An emerging infectious disease is a disease caused by a pathogen that is newly recognized, is increasing in incidence or geographic range, or is changing in ways that create a new threat to human or animal health. 

Emerging infectious diseases can include newly identified viruses and bacteria, diseases that spread into new geographic regions, and familiar diseases that develop new characteristics such as drug resistance. 

Scientists study emerging infectious diseases to understand where they come from, how they spread and how they can be detected, prevented and treated. At the Texas Biomedical Research Institute (Texas Biomed) in San Antonio, researchers study some of the world’s most challenging infectious diseases and work to develop vaccines, therapeutics and other tools to help protect against emerging threats. 

What makes a disease “emerging”? 

An infectious disease does not have to be completely new to be considered emerging. 

A disease may be considered emerging when: 

• A pathogen is newly identified or has only recently begun causing human disease. 

• An existing disease begins appearing in a new geographic region. 

• The number of cases increases significantly. 

• A pathogen changes in a way that affects how easily it spreads or causes disease. 

• A pathogen develops resistance to available treatments. 

• An infection that primarily affects animals begins infecting people. 

Emergence can therefore happen gradually or suddenly. Scientists monitor pathogens and disease patterns to identify changes that could signal a growing public-health threat. 

What are some examples of emerging infectious diseases? 

Examples of emerging infectious diseases include Ebola virus disease, Marburg virus disease, Zika virus disease and COVID-19. 

Influenza viruses also demonstrate how infectious diseases can continue to evolve. New influenza strains can emerge through genetic changes and reassortment, creating viruses that may behave differently from previously circulating strains. 

Some diseases that are now well recognized were once emerging threats. Understanding how diseases emerge can help scientists prepare for the next one. 

Why do infectious diseases emerge? 

There is no single reason why an infectious disease emerges. Disease emergence is usually the result of multiple biological, environmental and social factors. 

Pathogens evolve 

Viruses, bacteria, parasites and fungi can change over time. Genetic mutations or other changes can alter a pathogen’s ability to infect hosts, spread or evade immune defenses. 

Pathogens can move between species 

Some infectious diseases originate in animals and can occasionally infect humans. These are called zoonotic diseases. 

A pathogen may acquire characteristics that allow it to cross a species barrier. Most pathogens that circulate in animals do not successfully establish themselves in humans, but when a pathogen does make that jump, it can create a new infectious-disease threat. 

People and animals are increasingly interconnected 

Human activity can increase opportunities for pathogens to move between animals and people. 

Changes in land use, agriculture, wildlife interactions, urbanization and travel can alter how humans encounter animals and their pathogens. 

This is one reason scientists increasingly use a One Health approach, recognizing that human health, animal health and environmental health are interconnected. 

Global travel can accelerate spread 

A pathogen that once would have remained geographically limited can potentially travel rapidly when infected people move between regions and countries. 

Modern transportation means an outbreak that begins in one location can become an international concern much more quickly than in the past. 

Environmental changes can affect disease patterns 

Changes in temperature, rainfall, ecosystems and animal populations can alter where certain pathogens and disease-carrying organisms can survive. 

These changes can potentially affect the geographic distribution of infectious diseases. 

Can scientists predict emerging infectious diseases? 

Scientists cannot predict every outbreak, but they can identify risk factors and monitor pathogens that could pose a threat. 

Researchers use tools such as genomic sequencing, disease surveillance, epidemiology, ecological studies and laboratory research to identify changes in pathogens and disease patterns. 

Scientists can also study how pathogens interact with their hosts and immune systems to better understand what makes an infection more or less likely to cause severe disease. 

This information can help researchers identify potential interventions before or during an outbreak. 

Why is early detection important? 

The earlier scientists recognize a new infectious-disease threat, the more opportunities there may be to contain it. 

Early detection can allow public-health officials and researchers to: 

• Identify infected individuals. 

• Track how a pathogen is spreading. 

• Determine how severe the disease may be. 

• Develop diagnostic tests. 

• Evaluate potential treatments. 

• Begin developing or testing vaccine candidates. 

• Implement appropriate public-health measures. 

The goal is not simply to respond after an outbreak becomes widespread. Scientists also work to understand pathogens before they become major threats. 

How do scientists study emerging infectious diseases? 

Researchers use multiple approaches because no single laboratory technique can answer every question about an emerging pathogen. 

Scientists may study: 

The pathogen: Researchers examine its genetics, structure, replication and ability to cause disease. 

The host: Scientists study how humans or animals respond to infection, including the immune response. 

Host-pathogen interactions: Researchers examine how the pathogen interacts with cells, tissues and the immune system. 

Transmission: Scientists investigate how pathogens move between hosts and what factors influence their spread. 

Potential countermeasures: Researchers test vaccines, antiviral drugs, antibodies and other approaches that could prevent or treat disease. 

Together, these approaches can provide a more complete understanding of an emerging infectious disease. 

What role does Texas Biomed play in emerging infectious disease research? 

Texas Biomed has conducted infectious-disease research for decades, including research on some of the world’s most dangerous and difficult-to-study pathogens. 

The Institute’s scientists study viruses, bacteria and other pathogens, including Ebola, Marburg virus, influenza, tuberculosis and hantaviruses. 

