Retrovirus Genome
(+)ssRNA
Retrovirus Virion
Enveloped
Retrovirus Incubation
Varies
Retrovirus Strains
A-Type
B-Type
C-Type
D-Type
Retrovirus A-Type
Shell and hollow center
Immature particle
Retrovirus B-Type
Circular nucleus
Eccentric location
Retrovirus C-type
Circular nucleus
Central location
Retrovirus D-Type
Cylindrical nucleus
Central location
Retrovirus Replication
As it enters the cell, it undergoes reverse transcription - ssRNA genome becomes dsDNA
The viral dsDNA integrates itself into the host, making it a provirus
Reverse Transcription
Defining Feature of Retroviruses
Occurs within a large complex similar to nucleocapsid
Infection cannot progress if reverse transcription does not occur
What initiates Reverse Transcription
Initiates once the nucleocapsid is inside the cytoplasm
What is necessary for Reverse Transcription to occur?
Need higher levels of NTP
Low levels of NTP prevent reverse trasncriptase
What happens to Revers Transcription between genome copies
Silent when the copies are identical
Many different recombinations can occur when different genomes are in the virion
What is necessary for Integration of a Retrovirus to occur
The retrovirus must access the nucleus
When does a Retrovirus access the nucleus?
During Mitosis
It can infect non-dividing cells, but the mechanism is unknown
Integration
3’ end of processing dsDNA atacks the target DNA, creating a nick
Host repairs the nick, but in doing so, integrates the viral DNA
Integration is permanent
Endogenous provirus
If a retrovirus is integrated into the germ-line
Retrovirus Complications
Integration may disrupt host genes, causing diseases such as cancer
Retrovirus Symptoms
Many infections are benign
But they can cause significant disease
Slow Retrovirus
Effect is like high-level mutagenesis
Eventually results in tumorigenesis
Cytopathic Retrovirus
Minority of Retroviruses carry cytopathic genes
Cause tissue damage directly
Actute Transforming Viruses
Induce rapid tumor formation
Carry host genes - mitogenic or antiapoptotic
Often replication defective because host gene replaces an essential gene
Human T-Cell Leukemia Virus Genome
(+)ssRNA
Human T-Cell Leukemia Virus Virion
Enveloped
What are the two diseases of Human T-Cell Leukemia Virus?
Adult T-Cell Lymphoma/Leukemia (ATLL)
HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP)
Human T-Cell Leukemia Virus Incubation
ATLL - 30-50 years
HAM/TSP - 3 years
What are the types of Human T-Cell Leukemia Virus?
Types 1, 2, 3, 4
Type 1 is the most common in humans
Human T-Cell Leukemia Virus Replication
Cytoplasm
ATLL Symptoms
Tumors, Immunosuppression
HAM/TSP Symptoms
Bladder issues, LL back pain, Leg weakness, ED, and impotence
Human T-Cell Leukemia Virus Transmission
Person to person:
- Mother-to child via breastfeeding
- Sharing needles
- Blood transfusions
- Sex
How does Human T-Cell Leukemia Virus spread in the body?
Via infected cells being in contact with naive cells
ATLL
Occurs in 2-4% of cases of HTLV-1
Antigen activation triggers transcription of provirus
Virus tax protein and others stimulate cell proliferation
Cells become transformed generating tumors
HAM/TSP
Occurs in 1-2% of cases
Following transfusions
Infected T-cells enter the CNS
-activates astrocytes and microglial cells
-recruit inflammatory cells and cause further tissue damage
Human T-Cell Leukemia Virus Prevalence
Millions of people worldwide
Human T-Cell Leukemia Virus Prevention
Eliminate breastfeeding for HTLV-1 positive mothers
Increased screening for blood products
Human T-Cell Leukemia Virus Treatment
ATLL - treat the leukemia/lymphoma with chemotherapy regardless of HTLV infetions
HAM/TSP - corticosteroids, interferon yields temporary relief of symptoms
HIV Genome
(+)ssRNA
HIV Virion
Enveloped
HIV Incubation
HIV - 2 weeks
AIDS - 6 months-25 years
HIV Strains
Two main types in humans - Types 1 and 2
HIV Replication
In the Cytoplasm
HIV immune response inhibition
Targets memory T-cells (CD4+)
HIV Symptoms
Immunosuppression
Wasting - weight loss
HIV Transmission
Sex
Needle sharing
Mother to infant
HIV Complications
Immunosuppression and AIDS development
HIV Prevalence
Worldwide pandemic
Highest impact is in Sub-Saharan Africa
HIV Prevention
Sexual behavior and protection
Blood screening
HIV Treatment
Antiviral treatments
- Nucleoside reverse transcriptase inhibitor
- Protease inhibitors
- Non-nucleoside RT inhibitor
- Highly active antiretroviral therapy