Viruses are microscopic infectious agents that can cause diseases ranging from the common cold and influenza to Ebola, COVID-19 and other serious illnesses. Unlike bacteria, viruses cannot reproduce on their own. Instead, they enter living cells and use the cells’ machinery to make more copies of themselves. 

Understanding how viruses work is essential to developing vaccines, antiviral drugs and other tools to prevent and treat infectious diseases. 

At the Texas Biomedical Research Institute (Texas Biomed) in San Antonio, scientists study viruses and the complex interactions between viruses and their hosts. Their research spans influenza, Ebola, Marburg virus, hantaviruses and other infectious diseases, helping scientists better understand viral disease and develop potential countermeasures. 

What is a virus? 

A virus is a microscopic infectious agent made up of genetic material surrounded by a protective structure. 

A virus typically contains: 

• Genetic material: DNA or RNA that contains the instructions needed to make new viruses. 

• A protein coat: Called a capsid, this structure protects the viral genetic material. 

• An envelope: Some viruses have an additional outer membrane called an envelope. This membrane often contains viral proteins that help the virus attach to and enter host cells. 

Viruses come in many different shapes and sizes. Some are relatively simple, while others have complex structures with multiple proteins that help them infect cells. 

One of the most important characteristics of viruses is that they are dependent on host cells for reproduction. 

Are viruses alive? 

Scientists have debated how to classify viruses because they do not meet all of the traditional characteristics of living organisms. 

Viruses contain genetic information and can evolve, but they cannot reproduce independently or carry out many of the metabolic processes associated with living cells. 

Outside a host cell, a virus is essentially an infectious particle. Once it enters a susceptible cell, however, it can use the cell’s machinery to produce new viral components and assemble new virus particles. 

Whether viruses are technically “alive” is therefore less important scientifically than understanding what they do: they use host cells to reproduce and spread. 

How do viruses infect cells? 

A viral infection begins when a virus encounters a cell with the right molecular receptor. 

Think of the interaction as a biological lock and key. Viral proteins recognize specific molecules on the surface of susceptible cells. If the virus can bind to the cell, it may be able to enter. 

The general process looks like this: 

1. Attachment 

Viral proteins bind to receptors on the surface of a host cell. 

2. Entry 

The virus or its genetic material enters the cell. 

3. Uncoating 

The virus releases its genetic material so it can be used inside the cell. 

4. Replication and protein production 

The virus directs the host cell to make viral genetic material and proteins. 

5. Assembly 

New viral components come together to form new virus particles. 

6. Release 

New viruses leave the cell and can infect additional cells. 

Different viruses use different strategies, and the details of this process can vary significantly between viruses. 

Why do viruses make people sick? 

Viral disease can result from both the virus itself and the body’s response to infection. 

As viruses replicate, they can damage or kill infected cells. Some viruses target particular tissues or organs, which can determine the symptoms and severity of disease. 

The immune system also responds to infection. 

Inflammation and other immune responses help the body fight the virus, but an excessive or poorly regulated immune response can sometimes contribute to tissue damage. 

This interaction between the pathogen and the host is one of the most important areas of infectious-disease research. 

How does the immune system fight a virus? 

The immune system uses multiple layers of defense against viral infections. 

The body’s innate immune system provides an early response. Cells recognize signs of infection and produce signaling molecules that help activate antiviral defenses. 

The adaptive immune system develops a more targeted response. B cells can produce antibodies that recognize specific viral proteins, while T cells can identify and destroy infected cells or help coordinate the immune response. 

After some infections or vaccinations, the immune system can develop immune memory, allowing it to respond more quickly if it encounters the same virus again. 

This is also the basic principle behind vaccination: expose the immune system to a safe representation of a pathogen so it can prepare for a future encounter. 

How do viruses spread? 

Viruses can spread in many different ways depending on the virus. 

Transmission can occur through: 

• Respiratory droplets or aerosols 

• Direct contact 

• Contaminated surfaces or materials 

• Blood and other bodily fluids 

• Sexual contact 

• Insect or tick bites 

• Animal-to-human transmission 

• Contaminated food or water 

Understanding how a virus spreads is essential for controlling an outbreak. 

For example, researchers may investigate how efficiently a virus transmits between hosts, which tissues it infects and how long an infected individual remains capable of transmitting the virus. 

Dr. Olena Shtanko, who studies Ebola virus in her lab at Texas Biomed, said, “The general model of spread of Ebola virus infection where a viral particle infects a cell, replication begins, new virus particles are made and released into the body to infect neighboring cells is probably a bit too simplistic.”

Understanding these mechanisms matters because researchers can potentially use them to identify new ways to interrupt viral spread and develop treatments.

What is a zoonotic virus? 

