| Once HIV enters the human body, it attaches itself to a White Blood Cell (WBC) called CD4. Also, called T4 cells, they are the main disease fighters of the body. Whenever there is an infection, CD4 cells lead the infection-fighting army of the body to protect it from falling sick. Damage of these cells, hence can affect a person's disease-fighting capability and general health. | ||
| After making a foothold on the CD4 cell, the virus injects its RNA into the cell. The RNA then gets attached to the DNA of the host cell and thus becomes part of the cell's genetic material. It is a virtual takeover of the cell. Using the cell's division mechanism, the virus now replicates and churns out hundreds of thousands of its own copies. These cells then enter the blood stream, get attached to other CD4 cells and continue replicating. As a result, the number of the virus in the blood rises and that of the CD4 cells declines. | ||
| Because of this process, immediately after infection, the viral load of an infected individual will be very high and the number of CD4, low. But, after a while, the body's immune system responds vigorously by producing more and more CD4 cells to fight the virus. Much of the virus gets removed from the blood. To fight the fast-replicating virus, as many as a billion CD4 cells are produced every day, but the virus too increases on a similar scale. The battle between the virus and the CD4 cells continues even as the infected person remains symptom-free. | ||
| But after a few years, which can last up to a decade or even more, when the number of the virus in the body rises to very high levels, the body's immune mechanism finds it difficult to carry on with the battle. The balance shifts in favour of the virus and the person becomes more susceptible to various infections. These infections are called Opportunistic Infections because they swarm the body using the opportunity of its low immunity. At this stage, the number of CD4 cells per millilitre of blood (called CD4 Count), which ranges between 500 to 1,500 in a healthy individual, falls below 200. The Viral Load, the quantity of the virus in the blood, will be very high at this stage. | ||
| Opportunistic infections are caused by bacteria, virus, fungi and parasites. Some of the common opportunistic infections that affect HIV positive persons are: Mycobacterium avium complex (MAC), Tuberculosis (TB), Salmonellosis, Bacillary Angiomatosis (all caused by bacteria); Cytomegalovirus (CMV), Viral hepatitis, Herpes, Human papillomavirus (HPV), Progressive multifocal leukoencephalopathy (PML) (caused by virus); Candidiasis, Cryptococcal meningitis (caused by fungus) and Pneumocystis Carinii pneumonia (PCP). Toxoplasmosis. Cryptosporidiosis (caused by parasites). HIV positive persons are also prone to cancers like Kaposi's sarcoma and lymphoma. | ||
| The Center for Disease Control (CDC), Atlanta has listed a series of diseases as AIDS-defining. When these diseases appear, it is a sign that the infected individual has entered the later stage of HIV infection and has started developing AIDS. The progression of HIV positive persons into the AIDS stage is highly individual. Some people can reach the AIDS stage in about five years, while some remain disease free for more than a decade. Measurement of the viral load and the CD4 count helps a doctor in assessing an infected person's health condition |
Saturday, January 24, 2009
What Happens Inside the Body?
What are the early symptoms of HIV infection?
| Many people do not develop any symptoms when they first become infected with HIV. Some people, however, get a flu-like illness within three to six weeks after exposure to the virus. This illness, called Acute HIV Syndrome, may include fever, headache, tiredness, nausea, diarrhoea and enlarged lymph nodes (organs of the immune system that can be felt in the neck, armpits and groin). These symptoms usually disappear within a week to a month and are often mistaken for another viral infection. | ||
| During this period, the quantity of the virus in the body will be high and it spreads to different parts, particularly the lymphoid tissue. At this stage, the infected person is more likely to pass on the infection to others. The viral quantity then drops as the body's immune system launches an orchestrated fight. | ||
| More persistent or severe symptoms may not surface for several years, even a decade or more, after HIV first enters the body in adults, or within two years in children born with the virus. This period of "asymptomatic" infection varies from individual to individual. Some people may begin to have symptoms as soon as a few months, while others may be symptom-free for more than 10 years. However, during the "asymptomatic" period, the virus will be actively multiplying, infecting, and killing cells of the immune system |
Thursday, January 15, 2009
AIDS origin
HIV, the infectious agent that causes AIDS, is thought to have originated in non-human primates in sub-Saharan Africa and to have been transferred to humans during the 20th century.
