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Microbiology > Patterns of viral infection > Flashcards

Patterns of viral infection Flashcards

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Biology 101 flashcards
1
Q

Latrogenic transmission

A

Health care worker e.g. contaminated needles

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2
Q

Noscomial transmission

A

Acquired in hospital

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3
Q

Vertical transmission

A

From parent to offspring

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4
Q

Horizontal transmission

A

All other forms

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5
Q

Germ line transmission

A

Part of the host genome (e.g. intergrated retrovirus)

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6
Q

Viral routes of entry to the body

A 
Skin
Mucosal surfaces (Respiratory, Enteric, Genital tract)
Conjunctiva
Blood
Bites
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7
Q

Arboviruses

A

Viruses spread by insects

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8
Q

Dissemination from site of entry

A 
Local infection
Primary viraemia
Amplification
Secondary viraemia
Target organ
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9
Q

Viraemia

A

Virus in blood

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10
Q

Viral rashes

A

Sign of systemic viral infection
Virus leaves blood and enters skin
Cells destroyed by virus replication

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11
Q

Example of viral rash

A

Koplik spots in mouth (measles)

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12
Q

When do symptoms of Varicella Zoster virus (chicken pox) appear?

A

After secondary viraemia

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13
Q

Varicella zoster virus mechanism of action

A

Enters body through respiratory route
Can infect many cell types including skin cells.
Leads to mild self-limiting illness in most childhood cases.
From the skin site, it can infect sensory neurones where it remains latent.

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14
Q

What happens in herpes zoster, or shingles, occurring in adulthood when cellular immunity is impaired?

A

Varicella zoster virus is reactivated in the sensory neurone and causes a painful rash at nerve endings

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15
Q

Tropism

A

predilection of viruses to infect certain tissues and not others

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16
Q

What 3 factors are tropisms based on?

A

Susceptibility: receptor interactions
Permissivity: ability to use the host cell to complete replication
Accessibility: ability of the virus to reach the tissue

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17
Q

Describe the type of tropism exhibited by HIV

A

Viral attachment protein GP120 on HIV interacts with CD4 on the T cell
It attaches to co-receptors CCR5 and CXCR4

18
Q

What mutation confers resistance to HIV in exposed uninfected?

A

Delta 32 mutation in CCR5

19
Q

Describe the type of tropism exhibited by Measles.

A

Bind to SLAM on immune cells when entering the host

Bind to Nectin 4 on airway epithelia when leaving the host

20
Q

Describe the type of tropism exhibited by Influenza.

A

Haemagglutinin on influenza binds to sialic acid that are ubiquitous to gain entry through endosomes
Low endosomal pH allows conformational change required for virus to fuse with the endosome membrane and uncoat
The cleaving of the protein of the virus is essential for the viral genome to gain access to the host cell genetic material
So can only infect cells with the necessary proteases to cleave the protein

21
Q

Pathogenicity

A

ability of the virus to cause disease

22
Q

Virulence

A

capacity of a virus to cause disease

23
Q

Patterns of virus infection

A

Acute infection followed by viral clearance
Acute infection but ‘accidental’ tissue infected with permanent damage despite viral clearance
Persistent infection: latent, slow, transforming
Long incubations
Oncogenesis

24
Q

Acute infection and clearance

A

e.g. Colds and influenza.
Many unapparent or asymptomatic infections.
Adaptive immune response provides immunity
Viruses continue to circulate in populations by antigenic variation

25
Q

Acute infection and death

A

Smallpox (Variola virus) Infection of skin. Viral growth factors induce proliferation of skin resulting in pox.
Dengue haemorrhagic fever. Leakage of blood plasma from capillaries. Tendency to severe bruising, and bleeding.

26
Q

Acute infection and accidental pathogenesis examples

A

Poliovirus (localised infection of small intestine)

Rubella (mild rash)

27
Q

How does poliovirus lead to accidental pathogenesis?

A

may lead to Poliomyelitis: Neurovirulent virus, infects motor neurons causing paralysis.

28
Q

How does Rubella lead to accidental pathogenesis?

A

In early stage fetus virus has a strong tropism for dividing neuronal tissue. Leads to a classic triad:

  1. Deafness
  2. Eye abnormalities (cataracts)
  3. Congenital heart disease
29
Q

Examples of persistent viral infections

hide in places immune system struggles to reach

A

Papillomaviruses in warts.
Chronic carriers of hepatitis B and C viruses.
Herpes viruses e.g. Herpes Simplex, Varicella Zoster

30
Q

Strategies for viral persistence

A

Evading immune surveillance e.g. Hepatitis C

Infecting tissues with reduced immune surveillance (CNS and skin) e.g. Herpes, papillomavirus

31
Q

Describe the latency of Herpes simplex virus.

A

Can remain latent on nerve cells and then become activated in an attack of shingles
The virus then moves to the end of the neurones and replicates through the skin (forming a cold sore)

32
Q

Give 4 examples of oncogenic viruses and the types of cancer that they cause.

A

HHV8: Kaposi Sarcoma
HTLV-1: Leukaemia
Merkel Cell Polyoma Virus: Merkel Cell Polyoma
HPV: Cervical Cancer

33
Q

Why would viruses encode oncogenes?

A

Enables them to interfere with the cell cycle in order to enhance their own replication

34
Q

What type of cancer do Hepatitis B and C cause?

A

Hepatocellular Carcinoma

35
Q

What types of cancer can Epstein-Barr Virus cause?

A

Burkitt’s Lymphoma
Hodgkin’s Lymphoma
Nasopharyngeal Carcinoma

36
Q

What is Epstein Barr Virus?

A

A gamma herpes virus, the most common virus infection of mankind.
In most, causes a lytic infection in childhood or infectious mononucleosis in young adulthood.
Remains latent in B cells.
Passed on in saliva.

37
Q

What effects the outcome of viral infections?

A

Viral sequence and load
Host immune response, co-morbidity, genetics and age
Co-infections

38
Q

Give an example of viral load affecting the outcome of an infection.

A

2nd child in a household infected with chicken pox will have a worse infection because they’ll get a large dose from the first child

39
Q

Give 2 examples of co-infections affecting the outcome of an infection.

A

HHV8 can cause Kaposi Sarcoma in people who are infected with HIV (immunocompromised)
Hepatitis Delta Virus only infects people with Hepatitis B

40
Q

Give an example of viral sequence affecting the outcome of an infection.

A

2 strains of poliovirus might vary in their virulence.
Single mutation in genome can mean 1 strain acts as a live attenuated vaccine (Sabin)
Another invades the motor neurone & causes flaccid paralysis (poliomyelitis).

41
Q

What can determine the outcome of a hepatitis C infection?

A

KIR genotype

42
Q

Predisposing co-morbidities and conditions for severe influenza

A 
Asthmatics and respiratory viruses
Obesity
Immunosuppression
Immunodeficiency
Elderly
Diabetes mellitus
Pregnancy

Microbiology (9 decks)

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