5.6 Sexually Transmitted Infections: HIV/AIDS

what type of virus is HIV

single-stranded, positive-sense RNA retrovirus (diploid)

what is notable about RNA vieus mutation rates (like HIV)

very high mutation rate due to error-prone reverse transcriptase (no proofreading)

what is the shape of the HIV capsid

irregular, cone-shaped (conical)

what enzyme allows HIV to convert RNA into DNA

reverse transcriptase

what is the function of integrase in HIV

inserts viral DNA into the host genome

what is the function of protease in HIV

cleaves viral polyproteins into functional proteins for viral maturation

does HIV have an envelope

yes, HIV is an enveloped virus

what is found on the HIV envelope

spike proteins

what is unusual about HIV spike proteins

they are made of two different proteins

what are the two proteins that make up the HIV spike

gp120 (larger) and gp41 (smaller)

what is the role of gp120 in HIV

binds to host cell receptors

what is the role of gp41 in HIV

facilitates fusion of the viral envelope with the host cell membrane

are both gp120 and gp41 required for HIV replication

yes, both are essential for the viral replication cycle

why are HIV’s multiple unique proteins important clinically

they provide targets for selective toxicity (antiviral drugs can target the virus without harming host cells as much)

what does gp stand for

glycoprotein

does HIV follow a unique replication cycle

no, it follows the typical viral replication cycle

what is unique about HIV’s replication cycle

many steps use HIV-specific proteins

why is the use of HIV-specific proteins important

they allow for selective drug targeting (selective toxicity)

what are steps 1 & 2 of HIV replication

attachment and entry

how many receptors does HIV require for entry

two receptors

which HIV protein binds to the CD4 receptor

gp120

which cells does HIV primarily infect and why

T-helper cells (CD4+) cells because gp120 binds to CD4

besides T-helper cells, what other cells can HIV infect

some antigen-presenting cells (APCs) that also have CD4

what co-receptor does HIV use on T-helper cells

CCR5

what happens after gp120 binds to CD4

it binds to the CCR5 co-receptor

which HIV protein is responsible for membrane fusion

gp41

what important structure is found in gp41

fusion peptide

what is the role of the fusion peptide in HIV infection

helos the viral envelope fuse with the host cell membrane

what activates gp41 during HIV entry

binding of the gp120 to the CCR5 co-receptor

what is the role of gp41 after activation

mediates membrane fusion, allowing HIV to enter T-helper cells

how does HIV enter T-helper cells

through membrane fusion facilitated by gp41

what is CCR5-delta32

a genetic mutation that makes the CCR5 co-receptor nonfunctional

how does CCR5-delta32 affect HIV infection (APPLICATION)

prevents HIV from entering cells, providing strong resistance/immunity to HIV

why are individuals with CCR5-delta32 resistant to HIV (APPLICATION - WHY)

HIV cannot bind the CCR5 co-receptor, so it cannot enter T-helper cells

what are steps 3 & 4 of HIV replication

uncoating and biosynthesis

what happens during uncoating of HIV

the capsid is removed, releasing viral RNA and enzymes into the host cell

what type of infection does HIV establish after uncoating

chronic, persistent infection

what enzyme converts HIV RNA into DNA

reverse transcriptase

what is the DNA form of an RNA virus called

provirus

what happens to the HIV provirus after it is made

it is permanently inserted into the host cell chromosome

which enzyme inserts HIV DNA into the host genome

integrase

why is HIV infection difficult to eliminate once established (APPLICATION)

the provirus is permanently integrated into the host DNA, allowing lifelong infection

how are new HIV genomes produced during biosynthesis

by transcription of the provirus

what happens to some of the transcribed HIV genomes

they are translated into viral proteins

how are HIV proteins initially produced

as 3 large polypeptides

why does HIV produce proteins as polyproteins

to simplify and coordinate viral assembly

what must happen to HIV polyproteins after assembly

they must be cleaved into individual functional proteins

which enzyme cleaves HIV polyproteins

HIV protease

what would happen if HIV protease is inhibited

viral proteins would not mature, producing non-infectious virus

what are steps 5 & 6 of HIV replication

assembly and release

what components are assembled into new HIV viruses

viral genomes and polyproteins

how does HIV exit the host cell

by budding

what does HIV gain during budding

its envelope

what happens to HIV polyproteins after budding

they are cleaved into functional proteins

what is HIV maturation

the process where protease cleaves polyproteins to form a fully functional virus

can immature HIV viruses infect cells

no, only mature viruses are infectious

how can HIV maturation be prevented (APPLICATION)