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-2 may have originated from the Sooty Mangabey , an Old World monkey of Guinea-Bissau, Gabon, and Cameroon.
HIV-1 is more virulent. It is easily transmitted and is the cause of the majority of HIV infections globally. HIV-2 is less transmittable and is largely confined to West Africa. HIV-1 is the species described below
Most HIV researchers agree that HIV evolved from the closely related Simian Immunodeficiency Virus (SIV), and that HIV was transferred from non-human primates to humans in the recent past (as a type of zoonosis). The details of how and where this occurred remain controversial, and no single hypothesis has been unanimously accepted..
One hypothesis is the so-called 'Hunter' Theory, according to which a human bushmeat hunter was bitten or cut while hunting or butchering an ape, resulting in infection.
Exactly where and when this occurred has been a matter of debate in the scientific community. Researchers announced in May, 2006 that HIV-1 most likely originated in wild chimpanzees in the southeastern rain forests of Cameroon (modern East Province).
Others place the origin of HIV-1 closer to Kinshasa. Seven years of research and 1,300 chimpanzee genetic samples led Dr. Beatrice Hahn, of the University of Alabama at Birmingham, to identify chimpanzee communities near Cameroon's Sanaga River as the most likely original reservoir of HIV-1.
Calculations based on viral mutation rates and HIV-1 sequences preserved in biological samples in 1959 ("ZR59") and 1960 (DRC60) suggest that the jump from chimpanzee to human likely happened during the late 19th century or the early 20th century, a time of rapid urbanisation in the colonial period.Comparative primatologist Jim Moore suggests that colonial practices may have created conditions conducive to the spread of the virus. The hardships of forced labour could have suppressed the immune system of the initial hunter, allowing the virus to infect and take hold in a new host. Rapid urbanisation brought infected people into close contact with others, and colonial commerce provided opportunities for further geographical spread.
Vaccination campaigns against illnesses such as sleeping sickness may have sped the initial spread of HIV-1 when immunisation needles were re-used, and needles were also shared in the booming colonial city of Kinshasa.
Other technological and social disruptions, especially those that affected the food supply and the hunting of bushmeat, are thought to have promoted the cross-over from chimpanzees and the spread amongst humans.
After the initial transfer of SIV from a non-human primate to humans, and the mysterious and sudden change or possible mutation into HIV, the virus ultimately spread via contact among humans to the rest of the world. Since a cross species jump is most likely the origin of HIV, and since HIV became a true epidemic, transmissible from human to human, then the following conditions were needed:
1. a large human population;
2. a large nearby population of the appropriate host animal;
3. an infectious pathogen in the host animal, that eventually produces a mutation that can spread from animal to human;
4. interaction between the species to transmit enough of it to humans to establish a human foothold, which may take millions of individual exposures;
5. a mutation of same pathogen that can spread from human to human;
6. some method that allows the pathogen to disperse widely. This prevents the infection from "burning out" by either killing off its human hosts or provoking immunity in a local population of humans.
Such requirements existed in the remote past with smallpox, and also with the 20th century Spanish flu, despite Spanish flu's New World origin at Fort Riley, Kansas. There the animal reservoir seems to have been two species, chickens and pigs, which were of Old World origin.
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-1 is more virulent and more easily transmitted. HIV-1 is the source of the majority of HIV infections throughout the world, while HIV-2 is less easily transmitted and is largely confined to West Africa.
Both species of the virus (HIV-1 and HIV-2) are believed to have originated in West-Central Africa and jumped species (zoonosis) from a non-human primate to humans. HIV-1 somehow came from Simian Immunodeficiency Virus (SIVcpz) found in the chimpanzee subspecies Pan troglodytes troglodytes. DNA sequencing indicates that HIV-1 (group M) entered the human population in the early 20th century, probably sometime between 1915 and 1941.
A 2008 paper using a recently-discovered 1960 biopsy suggested a common ancestor between 1884 and 1924.[6] HIV-2 crossed species from a different strain of SIV, this one found in sooty mangabeys (an Old World monkey) of Guinea-Bissau.
SIV in non-human primates tends to cause a non-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 nef 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.