Texas Biomed is also home to one of the few privately operated Biosafety Level 4 laboratories in the United States. BSL-4 laboratories are designed for research involving pathogens that pose a high risk of severe or potentially fatal disease and for which limited or no widely available countermeasures may exist. 

The Institute’s high-containment capabilities allow scientists to study certain pathogens under carefully controlled conditions. 

How does Texas Biomed help prepare for emerging diseases? 

Research conducted before an outbreak can be particularly valuable. 

Scientists can study pathogens, identify potential drug or vaccine targets and evaluate candidate countermeasures before those tools are urgently needed. 

Texas Biomed conducts preclinical research, which can help determine whether potential vaccines, therapeutics or other medical countermeasures show promise before they advance to human clinical testing. 

For example, Texas Biomed researchers have contributed to preclinical research involving Ebola vaccines and antibody-based treatments. 

This type of research is part of a larger process of pandemic preparedness: understanding pathogens, developing potential countermeasures and building the scientific infrastructure needed to respond when new threats emerge. 

Why are BSL-4 laboratories important? 

Some pathogens require the highest levels of laboratory containment because of the potential risks associated with working with them. 

BSL-4 laboratories use specialized engineering controls, equipment, procedures and training to help protect researchers and the surrounding community. 

These facilities allow scientists to conduct research that may not be possible in lower-containment environments. 

For emerging infectious diseases, this capability can be particularly important because scientists may need to study a newly identified or highly dangerous pathogen directly to understand how it causes disease and to evaluate potential countermeasures. 

What is pandemic preparedness? 

Pandemic preparedness is the ongoing work of preparing for infectious diseases that could spread widely across populations or geographic regions. 

It includes much more than developing vaccines. 

Preparedness can involve: 

• Monitoring pathogens. 

• Improving diagnostic testing. 

• Studying how diseases spread. 

• Developing vaccines and therapeutics. 

• Maintaining high-containment research capabilities. 

• Training scientists and healthcare professionals. 

• Strengthening public-health systems. 

• Establishing partnerships among government, academia, industry and research organizations. 

Biomedical research is an important part of this preparedness because scientific knowledge can help shorten the time between identifying a new pathogen and developing tools to respond to it. 

Why is research on emerging infectious diseases important? 

Emerging infectious diseases are a reminder that the relationship between humans, animals and microbes is constantly changing. 

New pathogens can appear. Existing pathogens can evolve. Diseases can move into new regions. And pathogens that normally infect animals can sometimes cross into humans. 

Researchers therefore need to study infectious diseases before they become crises as well as during outbreaks. 

At Texas Biomed, scientists work to understand pathogens and the biological processes that allow them to cause disease. By studying these threats and developing potential vaccines, therapeutics and other countermeasures, researchers aim to help society prepare for infectious diseases that may emerge in the future. 

Frequently Asked Questions About Emerging Infectious Diseases 

What is an emerging infectious disease? 

An emerging infectious disease is a disease caused by a pathogen that is newly recognized, increasing in incidence or geographic range, or changing in a way that creates a new health threat. 

What causes infectious diseases to emerge? 

Disease emergence can result from pathogen evolution, animal-to-human transmission, environmental changes, human activity, increased travel, changes in animal populations and other biological and social factors. 

What is a zoonotic disease? 

A zoonotic disease is an infectious disease that can be transmitted between animals and people. Many emerging infectious diseases have zoonotic origins. 

Is COVID-19 an emerging infectious disease? 

COVID-19 was considered an emerging infectious disease when the disease caused by the newly identified SARS-CoV-2 virus first appeared in humans and began spreading internationally. The emergence of SARS-CoV-2 demonstrated how quickly a new infectious disease can become a global public-health challenge. 

Are Ebola and Marburg emerging infectious diseases? 

Ebola and Marburg are viral diseases that can cause severe illness in humans. While the viruses themselves have been known for decades, new outbreaks and changes in geographic distribution or transmission patterns can continue to make them important infectious-disease threats. 

Can scientists prevent emerging infectious diseases? 

Scientists cannot prevent every emerging infectious disease, but research and surveillance can reduce risks and improve preparedness. Studying pathogens, developing vaccines and therapeutics, monitoring disease patterns and improving diagnostic tools can all help communities respond more effectively. 

Why does Texas Biomed study emerging infectious diseases? 

Texas Biomed studies emerging infectious diseases to better understand how pathogens cause disease and to help develop tools to prevent and treat infections. Its research capabilities include infectious-disease expertise, high-containment laboratories and specialized preclinical research resources. 

What is a BSL-4 laboratory? 

A Biosafety Level 4 laboratory is a highly specialized research facility designed for work with certain dangerous pathogens that pose a high risk of severe disease. BSL-4 laboratories use multiple layers of containment and specialized safety procedures to protect researchers and the community. 

What is One Health? 

One Health is an approach that recognizes the interconnected health of people, animals and the environment. Because many emerging infectious diseases involve interactions among these three areas, One Health is an important framework for understanding and preventing disease emergence. 

How can I learn more about emerging infectious diseases? 

Organizations such as Texas Biomed conduct research to better understand infectious-disease threats, while public-health agencies monitor disease activity and provide information about emerging outbreaks. Learning how diseases emerge and spread is an important part of public-health preparedness.