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IMED2001 > Patterns of Viral Infection > Flashcards

Patterns of Viral Infection Flashcards

1
Q

What is pathogenesis?

A

Is the complex interaction between virus and host that results in disease

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2
Q

What is pathogenicity?

A

A comparison of the severity of disease caused by different microorganisms

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3
Q

What is virulence?

A

A comparison of the severity of disease caused by different strains of the same microorganism

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4
Q

What are the 2 components of pathogenicity in viruses?

A

Effects of viral replication on the host

Effects of host response on virus and host

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5
Q

What are the fundamental questions of pathogenesis in regards to viral infections?

A

How does a virion enter the host?

How does it overcome local defences?

How does it spread to other areas of the body?

How does it exit from the host to infect other susceptible hosts?

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6
Q

Why is one viral strain more virulent than another?

A

Replication rate

Tropism

Ability to evade host immune defences

Changes in ability to disseminate within the host

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7
Q

How can virulence change?

A

Very small changes in the viral genome (eg influenza B can change to bind to human entry protein as well)

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8
Q

What cellular factors determine pathogenicity of viruses?

A

Presence of receptors for binding

Physical and molecular environment of host cell must enable initial replication cycle (eg upper respiratory viruses may ideally want 33 degrees cells)

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9
Q

What is the cytopathic effect?

A

Many viruses kill the cells in which they replicate. Infections induce characteristic appearance.

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10
Q

What can CPE be used for?

A

Diagnosis of infecting virus

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11
Q

How can viruses enter host through the skin?

A

Through abrasians

Entry via inoculation with contaminated needles

Through insect or animal bites

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12
Q

How can viruses enter host through mucous membrane?

A

Entry via respiratory tract

Entry via GI tract (faecal-oral route, eg poliovirus causing poliomyelitis)

Entry via conjunctiva (Enterovirus type 70 causes conjunctiva)

Entry via genital tract (eg. STIs)

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13
Q

How do viral infections of the respiratory tract manifest themselves?

A

Could show symptoms above the neck and below the neck.

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14
Q

How do viruses spread?

A

Through blood (either through capillaries by replicating in endothelial cells or through insect bite)

Through lymphatic capillaries they can enter circulation as well

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15
Q

What is viraemia?

A

Presence of infectious virus in the blood

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16
Q

What causes active viremia vs passive viremia?

A

Virus replication causes active

Virus introduction causes passive

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17
Q

What is primary viremia?

A

Virus enters blood after initial replication at site of entry

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18
Q

What is secondary viremia?

A

Virus produced by disseminated infections

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19
Q

How is there diagnostic value in viremia?

A

The secondary viremia is stronger allowing blood samples to give us more information

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20
Q

What are the important target organs for viral infections?

A

Skin

Lungs

Liver

Kidneys

CNS

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21
Q

What do viral infections of the skin typically look like?

A

A skin rash or exanthem

Vesicular erutions caused by replication of viruses in epthelial cells

Maculopapular rash (destruction of cells by Cytotoxic T Lymphocytes)

Purpuric rash causing haemorrhaging (as seen in dengue virus)

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22
Q

What type of infections hit the lungs?

A

Most respiratory infections are localized

Some are part of a generalized infection (e.g. Measles –
pneumonitis is a common feature)

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23
Q

What type of infections hits the liver?

A

Hepatitis viruses

Also infected during generalized infections like yellow fever

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24
Q

What type of infections affect the kidneys?

A

Rarely infected: CMV infects proximal renal tubules; hantaviruses cause haemorrhagic fever with nephritis

25
Q

How is CNS reached by viruses?

A

Access from bloodstream during viremia via nerves in periphery connected to CNS

26
Q

Is neural spread characteristic of all viral infections?

A

Only for some like rabies, herpes simplex and varicella zoster.

For others it is an infrequent diversion from normal actions

27
Q

What is a neurotropic virus?

A

A virus that can infect neural cells

28
Q

What is a neuroinvasive virus?

A

Virus that can enter CNS after infection of a peripheral site

29
Q

What is a neurovirulent virus?

A

A virus that can cause disease in nervous tissue

30
Q

Why don’t all viruses get transmitted as easily as influenza?