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-2 may have originated from the Sooty Mangabey , an Old World monkey of Guinea-Bissau, Gabon, and Cameroon.
HIV-1 is more virulent. It is easily transmitted and is the cause of the majority of HIV infections globally. HIV-2 is less transmittable and is largely confined to West Africa. HIV-1 is the species described below
Likely spread from animal to human populations
Most HIV researchers agree that HIV evolved from the closely related Simian Immunodeficiency Virus (SIV), and that HIV was transferred from non-human primates to humans in the recent past (as a type of zoonosis). The details of how and where this occurred remain controversial, and no single hypothesis has been unanimously accepted..
Cameroon chimpanzees hypothesis
One hypothesis is the so-called 'Hunter' Theory, according to which a human bushmeat hunter was bitten or cut while hunting or butchering an ape, resulting in infection.
Exactly where and when this occurred has been a matter of debate in the scientific community. Researchers announced in May, 2006 that HIV-1 most likely originated in wild chimpanzees in the southeastern rain forests of Cameroon (modern East Province).
Others place the origin of HIV-1 closer to Kinshasa. Seven years of research and 1,300 chimpanzee genetic samples led Dr. Beatrice Hahn, of the University of Alabama at Birmingham, to identify chimpanzee communities near Cameroon's Sanaga River as the most likely original reservoir of HIV-1.
Calculations based on viral mutation rates and HIV-1 sequences preserved in biological samples in 1959 ("ZR59") and 1960 (DRC60) suggest that the jump from chimpanzee to human likely happened during the late 19th century or the early 20th century, a time of rapid urbanisation in the colonial period.Comparative primatologist Jim Moore suggests that colonial practices may have created conditions conducive to the spread of the virus. The hardships of forced labour could have suppressed the immune system of the initial hunter, allowing the virus to infect and take hold in a new host. Rapid urbanisation brought infected people into close contact with others, and colonial commerce provided opportunities for further geographical spread.
Vaccination campaigns against illnesses such as sleeping sickness may have sped the initial spread of HIV-1 when immunisation needles were re-used, and needles were also shared in the booming colonial city of Kinshasa.
Other technological and social disruptions, especially those that affected the food supply and the hunting of bushmeat, are thought to have promoted the cross-over from chimpanzees and the spread amongst humans.
Method of spread
After the initial transfer of SIV from a non-human primate to humans, and the mysterious and sudden change or possible mutation into HIV, the virus ultimately spread via contact among humans to the rest of the world. Since a cross species jump is most likely the origin of HIV, and since HIV became a true epidemic, transmissible from human to human, then the following conditions were needed:
1. a large human population;
2. a large nearby population of the appropriate host animal;
3. an infectious pathogen in the host animal, that eventually produces a mutation that can spread from animal to human;
4. interaction between the species to transmit enough of it to humans to establish a human foothold, which may take millions of individual exposures;
5. a mutation of same pathogen that can spread from human to human;
6. some method that allows the pathogen to disperse widely. This prevents the infection from "burning out" by either killing off its human hosts or provoking immunity in a local population of humans.
Such requirements existed in the remote past with smallpox, and also with the 20th century Spanish flu, despite Spanish flu's New World origin at Fort Riley, Kansas. There the animal reservoir seems to have been two species, chickens and pigs, which were of Old World origin.
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-1 is more virulent and more easily transmitted. HIV-1 is the source of the majority of HIV infections throughout the world, while HIV-2 is less easily transmitted and is largely confined to West Africa.
Both species of the virus (HIV-1 and HIV-2) are believed to have originated in West-Central Africa and jumped species (zoonosis) from a non-human primate to humans. HIV-1 somehow came from Simian Immunodeficiency Virus (SIVcpz) found in the chimpanzee subspecies Pan troglodytes troglodytes. DNA sequencing indicates that HIV-1 (group M) entered the human population in the early 20th century, probably sometime between 1915 and 1941.
A 2008 paper using a recently-discovered 1960 biopsy suggested a common ancestor between 1884 and 1924.[6] HIV-2 crossed species from a different strain of SIV, this one found in sooty mangabeys (an Old World monkey) of Guinea-Bissau.
SIV in non-human primates tends to cause a non-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 nef 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.
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