A2/A-level Biology - HIV

When it comes to A2/A-level Biology, do you know how does HIV cause AIDS?

• HIV can be transmitted via sexual contact.
• Through infected blood.
• Through intravenous drug use.
• From a mother to a foetus, during birth or through breastfeeding.

Stage 1: Acute HIV Syndrome

• Experience symptoms in the first few weeks.
• HIV antibodies appear in the blood 3-12 weeks after infection.

Stage 2: Asymptomatic Stage

• All symptoms disappear.
• The virus replicates, infecting CD4 T helper cells.
• Secondary infections develop.

Stage 3: Symptomatic Disease

• Immune system starts to fail.
• T helper cell count falls rapidly.
• Patients suffer HIV-related symptoms.

Stage 4: Advanced AIDS

• Severe symptoms appear (weight loss, dementia, cancers, TB).

Final Stage: Death

• HIV binds to CD4 receptors on the T helper cells and infects them.
• HIV takes over the host DNA and replicates.
• When the new virus leaves the host cell, it is destroyed.
• T killer cells destroy some of the heavily infected T helper cells.
• The number of T helper cells decreases so macrophages and T killer cells are not activated.
• The T helper cells cannot function properly.
• Increased vulnerability to secondary infections.

• Education programmes
• Less promiscuous sex
• Use of condoms
• Use of clean needles

That's the end of the topic!

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