Q.The immune system of a person is suppressed. In the ELISA test, he was found positive to a pathogen.
a. Name the disease the patient is suffering from.
b. What is the causative organism?
c. Which cells of body are affected by the pathogen?

Let’s start with an everyday picture. Think of your body as a country, and your immune system as its army and police force. This army is always on patrol, looking for invaders — viruses, bacteria, fungi — and destroying them before they can cause trouble. Now imagine a spy so clever that it doesn’t just attack the army; it actually enters the army’s command centre, takes over the generals, and slowly disables the entire defence system. That is exactly what the HIV virus does.

HIV stands for Human Immunodeficiency Virus. The key word is immunodeficiency — a deficiency, or shortage, of immunity. The virus does not kill you directly. Instead, it systematically destroys the very cells that coordinate your body’s defence, leaving you defenceless against even mild infections.

The precise mechanism

The immune system has many types of soldiers. The most important commander cell is the helper T-cell (also called CD4+ T-cell). This cell does not kill germs itself; it sends signals that activate other cells — the killer T-cells and antibody-producing B-cells — to attack.

HIV has a special protein on its surface that fits perfectly into a receptor on the helper T-cell, like a key into a lock. Once inside, the virus hijacks the cell’s machinery. It forces the cell to produce thousands of copies of the virus. Eventually, the cell bursts open and dies, releasing new viruses that go on to infect more helper T-cells.

Over months or years, the number of helper T-cells in the blood drops steadily. When the count falls below a critical level (around 200 cells per microlitre of blood), the immune system can no longer mount a proper defence. At this stage, the person is said to have AIDS — Acquired Immunodeficiency Syndrome.

Why it matters

A person with HIV can look and feel healthy for many years. During this asymptomatic phase, the virus is still active, but the body is producing new T-cells to replace the ones being destroyed. This is a losing battle — eventually, production cannot keep up.

The virus is transmitted only through specific routes:

• Unprotected sexual contact
• Sharing of infected needles (common among drug users)
• From an infected mother to her child during pregnancy, childbirth, or breastfeeding
• Transfusion of infected blood (rare now due to screening)

It is not transmitted by casual contact — shaking hands, sharing food, mosquito bites, or living in the same room. …