Infectious diseases are caused by infectious organisms. Typically, these are bacteria, viruses, fungi, or worms/ helminths. Under normal circumstances, when the immune system of the host is fully functional, disease symptoms may not develop. If the host immune system is compromised, or the infectious agent overwhelms the immune system, an infectious disease ensues. Most infections are caused by bacteria, viruses, protozoa, helminthes, rickettsia, and fungi.
What are infectious diseases?
Infectious diseases can be caused by many pathogens, including bacteria, viruses, fungi, and parasites that may cause illness and disease. For humans, transmission of pathogens may occur in a variety of ways: spread from person-to-person by direct contact, water or foodborne illness or aerosolization of infected particles in the environment and through insects mosquitos and ticks.
Signs and symptoms and treatment of infectious diseases depend on the host and the pathogen.
What causes infectious diseases?
Infectious diseases in humans are caused by microorganisms including:
- Viruses that invade and multiply inside healthy cells
- Bacteria, or small, single-celled organisms capable of causing disease
- Fungi, which include many different kinds of fungus
- Parasites, which are organisms that live inside host bodies causing sickness
Infectious diseases spread in multiple ways. In many cases, direct contact with a sick individual, either by skin-to-skin contact (including sexual contact) or by touching something another person touches, transmits the disease into a new host. Contact with body fluids, such as blood and saliva, also spreads infectious diseases.
Some diseases spread through droplets discharged from a sick person’s body when they cough or sneeze. These droplets linger in the air for a short period of time, landing on a healthy person’s skin or inhaled into their lungs.
In some cases, infectious diseases travel through the air for long periods of time in small particles. Healthy people inhale these particles and later become sick. Only certain diseases spread with airborne transmission, including tuberculosis and the rubella virus.
What are the symptoms of infectious diseases?
Symptoms of infectious disease are particular to the type of disease. For example, symptoms of influenza include:
- Fever
- Chills
- Congestion
- Fatigue
- Muscle aches and headache
Other infectious diseases, such as Shigella, cause more serious symptoms, including:
- Bloody diarrhea
- Vomiting
- Fever
- Dehydration (lack of fluid)
- Shock
You may experience one or several symptoms of an infectious disease. It’s important to see a doctor if you have any chronic (ongoing) symptoms or symptoms that get worse over time.
How are infectious diseases diagnosed?
Doctors diagnose infectious diseases using a variety of laboratory tests. Samples of blood, urine, stool, mucus or other body fluids are examined and provide information used in the diagnostic process.
In some cases, doctors identify infectious organisms by examining them under a microscope. Occasionally, laboratories must grow, or culture, the infectious organism from a sample to confirm its presence.
How are infectious diseases treated?
Treatment depends on which microorganism causes the infection.
- If bacteria cause a disease, treatment with antibiotics usually kills the bacteria and ends the infection.
- Viral infections are usually treated with supportive therapies, like rest and increased fluid intake. Sometimes people benefit from antiviral medications like oseltamivir phosphate (Tamiflu®).
- Doctors treat fungal and parasitic infections with antifungal medications, like fluconazole (Diflucan®), and antiparasitic drugs, such as mebendazole (Emverm®).
In all cases, doctors treat specific symptoms of infectious diseases according to the latest medical guidelines. Talk with your doctor about your symptoms to explore possible treatment options.
Can infectious diseases be prevented?
You can also reduce your risk of contracting an infectious disease by:
- Washing your hands with soap and water, thoroughly and frequently.
- Covering your nose and mouth when you sneeze or cough.
- Disinfecting frequently touched surfaces in your home and workplace.
- Avoiding contact with sick people or sharing personal items with them.
- Not drinking or swimming in contaminated water supplies.
- Not eating or drinking food and beverages prepared by people who are sick.