Viruses (LC 2026) (Leaving Cert Biology): Revision Notes

Control and Immunity

Viruses are controlled by two main defence systems in the body:

1. The General Defence System

• This is the body's first line of defence and is not specific to any one virus.
• It includes physical barriers such as the skin, which prevents viruses from entering, and tiny hairs and mucus in the nose, which trap pathogens before they can reach the lungs.
• Stomach acid destroys many viruses that are swallowed with food or mucus.
• Together, these barriers act quickly to stop most viruses before they can cause infection.

2. The Specific Defence System

• This system targets particular viruses and provides a stronger, tailored response.
• Specialised white blood cells recognise virus particles as foreign.
• These cells produce antibodies, which are proteins that attach to the virus and either neutralise it directly or mark it for destruction by other immune cells.
• This system also creates memory cells, so if the same virus infects the body again, the immune response is much faster and often prevents illness altogether.

Vaccination

• Vaccines provide protection against certain viral diseases by stimulating the immune system to produce antibodies without causing illness.
• This means the body develops memory cells that recognise the virus quickly if exposed in the future.
• For example, the MMR vaccine protects against measles, mumps, and rubella, three serious viral infections that can lead to severe complications if left untreated.