A zoonotic virus is a virus that can be transmitted between animals and people. 

Many emerging infectious diseases have zoonotic origins. Viruses circulating in wildlife or other animal populations may occasionally cross a species barrier and infect humans. 

Most viruses that infect animals do not successfully establish sustained transmission in humans. But when a virus acquires the ability to infect and spread among people, it can become a significant public-health concern. 

Ebola, Marburg virus and some influenza viruses are examples of viruses that involve animal reservoirs or animal-to-human transmission. 

Studying viruses in their natural hosts can therefore help researchers understand where infectious-disease threats originate and how they might emerge. 

Why do viruses evolve? 

Viruses evolve because genetic changes occur as they replicate and because viruses are subject to natural selection. 

The rate and type of viral evolution varies considerably among viruses. 

Some viruses accumulate genetic changes relatively quickly. These changes can sometimes affect characteristics such as how efficiently a virus spreads, how it interacts with host cells or how well existing immune defenses recognize it. 

Influenza provides a particularly important example. 

Influenza viruses continually change, which is one reason seasonal influenza vaccines are reviewed and updated over time. 

Researchers at Texas Biomed are studying influenza with the goal of developing longer-lasting and broader protection against the virus. 

What is the difference between a virus and bacteria? 

Viruses and bacteria can both cause infectious diseases, but they are fundamentally different types of biological entities. 

Viruses	Bacteria
Require host cells to reproduce	Can reproduce independently
Much smaller than most bacteria	Larger than viruses
Contain DNA or RNA as genetic material	Contain DNA and RNA
Cannot be treated with antibiotics	Some bacterial infections can be treated with antibiotics
Include influenza, Ebola and Marburg viruses	Include bacteria that cause tuberculosis, strep throat and other infections

This distinction is important because antibiotics do not work against viruses. 

Viral infections may instead be prevented with vaccines or treated with antiviral medications, depending on the virus and available medical interventions. 

What are antiviral drugs? 

Antiviral drugs are medications designed to interfere with specific stages of a virus’s life cycle. 

Depending on the drug, an antiviral may prevent a virus from entering cells, replicating its genetic material, producing viral proteins or releasing newly formed viruses. 

Because viruses differ significantly from one another, an antiviral that works against one virus may not work against another. 

Developing antiviral drugs therefore requires a detailed understanding of how a particular virus infects cells and replicates. 

Texas Biomed scientists conduct research aimed at understanding viral biology and evaluating potential antiviral compounds against serious infectious diseases. 

How are vaccines different from antiviral drugs? 

Vaccines and antiviral drugs serve different purposes. 

Vaccines prepare the immune system before infection by generating an immune response and, in many cases, immune memory. 

Antiviral drugs are used to treat an infection by targeting the virus or one of the processes it needs to reproduce. 

Both approaches are important tools for controlling infectious diseases. 

Researchers may also investigate combinations of vaccines, antiviral drugs and antibody-based treatments to determine which strategies provide the greatest protection. 

How do scientists study viruses? 

Scientists study viruses using a variety of approaches. 

Researchers may examine: 

• Viral genetics 

• Viral structure 

• How viruses enter cells 

• How viruses replicate 

• How viruses interact with host cells 

• How the immune system responds to infection 

• How viruses spread between hosts 

• How genetic changes affect viral behavior 

• Whether potential vaccines or treatments can prevent disease 

This multidisciplinary approach is known as host-pathogen research: studying both the pathogen and the host it infects. 

Understanding one without the other can provide an incomplete picture of disease. 

How does Texas Biomed study viruses? 

Texas Biomed has decades of experience studying viruses that cause serious human disease. 

Its scientists investigate viruses including influenza, Ebola, Marburg virus and hantaviruses, among others. 

The Institute combines expertise in virology, immunology, genetics, infectious disease and animal research. Texas Biomed also operates a specialized Biosafety Level 4 laboratory, where appropriately trained researchers can study certain high-consequence pathogens under highly controlled conditions. 

This research can help answer fundamental questions about how viruses cause disease and support the development of potential vaccines, antiviral drugs and other medical countermeasures. 

Texas Biomed and influenza research 

Influenza is one example of how scientists can use basic virology to address a major public-health challenge. 

Influenza viruses change over time, and different strains can circulate from year to year. This can make it difficult to develop a single vaccine that provides broad, long-lasting protection against all influenza viruses. 

Texas Biomed virologist Luis Martinez-Sobrido, Ph.D., and his team are working toward a universal influenza vaccine designed to provide broader and longer-lasting protection. 

His research focuses on targeting parts of influenza viruses that are more conserved, with the long-term goal of developing protection that could extend across multiple influenza strains. 

Texas Biomed and Ebola research 

Texas Biomed has also studied Ebola virus for decades. 

