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What Are Infectious Diseases and How Do They Spread?

What Are Infectious Diseases and How Do They Spread?

Last Updated: April 01, 2021

This is part 3 of the COVID-19 Misinformation Toolkit for Parents and Kids.

Infectious diseases are caused by pathogens (disease-causing microorganisms, such as viruses, bacteria, parasites, and fungi). Some infectious diseases can be so mild that you might not even notice symptoms; however, others can be life-threatening. 

With the wonders of modern medicines, such as vaccines and antibiotics, you might think there’s no need to worry about infectious diseases anymore. Unfortunately, that’s not true - and the current coronavirus (COVID-19) pandemic is an example of this. The good news is that COVID-19 vaccines have been developed all over the world and the approved vaccines are helping us to fight this pandemic!

There are many different ways that infectious diseases spread. By knowing more about this, you can lower your chance of getting an infectious disease or spreading one to others. 

Here are some of the most common ways that infectious diseases spread: 

Through droplet contact

 Some infectious diseases can spread through large respiratory droplets when an infected person coughs or sneezes without covering their nose or mouth. This is why it’s important to always cover your mouth and nose when you cough or sneeze. These droplets typically spread only one to two meters and are too large to float in the air (i.e. airborne) and quickly fall to the ground.


Through direct contact

Many infectious diseases are easily spread through direct physical contact, like touching (when an infected person touches another person after using their hands to cover their mouth or nose when they cough) or kissing. That’s why we recommend you cough or sneeze into your arm and wash your hands regularly. Some diseases can also spread when blood or body fluids enter the bloodstream or mucus membranes of another person (for example, through sexual contact).

(germs aren't this big, but germs are everywhere!)


Through indirect contact

Infectious diseases can also spread through indirect contact, such as touching something that an infected person has touched. Some pathogens can survive on objects such as doorknobs, faucets, desks, phones, and money for hours or even days. If you touch an object an infected person has touched, you can pick up the pathogens they have left behind. If you then touch your mouth or eyes before washing your hands, you could get infected. Also, sharing things like water bottles, cups, and eating utensils with an infected person can cause you to get infected. It takes a real change in thinking to become aware that what you are touching could carry pathogens. 

Many vaccine-preventable diseases spread through these ways. Here are two examples: 

  1. Pertussis (whooping cough) spreads easily when an infected person coughs or sneezes (droplet contact), shares food, drinks or cigarettes, (indirect contact) or kisses someone who has pertussis bacteria (direct contact).

  2. The mumps virus spreads easily when an infected person coughs or sneezes (droplet contact). Mumps also spreads through contact with saliva or mucus from the mouth, nose, or throat of an infected person (direct or indirect contact). It can also be spread by sharing food, drinks, or cigarettes (indirect contact), or kissing someone with the mumps virus (direct contact).

Many other infectious diseases that are not vaccine-preventable - like coronavirus - are also spread in these ways. Knowing how coronavirus spreads, it makes sense that the best way to protect yourself against it is to wash your hands regularly and avoid touching your face, eyes, nose or mouth. It’s also important to cover your mouth and nose with a disposable tissue or the crease of your elbow when you sneeze or cough.

Here are some other ways infectious diseases can spread. 

Through airborne transmission

This occurs when much smaller evaporated droplets or dust particles containing the pathogen float in the air for long periods of time. Transmission occurs when others breathe the pathogen into their throat or lungs. Measles is an example of a virus that is spread this way. The measles virus spreads through the air when an infected person breathes, coughs, or sneezes. It can survive in small droplets in the air for several hours. You can become infected when you breathe in these droplets or touch objects contaminated with the virus. The airborne spread of the measles virus makes the disease very contagious. Currently, health experts believe that coronavirus cannot be spread through airborne transmission.

Through contaminated food or water

Another way infectious diseases spread is through food and water contaminated with pathogens. Hepatitis A is an example of a vaccine-preventable disease that spreads this way. The hepatitis A virus is found in the stool (poop) of an infected person. It often spreads when someone with the virus doesn’t wash their hands after using the toilet and then prepares food. It also spreads when someone drinks contaminated water or eats raw or under-cooked shellfish that have been polluted with sewage. This is why it’s important always to wash your hands, follow food safety guidelines, and not drink untreated water.

Through insect or animal bites

Some insects and animals can carry pathogens and pass them on to people when they bite them. An example of a disease spread this way is rabies. Rabies is a very serious and almost always fatal disease. It spreads through close contact with the saliva or nervous system tissue of an animal infected with the rabies virus - for example, a scratch or bite from a bat. Avoid touching or feeding unknown, stray, or wild animals as they could be infected with the rabies virus.