19 April 2011

HIV and AIDS: briefly about the main thing

10 most important facts about HIV and AIDS
Egor Voronin (Global HIV Vaccine Enterprise), Troitsky Variant newspaper No. 76-2011

Today, the human immunodeficiency virus (HIV) is the most studied of all viruses. More than 200 thousand scientific articles have been published about HIV. For 30 years we have learned its structure, epidemiology, life cycle, functions of its proteins and much more. How do I choose 10 key facts here? I tried to cover all areas – from basic science to medicine.

1. HIV infects helper lymphocytes, which regulate the immune response. The death of these cells leads to the deregulation of immunity – its excessive activation and at the same time inability to focus on pathogenic microorganisms.

2. HIV strikes the immune system during the first weeks of infection, but the symptoms of impaired immunity appear on average after 8 years in the form of acquired immunodeficiency syndrome (AIDS). This happens when the immune system, which had been feverishly replenishing the loss of helper lymphocytes, is exhausted and loses the fight against the virus.

3. HIV belongs to the family of retroviruses, the genus of lentiviruses. HIV particles contain a genome in the form of two copies of RNA, which the virus converts into DNA after entering the cell. This DNA is embedded by the virus into the DNA of the host cell and remains there until the cell dies.

HIV model created by Visual Science (Moscow, www.vsci.ru )
based on data on crystallography, stoichiometry and the structure of viral particles.
The model has a cutout that allows you to look inside the particle.
The orange color indicates the virus' own proteins,
gray is the components that the virus takes from the host cell.

4. Lentiviruses have been around for millions of years and have been found in rabbits, cats, horses and a number of African monkeys. HIV entered the human population from chimpanzees about 100 years ago in West Africa.

5. HIV is transmitted through blood, during sex, or from mother to child during childbirth. In everyday life, with kisses, bites and handshakes, HIV is not transmitted. It is not transmitted by mosquitoes either.

6. The most reliable way to prevent HIV infection during sex is a condom. Over the past 2 years, three new ways to prevent HIV have shown encouraging results: a vaccine, taking medications before sex and a lubrication gel with medications, but the effectiveness of all three is still too low (30-50%) to be widely used.

7. More than 20 drugs have been developed to stop HIV replication (this is more than for any other virus). Medications reduce the amount of virus in the blood to a negligible level and prevent AIDS. Also, medications can prevent the transmission of the virus from mother to child during childbirth and breastfeeding.

8. Embedded in the DNA of a cell, HIV sometimes passes into a latent form that does not manifest itself in any way, and therefore neither drugs nor the immune system can affect it. In this form, it can exist for decades. Because of latent viruses, HIV medications have to be taken all your life. In the body of a person who has stopped taking medications, the virus comes out of its latent form, and the disease develops again.

9. HIV is very flexible genetically, which allows it to evade the immune response, as well as acquire resistance to drugs. To prevent drug resistance during treatment, they are used three at a time.

10. 33 million people in the world are living with HIV, more than half of them are women. Despite huge progress in preventing HIV infection (the epidemic is declining in many countries) and treating AIDS (more than 5 million people receive medicines), every year 2 million people die from AIDS because they do not have access to medicines.

The spread of HIV in the world (UNAIDS Report on the Global HIV Epidemic 2010)

In his blog , Egor added:

At the request of TrV, he wrote "10 most important facts about HIV and AIDS". This is a new category for them – the main facts from any scientific field, presented in a format accessible to a person with a school education. 3000 characters are given for everything. Naturally, it turned out to be very primitive, so I decided to write here "10 additional important facts about HIV" for those who already know the basic facts and with a somewhat greater bias in science.

11. HIV transmission from person to person is quite ineffective. With heterosexual contact, the probability of infection is less than one percent, and when infection occurs, only one viral particle is usually transmitted. With homosexual contact, the probability of infection is a couple percent and usually more than one virus is transmitted. Transmission through the blood depends on the amount of blood – hemophiles who received liters of blood were infected almost all the first time. Drug addicts have the transmission of dozens of viral particles at a time. Circumcision reduces the likelihood of infection for a man by 60%.

12. HIV infection does not prevent superinfection, re-infection of an already infected person. For most viruses, this does not happen, because the immune response against the first virus protects the body from repeated infection.

13. The years between infection and the manifestation of AIDS symptoms are years of active viral replication. In the blood of an HIV-infected person, 10 5-10 6 viruses per 1 ml of blood can often be seen. This amount of virus is produced every few days.

14. Reverse transcription, copying the virus genome from RNA to DNA, is one of the most complex replication strategies of viral genomes: it is initiated in different places for + and - chains, requires two jumps from one end of the genome to the other, uses three different enzymatic activities (performed by one protein), and as a result, a DNA copy it turns out to be longer than the RNA matrix.

15. When copying the genome, reverse transcriptase very often, about ten times, jumps from one RNA to another, which leads to effective recombination of viral genomes accidentally trapped in one cell.

16. HIV does not mutate more often than many other viruses. But he is so arranged that a much larger part of these mutations does not harm him. It is this property, as well as the recombination mentioned above, that allows HIV to evolve so quickly.

17. There are a number of antiviral proteins that are present in every cell and act against HIV. Some mutate viral RNA, disabling it. Others bind to the capsid entering the cell and destroy it. Still others do not allow the newly formed virus to leave the host cell. The virus has special proteins that neutralize these additional levels of protection or mutates so as to avoid them.

18. The outer part of the HIV envelope protein can change almost indefinitely, while the inner part, hidden from the immune system, performs the function of fusion with the cell. The protein uses a two-step recognition of the target cell - first the receptor is recognized, this signals the protein to "open" and allows the inner part of the envelope protein to contact the coreceptor, with which the virus penetrates into the cell. The little-changing part of the protein, against which the immune system could act, is exposed only for seconds.

19. Lymphocytes often come into contact with each other, and HIV concentrates the assembly of viral particles at the sites of these contacts, which allows it to directly move from one cell to another. The mechanism of spread, in which the virus separates from one cell and floats in the blood in search of another, is much less effective. Dendritic cells, whose role is to collect pathogens and present them to the immune system, pick up a free-floating virus and deliver it to lymphocytes, thereby significantly increasing the infectivity of free viral particles.

20. In many species of monkeys that are natural carriers of VIO (monkey immunodeficiency virus), the infection proceeds without symptoms and does not lead to AIDS, although the virus is actively replicated in them. In those species that are not natural carriers, infection with HIV quickly leads to AIDS.

Portal "Eternal youth" http://vechnayamolodost.ru19.04.2011

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