A

The reproduction number (Ro) (average number of secondary cases generated by one primary case)

31
Q

Rank the following from lowest Ro to highest Ro:

Smallpox

SARS

Influenza

Measles

A

Ro of SARS and smallpox is about 2

Influenza 4

Measles 10

32
Q

What kind of viruses can create significant public health problems?

A

Viruses with short incubation periods and high Ro’s

Viruses with long incubation periods are also of serious concern due to viral shedding

33
Q

What kind of course does an acute infections often have?

A

A quick peak followed by complete recovery soon after

34
Q

What kind of course does a persistent viral infection have?

A

Can have 3 courses:

Smoldering (increases then remains the same for a long time until death)

Latent (comes and goes)

Slow (comes on once and then goes and then comes back to near time of death)

35
Q

What is the incubation period?

A

Period between infection and before characteristic symptoms of disease are apparent

36
Q

What are the normal steps of an acute viral infection?

A

Rapid onset with shory but severe course

Disease recovers over a period of days

Rapid production of virions followed by resolution of infection by immune system of the host

37
Q

What is the prodromal period?

A

The period just before symptoms of illness start to show

38
Q

What is happening during incubation period?

A

Viral replication and host response but not at a noticeable level

39
Q

What causes most symptoms of viral infections?

A

The host immune system

40
Q

Why do acute infections often present common public health problems?

A

Often associated with serious epidemic affecting millions of people

Infected host is often infectious before symptoms manifest

Infections hard to control in large populations

Effective antivirals require early action which is rarely the case

41
Q

How does measles virus typically present?

A

Fever >38 degrees

Respiratory problems (coryza cough)

Conjunctivitis

Koplik’s spots

Rash (3 - 5 days after onset of symptoms)

42
Q

What is subacute sclerosing panencephalitis?

A

A complication of measles which presents after 6 - 10 years of initial infection

43
Q

What happens in subacute sclerosing panencephalitis?

A

It is a persistent infection of the CNS.

Neurons and oligodendrosites contain measles virus exclusion bodies. This triggers extensive mononuclear inflammation including CD4+ and CD8+ T cells as well as monocytes and antibody secreting B cells. The immune cells are unable to clear MeV infection from the brain.

It is unknown whether the cause of death in this condition is the MeV infection or immune response

44
Q

In who does MeV + SSPE typically happen?

A

If primary infection occurred before 2 years of age

45
Q

What are persistent viral infections?

A

Virions, genomes, proteins are produced or persist for long periods,
often for lifetime of host

46
Q

Can viral genomes persist in absence of viral proteins?

A

Yes they can persist in host genomes

47
Q

What are the types of persistent infections?

A

– Chronic: virus is always detectable

– Latent: virus sequesters in a tissue with recrudescence

48
Q

How is hep B transmitted?

A

Exposure to blood + blood products

Childbirth

Transfusion

Sex

Contaminated needles

Nosocomial infections

49
Q

What is the main target cell for hep B?

A

Hepatocytes

50
Q

What is the result of persistent hepB virus?

A

Cirrhosis and development of hepatocellular carcinoma

51
Q

What is the estimated number of hepB carriers?

A

350million

52
Q

How does hepB virus (HBV) persist?

A

In the nucleus of infected hepatocytes as covalently closed circles of DNA. HBV cccDNA may be reactivated and allow virus to replicate.

HBV includes a reverse transcriptase enzyme which enables antiretroviral drugs developed for HIV to be used to work on HBV.

53
Q

How does age affect the carrier risk of HBV?

A

The older you are the less likely you are to suffer from chronic HBV.

54
Q

What is herpesvirus infection like?

A

A latent infection following a primary infection.

55
Q

What happens after primary herpesvirus infection?

A

Viral genome sits in the host and is reactivated in response to certain stimuli

56
Q

What stimulates herpesvirus recurrence?

A

Fever, physical or emotional stress, hormones, menstruation

57
Q

Where does the herpesvirus replicate in following reactivation?

A

In the sensory neuron and is transported to site at or near entry

58
Q

Can herpesvirus cause infection in CNS?

A

Rarely

59
Q

Where in the neuron does the herpesvirus lay dormant?

A

In the cell body of sensory neuron

IMED2001 (44 decks)

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