Definitions

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. HIV attaacks the immunes sytems by targetting the cells (e.g. CD4) which would normally infectious fight foregin bodies eg bacteria. The less CD4 cells the more prone to opportunistic infections or AIDS.

Viral Load is how many RNA copies (viruses) are  in 1ml (small drop) of blood plasma. The limit of detection for the viruses in 1ml  is below 200 copies/ml,

CD4 Count:  your immune system contains different types of cells that help protect the body from infection. One of these types of specialized cells are called the CD4 or T-cells. HIV attacks these types of cells and uses them to make more copies of HIV/multiply. And in doing so, HIV weakens the immune system, making it unable to protect the body from illness and infection.

HIV Infection:  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, and transmission from an infected mother to her baby at birth, or through breast milk.

Screening of blood products for HIV in the developed world has largely eliminated transmission through blood transfusions or infected blood products in these countries. 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.

Symptoms Early After Infection
Fever
Headache
Muscle and Joint pain
Sore Throat
Rash and Diarrhoea usually diagnosed as flu by doctors.

Acute HIV Syndrome: During the initial period of infection, HIV replication is very rapid. As the level of HIV in the blood rises, it begins to attack the immune system, catching it off guard so to speak, and weakening it to the point of causing symptoms. Because of its similarity to common illnesses such as influenza or mononucleosis, the diagnosis of acute HIV syndrome is often missed and the patient is sent home unaware that they have a serious illness that can do great harm to themselves and others.

Symptoms of the Immune System: The immune system is the body's natural defence against invading foreign agents such as viruses and bacteria. HIV attacks the immune system, weakening it and making the body more susceptible to infection. After HIV infection, some of these symptoms affect the immune system.
Swollen lymph nodes in the neck
Axilla or groin (lymphadenopathy)
Fever
Night sweats

Symptoms of the GI Tract: HIV can have a profound affect on the gastrointestinal system and nutrition. Like any virus, HIV can cause symptoms ranging from poor appetite to diarrhoea.
Rapid weight loss
Diarrhoea
Poor appetite
Profound fatigue

Respiratory Symptoms: Some of the most serious symptoms of HIV involve the respiratory system. Symptoms associated with breathing and respiration usually occur later in course of the disease. Unfortunately, many people's first symptom of HIV involves the respiratory system, illustrating why HIV testing is so important. Any cough or shortness of breath could be a sign of bacterial pneumonia or pneumocystis (carinii) jiroveci pneumonia (PCP). 
Shortness of breath
Dry cough / productive cough
Pneumonia

Symptoms of the Skin and Mucous Membranes: Many of the symptoms of HIV are a result of infection by other viruses, fungi or bacteria. Often, these infections involve the skin or mucous membranes (for example, inside the mouth).
Skin rash
Red, brown, pink or purple lesion on the skin - suggestive of Kaposi's sarcoma
White patches on the tongue, inside of the mouth, or gums - could be signs of thrush, Candida, or hairy oral Leukoplakia
Canker sores / apthous ulcers

Neurological / Emotional Symptoms: Very early on in the epidemic, experts realized that HIV affected both the physical and emotional self. Neurological and emotional symptoms of HIV can include the following.
Depression
Numbness, tingling, or burning in the feet, hands, or face. (peripheral neuropathy) Confusion
Weakness, or changes in level of consciousness