Ebola can cause severe disease and requires specialized containment for certain types of laboratory research. Scientists study how the virus enters cells, replicates and interacts with the immune system, as well as potential vaccines and treatments. 

Texas Biomed researchers have contributed to preclinical research supporting Ebola countermeasures, including vaccine and antibody-based approaches. 

This type of research illustrates why understanding viral biology matters: scientists need to understand how a virus works before they can effectively target it. 

Why is virus research important? 

Viruses are constantly changing, and new viral threats can emerge. 

Scientists therefore need to understand not only the viruses that cause disease today, but also the biological characteristics that could allow a virus to become a future threat. 

Research can help scientists: 

• Identify potential targets for vaccines and drugs. 

• Understand why some viruses cause severe disease. 

• Track genetic changes in viruses. 

• Understand how viruses move between animals and people. 

• Develop better diagnostic tools. 

• Evaluate potential treatments. 

• Prepare for emerging infectious diseases. 

The goal is to turn fundamental knowledge about viruses into practical tools that protect human health. 

The future of virology 

Advances in genomics, structural biology, immunology, computational science and other fields are changing how scientists study viruses. 

Researchers can now analyze viral genomes more rapidly, visualize viral structures in greater detail and study interactions between pathogens and host cells with increasingly sophisticated tools. 

These advances could help scientists respond more quickly when new viruses emerge and develop more targeted vaccines and treatments. 

At Texas Biomed, researchers continue to study viruses from multiple perspectives — from the molecular mechanisms of infection to the development and evaluation of potential medical countermeasures. 

Understanding viruses is one of the first steps toward controlling them. 

Frequently Asked Questions About Viruses 

What is a virus? 

A virus is a microscopic infectious agent containing genetic material surrounded by a protective structure. Viruses cannot reproduce independently and must infect a host cell to make new copies of themselves. 

Are viruses alive? 

Viruses do not meet all of the traditional criteria for living organisms because they cannot reproduce or carry out many metabolic processes independently. Scientists generally describe them as infectious biological entities or particles rather than fully living organisms. 

How does a virus infect a cell? 

A virus typically attaches to a specific receptor on a susceptible cell, enters the cell, releases its genetic material and uses the cell’s machinery to produce new viral components. Those components assemble into new virus particles that can spread to other cells. 

How do viruses make you sick? 

Viruses can damage infected cells as they replicate. The body’s immune response to the infection can also contribute to symptoms and, in some cases, tissue damage. 

What is the difference between a virus and bacteria? 

Viruses require host cells to reproduce, while bacteria are living single-celled organisms that can generally reproduce independently. Antibiotics target bacteria and do not treat viral infections. 

How do vaccines work against viruses? 

Vaccines expose the immune system to a safe representation of a virus or one of its components. This helps the immune system develop antibodies and immune memory so it can respond more effectively to a future infection. 

Can viruses change? 

Yes. Viruses can acquire genetic changes as they replicate. Some viruses evolve relatively quickly, and these changes can affect characteristics such as transmission, disease severity or recognition by the immune system. 

What is a zoonotic virus? 

A zoonotic virus is a virus that can be transmitted between animals and people. Understanding animal reservoirs and how viruses cross species barriers is an important part of emerging infectious-disease research. 

What is an antiviral? 

An antiviral is a medication designed to interfere with a virus’s ability to infect cells or reproduce. Antivirals are different from antibiotics, which target bacterial infections. 

Does Texas Biomed study viruses? 

Yes. Texas Biomed researchers study viruses including influenza, Ebola, Marburg virus, hantaviruses and other infectious pathogens. Their research includes understanding viral biology and host responses and evaluating potential vaccines, antiviral drugs and other countermeasures. 

Why does Texas Biomed study dangerous viruses? 

Studying certain high-consequence pathogens under appropriate containment conditions allows scientists to better understand how they cause disease and evaluate potential ways to prevent or treat infection. Texas Biomed’s specialized research infrastructure includes a Biosafety Level 4 laboratory and other facilities designed for infectious-disease research. 

How can scientists prepare for new viruses? 

Scientists can prepare by monitoring pathogens, studying how viruses evolve and spread, developing diagnostic tools, researching vaccines and antiviral treatments, and maintaining the specialized infrastructure needed to study high-consequence pathogens safely. 

Key Takeaway 

Viruses are tiny but complex infectious agents that depend on living cells to reproduce. Understanding how viruses enter cells, replicate, evolve and interact with the immune system is essential to developing vaccines, antiviral treatments and strategies for preventing infectious diseases. 

At Texas Biomed, researchers study these processes across a range of viruses, helping advance scientific knowledge and prepare for both today’s infectious diseases and the viral threats of tomorrow.