Education, Epidemiology, Infectious Diseases, Wellness

How Do Infectious Diseases Spread?

Author Chandana Balasubramanian , 05-Sep-2023

Over half the world’s population is at risk of getting sick from infectious diseases. Infectious diseases significantly challenge global healthcare, leading to devastating outbreaks and pandemics. With globalization, a cough or sneeze could trigger widespread infection across the world. 


This article delves into the types of infectious diseases, how they spread, and how prevention strategies can help curb transmission. Additionally, it highlights the remarkable impact of vaccines and immunization that played pivotal roles in controlling formidable diseases in history.


Types of infectious diseases

There are many types of infectious diseases; they can be bacterial, viral, fungal, or parasitic.

Bacterial infections

Bacterial infections are infectious diseases caused by bacteria. Examples include Lyme disease, syphilis, and meningococcal meningitis, to name a few.

Viral infections

Viruses are responsible for these infectious diseases. The common cold, HIV, and hepatitis are a few examples.

Fungal infections

Fungi can lead to illnesses like ringworm or yeast infections. Examples include mycosis, cryptococcal meningitis, and candida auris infections.

Parasitic infections

Parasitic infections are caused by parasites such as protozoans or worms. Malaria is a well-known example. Treatment for each type of disease varies based on the individual pathogen and the severity of the infection. 


How infectious diseases spread

Infectious diseases can be transmitted through close contact with infected individuals or surfaces contaminated by them. Additionally, respiratory droplets released through coughs and sneezes can carry disease-causing germs. 

Bloodborne pathogens can be transmitted through sharps injuries, such as needle pricks. Moreover, certain infections can spread through sexual activity and direct bodily contact. 

Here’s a closer look.

Direct contact

The most common way infectious diseases spread is through direct contact. Person-to-person, sexual, and mother-to-child transmission are all ways diseases can spread through direct contact. Examples include STIs like HIV, syphilis, and gonorrhea.  

Indirect contact

Diseases can also spread indirectly through contaminated objects or surfaces, like doorknobs and utensils. Even air particles can be contaminated. For instance, gastrointestinal infections like rotavirus and norovirus can spread through contaminated surfaces. 

Airborne transmission

Some diseases can survive in tiny droplets expelled during coughing or sneezing and infect others who breathe them in. For example, Tuberculosis (TB) and measles can endure in air currents for considerable distances, resulting in infections upon inhalation of the contaminated air by individuals.

Zoonotic transmission: From animals to humans

Some diseases can be passed from animals to humans through bites, scratches, or handling of animal products unsafely. Tick-borne diseases including babesiosis, Lyme disease, and Rocky Mountain spotted fever (RMSF) to name a few, are a few examples of zoonotic transmission. 


How to prevent the spread of infectious diseases

Effective prevention is crucial in combating infectious diseases. 

By understanding how diseases spread and implementing strategic preventive measures, we can significantly mitigate their impact. 

Here are some common prevention methods: 

Hand hygiene

The easiest and most effective way to prevent many infections is by practicing good hand hygiene. Regularly washing hands with soap and water or using a hand sanitizer when soap is not available can significantly reduce transmission rates.


Vaccines provide immunity against specific pathogens, reducing the risk of infection and preventing disease spread. Encouraging communities to stay up to date with their recommended vaccines and boosters can go a long way in preventing disease transmission.

Creating awareness

Educating people about how infectious diseases spread, and ways they can protect themselves is crucial in disease prevention. 

This includes teaching them about safe food handling practices, sexual health safety measures, and tick bite prevention methods for Lyme disease, among others.

Infection control in healthcare settings

In healthcare facilities, there is a high risk of pathogen transmission due to close contact between sick individuals. As a result, there are stringent infection control measures that need to be implemented. 

These include isolation procedures for infected people, the use of personal protective equipment (PPE), proper waste disposal systems, and more. The US CDC (Centers for Disease Control and Prevention) offers more details


Vaccines and immunization

In the battle against infectious diseases, vaccines, and immunization are the ultimate weapons. Vaccination trains the body’s defense system and empowers it to combat illnesses like measles, polio, and hepatitis B.

Vaccines are made from small amounts of weakened or dead germs that can cause diseases. When a person gets vaccinated, their immune system learns to recognize and defend against disease-causing organisms if encountered in the future.

Thanks to immunizations, many deadly infectious diseases like smallpox have been eradicated worldwide. The WHO (World Health Organization) estimates that immunizations save millions of lives annually.

Some examples of notable diseases that were controlled as a result of mass-vaccination efforts:


Vaccination played an important role in eradicating smallpox. WHO’s global campaign, the Intensified Eradication Program, and improved vaccine production and mass vaccination efforts led to the disease’s elimination from South America in 1971, Asia in 1975, and Africa in 1977. On May 8, 1980, the World Health Assembly declared the world free of smallpox, marking a historic achievement in global health.


During the pre-vaccination era, nearly all children in the US contracted measles before reaching the age of 15, with around 3-4 million each being reported across the country each year. Once the vaccines were introduced, the numbers dropped drastically. 


In 1988, a resolution was adopted by the World Health Assembly, initiating the Global Polio Eradication Initiative. Since then, wild poliovirus cases have decreased by over 99%, from approximately 350,000 cases in 125 endemic countries in 1988 to just six reported cases in 2021.


WHO is dedicated to enhancing COVID-19 vaccine accessibility and aiding countries in accelerating vaccine distribution to protect lives and minimize severe illness. 

Governments are urged to target vaccinating at least 70% of their populations, focusing on immunizing 100% of healthcare workers and the most vulnerable individuals, including those over 60 and those with underlying health conditions or weakened immune systems.



What are the different ways through which infectious diseases spread?

Infectious diseases can spread through:

Direct contact:

  • Person to person 
  • Animal to person (zoonotic disease)
  • Mother to unborn child


Indirect contact:

  • Contaminated objects
  • Airborne transmission
  • Vector-borne transmission by insects.


Why is there a greater risk of pandemics in today’s world?

In current times, the risk of a global pandemic is greater than before. This is because of:

  • Climate change: According to an article in Nature, over half of human infectious diseases can be aggravated by climate change. Warmer temperatures make it more favorable for mosquitoes to breed and survive. They also spread faster and increase the transmission efficiency of the West Nile Virus. Dengue and CCHF (Crimean Congo hemorrhagic fever) are two other diseases that are expanding in previously non-endemic regions due to climate change. 
  • Travel: Due to more airports, trains, and multi-lane highways, travel within a country and between nations has increased significantly. With this comes a greater risk of a small outbreak in one corner of the world spreading all over. The latest example of this was the COVID-19 pandemic. 
  • Urbanization: According to data from the World Bank, 56% of the world lives in urban areas today. And by 2050, 7 in 10 people will live in cities. This means a larger density of people living in close quarters, increasing the risk of spreading infections.  
  • Inadequate sanitation and resources: Infectious diseases spread faster with contaminated water, soil, and food, and without proper handling of animals and meat. 
  • Insufficient healthcare infrastructure: Many nations are experiencing a shortage of healthcare workers and adequate facilities to deal with the spread of infectious diseases. 



Infectious diseases spread through various methods, and in these times, globalization, climate change, urbanization, and other factors can increase disease transmission rates. 

Healthcare professionals, public health officials, and epidemiologists must understand the spread of infectious diseases to prevent and control outbreaks. Additionally, they must advocate the use of preventive strategies like hand hygiene, isolation precautions, use of personal protective equipment, and vaccines.

By taking these steps, healthcare professionals can help stop the spread of infectious diseases and protect public health.


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Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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