How Many Times Would Siv Need To Be Introduced Into The Human Population In Order To Seed An Epidemic Of The Size That Became Apparent By The Early 1980s
Three groups of HIV-1 exist today – group M, group O and group N. While group M is diverse, groups O and N are not, and remain highly restricted in one location. HIV-2 has one clear group with a separate path of descent, from the form of SIV found in sooty mangabeys in West Africa. This genetic tree suggests four separate transfers to humans, a puzzlingly rare chain of events given the potentially frequent contact with chimps in Central Africa, and the dating of chimp to human virus transfer back to the 18th century or even earlier.
In the opinion of Daniel Law-Beer, an epidemiologist from the University of Oxford, a star-like geography of infection would need to have been established early on in the epidemic, otherwise chance extinction events in one village could have eliminated the new virus from the human population quickly. He estimates that at least 60% of SIV transfers were dead-end infections of this sort which may have flared and died in remote locations.
Sir Robert May of Oxford University also suggested that it was quite plausible for many viral transfers to have remained confined in locations where local custom did not encourage mixing between populations in different villages.
Hiv Doesnt Always Produce Symptoms
HIV usually causes flu-like symptoms about two to four weeks after transmission. This short period of time is called acute infection. The immune system brings the infection under control, leading to a period of latency.
The immune system cant completely eliminate HIV, but it can control it for a long time. During this latency period, which can last for years, a person with HIV may experience no symptoms at all. Without antiretroviral therapy, however, that person may develop AIDS and as a result will experience many symptoms associated with the condition.
Pathogenicity Of Siv In Non
In most non-human primate species, natural SIV infection does not cause a fatal disease . Comparison of the gene sequence of SIV with HIV should, therefore, give us information about the factors necessary to cause disease in humans. The factors that determine the virulence of HIV as compared to most SIVs are only now being elucidated. Non-human SIVs contain a nef gene that down-regulates CD3, CD4, and MHC class I expression most non-human SIVs, therefore, do not induce immunodeficiency the HIV-1nef gene, however, has lost its ability to down-regulate CD3, which results in the immune activation and apoptosis that is characteristic of chronic HIV infection.
In addition, a long-term survey of chimpanzees naturally infected with SIVcpz in Gombe, Tanzania found that, contrary to the previous paradigm, chimpanzees with SIVcpz infection do experience an increased mortality, and also suffer from a Human AIDS-like illness. SIV pathogenicity in wild animals could exist in other chimpanzee subspecies and other primate species as well, and stay unrecognized by lack of relevant long term studies.
Cancers Common In People With Hiv Infection
Kaposi sarcoma Kaposi Sarcoma Kaposi sarcoma is a skin cancer that causes multiple flat pink, red, or purple patches or bumps on the skin. It is caused by human herpesvirus type 8 infection. One or a few spots may appear… read more , a cancer caused by a sexually transmitted herpesvirus, appears as painless, red to purple, raised patches on the skin. It occurs mainly in men who have sex with men.
Cancers of the immune system . Often, lymph nodes in the neck, under the arms, or in the groin enlarge rapidly and painlessly… read more ) may develop, sometimes first appearing in the brain. When the brain is affected, these cancers can cause weakness of an arm or a leg, headache, confusion, or personality changes.
Having AIDS increases the risk of other cancers. They include cancer of the cervix, anus, testes, and lungs as well as melanoma and other skin cancers. Men who have sex with men are prone to developing cancer of the rectum due to the same human papillomaviruses Human Papillomavirus Infection Human papillomavirus causes warts. Some types of HPV cause skin warts, and other types cause genital warts . Infection with some HPV… read more that cause cancer of the cervix in women.
Spread To The Western Hemisphere
Further isolated occurrences of this infection may have been emerging as early as 1966. The virus eventually entered gay male communities in large United States cities, where a combination of casual, multi-partner sexual activity and relatively high transmission rates associated with anal intercourse allowed it to spread explosively enough to finally be noticed.
Because of the long incubation period of HIV before symptoms of AIDS appear, and because of the initially low incidence, HIV was not noticed at first. By the time the first reported cases of AIDS were found in large United States cities, the prevalence of HIV infection in some communities had passed 5%. Worldwide, HIV infection has spread from urban to rural areas, and has appeared in regions such as China and India.
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How Do You Get Hiv
HIV is carried in semen , vaginal fluids, anal mucus, blood, and breast milk. The virus gets in your body through cuts or sores in your skin, and through mucous membranes . You can get HIV from:
having vaginal or anal sex
sharing needles or syringes for shooting drugs, piercings, tattoos, etc.
getting stuck with a needle that has HIV-infected blood on it
getting HIV-infected blood, semen , or vaginal fluids into open cuts or sores on your body
HIV is usually spread through having unprotected sex. Using condoms and/or dental dams every time you have sex and not sharing needles can help protect you and your partners from HIV. If you do have HIV, treatment can lower or even stop the chances of spreading the virus to other people during sex. If you dont have HIV, theres also a daily medicine called PrEP that can protect you from HIV.
