Infectious diseases are illnesses caused by harmful agents (pathogens) that get into your body. The most common causes are viruses, bacteria, fungi and parasites. Infectious diseases usually spread from person to person, through contaminated food or water and through bug bites. Some infectious diseases are minor and some are very serious.

Symptoms 

Symptoms of infectious diseases depend on the type of illness. Fungal infections usually cause localized symptoms, like rash and itching. Viral and bacterial infections can have symptoms in many areas of your body, like:

• Fever.
• Chills.
• Congestion.
• Cough.
• Fatigue.
• Muscle aches and headache.
• Gastrointestinal symptoms (diarrhea, nausea, vomiting).

Causes infectious diseases

Infectious diseases are caused by a variety of agents that invade your body from the outside. These include:

• Viruses.
• Bacteria.
• Fungi.
• Parasites.
• Prions.

You may develop symptoms when your cells are damaged or destroyed by the invading organism and as your immune system responds to the infection.