What are Emerging and Re-Emerging Diseases?

Fifty years ago people believed that the war of humankind against infectious diseases was virtually over. They thought that science had won over diseases such as pneumonia, whooping cough, polio, and smallpox with the help of antibiotics, vaccines, and some aggressive public health campaigns. But, after the 1980s, emerging and re-emerging diseases have caused havoc.

In the last 30 years, at least, a dozen new diseases have emerged and traditional diseases that were gone are re-emerging. In these years, the world has seen the global spread of AIDS, the resurgence of Tuberculosis, and the appearance of new enemies like hantavirus pulmonary syndrome, hepatitis C and E, Ebola virus, Lyme disease, etc.

What are Emerging Diseases?

Emerging diseases are the diseases that

  • Have not occurred in humans before. This type of emergence is very rare.
  • Have occurred previously but affected only small numbers of people in isolated places. For example, AIDS and Ebola Hemorrhagic Fever.
  • Have occurred throughout human history but has only recently been recognized as a distinct disease due to a causative agent. For example, Lyme disease and Gastric Ulcers.

So, we can conclude that the emerging diseases are the diseases caused by some newly identified and previously unknown causative agents. 

What are Re-emerging Diseases?

Re-emerging diseases are the diseases that once were major health problems globally or in a particular country and then declined dramatically, but are again becoming a health problem for a significant proportion of the population. Malaria, tuberculosis, cholera, pertussis, influenza, and gonorrhea are some examples of re-emerging diseases.

What are factors contributing to the emergence of diseases?

Several factors are contributing to the emergence and re-emergence of diseases. Some of them are listed below.

1. Climate and Environmental Changes:

Humans are cutting trees and clearing natural habitats on a very large scale. This has forced wild animals to come closer to human habitats. This displacement has increased the possibility for causative agents to breach the species barrier between animals and humans.

For example, Lyme disease, Hantavirus Pulmonary Syndrome (HPS), Lassa fever all emerged when humans began encountering the arachnid vector (For Lyme disease) or rodent host (for HPS and Lassa fever) of the causative agents in greater number than ever before.


Global Warming is also indirectly responsible for the outbreak of diseases. This is because global warming leads to unpredictable and extreme climatic changes such as floods, tsunami, cyclones, etc. These changes then help in the rapid transmission of diseases such as malaria, dengue, cholera, etc.

2. Uncontrolled Urbanization and Population Displacements:

Urbanization often crowds humans and increases exposure to microbes. Crowding of the population leads to unsanitary conditions and also hinders the effective implementation of adequate medical care. Thus, enabling more widespread transmission and propagation of pathogens.

For example, the re-emergence of diseases such as diphtheria and whooping cough (Pertussis) is related to inadequate vaccination of the population.

Land Development and the exploration or destruction of natural habitats have increased the likelihood of human exposure to new pathogens and may put selective pressure on pathogens to adapt to new hosts and changing environments.

For example, the spread of Lyme diseases in New England probably was due to the ecological distribution that eliminated predators of deer. An increase in the deer population and deer tick populations provided a favorable situation for pathogens to spread among humans.

3. Human Behavior and Activities:

The food processing and supply centers, which carry out processes such as handling, cutting, refrigeration of food, and other treatments have the potential of becoming breeding grounds for foodborne microbial diseases.

For example, the emergence of diseases such as hemolytic uremic syndrome was related to the consumption of raw or uncooked beef and unpasteurized apple juice.

The unnatural and unprotected sexual practices have also created a higher risk of getting infected with sexually transmitted diseases(STDs). Diseases like AIDS (Acquired Immune Deficiency Syndrome), Gonorrhea, and Syphilis spread through unprotected sexual practices.

4. Antimicrobial Drug Resistance:

The key factor responsible for the rise in drug-resistant pathogens has been the excessive or inappropriate use of antimicrobial drugs or therapy. Moreover, the indiscriminate use of broad-spectrum antibiotics has also led to antimicrobial drug resistance.

For example, Tuberculosis has re-emerged due to the evolution of the causative bacteria. The bacteria have acquired resistance to the antibiotics used to treat Tuberculosis (either through mutation or genetic exchange).


Immunosuppression, either by another disease agent such as the AIDS virus or by drugs taken upon organ transplantation, increases the number of individuals susceptible to new pathogens.

Also Read: How do Bacteria become Resistant to Antibiotics?

So, now you know what is emerging and re-emerging diseases? And, what are the various factors contributing to their emergence and re-emergence? So that is all for now, meet you in my next article. Keep Reading, Keep Exploring, and Keep Sharing your Knowledge, and above all BE CURIOUS. 🙂

Also Read:11 Things Parents should know about giving Antibiotics.


  • (US), National, and Biological Study. ‘Understanding Emerging And Re-Emerging Infectious Diseases. National Institutes of Health (US) (2007): n. pag. Web. 3 Oct. 2015.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s