Acquired Immuno Deficiency Syndrome (AIDS)

Immunodeficiency diseases:

Immunodeficiency results from the failure of one or more components of the immune system. Primary immune deficiencies are caused by genetic developmental defects. Secondary immune deficiencies arise due to various reasons like radiation, use of cytolytic and immunosuppressive drugs, and infections.

AIDS:

• AIDS is an acronym for Acquired Immuno Deficiency Syndrome.
• It is the deficiency of the immune system, acquired during the lifetime of an individual indicating that it is not a congenital disease.
• AIDS is caused by Human Immuno Deficiency Virus (HIV), a member of a group of viruses called a retrovirus, which have an envelope enclosing the RNA genome.
• It selectively infects helper T cells. The infected helper T cells will not stimulate antibody production by B-cells resulting in loss of natural defence against viral infection.
• On the basis of genetic characteristics and differences in the viral antigens, HIV is classified into types 1 and 2 (HIV-1, HIV-2).
• AIDS was first reported in 1981 and in the last twenty-five years or so, it has spread all over the world killing more than 25 million persons.

Structure of HIV:

• The human immunodeficiency virus belongs to the genus Lentivirus.
• When observed under the electron microscope, HIV is seen as a spherical virus, 100-120 nm in diameter, containing a dense core surrounded by a lipoprotein envelope.
• The envelope has glycoprotein (gp) spikes termed gp 41 and gp 120.
• At the core, there are two large single stranded RNA.
• Attached to the RNA are molecules of reverse transcriptase.
• It also contains enzymes like protease and ribonuclease.
• The core is covered by a capsid made of proteins.
• This is followed by another layer of matrix proteins as shown in the figure.
  

  Structure of HIV

Transmission of HIV infection:

The HIV is often located within the cells, especially in macrophages. HIV can survive for 1.5 days inside a cell but only about 6 hours outside a cell. 

1. Sexual contact with an infected person or having multiple sexual partners
2. Transfusion of contaminated blood and blood products,
3. Sharing infected needles as in the case of intravenous drug abusers and
4. Infected mother to her child through the placenta.

High risk people of getting HIV: 

• Drug abusers who inject drugs intravenously. 
• Individuals who have several sexual partners  
• People who need blood transfusions on a regular basis.
• Children born to a mother who has HIV. 

HIV/AIDS is not spread by mere touch or physical contact; it spreads only through body fluids. 

• There is always a time lag between the infection and the appearance of AIDS symptoms.  
• This period may vary from a few months to many years (usually 5-10 years).

Replication of HIV:

• After getting into the body of the person, the virus enters into macrophages where the RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase.
• This viral DNA gets incorporated into the DNA of host cells and directs the infected cells to produce viral particles.
• The macrophages continue to produce the virus, thus acting like an HIV factory. Simultaneously, HIV enters into helper T-lymphocytes (T_H), replicates and produces progeny viruses.
• The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated, leading to a progressive decrease in the number of helper T lymphocytes in the body of the infected person.

Symptoms:

• During this period, the person suffers from bouts of fever, diarrhoea, and weight loss.
• Due to a decrease in the number of helper T lymphocytes, the person starts suffering from infections that could have been otherwise overcome such as those due to bacteria especially Mycobacterium, viruses, fungi, and even parasites like Toxoplasma. The patient becomes so immuno-deficient that he/she is unable to protect himself/herself against these infections.

Diagnostic test:

• A simple blood test is available that can determine whether the person has been infected with HIV. The ELISA test (Enzyme-Linked ImmunoSorbent Assay) detects the presence of HIV antibodies. It is a preliminary test.
• The western blot test is more reliable and a confirmatory test. It detects the viral core proteins. If both tests detect the presence of the antibodies, the person is considered to be HIV positive.

Treatment of AIDS:

Treatment of AIDS with anti-retroviral drugs is only partially effective. They can only prolong the life of the patient but cannot prevent death, which is inevitable.

Prevention of AIDS:

AIDS has no cure. Prevention of AIDS is the best option.

1. AIDS awareness programmes by the National AIDS Control Organisation (NACO), Non-Governmental Organisations (NGOs), and WHO are to prevent the spreading of AIDS.
2. Advocating safe sex
3. Promoting regular check-ups for HIV in susceptible populations
4. Safe blood for transfusion
5. Use of disposable needles
6. Use of condoms during sexual contact
7. Prevention of drug abuse