by inhibiting the HIV protease enzyme

why do protease inhibitors stop HIV replication (APPLICATION - WHY)

they prevent maturation, producing non-infectious viruses

how many stages does HIV pathogenesis have

3 stages

what are the 3 stages of HIV infection

acute phase, chronic, phase, AIDS

how long does the acute phase of HIV typically last

about 3 months

what happens during the acute phase of HIV

the virus establishes a chronic, persistent infection

how long does the chronic phase of untreated HIV typically last

about 7-10 years

what characteristics the chronic phase of HIV

ongoing viral replication with gradual weakening of the immune system

what does AIDS stand for

acquired immune deficiency syndrome

what happens in AIDS

the immune system is severely weakened and cannot effectively fight infections or cancer

what happens in the acute phase of HIV infection

initial infection causes T-helper cell destruction and rising viral load

what is viral load

the amount of virus present in the blood

what happens after ~6 weeks of HIV infection

the immune system begins to respond and reduces viral levels

why can HIV not be completely eliminated after infection

the viral genome integrates into the host T-helper cell chromosome (provirus)

why does HIV cause a persistent lifelong infection

because integrated provirus remains in host DNA and cannot be fully removed

what are common symptoms of the acute phase of HIV

mild, flu-like symptoms

why do HIV symptoms often resemble the flu in early infection (APPLICATION)

because initial immune response and viral replication cause systemic inflammation

what happens in the chronic phase of HIV infection

slow viral replication with gradual destruction of T-helper cells

is the chronic phase of HIV usually symptomatic or asymptomatic

typically asymptomatic

what immune cell is progressively destroyed during the chronic phase of HIV

T-helper (CD4+) cells

what CD4 T-cell count marks progression toward AIDS

around 200 cells per mL of blood

why is a CD4 count of ~200 significant in HIV infection

below this level, the adaptive immune system cannot effectively activate

what is the main danger of the chronic phase of HIV if untreated (APPLICATION)

silent immune system decline leading to AIDS

what is AIDS in HIV infection

the final stage of HIV where the immune system is severely compromised

what causes AIDS in HIV infection

extensive viral replication leading to severe immune system impairment

what is the main immune problem in AIDS

the immune system can no longer effectively fight infections or cancer

are AIDS symptoms consistent in all patients

no, symptoms vary widely between individuals

what are common symptoms of AIDS

recurrent respiratory infections, muscle wasting, and prolong diarrhea

what is the most common cause of death in AIDS patients

severe opportunistic infections or virus-associated cancers

what is the reservoir for HIV

humans (infected hosts or carriers)

what are the main portals of exit for HIV

blood, sexual secretions, and breastmilk

how is HIV present in blood and bodily fluids

in blood or fluids contaminated with blood

what sexual secretions transmit HIV

semen and vaginal secretions

what is found in semen and vaginal secretions that allows HIV transmission

free virus and infected immune cells

how is HIV transmitted through breastfeeding

breastmilk contains both free virus and infected immune cells

what are the main modes of HIV transmission

direct person-to-person contact, vehicle transmission, and vertical transmission

what is the primary form of direct HIV transmission

unprotected sexual contact

can HIV be transmitted through blood contact

yes, any contact with infected blood can transmit HIV

what is vehicle transmission of HIV

transmission via contaminated objects like needles or medical/dental equipment

how can blood transfusions or organ transplants transmit HIV

if taken from an untreated infected individual (now very rare due to screening)

why is HIV transmission through blood transfusion rare in the U.S.

donated blood and organs are rigorously treated

what is vertical transmisison of HIV

transmission from mother to child

how can HIV be transmitted from mother to baby

across the placenta, during childbirth, or through breast milk

what are the primary portals of entry for HIV

broken skin and mucous membranes