HIV can also be passed to babies during pregnancy, birth, or breastfeeding. A pregnant woman with HIV can take medicine to greatly reduce the chance that her baby will get HIV.
HIV isnt spread through saliva , so you CANT get HIV from kissing, sharing food or drinks, or using the same fork or spoon. HIV is also not spread through hugging, holding hands, coughing, or sneezing. And you cant get HIV from a toilet seat.
What Is The Evidence That Hiv Causes Aids
The epidemic of HIV and AIDS has attracted much attention both within and outside the medical and scientific communities. Much of this attention comes from the many social issues related to this disease such as sexuality, drug use, and poverty. Although the scientific evidence is overwhelming and compelling that HIV is the cause of AIDS, the disease process is still not completely understood. This incomplete understanding has led some persons to make statements that AIDS is not caused by an infectious agent or is caused by a virus that is not HIV. This is not only misleading, but may have dangerous consequences. Before the discovery of HIV, evidence from epidemiologic studies involving tracing of patients sex partners and cases occurring in persons receiving transfusions of blood or blood clotting products had clearly indicated that the underlying cause of the condition was an infectious agent. Infection with HIV has been the sole common factor shared by AIDS cases throughout the world among men who have sex with men, transfusion recipients, persons with hemophilia, sex partners of infected persons, children born to infected women, and occupationally exposed health care workers.
The conclusion after more than 28 years of scientific research is that people, if exposed to HIV through sexual contact or injecting drug use for example, may become infected with HIV. If they become infected, most will eventually develop AIDS.
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Do Condoms Stop Hiv Being Passed On
Yes.Using a condom correctly prevents contact with semen or vaginal secretions , stopping HIV from being passed on. The virus cannot pass through the latex of the condom.
Condoms should only be used with a water-based lubricant as oil-based lube weakens them.
People with HIV who are on effective treatment and have an undetectable viral load cannot pass on HIV through any of their body fluids.
Its also important to remember that if you have sex without a condom other sexually transmitted infections can be passed on.
Sex without a condom can also result in pregnancy if other contraception is not being used.
Side Effects And Costs
Side effects of antiretroviral therapy vary and may include nausea, headache, and dizziness. These symptoms are often temporary and disappear with time.
Serious side effects can include swelling of the mouth and tongue and liver or kidney damage. If side effects are severe, the medications can be adjusted.
Costs for antiretroviral therapy vary according to geographic location and type of insurance coverage. Some pharmaceutical companies have assistance programs to help lower the cost.
Although many researchers are working to develop one, theres currently no vaccine available to prevent the transmission of HIV. However, taking certain steps can help prevent the transmission of HIV.
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How Does Hiv Spread
HIV spreads when infected blood, semen or vaginal fluids enter the body. Because symptoms can be mild at first, people with HIV might not know they’re infected. They can spread HIV to others without knowing it.
HIV can spread:
- during sex
- through sharing needles for injecting drugs or tattooing
HIV also can pass from mother to child during pregnancy, childbirth, or breastfeeding.
HIV does not spread through:
- pee, poop, spit, throw-up, or sweat
- coughing or sneezing
- sharing eating utensils or drinking glasses
Where Did The Virus Cross Into Humans
If SIV crossed in several places and then began to spread slowly, where are the most likely places for this to have occurred?
A review of sub-type diversity by Martine Peeters found that the greatest diversity lies in the region of Kinshasa, and that Zaire generally shows the greatest degree of sub-type diversity of any region in Africa. But does this necessarily make Zaire the ancestral hearth of HIV, or just the crossroads at which a number of viruses were able to come together?
At the moment this question is still highly debatable. As sequence information accumulates and phylogenetic dating becomes more sophisticated it may become easier to answer, but at present any assertions on the location of first transfer are highly speculative.
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How Do You Get Or Transmit Hiv
You can only get HIV by coming into direct contact with certain body fluids from a person with HIV who has a detectable viral load. These fluids are:
- Semen and pre-seminal fluid
- Rectal fluids
- Vaginal fluids
- Breast milk
For transmission to occur, the HIV in these fluids must get into the bloodstream of an HIV-negative person through a mucous membrane open cuts or sores or by direct injection.
People with HIV who take HIV medicine daily as prescribed and get and keep an undetectable viral load have effectively no risk of sexually transmitting HIV to their HIV-negative partners.
