Viruses, Viroids, and Prions

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DNA

Capsid

Tail fibers

Slide 51

One-step Growth Curve

Slide 52

Viral Latency

Some viruses have the ability to become dormant inside the cell

Called latent viruses

They may remain inactive for long periods of time (years)

Later, they activate to produce new viruses in response to some external signal

HIV and Herpes viruses are examples

Slide 53

Lysogenic Cycle

Phage DNA injected into host cell

Viral DNA joins host DNA forming a prophage

When an activation signal occurs, the phage DNA starts replicating

Slide 54

Lysogenic Cycle

Viral DNA (part of prophage) may stay inactive in host cell for long periods of time

Replicated during each binary fission

Over time, many cells form containing the prophages

Slide 55

Viral Latency

Once a prophage cell is activated, host cell enters the lytic cell

New viruses form a & the cell lyses (bursts)

Virus said to be virulent (deadly)

INACTIVE STAGE

ACTIVE STAGE

Slide 56

Virulent Viruses

HOST CELL LYSES & DIES

Slide 57

The Lysogenic Cycle

Slide 58

Latency in Eukaryotes

Some eukaryotic viruses remain dormant for many years in the nervous system tissues

Chickenpox (caused by the virus Varicella zoster) is a childhood infection

It can reappear later in life as shingles, a painful itching rash limited to small areas of the body

SHINGLES

Slide 59

Latency in Eukaryotes

Herpes viruses also become latent in the nervous system

A herpes infection lasts for a person’s lifetime

Genital herpes (Herpes Simplex 2)

Cold sores or fever blisters (Herpes Simplex1)

SKIN TO SKIN CONTACT

PASSED AT BIRTH TO BABY

Slide 60

Virulence

VIRUS DESTROYING HOST CELL

Slide 61

Lytic and Lysogenic Cycles

Slide 62

Treatment for Viral Disease

Slide 63