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Biology

Acquired Immuno Deficiency Syndrome(AIDS)

AIDS Acquired Immuno Deficiency Syndrome
First reported 1981
Etiology

AIDS is caused by theretrovirus called Human Immunodeficiency Virus(HIV) of Lentivirus family.

There are two genetic but antigenically different variants of HIV noted among AIDS patients.

  1. HIV-1 - commonly found in U.S., Europe, and Central Africa.
  2. HIV-2 - commonly found in West Africa.

AIDS also occur in other species such as

  1. Felines or cats - Feline Immunodeficiency Virus(FIV) of Lentivirus family.
  2. Monkeys - Simian Immunodeficiency Virus(SIV) of Lentivirus family.
Epidemiology

HIV transmission occurs broadly through exchange of blood or body fluids contaminated by the virus or virus-infected cells.

Sexual transmission is responsible for more than 75% of all cases of HIV transmission and especially heterosexual transmission accounts for most infections. Transmission among intravenous drug abusers occurs through shared needles, syringes etc… contaminated with HIV.  About 1% of all AIDS cases in infants results from vertical transmission of virus from infected mother to the fetus or newborn. Mother-to-infant vertical transmission occurs in three modes

  1. In utero - through placental infection
  2. Intrapartum - during delivery and
  1. Breast feeding.

HIV cannot transmit through normal day-to-day personal contacts and there is no evidence of infection through insect bites.

Structure of HIV

HIV-1 virion is spherical in shape. The virus core contains:

  1. Capsid protein p24
  2. Nucleocapsid protein p7/p9
  3. Two copies of genomic RNA and
  4. Three viral enzymes(protease, reverse transcriptase, and integrase).

Capsid protein or p24 is the most readily detected viral antigen and is therefore the target for the antibodies used to diagnose HIV infection in blood screening. Extreme variability in antigen structure poses a formidable barrier for vaccine development.

Symptoms

Initial stage symptoms include fever, headache, sore throat, and swollen lymph nodes.

Symptoms post clinical latency include swollen lymph nodes, fever, diarrhea, weight loss, and fatigue.

Pathogenesis

HIV is a retrovirus, which has the ability to reproduce by synthesizing DNA from the RNA genome. It mainly infects immune system and CNS. 

Infection and progression of virus occurs through following stages,

  1. The retrovirus inserts the synthesized DNA into a host chromosome.
  2. The enzyme called reverse transcriptase in the capsid reads the RNA template and synthesize the DNA from it.
  3. After the penetration of virus into the host cell, the genome gets converted into DNA.
  4. This DNA enters into the host genome and reside dormant for a long time.
  5. Future stimulation of immune system by an unknown cause activates the replication of virus.
  6. Newly assembled virions(a complete virus particles) are released which subsequently affect other cells and destroys the T cells having CD4 receptors.
  7. B and T lymphocytes attack and destroy the virus from circulation, but the virus persists in the lymph nodes.
  8. Virus replicates at a faster rate than the body can replenish its T cells and infects other immune system components such as monocytes, macrophages, and B cells but does not kill these cells, so they serve as an additional and continual source of new virions.
  9. The person gradually loses the ability to fight infections and begins to develop opportunistic infections(Diseases caused by a microorganism that is pervasive in the environment and to which people are generally resistant, but that affects someone with

an impaired immune system).

  1. When CD4 T cell count reduces to less than 200 per cubic millimeter of blood(normal range is between 500 and 1,800), common opportunistic infections such as toxoplasmosis, histoplasmosis, Pneumocystis pneumonia, cervical cancer, herpes, hepatitis C, candidiasis, bacterial diarrheas, and tuberculosis attacks easily.
  2. Successive suppression and inactivity of immune system leads to the proliferation of diseases and gradual deterioration of the body.
Diagnosis

Two types of diagnosis are common, which includes screening a blood sample for the presence of antibodies against the virus.

  1. Enzyme-Linked ImmunoSorbent Assay(ELISA)detects antibodies specific for viral proteins. The test takes a few weeks to get results. The production of a detectable level of antibodies by the specific immune system can take up to eight weeks after the initial exposure to the virus, so this test is not much accurate when performed immediately after infection.
  1. Western Blot Analysis - detects the presence of HIV proteins in the blood and is used toconfirm a positive antibody screen result. Results from these tests can be obtained within 20 minutes.
Treatments

There is no cure for AIDS. The drugs are expensive and causes serious side effects.  All contemporary drugs can either slow or stop viral replication but cannot inactivate all viral particles, which makes eradication impossible.

Also the problem of the rapid mutation rate exacerbates the situation to formulate a vaccine for the virus.

Antiviral therapy effectively reduces mother-to-child transmission, but only 5 percent of women receive this therapy.

Drugs

Reverse transcriptase inhibitors:

Reverse transcriptase inhibitor drugs work by inhibiting the enzyme and halting the life cycle of the virus.

e.g. Azidothymidine(AZT) was the first drug approved for treating HIV infection.

Protease inhibitors:

Protease inhibitor drugs work by interfering with a viral protein called HIV protease. Without this protein the viral particles cannot assemble properly and become inert.

Fusion inhibitors inhibit the viruses from fusing with the host cell membranes and stops the replication of virus.
e.g. Selzentry a drug that works by blocking a receptor CCR5, that the virus often uses to gain entry into the host’s white blood cells.

Highly Active Antiretroviral Therapy(HAART) uses Cocktail drugs(a combination of three or more drugs with different mechanisms of action) to overcome potential resistance. HIV mutates very rapidly and quickly becomes resistant to a once-effective drug.

Statistics

Around 95% of HIV infections are recorded in developing countries.

AIDS is the fifth major cause of death in adults between the ages of 25 and 44.

Africa alone carries more than 50% of the HIV patients.

Around 90 percent of the children infected with HIV belong to sub-Saharan Africa.

Liable factors.

Injected drug use.

Commercial prostitution.

Refusal of men to wear a condom during sex.

Forced sex.
Extramarital sex affairs.

Govt. Schemes

Govt. has setup State AIDS bodies in 25 states and 7 union territories in 1992.

India’s first National AIDS Control Programme NACP-I was launched in 1992

National AIDS Control Organization (NACO) was put into operation.

The National AIDS Committee was formed in the Ministry of Health and Family Welfare.