Download (AIDS) is a disease of the human immune system caused by the

AIDS
Acquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS) is
a disease of the human immune system caused by the human immunodeficiency virus (HIV).
The illness interferes with the immune system making people with AIDS much more likely to
get infections, including tumors that do not affect people with working immune systems. This
susceptibility gets worse as the disease continues.
HIV is transmitted in many ways, such as anal, vaginal or oral sex, blood transfusion,
contaminated hypodermic needles, exchange between mother and baby during pregnancy,
childbirth, and breastfeeding. It can be transmitted by any contact of a mucous membrane or the
bloodstream with a bodily fluid that has the virus in it, such as the blood, semen, vaginal fluid,
preseminal fluid, or breast milk from an infected person.
The virus and disease are often referred to together as HIV/AIDS. The disease is a major health
problem in many parts of the world, and is considered a pandemic.
Although treatments for HIV/AIDS can slow the course of the disease, there is no known cure or
HIV vaccine. Antiretroviral treatment reduces both the deaths and new infections from
HIV/AIDS, but these drugs are expensive and the medications are not available in all countries.
Due to the difficulty in treating HIV infection, preventing infection is a key aim in controlling
the AIDS pandemic, with health organizations promoting safe sex and needle-exchange
programmes in attempts to slow the spread of the virus.
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Signs and symptoms
Main symptoms of AIDS.
The symptoms of AIDS are primarily the result of conditions that do not normally develop in
individuals with healthy immune systems. Most of these conditions are infections caused by
bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune
system that HIV damages.
People with AIDS also have an increased risk of developing various cancers such as cervical
cancer and cancers of the immune system known as lymphomas. Additionally, people with AIDS
often have systemic symptoms of infection like fevers, sweats (particularly at night), swollen
glands, chills, weakness, and weight loss. The specific opportunistic infections that AIDS
patients develop depend in part on the prevalence of these infections in the geographic area in
which the patient lives.
THE IMMUNE REACTION
The immune system consists of a series of mechanisms that work together to protect the host
from any number of foreign invaders. Together, these systems protect the body against
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potentially deadly attackers. Thus whenever a pathogen invades the body it elicits an almost
immediate response from the innate immune system. This produces a rather unspecific defense
against any pathogen. This defense includes barriers such as skin, the cilia in mucous membranes
that sweep away airborne invaders, and tears, secretions, and saliva whose enzymes can destroy
bacteria and other pathogens.
When this first line of defense fails to prevent an invader from entering the human body, a more
specific set of responses can be evoked. The adaptive immune system mounts a specific response
against a foreign molecule or antigen. It involves both B cells and T cells.
B cells originate in the bone marrow and circulate in the bloodstream. They are white blood cells
that produce antibodies whose purpose is to interact with foreign particles or antigens; an antigen
is a molecule that can elicit the production of antibodies (Abs) to a specific antigen (Ag).
Antibodies generally recognize only one antigenic determinant, in a process known as the lock
and key phenomenon. T cells, meanwhile, form in the thymus. The two main varieties are helper
T cells that help other immune cells in their functions and cytotoxic T cells that kill damaged or
foreign cells in the body.
When a foreign particle or organism enters the body, the immune system goes from alert status
to active duty. Both B cells and T cells respond to the threat and eliminate the foreign substance
from the host's body. If the invader is located in the bloodstream or outside the individual cells of
the body, the B cells take charge. They bind to the foreign particle, an action that prompts
another series of events which ends with the elimination of the Ab-Ag complex. If, on the other
hand, the pathogen enters a cell, as viruses do, the body responds by activating cytotoxic T cells.
These cells circulate in the bloodstream and lymph system and eliminate the foreign body by
killing the host cell that is infected with the foreign agent
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