Infectious disease

Infectious diseases are illnesses caused by pathogens such as viruses, bacteria, fungi, and parasites. They can affect nearly every organ system in the body and remain a significant cause of illness worldwide.

Disease outcomes vary widely—from mild symptoms to life-threatening complications—and are shaped by complex interactions between pathogens and the immune system. Understanding why some individuals develop severe disease while others remain resilient is critical to advancing prevention, diagnosis, and treatment.

What are infectious diseases?

Infectious disease is an umbrella term for illnesses caused by pathogens including viruses, bacteria, fungi, and parasites. These diseases can spread through direct contact, airborne transmission, contaminated food or water, insect vectors, or other environmental exposures.

Disease outcomes depend not only on the pathogen itself, but also on how the body responds to infection. Age, genetics, underlying health conditions, and environmental factors can all influence susceptibility, disease severity, and recovery. Understanding these interactions is essential for developing more effective strategies to prevent, diagnose, and treat infectious diseases.

Types of infectious disease

• Viral infections: Caused by viruses—microscopic infectious agents that contain genetic material (DNA or RNA) enclosed within a protective protein shell. Viruses invade living cells and use the host’s cellular machinery to reproduce.
• Bacterial infections are caused by bacteria, single-celled microorganisms that can live in a wide range of environments. While many bacteria are harmless or beneficial, some can cause disease when they invade the body or multiply uncontrollably.
• Fungal infections occur when fungi that naturally exist in the environment—or on and within the human body—grow excessively or spread to areas where they do not normally belong. These infections can range from mild skin conditions to serious systemic diseases.
• Parasitic infections are caused by organisms that live on or within a host and depend on that host for survival. Parasites can disrupt normal biological functions and contribute to a wide range of diseases.
• Prion diseases are rare, progressive disorders caused by abnormally folded proteins called prions. These faulty proteins trigger normal proteins in the brain to misfold, leading to severe neurological damage. Although uncommon, prion diseases represent a unique class of infectious disorders.

Why can infectious diseases be difficult to prevent and treat?

Pathogens continually evolve, generating new variants and strains that can evade immune defenses and reduce the effectiveness of existing treatments. At the same time, individuals respond differently to infection based on their genetics, age, immune status, and environmental exposures. Many infectious diseases are also characterized by complex interactions between pathogens and the host immune system. Understanding these biological mechanisms is essential for improving diagnostics, predicting disease severity, developing vaccines, and identifying new therapeutic targets.

Infectious Disease Research at JAX

At JAX, scientists are advancing infectious disease research by uncovering how pathogens interact with the immune system and why disease outcomes differ across individuals and populations, with particular strengths in viral infectious diseases, including influenza, RSV, and SARS-CoV-2. Building on decades of leadership in immunology and genetics, JAX researchers study the biological mechanisms that shape immune responses, influence disease susceptibility, and drive protection against infection.

JAX researchers utilize mouse models, human immune cell and clinical studies, single-cell genomics, computational biology, and systems immunology to investigate the mechanisms that drive infection, inflammation, and recovery. Our scientists are also expanding efforts to understand how microbes—including pathogens and the beneficial organisms that make up the human microbiome—interact with the immune system and influence health and disease.

Our researchers, including Duygu Ucar and Silke Paust, are advancing our understanding of immune resilience, vaccine responses, and antiviral immunity. Their work is helping to accelerate the development of more effective vaccines, therapies, and precision medicine approaches for infectious diseases.

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