Lesson 31: Environment and human health


The AIDS (acquired immune deficiency syndrome) due to Human immuno deficiency virus (HIV) has caused a worldwide epidemic, called as pandemic as it continues to spread all over the world. The disease is spread through direct transfer of body fluids containing the virus into the bloodstream of another person. Sharing of contaminated needles among intravenous drug users and sexual contact are the most likely methods of passage. This is a problem with homosexual community in US. WHO estimated that 42 million adults and children are living with HIV/AIDS. Nearly 4 million are affected in India. The distribution of the virus is lowest in the economically developed countries and highest in less developed countries. Sub-saharan Africa has been hit hardest by this disease. The economic burden on these countries is tremendous. Those with AIDS symptoms are unable to work and need medical care. Because of poverty there is often little medical care available.


Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans which the immune system begins to fail, leading to life-threatening opportunistic infections . Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The four major routes of transmission are unsafe sex , contaminated needles, breast milk, and transmission from an infected mother to her baby at birth (Vertical transmission). Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world.

HIV primarily infects vital cells in the human immune system such as helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. HIV infection leads to low levels of CD4+ T cells through three main mechanisms: firstly, direct viral killing of infected cells; secondly, increased rates of apoptosis in infected cells; and thirdly, killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.

Last modified: Friday, 6 January 2012, 10:23 AM