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Microbiology > Unit 10 > Flashcards

Unit 10 Flashcards

1
Q

Describe viruses

A

Found everywhere

Goal: to infect cells

Can exists but cannot replicate outside of cells (can only replicate inside host cells) And their life cycle depends on infection

Can infect bacterial/animal/plant cells

10-1000 nanometers (smaller than bacteria) (second smallest -first is a prion) can only see with an electron microscope

NOT cells, considered particles

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2
Q

Define Bacteriophage

A

Viruses that infect bacteria

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3
Q

What is a virion

A

A completely assembled infectious virus particle outside its host cell

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4
Q

What are 4 components of viruses (which 2 do ALL viruses have?)

A

Every virus has
A protein shell called a Capsid
Genetic material

SOME have protein protruding from the surface (spikes)
SOME have an envelope

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5
Q

A capsid and the enclosed genome is called the

A

Nucleocapsid

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6
Q

Capsid is made up of protein sub units called

A

Capsomeres (usually 1-3 different proteins arranged in repeating units)

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7
Q

Viral proteins located on the outside of viruses are

A

Important for attaching to host cells during infection and are what the immune system identifies viruses by

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8
Q

What are the 3 basic shapes of viruses

A

Icosahedral (20 sided structure)

Helical (hollow tube)

Complex (doesn’t fit into other categories)

Each can have an envelope or not

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9
Q

Describe enveloped viruses

A

Viruses surrounded by a phospholipid membrane called the envelope

The envelope is derived from the host cell membrane

More easily damaged (detergents, drying, heat and disinfectants easily damage the phospholipid layer that is needed for structure)

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10
Q

Describe naked viruses compared to enveloped viruses

A

Naked viruses are more resistant to heat, drying, and many disinfectants (only some disinfectants are labeled against naked viruses)

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11
Q

Describe complex viruses

A

Includes bacteriophages

Distinct shape with;

1) head: contains genetic info
2) spikes: attach to bacterial surface
3) tails: insert into bacterial cell and acts as a tube that the viral genome enters into the cytoplasm through

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12
Q

Describe the viral genome

A

Depending on the virus the genome can be made up of:

1) double or single stranded DNA
2) double or single stranded RNA

Viruses are classified by their genome type

The type of genome they have affects how viruses infect cells and how drugs are designed to stop infections

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13
Q

True or false

Viruses have very few genes

A

True

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14
Q

Most of the genes viruses have encode what?

A

Capsid proteins

Proteins that allow the virus to attach to host cells

Special enzymes involved in replication of genomes made up of RNA and single stranded DNA

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15
Q

In order to replicate, viruses need more enzymes than they have genes for, where do they get these enzymes and what does this explain?

A

Extra enzymes come from the cells they infect

Explains why viruses can only replicate inside cells

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16
Q

Describe the virus life cycle

A

Virions exist in host of environment

Virus attaches to a host cell (determined by viral attachment proteins that bind to proteins in the surface of the cell)

Either the viral genome alone or within the capsid enter the host cell

It hijacks the DNA replication machinery and the protein synthesis machinery of the cell

Synthesis of copies of the viral genome and viral proteins begins

Capsid proteins self assemble around a copy of the viral genome

The new virus particles are released from the host cell

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17
Q

What is the Lytic Virus Cycle

A

Only applies to viruses WITHOUT an envelope

Cells that are infected continue to produce virus particles, when the cell releases these virus particles the cell lysis

Host cell dies once the virus particles are released

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18
Q

What is the non lytic virus cycle

A

Only applies to enveloped viruses

Virus particles self assemble in the cytoplasm, at the same time special virus proteins are inserted into the host cells’ plasma membrane. The virus capsule binds to the proteins in the cell membrane, the virus wraps itself in a phospholipid bilayer in the process of budding

Virus are continually being produced and released from the cell -the cell remains infected for longer periods of time and does not lyse on release of the virus

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19
Q

True or false

Many viruses are considered part of normal flora

A

FALSE

there a very few viruses considered to be part of normal flora

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20
Q

What do the bacteriophages that are considered to be part of normal flora do

A

Bacteriophages in rumen infect bacteria and cause lysis -this releases nutrients for the animal to use

Intestines also have a few bacteriophages -lyse intestinal bacteria to release nutrients

21
Q

What are the stages of viral infection

A

Transmission (same route as bacteria)

