HIV
Human immunodeficiency virus (HIV) is a retrovirus that can lead to acquired immunodeficiency syndrome (AIDS), a condition in humans in 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 unprotected sexual intercourse, contaminated needles, breast milk, and transmission from an infected mother to her baby at birth. Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world.

Prevalence
HIV infection in humans is now pandemic. As of January 2006, the Joint United Nations Programme on HIV/AIDS (UNAIDS) and the World Health Organization (WHO) estimate that AIDS has killed more than 25 million people since it was first recognized on December 1, 1981, making it one of the most destructive pandemics in recorded history. It is estimated that about 0.6% of the world's population is infected with HIV.[3] In 2005 alone, AIDS claimed an estimated 2.4–3.3 million lives, of which more than 570,000 were children. A third of these deaths are occurring in sub-Saharan Africa, retarding economic growth and increasing poverty. According to current estimates, HIV is set to infect 90 million people in Africa, resulting in a minimum estimate of 18 million orphans.[5] Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but routine access to antiretroviral medication is not available in all countries.

Biochemistry
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. If untreated, eventually most HIV-infected individuals develop AIDS (Acquired Immunodeficiency Syndrome) and die; however about one in ten remains healthy for many years, with no noticeable symptoms. Treatment with anti-retrovirals, where available, increases the life expectancy of people infected with HIV. It is hoped that current and future treatments may allow HIV-infected individuals to achieve a life expectancy approaching that of the general public.

Syphilis
Syphilis is a curable sexually transmitted disease caused by the Treponema pallidum spirochete. The route of transmission of syphilis is almost always by sexual contact, although there are examples of congenital syphilis via transmission from mother to child in utero. The signs and symptoms of syphilis are numerous; before the advent of serological testing, precise diagnosis was very difficult. In fact, the disease was dubbed the "Great Imitator" because it was often confused with other diseases, particularly in its tertiary stage. Syphilis (unless antibiotic-resistant) can be easily treated with antibiotics including penicillin. The oldest and still most effective method is an intramuscular injection of benzathine penicillin. If not treated, syphilis can cause serious effects such as damage to the heart, aorta, brain, eyes, and bones. In some cases these effects can be fatal. In 1998, the complete genetic sequence of T. pallidum was published which may aid understanding of the pathogenesis of syphilis.

• Primary Syphilis Primary syphilis is typically acquired via direct sexual contact with the infectious lesions of a person with syphilis.[15] Approximately 10-90 days after the initial exposure (average 21 days), a skin lesion appears at the point of contact, e.g. the genitalia. Syphilis can not be contracted through toilet seats, daily activities, hot tubs, or sharing eating utensils or clothing.[

• Secondary Syphilis Secondary syphilis occurs approximately 1-6 months (commonly 6 to 8 weeks) after the primary infection. There are many different manifestations of secondary disease. There may be a symmetrical reddish-pink non-itchy rash on the trunk and extremities. Other symptoms common at this stage include fever, sore throat, malaise, weight loss, headache, meningismus, and enlarged lymph nodes.

• Latent Syphilis Latent syphilis is defined as having serologic proof of infection without signs or symptoms of disease. Latent syphilis is further described as either early or late. Early latent syphilis is defined as having syphilis for two years or less from the time of initial infection without signs or symptoms of disease. Late latent syphilis is infection for greater than two years but without clinical evidence of disease.

• Tertiary Syphilis Tertiary syphilis usually occurs 1-10 years after the initial infection, though in some cases it can take up to 50 years. This stage is characterized by the formation of gummas which are soft, tumor-like balls of inflammation known as granulomas.

• Neurosyphilis
Neurosyphilis refers to a site of infection involving the central nervous system (CNS). Neurosyphilis may occur at any stage of syphilis. Before the advent of antibiotics, it was typically seen in 25-35% of patients with syphilis. Neurosyphilis is now most common in patients with HIV infection.

Management
While abstinence from any sexual activity is very effective at helping prevent Syphilis, it should be noted that T. pallidum readily crosses intact mucosa and cut skin, including areas not covered by a condom. Proper and consistent use of a latex condom can reduce, but not eliminate, the spread of syphilis.

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