The document discusses immunity and infection, including:
1) The chain of infection involves a pathogen, reservoir, transmission, entry and establishment in a new host. Breaking the chain prevents spread of disease.
2) The immune system defends against pathogens through physical and chemical barriers, and cells and antibodies that fight infection.
3) Pathogens like bacteria, viruses, fungi and parasites can cause infectious diseases. Emerging diseases are on the rise due to factors like drug resistance, travel and human behavior.
4) Maintaining a healthy immune system involves good nutrition, exercise, rest and controlling stress. Sexually transmitted diseases pose major health risks and can be prevented through education and safe practices.
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