Entry into and movement throughout the body

Attachment to The host cell

Entry into the host cell

Replicate within the host cell

Released from the host cell

Spread to other cells and animals

22
Q

In order for viral infections to occur, what must the virus do

A

Avoid the immune system

23
Q

Define tropism

A

Attraction

24
Q

What is cell/tissue tropism

Give an example

A

When a virus can only bind to certain types of cells or tissues

Ex. Papilloma virus can only bind to and infect epithelial cells

25
Q

What is host tropism

Give an example

A

When a virus can only bind to cells in a certain species

Ex. Ovine herpes virus can only infect sheep

26
Q

Transmission and infection of the host much be at

A

Minimum infectious dose to cause disease

27
Q

What happens during incubation

A

Virus is finding its specific cell/tissue, attaching, entering and replicating

28
Q

What happens during the prodromal period

A

Fever, lethargy

Usually related to the immune system’s initial response to the virus

29
Q

What happens during the clinical period

A

Clinical signs Specific to the tissue/cell infected appear

30
Q

What stage is after clinical period

A

resolution

31
Q

What stage is after resolution

A

Convalescence

32
Q

What stage is after convalescence

A

Recovery

33
Q

What are alternate ways an infection can result in

A

Chronic clinical disease

Chronic latent infections

Death

34
Q

Describe latent infections

A

Certain viruses can “hide” inside infected cells -very slow replication or complete dormancy

There is NO SHEDDING during a latent infection

Periodically, it will replicate faster -may be able to shed and cause disease again

Stress events trigger replication

35
Q

Explain how damage occurs in the cell from a viral infection

A

Viruses can inhibit synthesis of host cell DNA/RNA

Some viruses will insert their genome into the host cell genome which damages essential genes

Some viral proteins can have direct toxic effects on the cell

Immune system attacks the viral proteins that are expressed on the surface of the host cell

The accumulation of virus particles inside the cell that damage normal cell structure

Cell can be lysed in the process of releasing non enveloped virus particles (lytic cycle)

Some viruses cause infected cells to become transformed -the cells become cancerous

36
Q

A few viruses can cause cancer, explain their mechanism for doing so

A

Virus inserts it’s genome directly into the host cell genome as part of the replication process

If the virus inserts into and disrupts a gene that stops cell growth > cell will begin to divide continuously

If the virus inserts right before a gene that encodes a growth promoter > excess production of the growth promoter along with synthesis of viral protein

37
Q

What are the 3 things viruses have to do in order to achiever their goal; to replicate

A

1) infect as many cells as possible (determined by virulence and immune status of host) (more virulent = faster spread)
2) try to avoid killing the host cell (lytic viruses kill the host cell they must be able to rapidly spread to continue replicating)
3) avoid the immune response (viruses have very few proteins which are mainly structural, these are recognized by the immune system but they replicate quickly and have a high rate of spontaneous mutation of capsid proteins -the immune system would have to re-train how to identify the virus)

38
Q

The seasonal fluid vaccine changes every year, explain how this works

A

The vaccine contains 2 viral antigens that the immune system is taught to recognize (Neuraminidase (N)) and (Hemagglutinin (H)) these are spike proteins found on the influenza envelope Used for attaching and tropism

Amino acid changes due to spontaneous mutation lead to a slightly different N and H protein

39
Q

Define antigen

A

Protein recognized by the immune system

40
Q

What is antigenic DRIFT

A

Gradual change in these proteins recognized by the immune system

The immune system has time to relearn how to fight the virus

41
Q

What is Antigenic SHIFT

A

Rapid, large change in antigens

Occurs when two influenza strains infect the same cell and the genes mix and match during virion assembly

Results in mixing of Hemagglutinin from one strain with Neuraminidase from another strain

42
Q

When is the best time to destroy the virus

A

BEFORE it infects the cell

43
Q

Once viruses enter cells, the immune system must destroy the infected cell in order to

A

control the infection

44
Q

What is one major cause of pathology in viral infections

A

Immune medicated destruction of the body’s own cells

45
Q

describe how antivirals are used in vet medicine

A

Very few exist

These target viral enzymes that take part in replication of virus genomes made up of single stranded DNA and double stranded RNA

46
Q

Describe vaccination in vet medicine

A

Best defence

Teaching the immune system to find and destroy free virion particles before the infect AND to identify and destroy infected cells

Some vaccines prevent infection, other only prevent clinical signs from occurring and the virus can still spread

47
Q

What are some other ways veterinary medicine control viral infections besides antivirals and vaccination

A

Disinfection
Must select appropriate disinfectant
Enveloped viruses are easiest to destroy

Small, non enveloped viruses are more difficult to destroy only certain disinfectants will destroy these (Virox, Accel, Virkon, bleach)

48
Q

Describe the scale of microbial resistance to chemical disinfectants from most resistant to least resistant

A

Bacterial spore

Mycobacterium

Hydrophilic viruses (non lipid, non enveloped)

Fungi

Vegetative bacteria

Lipophilic viruses (lipid containing, enveloped)

Microbiology (12 decks)

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