HIV
A single HIV particle measures roughly 120 nanometers in diameter. This sphere is about one hundred thousand times smaller than a red blood cell. The virus contains two copies of positive-sense single-stranded RNA enclosed within an ovoidal capsid. That capsid holds approximately two thousand copies of the viral protein p24. Enzymes like reverse transcriptase and integrase travel inside this shell to begin their work once infection starts.
The outer layer consists of a lipid bilayer taken directly from the human host cell membrane. Embedded within this envelope are proteins known as gp120 and gp41. These molecules form a trimeric spike that allows the virus to attach to target cells. Over half the mass of this spike comprises N-linked glycans. This high density shields the underlying protein from neutralization by antibodies.
HIV enters macrophages and CD4+ T cells through specific interactions between glycoproteins on its surface and receptors on the target cell. The initial step involves the attachment of gp120 to the CD4 molecule. A structural change then exposes chemokine receptor binding domains for interaction with CCR5 or CXCR4. This dual-pronged attachment allows the fusion peptide gp41 to penetrate the cellular membrane.
Sexual intercourse remains the major mode of transmission globally. Both X4 and R5 HIV types exist in seminal fluid, enabling spread from male to partner. However, selection processes often favor the transmission of R5 viruses during this pathway. Macrophage-tropic strains use the beta-chemokine receptor CCR5 for entry into both macrophages and CD4+ T cells. Non-syncytia-inducing strains typically rely on this specific co-receptor mechanism.
Once inside the host cell, reverse transcriptase converts the viral RNA genome into double-stranded DNA. This process is extremely error-prone, generating mutations that may cause drug resistance. The resulting DNA moves into the nucleus where integrase inserts it into the host's own genetic code. Some integrated DNA lies dormant while other copies actively produce new virus particles.
The full-length genomic RNAs package themselves into new viral particles in a pseudodiploid form. Certain guanosine residues become available for binding nucleocapsid proteins. Mature messenger RNAs export from the nucleus to the cytoplasm for translation. These mRNAs produce structural proteins like Gag and Env which assemble at the plasma membrane. New virions bud off as immature forms before maturing through protease cleavage.
HIV exhibits very high genetic variability due to its rapid replication cycle. Approximately ten billion virions generate every day within an infected individual. The mutation rate reaches roughly three times ten to the negative five per nucleotide base per cycle. Some estimates place HIV's mutation rate even higher than four times ten to the negative three substitutions per base pair.
Recombination events occur throughout the genome during reverse transcription. Between two and twenty recombination events can happen per genome each replication cycle. A 2014 study estimated fifteen to twenty percent of all HIV mutations result from recombination. This complex scenario generates many variants within a single patient daily. Co-infection with distinct subtypes gives rise to circulating recombinant forms that shuffle genetic information rapidly.
Many people remain unaware they carry the virus until testing occurs. In 2001 less than one percent of sexually active urban populations in Africa had been tested. Initial screening typically uses enzyme-linked immunosorbent assays to detect antibodies against HIV-1. Specimens showing non-reactive results are considered negative unless new exposure has occurred.
Specimens with reactive ELISA results undergo confirmatory testing via western blot or polymerase chain reaction methods. Modern HIV testing achieves over ninety-nine percent accuracy when accounting for the window period. False-positive rates in standard protocols estimate around one in two hundred fifty thousand for low-risk populations. The US Centers for Disease Control now recommend starting with an immunoassay combination test for both HIV-1 and HIV-2 antibodies plus p24 antigen.
Management of HIV/AIDS involves using multiple antiretroviral drugs simultaneously. Transmission through sexual contact does not occur when an individual maintains a consistently undetectable viral load below fifty copies per milliliter. This concept known as U equals U gained prominence following studies like PARTNER 1 and HPTN052. These trials involved thousands of couples reporting hundreds of acts of condomless sex without transmission events.
HIV latency within CD4+ T cells, dendritic cells, and macrophages remains the main barrier to eradication. While highly virulent, the virus can become a chronic condition with progression to AIDS increasingly rare under treatment. Studies established that zero risk exists for transmission when the positive partner maintains consistent undetectability. Over eight hundred organizations from nearly one hundred countries endorsed this consensus statement by August 2018.
Both HIV-1 and HIV-2 originated in non-human primates in West-central Africa before transferring to humans. HIV-1 appears to have evolved from SIVcpz found in wild chimpanzees in southern Cameroon. The earliest well-documented case of HIV in a human dates back to 1959 in the Belgian Congo. Genetic studies suggest the most recent common ancestor of the HIV-1 M group existed around the early twentieth century.
The first news story on an exotic new disease appeared the 18th of May 1981, in the gay newspaper New York Native. AIDS was clinically observed in 1981 in the United States among injection drug users and gay men. Researchers at NYU School Medicine studied cases of Kaposi's sarcoma emerging alongside Pneumocystis pneumonia. By September 1982 the CDC officially adopted the name AIDS after realizing it affected communities beyond initial assumptions.
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Common questions
What is the diameter of a single HIV particle?
A single HIV particle measures roughly 120 nanometers in diameter. This sphere is about one hundred thousand times smaller than a red blood cell.
When did the first news story on AIDS appear and what was the name of the newspaper?
The first news story on an exotic new disease appeared the 18th of May 1981, in the gay newspaper New York Native. AIDS was clinically observed in 1981 in the United States among injection drug users and gay men.
How many copies of the viral protein p24 does the HIV capsid hold?
That capsid holds approximately two thousand copies of the viral protein p24. Enzymes like reverse transcriptase and integrase travel inside this shell to begin their work once infection starts.
Which year marks the earliest well-documented case of HIV in a human?
The earliest well-documented case of HIV in a human dates back to 1959 in the Belgian Congo. Genetic studies suggest the most recent common ancestor of the HIV-1 M group existed around the early twentieth century.
What date did the CDC officially adopt the name AIDS after realizing it affected communities beyond initial assumptions?
By September 1982 the CDC officially adopted the name AIDS after realizing it affected communities beyond initial assumptions. Researchers at NYU School Medicine studied cases of Kaposi's sarcoma emerging alongside Pneumocystis pneumonia.