Infectious Diseases: Defined


Infectious diseases are caused by bacteria, fungi, parasites and viruses.

hiv virus cellThese diseases can be passed directly from one person to another, through animal bites, and through contaminated water, food or other substances. When the body’s immune system weakens (due to illnesses or medications), it is less able to fight these foreign invaders, allowing infectious diseases to take over the body’s defenses.

Common symptoms of infectious diseases may include fever and chills, among many others. While some infectious diseases can be treated with simple home remedies, others may require hospitalization.

Vaccines can prevent a number of infectious diseases. Routine hand-washing also helps to prevent the spread of diseases.


The symptoms of infectious diseases vary depending on the specific infection. However, symptoms often include fatigue, fever, muscle pain and appetite loss.

You should see your doctor if you have difficulty breathing, swelling or sudden fever. Also see your doctor if you’ve been bitten by an animal.

Other signs of infectious disease may include bad headache or seizures with fever and a cough that lasts longer than a week.


There are many types of infectious diseases, all of which have different combinations of symptoms. To make a proper diagnosis, your doctor may suggest certain tests depending on the symptoms you are showing. Such tests may include lab tests, imaging scans or biopsies (surgical removal of tissue).

Lab work may include:

  • Blood tests, in which a blood sample is taken through inserting a needle into a vein or through a finger prick.
  • Urine tests, in which you urinate into a container so that the urine sample can be examined for signs of disease.
  • Lumbar puncture, also known as a spinal tap, in which cerebrospinal fluid (the fluid surrounding the brain and spinal chord) is drawn from the lower spine.
  • Throat culture, in which the back of your throat is scraped with a cotton swab to locate any germs.

Imaging scans that may be used to help diagnose infectious diseases include:

  • X-rays, which use electromagnetic waves of radiation to show general internal structures of the body.
  • Computed tomography (CT) scans, which use x-ray methods to show a more detailed cross section of the bones, organs and other tissues within the body.
  • Magnetic resonance imaging (MRI), which produces high-resolution pictures of your bones and soft tissues are shown through magnetic scanning. Unlike x-rays and CT scans, MRI doesn’t use radiation.

A biopsy is done by sampling a small piece of a living tissue from an internal organ to locate any damage or diseases.


Common infectious diseases, such as cold, can be treated with simple home remedies and over-the-counter medications. For these types of infections, getting enough rest and drinking ample fluids may help speed up recovery.

More complex diseases may require medications.

Bacterial infections: Bacteria are organized into groups of similar kinds. The antibiotics to treat these infections are also grouped by similar types. Your doctor will decide which antibiotic is best suited to treat your bacterial infection. For example, penicillin is often used to treat urinary tract infections.

influenza-virus-fulltextViral infections: Antibiotics are not effective in treating viral infections. However, medications called antivirals have been designed to treat some viral infections. Certain antivirals are used to treat HIV and the flu.


meningitis-aspergillus-fumigatus_fungal infectionFungal infections: Some fungi can reproduce by spreading small spores through the air. These spores can be inhaled or land on the skin, which is why fungal infections are often found in the lungs or on the skin. Antifungals are used to treat fungal infections. Tolnaftate is an antifungal usually used to treat skin infections like athlete’s foot.

parasitic infection in jarParasitic infections: Infections caused by parasites need condition-specific treatments. Chloroquine, for example, is used both to prevent and treat malaria.


The causes of infectious diseases are grouped into four main categories:

  • Bacteria: Bacteria are organisms with just one cell that can quickly multiply in the body. They often release chemicals that make people ill. An example of bacterial infection is tuberculosis.
  • Viruses: These foreign invaders spread by using people’s own cells. Both the common cold and AIDS are viral infections.
  • Fungi: Fungi are spread mostly through the air. They get into the body through the lungs or the skin. Athlete’s foot is just one example of infection caused by fungi.
  • Parasites: These invaders use the human body both for food and as a place to live. An example of parasitic infection is malaria.

Infectious diseases can be spread in a number of ways. One infected person can pass an infection on to another. Infected animals also may spread infectious diseases to humans. People may even catch an infectious disease through the food they eat.

Here are the primary ways that infectious diseases are spread:

  • Direct contact: The quickest way is through a direct contact with another person or animal with the infection. It can be from one person to another (touch, cough, kisses, sexual contact, or blood transfusion), animal to person, or mother to unborn baby. A common example is influenza.
  • Indirect contact: Infection can also be spread through an indirect contact with items that have germs. Some examples are doorknob and faucet handle.
  • Animal and insect bites: Some germs can be passed on through animal or insect hosts. For example, mosquitoes may carry Malaria parasite or West Nile virus.
  • Food contamination: Germs can also infect you through contaminated food and water, which results in food poisoning. For example, Salmonella is often found in uncooked meat or unpasteurized milk.


If you think you have an infection, you may call your family doctor for treatment. Depending on your infection, your doctor may refer you to a specialist.

In order to get a proper diagnosis and treatment, you may want to prepare some information for your doctor. Make a detailed list of your symptoms, your medical history, your family’s medical history, any medications and supplements that you take and questions you may have for your doctor.


Infectious diseases are the main cause of death of children and teens and one of the leading causes of death among adults around the world.

Most deaths from infectious diseases happen in low- and middle-income countries. Many of these deaths are caused by preventable or treatable diseases like diarrhea, lower respiratory infections, HIV/AIDS, tuberculosis and malaria.

Even with major improvements in medicine, infectious diseases continue to spread. Many of the interventions to prevent and treat infectious diseases are not available to the populations that need them the most. However, through collective efforts, the public health community has had some successes in reducing or eliminating some infectious diseases.


Many of the most common infectious diseases, such as the cold, will go away on their own. Remember to drink lots of water and other fluids and to get plenty of rest.

If you develop an infection, here are some tips to prevent further spread of the disease:

  • Wash your hands regularly, especially before eating and after using the restroom.
  • Stay home when having diarrhea, vomiting or running a fever.
  • Do not share personal items.
  • Practice safe sex.
  • Avoid flight travel when you’re sick.
  • Discuss vaccinations with your doctor.