Infectious Diseases: An Introduction

Infectious diseases are illnesses caused by pathogenic microorganisms, often referred to as pathogens. These pathogens can include bacteria, viruses, fungi, and parasites. A key characteristic of infectious diseases is their ability to be transmitted from one individual or organism to another.

What are Pathogens?

Pathogens are biological agents that can cause disease. They invade and multiply within the host organism, disrupting normal bodily functions and leading to illness.

Transmission of Infectious Diseases

Infectious diseases can be transmitted through various routes:

• Direct Contact: Transfer of pathogens through physical contact, such as shaking hands or touching.
• Indirect Contact: Transfer of pathogens through contaminated objects (e.g., doorknobs, surfaces).
• Airborne Transmission: Spread of pathogens through the air via droplets or aerosols (e.g., coughing, sneezing).
• Waterborne Transmission: Contamination of water sources with pathogens.
• Foodborne Transmission: Consumption of food contaminated with pathogens.
• Vector-borne Transmission: Transmission through the bite or other interaction with vectors like mosquitoes, ticks, or fleas.

Summary Table

Pathogen Type	Examples	Transmission Routes
Bacteria	Streptococcus, E. coli	Direct contact, Indirect contact, Airborne, Waterborne, Foodborne
Viruses	Influenza, HIV, SARS-CoV-2	Airborne, Direct contact, Indirect contact, Vector-borne
Fungi	Athlete's foot, Ringworm	Direct contact, Indirect contact, Airborne
Parasites	Malaria, Tapeworms	Direct contact, Vector-borne, Waterborne, Foodborne

Understanding how infectious diseases are caused and transmitted is fundamental to developing strategies for prevention and control.