localised within epithelium or within one system - some cause disseminated or systemic infection Viral release - apical e.g. flu- facilitate viral dispersal, but virus does no invade underlying tissues - basolateral e.g. rabies- provides access to underlying tissues and may facilitate systemic spread

Question 34

Haematogenous spread

Answer 34

Ways of viral entry to blood: - directly through capillaries - by replicating in endothelial cells - through vector bite - by lymphatic capillaries Once in the blood, virus has access to almost every tissue

Question 35

Viraemia

Answer 35

Presence of infectious virus in the blood - passive/ active viraemia - primary/ secondary viraemia Diagnostic value- measuring viral replciation Practical problem- need to screen blood donors

Question 36

Neural spread

Answer 36

Less common than haematogenous spread Viruses can go either way - from peripheral sites to CNS - from CNS to peripheral sites

Question 37

Infection of the CNS

Answer 37

Neurotropic- virus can infect neural cells Neuroinvasive- virus can enter CNS following infection of peripheral site Neurovirulent- virus can cause disease of nervous tissue

Question 38

Tissue tropism

Answer 38

Limited or pantropic Determinants of tropism - cell receptors- HIV/CD4+ - cellular proteins that regulate viral transcription- JC/ viral enhancers in oligodendrocytes - cell proteases- flue/ serine proteases

Question 39

Viral genes affecting virulence

Answer 39

Those that affect the ability of virus to replicate Those that modify host's defense mechanism Those that enable virus to spread Those that have intrinsic cell killing effects

Question 40

Cytolytic viruses

Answer 40

Inhibition of host protein and RNA synthesis leads to loss of membrane integrity Syncytium formation Induction of apoptosis

Question 41

Non-cytolytic viruses

Answer 41

CD8+ mediated CD4+ mediated B cell mediated

Question 42

Chronic/ persistent infection

Answer 42

Continuous replication Latency- restricted viral gene expression

Question 43

Latent infection

Answer 43

DNA viruses or retroviruses Persistence of viral DNA During cell growth the viral genome is replicated along with the host cell chromosomes

Question 44

Herpes simplex virus reactivation

Answer 44

Fever, blisters or cold sores

Question 45

How influenza viruses evade host defense mechanisms?

Answer 45

The virus can change its surface antigens- the immune response no longer able to identify them Mechanisms of antigenic variation on HA and NA - antigenic drift - antigenic shift