How Did Hiv Cross From Chimps To Humans
The most commonly accepted theory is that of the ‘hunter’. In this scenario, SIVcpz was transferred to humans as a result of chimps being killed and eaten, or their blood getting into cuts or wounds on people in the course of hunting.5 Normally, the hunter’s body would have fought off SIV, but on a few occasions the virus adapted itself within its new human host and became HIV-1.
There are four main groups of HIV strains , each with a slightly different genetic make-up. This supports the hunter theory because every time SIV passed from a chimpanzee to a human, it would have developed in a slightly different way within the human body, and produced a slightly different strain. This explains why there is more than one strain of HIV-1.6
The most studied strain of HIV is HIV-1 Group M, which is the strain that has spread throughout the world and is responsible for the vast majority of HIV infections today.
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Stages Of Hiv Infection
The stages of infection from person to person vary slightly, both in severity and the speed of progression. These stages map the depletion of immune cells as the body’s defenses further and further degrade.
With each progression, the risk of opportunistic infections increases until the immune system is said to be fully compromised. It is at this stage that the risk of illness and death is particularly high.
The stages of infection can be roughly classified as follows:
Preventive Treatment After Exposure
People who have been exposed to HIV from a blood splash, needlestick, or sexual contact may reduce the chance of infection by taking antiretroviral drugs for 4 weeks. These drugs are more effective when they are started as soon as possible after the exposure. Taking two or more drugs is currently recommended.
Doctors and the person who was exposed typically decide together whether to use these preventive drugs. They base the decision on the estimated risk of infection and the possible side effects of the drugs. If they do not know whether the source is infected with HIV, they consider how likely the source is to be infected. However, even when the source of the exposure is known to be infected with HIV, the risk of infection after exposure varies, depending on the type of exposure. For example, risk from a blood splash is less than that from a needlestick.
Immediately after exposure to HIV infection, what is done depends on the type of exposure:
If skin is exposed, it is cleaned with soap and water.
Puncture wounds are cleaned with antiseptic.
If mucous membranes are exposed, they are flushed with large amounts of water.
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Chimp Siv Is Different
Chimpanzee SIV is an exception. Two papers published last summer point out that the SIV carried by chimpanzees appears to be a recombinant of SIVs carried by cercopithecids, upon which chimpanzees prey. As chimpanzee SIV appears to be most similar to HIV, it will aid in our understanding of the infectivity of HIV to find out how SIVcpz evolved and whether chimpanzees, which still prey on monkeys, are being reinfected. Because SIVcpz apparently is the root of HIV-1, it is essential that researchers understand where it came from.
There are four subspecies of chimpanzees: Pan troglodytes troglodytes, Pan troglodytes verus, Pan troglodytes vellerosus, and Pan troglodytes schweinfurthii. P. t. troglodytes is the subspecies present in Cameroon, Equatorial Guinea, Gabon, and Republic of the Congo. The SIV that infects this subspecies is similar to all known groups of HIV-1. A small percentage of P. t. schweinfurthii, which is endemic to the area east of the southward-flowing Ubangi River, also carries a chimpanzee SIV. That SIV, however, differs from the one that infects P. t. troglodytes and has not so far been implicated in human disease.
But, says Marx, the next question is not just how and where SIV jumped from nonhuman primates, but what makes HIV infectious and transmissible in humans. Answers to these questions may aid in determining why HIV makes humans very, very sick, while SIV causes no disease in other higher primates.
Did Hiv Start In Africa
Using the earliest known sample of HIV, scientists have been able to create a ‘family-tree’ ancestry of HIV transmission, allowing them to discover where HIV started.
Their studies concluded that the first transmission of SIV to HIV in humans took place around 1920 in Kinshasa in the Democratic Republic of Congo .10
The same area is known for having the most genetic diversity in HIV strains in the world, reflecting the number of different times SIV was passed to humans. Many of the first cases of AIDS were recorded there too.
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Symptoms Of Hiv Infection
Most people experience a short flu-like illness 2 to 6 weeks after HIV infection, which lasts for a week or 2.
After these symptoms disappear, HIV may not cause any symptoms for many years, although the virus continues to damage your immune system.
This means many people with HIV do not know they’re infected.
Anyone who thinks they could have HIV should get tested.
Some people are advised to have regular tests as they’re at particularly high risk.
Simplified Life Cycle Of The Human Immunodeficiency Virus
Like all viruses, human immunodeficiency virus reproduces using the genetic machinery of the cell it infects, usually a CD4+ lymphocyte.
Drugs used to treat HIV infection were developed based on the life cycle of HIV. These drugs inhibit the three enzymes that the virus uses to replicate or to attach to and enter cells.
HIV also infects other cells, such as cells in the skin, brain, genital tract, heart, and kidneys, causing disease in those organs.
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