How does AIDS spread?

How does AIDS spread? Epidemiological and Clinical Overview Dr.D.K.Giri-Ph.D Introduction It is very important to understand the causative agent, reservoir of infection, sources of infection of AIDS. The „host factors‟ like age and sex, high risk groups and the presence of STDs, frequency of exposure, mixing pattern of population are need to discuss for developing a clear conceptual foundation on AIDS epidemic. The mode of transmission, prevention and infection deserve detail description for a layman understanding about AIDS. The causative factors, such as political and cultural, social and economic etc. are indispensable areas to comprehend. The natural history of HIV/AIDS deserves adequate discussion for everybody. History and Origin of AIDS AIDS was officially recognized for the first time in June 1981, at the centers for Disease control, USA, in previously homosexual man dying with “Pneumocystis Carinci Pneumonia and Candidiasin”. Since then, AIDS has been reported from all the continents. The virus causing AIDS was independently identified by a team of French scientists and American scientists in 1983. The International Committee on Nomenclature of viruses named it the “Human Immune deficiency virus” (HIV) and till date two types of HIV, such as HIV-1 and HIV-2 are identified. The probable origin of HIV depicted in, fig.2.1 and Fig.2.2. Figure 2.1 Probable origin of HIV SIV (Natural Host+ African Ape)

Chimpanzee

HIV 1 N HIV

–

HIV 1A

HIV 1B

HIV 1C

HIV 11-0

HIV 1C

(Highly Infection and High Transmission)

1

HIV 1E

(Progenitor)

HIV 1F

Figure 2.2 SIV Monkey Natural Host Asian Monkey

African Monkey

Human

Human

Some diseases(SIV 1) (Less Transmission) Sources :

Some diseases(SIV 2) (Less Transmission)

Epidemiological Background of AIDS, A Doctors’ Manual 1997 (NACO)

AIDS a Clinical Overview AIDS in short for Acquired Immune Deficiency Syndrome is a medical condition caused by a virus called HIV (Human Immune-Deficiency Virus). It is a medical diagnosis for a combination of symptoms which results from the breakdown of the immune system. The immune systems defend the body against infections and diseases. AIDS is not a disease. It is only a symptom of immune deficiency. This deficiency is caused by HIV. HIV is not a single virus, rather 2 viruses such as HIV-1 and HIV-2. These two viruses cause for AIDS. HIV belongs to a family of viruses called „Retroviruses‟. The main aim of this virus is to break down of body‟s immune system. In healthy individuals infections are kept at a distance by virtue of an array of defenders which constitute the immune system; the most important components are the „WBC‟ (white blood corpuscles) present in the blood and consists of white blood and lymphatic system including the lymph gland. Human blood consists of WBC and RBC. WBC is lymphocytes come in B-cells and T-cells. Some T cells are called helper cells, while others are called suppressor cells. The helper cells help the „B-cell‟ to produce antibodies that fight against diseases carrying organism. On the other hand, the suppressor cells work to suppress this fight against invading germs. How does AIDS virus weaken body’s immune system? In people with AIDS, the suppressor cells outnumber the helper cells (T –cells), rendering the Immune system weak or ineffective in the fight against disease. AIDS virus directly attacks the WBC, the defense system of our body territory. Human Immune Viruses intrude into the blood without giving any suspicion to the white cells. This is where it differs from all other bacterial and viral infections. Once entered into the body, it creates a strong base for them by multiplying in an exponential way. By the time, the white cells are able to identify the virus as mercenaries of the enemy, the battle is already lost. It is no longer in a position to fight against HIV giants because of its Lilliputian nature. Now the immune system of the body is on the decline. All types of infections freely enter the human body without any resistance put up by the white blood cells. The human defense system

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once shattered by the intrusion of HIV cannot be regained at all. Even a simple cold can be a death warrant to the patient. HIV/AIDS – A Pathological Conceptualization In AIDS, „A‟ stands for “acquired”, means that it is obtained or received by a person and it is something which does not ordinarily exist within one‟s body. „ID‟ stands for Immune Deficiency in the immune system or the immune system is weakened, „S‟ stands for syndrome, which means AIDS is not one particular isolated disease but which has a variety of symptoms leading to various disorders and a set of diseases.HIV is tiny, a thousand times smaller than the thickness of the hair. It looks like a rolled up porcupine. It contains two snakes like single stands of Ribose Nucleic Acid (RNA) along with a reverse transcript, which lies firmly wrapped of in a core, which resembles a cone with a dimple at its base. This core is protected by an envelope which has a knob like protein sticking out its surface, giving HIV, its characteristics appearance. The following figure shows the microscopic view of AIDS virus. Representation of the structures of the Human Immune Deficiency Virus (HIV). Fig. 2.3

Mechanism of Transmission Risk factors of HIV infection include multiple homo-sexual or heterosexual partners, contaminated blood transfusion, and injection with contaminated needles and syringes and infected mother to fetus /infant before, during or shortly after birth.The efficiency of transmission of HIV is determined by the amount of virus in a body fluid and the extent of contact. High concentrations have been reported in blood, genital fluids and cerebrospinal fluid. Breast milk and saliva yield varying numbers, where as other body fluids have a low viral content. The substances of saliva prevent cell to cell transfer of virus. Urine, sweat, milk, amniotic and synovial fluid, feces and tears have been reported to yield zero or a few HIV particles. Breast milk at the time of primary infection in a feeding mother has a high content of virus and may transmit the infection to the baby. Cerebral fluid (CSF) contains high content of HIV+ particularly in individuals with neurological diseases.

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The most efficient vehicle of HIV transmission is blood and blood products, like semen / vaginal secretion. Unprotected, penetrative sexual contact and different form of sexual practices oral, anal and vaginal carry a variable risk gradient of acquiring HIV. The following flow chart shows the different mode of HIV transmission. Flow Chart – 2.1 Different Modes of HIV Transmission HIV (virus) Human being is the reservoir or host. HIV Transmission through     

Blood/Blood products Vaginal Fluid Seminal Fluid Breast Milk Other Body Fluids

   

Infects others uninfected person through Unprotected sexual contact Transformation of contaminated blood and blood products Use of un-sterilized syringes, needles and others. Mother to child (inside the womb and during delivering and breast feedings)

HIV infected person increases

AIDS cases

The following table shows the efficiency of different routes of HIV transmission and their contribution to total number of cases. Table – 2.1 The efficiency of different routes of HIV transmission and their contribution to total number of cases. Exposure Rate

Percentage efficiency (worldover)

Percentage of total (World over)

Blood Transfusion Perinatal

90-95 20-40

Sexual intercourse Vaginal and Anal

0.01 to 1

Injecting drugs use Needle stick exposure Others

0.5-1.0