HIV is a virus that can cause serious health problems. It is spread through the exchange of bodily fluids, such as semen and vaginal fluids during sexual intercourse, blood due to needle-sharing, and breast milk from mother to child. HIV targets the body's CD4+ T lymphocytes, an immune cell involved in the adaptive immune response. If left untreated, HIV-positive patients can develop acquired immunodeficiency syndrome (AIDS).
HIV is surrounded by a lipid envelope containing attachment proteins. These proteins help the virus to fuse with the host cell, allowing it to replicate. Inside the lipid envelope is a nucleocapsid, which contains two molecules of viral RNA and the reverse transcriptase enzyme. The reverse transcriptase enzyme helps to create complementary DNA (cDNA) from the viral RNA, which is then integrated into the host genome.
To establish infection, HIV binds to a protein called CD4, which is found on immune cells such as helper T lymphocytes, dendritic cells and macrophages. This allows the virus to enter the host cell. The HIV replication cycle then proceeds in seven stages: binding, fusion, reverse transcription, integration, replication, assembly, and budding.
Once the virus has replicated, it is released from the host cell in the form of virions. These virions can then go on to infect other cells and spread the virus.
HIV infects immune cells, specifically helper T lymphocytes, by binding to the CD4 protein on their surface using viral attachment proteins. The viral attachment protein gp120 binds to CD4, allowing the virus to enter the host cell.
Once inside the host cell, the viral RNA and enzymes are released into the host cytoplasm, and the viral reverse transcriptase enzyme converts viral RNA into cDNA. The cDNA is then integrated into the cell's DNA using the viral enzyme integrase.
The integrated viral cDNA is transcribed into mRNA, which creates viral proteins using the host's protein synthesis organelles. These viral proteins migrate to the host cell's plasma membrane, where they assemble into viral particles that bud from the membrane, taking a piece of the plasma membrane with them to create their lipid envelope.
Acute HIV infection can manifest as flu-like symptoms, including fever, headache, swollen glands, rashes, and fatigue. After this acute phase, patients enter a clinically latent phase where the virus becomes dormant and resides in host cells, continuing to infect immune cells. As the adaptive immune response grows weaker, patients become vulnerable to opportunistic infections, including Mycobacterium tuberculosis and Salmonella species.
When the patient's CD4 cell counts decline to the stage where they are severely susceptible to opportunistic infection, they have developed AIDS.
AIDS is the late stage of HIV infection that severely damages a patient's immune system, leaving them susceptible to opportunistic infections. Symptoms of AIDS include rapid weight loss, extreme tiredness, swollen lymph glands, and pneumonia. Opportunistic infections are the main cause of death for AIDS patients.
AIDS is diagnosed by quantifying the number of T lymphocytes in a patient's blood. An uninfected person typically has between 800 to 1200 T lymphocytes per mm³ of blood, while patients with AIDS usually have cell counts below 200 per mm³.
The enzyme-linked immunosorbent assay (ELISA) is a useful diagnostic test for HIV. This test uses antibodies to detect and quantify proteins in a sample. To detect antibodies against HIV, HIV antigens are applied to a slide and a blood or oral fluid sample is added. Any antibodies against HIV present in the sample will bind to the HIV antigens. A second antibody conjugated to a specialised enzyme and complementary to human HIV antibodies is then added, followed by a colourless substrate for the enzyme. If HIV antibodies are present in the sample, the enzyme will change the colour of the substrate.
To summarize, HIV is a retrovirus that infects CD4 T lymphocytes by binding to the CD4 protein on their surface using viral attachment proteins. HIV replication involves the integration of viral cDNA into the host genome using the enzyme reverse transcriptase. The host cell's protein synthesis components will create viral particles that are eventually released to infect more cells.
HIV infection causes a drastic decline in a patient's CD4 cell counts, severely weakening the immune system and making them highly susceptible to opportunistic infections. HIV infection can be diagnosed using the ELISA test, which uses antibodies to detect the presence of HIV antibodies or proteins in a sample.
Treatments for HIV include ART, which involves the daily combinative administration of HIV drugs that target different stages of the HIV replicative cycle. The goal of ART is to suppress viral replication to undetectable levels, reduce transmission, and prolong the patient's life. However, there is no cure for HIV yet due to the challenges posed by the latent reservoir, which consists of CD4 positive cells that contain the inactive but replication-competent virus.
It is important to note that antibiotics are ineffective against HIV as they are designed to target bacterial pathogens, not viruses. Antibiotics inhibit the synthesis of the bacterial cell wall made of peptidoglycans, which bacteria need to survive. Viruses do not contain cell walls composed of peptidoglycans, so antibiotics are ineffective against them.
What type of virus is HIV?
HIV is a retrovirus because it contains the enzyme reverse transcriptase and uses RNA as its genetic material.
How does HIV lead to AIDS?
HIV infection develops into AIDS when the patient's CD4 T lymphocyte blood count declines below 200 per mm³.At this stage, the patient is extremely susceptible to opportunistic infections.
What is HIV?
HIV stands for the human immunodeficiency virus. It is a retrovirus that binds to CD4 proteins, most commonly found on T lymphocytes.
How does HIV replicate?
HIV attachment proteins bind to CD4 on the host cell The lipid envelope fuses with the host membrane The capsid enters the cytoplasm and releases the viral RNA and viral enzyme Reverse transcriptase forms cDNA which integrates into the host genome Viral particles are synthesised and bud off from the host plasma membrane, forming its lipid envelope
Why can't HIV be treated with antibiotics?
Antibiotics target bacterial cell walls and are therefore ineffective against viruses. Antibiotics form pores in the peptidoglycan cell wall of bacteria and this leads to lysis. Viruses, however, do not have cell walls.
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