Lecture 18 - HIV Flashcards
What is the mode of transmission of HIV-1 and HIV-2
Transmission is due to the direct transfer of infected body fluids and infected cells. Sexual contact, contaminated IV needles during drug abuse, medical tissue transfer and fetal or neonatal transfer by infected mothers
Retroviruses enter into a cell as what?
2 copies of +ssRNA and are converted to DNA
What enzyme is required for retrovirus to enter cell?
RNA-dependent, DNA-polymerase catalyzes step of +ssRNA to DNA
What occurs to the retrovirus genome after it enters cell and is converted to DNA
The DNA subsequently integrates into the host genome
Retroviruses ‘specialize’ in doing what?
carrying genes (including oncogenes) from cell to cell and inducing tumors and/or immunosuppression.
What two things in humans can retroviruses cause?
- A known T-cell leukemia
2. Aids
What is meant by retroviruses having long incubation periods
The time between exposure to the pathogen and onset of symptoms. Retroviruses have a long incubation period that can last years.
What is a reverse transcriptase?
An enzyme used to generate DNA from an RNA template. Termed reverse transcription. This is the main key of a retrovirus converting ssRNA to DNA
When was the first discovery that viruses could cause tumors and how did it occur?
In 1902 Dr. Rouse was studying chicken tumors. He discovered that he could infect other chickens with the filtrate (allows only very tiny particles like viruses to pass) from the tumor
T or F, Retro viruses are enveloped viruses that contain two identical copies of positive-strand RNA
True. THEY ARE ENVELOPED!
Retroviruses can be classified into what four major groups?
Exogenous: 1. Oncoviruses 2. Lentiviruses 3. Spumaviruses Endogenous: 4. Endogenous Viruses
Describe action of Oncoviruses
They cause cancers in many different animals. They typically cause cancer by expressing analogs of cell growth-controlling genes (oncogenes).
4 divisions of tumors in Oncoviruses
- Avian Tumors
- Mammary Tumors
- Leukemias (most species)
- HTLV I & II (Human Leukemias)
What are human leukemias called and how are they classified?
HTLV I & II
Classified as an Oncovirus (Exogenous viruses category)
How does HTLV I & II work and how is it transmitted?
They integrate into T cells. It is transmitted through sexual contact
Describe action of Lentiviruses
Cause slow-developing CNS and immunosuppressive diseases in a variety of animals. Characterized by long incubation periods
What are the main Lentiviruses?
HIV 1 and 2 (AIDS)
Exogenous viruses work through what type of transmission? (Vertical or Horizontal)
Horizontal. They are transferred from person to person
Endogenous viruses work through what type of transmission? (Vertical or Horizontal)
Vertical. Passed from Mother to Child
Spumaviruses are associated with what disease?
Not associated with any known diseases. They were also the first human retroviruses discovered.
What do Endogenous viruses cause?
They are the ultimate parasite, having permanently integrated into our germ-line DNA. These viruses (no longer fully functional viruses) are transmitted vertically and make up as much as 8% of the human genome.
Endogenous viruses are associated with what disease?
Not associated with any known disease but research is being conducted on their possible involvement in both disease and health.
What three things increase the risk of HIV?
Increased number of partners
Increased loss of epithelial barrier
Increased virus, #/time
HIV is spread by what three means?
Blood, Sex, perinatal
What is the primary means of HIV transmission worldwide?
heterosexual sex
What is the major mode of transmission in the U.S.
Homosexual sex but heterosexual transmission is growing steadily and will probably in the near future be the primary means.
Are children who are born of HIV infected mothers at risk for infection of AIDS?
Yes. Unless the mother is undergoing anti-HIV therapy. With proper anti-viral therapy babies can now be born HIV free.
Is there a vaccine for HIV?
No not currently.
Evidence tells us that HIV-1 first infected humans how long ago?
100 year ago. That means HIV was spreading among humans for 60-80 years before AIDS was first recognized.
HIV and AIDS primarily impacts who?
The poor. In U.S., close to 2/3 of newly infected are now from the black and hispanic/latino communities
All retroviruses have a similar non-segmented genome structure with what four major gene segments?
gag pro pol env (with LTR at each end)
What do the gag genes code for?
structural proteins such as the nucleocapsid
What do the pro genes code for?
Viral protease
What genes code for the enzymes such as reverse transcriptase?
pol genes
What genes code for the two major spike proteins, GP41 and GP120?
env genes
HIV infection involves six main steps
- Attachment
- Entry into cell
- Reverse transcription of viral RNA
- Integration of viral dsDNA into host cell
- Transcription and translation of the viral DNA into mRNA and proteins
- Assembly and maturation of new infectious HIV
When HIV binds to T lymphocyte, how does it occur?
HIV binds via GP120 specifically to CD4 and a chemokine receptor (CCR5 or CXCR 4)
What cells does HIV infect?
Th cells (and monocytes and dendritic cells)
What is required for the virus to fuse with the cell membrane in prep for the virus to enter cell
Additional viral protein, GP41
What must HIV to have reverse transcriptase present within the cell.
It must carry the enzyme with it since cells do not produce this enzyme.
How is the viral HIV integrated into the host DNA after it has been made?
HIV also carries an integrase that cleaves the host DNA so the viral DNA can be inserted into it.
