Human Pathogenic Diseases

Pathogenic diseases are those that result from disease-causing agents or "pathogens," whose name comes from Greek words meaning "giving rise to suffering." There are several major types of pathogen, including viruses, bacteria, fungi and prions, each of which causes a wide variety of conditions. Understanding pathogenesis gives doctors and researchers insight into how to treat and prevent/curb the spread of these conditions.

Significance

• Human pathogenic diseases are a major cause of death the world over. They can cause serious discomfort, lingering effects and even long-term health problems (such as virus-linked cancer) for infected persons. Pathogens have been the root cause of major pandemics such as the "Black Plague" and the infamous 1918 influenza epidemic. Groups such as the World Health Organization (WHO) keep track of the distribution and effects of infectious diseases.

Subcategories of Pathogens

• Human pathogens can be divided into a number of categories, which include viruses, bacteria, fungi and prions. Viruses are infectious agents that are composed of genetic information (DNA or RNA), a protein coat and sometimes a protective membrane. Viruses integrate themselves into host cells, thereby taking over the function of the cell since viruses are unable to reproduce on their own. Bacteria are unicellular organisms, many of which are found naturally in the human system, that can cause diseases. Fungi, which can be both unicellular and multicellular, are distinct from both plants and animals and can cause a number of diseases. Prions are variant forms of proteins that have become misfolded (chemically identical to but shaped differently than standard proteins). Prions cause disease by causing other proteins in the sufferer's brain to also become misfolded, leading to brain damage and other symptoms.

Types

• Viral diseases can be very difficult to treat because viruses are not alive, and so cannot be eradicated with existing medications. Serious viral infections include HIV, influenza, hepatitis, rabies and rubella.

  The most common bacterial pathogen in humans is tuberculosis. Others include chlamydia, E. coli, Legionnaire's disease, listeria and salmonella.

  Fungi cause conditions like athlete's foot, jock itch and more serious diseases like thrush and Pneumocystis, which can lead to a severe type of pneumonia in people with compromised immune systems.

  All prion diseases are untreatable and fatal. They include Creutzfeldt-Jakob disease and Kuru. Prions cause the development of plaques in the brain. Prion diseases, as all whole, are known as transmissible spongiform encephalopathies.

Identification

• In diagnosing and treating a pathogenic disease, it is important to identify both the generic type of pathogen (bacterium, virus, etc.) and the specific pathogen (its species, subspecies, strain, etc.) in order to properly treat sufferers and other people who may have come in contact with the infected individual. This is because not all pathogens respond to the same treatment and because some are more virulent (causing more severe disease) and more infectious (more easily spread) than others.

Prevention/Solution

• Proper sanitation and other disease-avoidance measures, ranging from hand washing to vaccination, are used in the prevention of the development of pathogenic diseases. Once a condition has developed within an individual and a diagnosis has been provided, a variety of treatments are considered. Antibiotics are often effective against bacterial infections but have no effect against viruses. Viral infections are often treated by focusing on symptoms instead of the underlying condition, although medications that can combat the properties of some viruses have been developed. One of the problems of treating fungal conditions is that fungi and human cells are more similar than bacteria and viruses are to humans. Nevertheless, a number of anti-fungal drugs are available. Researchers are developing vaccines against some known prion diseases as well.