Diseases or infections which are transmitted through sexual intercourse called sexually transmitted diseases (STD) or VD (Venereal diseases) or RTI (Reproductive tract infections).
Examples of STDs:
(i) HIV (AIDS)
(iii) Genital herpes
(vi) Genital warts
AIDS is caused by HIV virus (Human Immuno deficiency virus or Human T-cell leukemia virus). There is always a time-lag between the infection and appearance of AIDS symptoms (incubation period). Incubation period may vary from a few month to many years (usually 5-10 years).
ARC (AIDS Related Complex) is a mild or initial form of AIDS which develop after a few month of infection. In AIDS patient, a reduction of 10% weight indicates ARC. After infection, HIV enters in macrophages where RNA of virus replicates to form viral DNA with the help of enzyme reverse transcriptase. Viral DNA incorporated into host cell DNA and directs the infected cell to produce new virus particles. The macrophages continue to produce virus therefore macrophages are called HIV Factory.
Simultaneously HIV enters into helper T-lymphocytes (TH) or T4 replicates and produce 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 infected person.
During this period person suffers from:
(i) Bouts of fever
(iii) Weight loss
Due to the decrease in TH cells, person start suffering from infections that could have been otherwise overcome such as those due to bacteria especially Mycobacterium, virus, 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 for AIDS is ELISA (Enzyme Linked Immuno Sorbent Assay). Western blot is used as confirmatory or supplemental test for AIDS. Routine test of AIDS is PCR.
Hepatitis-B virus is horizontally transmitted by blood transfusions, contaminated needles, body fluids like semen, saliva, sweat, tear and breast milk. Hepatitis-B is also transmitted vertically from infected mother to foetus through placenta. For prevention and control hepatitis-B vaccine is now available. Hepatitis-B vaccine was developed by Blumberg, for which he was awarded Nobel Prize in 1976.