Despite remarkable breakthroughs in medical research and advancements in immunization and treatments, infectious diseases are undergoing a global resurgence. Worldwide, infectious diseases are the leading killer of children and adolescents and are one of the leading causes of death for adults. The impact of emerging infectious diseases in developing countries is well documented. But these diseases also impact Americans, with consequences for the public health system, the delivery of medical care, the economy, and national security. 

At least 170,000 Americans die annually from newly emerging and re-emerging infectious diseases, a number that could increase dramatically during a severe flu pandemic or yet-unknown disease outbreak.  Factors including globalization, increased antimicrobial (drug) resistance, and climate and weather changes are contributing to the increased threat.  "Infectious diseases are not just a crisis for the developing world. They are a real threat right here, right now to America's economy, security, and health system," said Jeffrey Levi, PhD, Executive Director of TFAH. "Infectious diseases can come without warning, crossing boarders, often before people even know they are sick.  Americans are more vulnerable than we think we are, and our public health defenses are not as strong as they should be."  From the Trust for America's Health website.

1. The Basics Defined:
   • Infectious Disease:
     • A disease caused by agents (pathogens that invade the body (host), and cause harm to the body tissues (cause disease).
   • Communicable Disease:
     • Also referred to as contagious disease, an infectious disease that has the ability to spread from person to person.
   • Infection:
     • Results when a pathogen invades and begins growing within a host.
     • Disease results only if and when, as a consequence of the invasion and growth of a pathogen, tissue function is impaired.
     Pathogens:
     • Disease causing agent or microorganisms.
   • Antigen:
     • Any substance capable of triggering an immune response; evokes production of one or more antibodies.
   • Antibody:
     • Also known as an immunoglobulin, a large Y-shaped protein produced by B-cells that is used by the immune system to identify and destroy foreign objects such as bacteria and viruses.
   • Microbes:
     • Tiny organisms, too tiny to see without a microscope
     • They are abundant on Earth, live everywhere (in air, soil, rock, and water).
   • Epidemic:
     • Disease outbreak that affects many people in a community or region at the same time.
   • Endemic:
     • Refers to a disease or condition regularly found among a particular people or certain area.
   • Pandemic:
     • A global epidemic.
2. The Chain of Infection:
   • A set of elements or processes that must be present for infection to occur. Each link must be present and in sequential order for an infection to occur; and include:
     • Infectious Agent or Pathogen must be present.
       • The five major types of infectious agents include bacteria, viruses, fungi, protozoa, and helminths. In addition, a new class of infectious agents, the prions, has recently been recognized.
         • The greater the organism's virulence (it's ability to grow and multiply), invasiveness (it's ability to enter tissue) and pathogenicity (it's ability to cause disease), the greater the possibility the pathogen will cause an infection.
• A Reservoir
  • A  site where the infectious agent can thrive and reproduce.
• Portal of Exit from the Reservoir
  • A place of exit providing a way for a microorganism to leave the reservoir, (e.g. the nose, mouth, or open wound, etc.)
• Mode of Transmission
  • Method of transfer by of the organism from one host to the other, (e.g. sneeze, cough, or being carried on contaminated hands, etc)
• Portal of Entry into a New Host:
  • An opening which allows the microorganism to enter the host  (e.g. mucus membranes, open sores or wounds, etc.)
• Susceptible Host:
  • Lacking immunity or physical resistance to overcome the invasion by the pathogen or microorganism.
3. Disease Causing Microbes:
   • Bacteria:
     • Single-cell organism that can thrive and are mobile in many environments can self-replicate (reproduce by themselves)
     • Most bacteria do not cause disease.
     • Most bacterial infections are treatable with Antibiotics
     • Three main types are:
       • Cocci (spherical shape)
         • Staphylococci (staph infection)
         • Streptococci (strep throat)
         • Streptococcus pneumoniae (pneumonia)
       • Bacilli (rod or tube shape)
         • Salmonella (food poisoning)
         • E-coli (food poisoning, bladder and kidney infection)
         • Pertussis (whooping cough)
       • Spirilla (spiral shape)
         • Syphilis (STD)
         • Borrelia burgdorferi (Lyme disease)
• Virus:
  • Among the smallest of all microbes, most viruses cause disease.
  • Virus is a non-cellular core of genetic material (DNA, RNA)
  • Viruses cannot reproduce on their own, they must invade healthy body cells and take over their reproductive machinery to reproduce.
  • Antibiotics have no effect on virus.
• Fungi:
  • Actually a primitive plant, found in air, in soil, on plants, and in water.
  • Fungal diseases are called mycoses.
• Protozoa:
  • A group of microscopic one-celled animals that usually cause disease in humans.
• Prions:
  • Derived from the words "protein" and "infection", it is an infectious protein particle that contains no genetic material (unlike virus) and does not trigger an immune response,
• Helminth:
  • Simple, invertebrate animals, some of which are infectious parasites.
  • Because they are animals, their physiology is similar to humans, making parasitic helminth infections difficult to treat because drugs that kill helminths are frequently very toxic to human cells.
4. Your Immune System:
   1. The immune system is a network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders.
   2. The immune system is amazingly complex in it's development of "Immunity" towards a pathogen. 
   3. It can recognize and remember millions of different enemies, and it can produce secretions (release of fluids) and cells to match up with and wipe out nearly all of them.
5. Types of Immunity:
   • Innate Immunity:
     • The immunity that you are born with and the initial response by the body to eliminate microbes and prevent infection.
     • Innate immune defenses are non-specific, meaning these systems respond to pathogens in a generic way, and include:
       • Anatomic Barriers such as skin, saliva, tears, stomach acid, mucus, and cilia in the respiratory and intestinal tracks
       • Humoral Barriers respond if pathogens penetrate the first line of defense (anatomic barriers above). This process includes
         • Inflammation and fever.
         • Complement System: a biochemical cascade (series of chemical reactions) that attacks the surfaces of foreign cells. It contains over 20 different proteins and is named for its ability to "complement" the killing of pathogens by antibodies.
       • Cellular Barriers which involves Leukocytes (white blood cells) acting like independent, single-celled organisms and are the second arm of the innate immune system, they include: 
         • Phagocytes (macrophages, neutrophils, and dendritic cells),
         • Mast cells
         • Eosinophils
         • Basophils
         • Lymphocytes (two types):
           • B cells produce antibodies. Antibodies attach to a specific antigen and make it easier for the immune cells to destroy the antigen.
           • T cells attack antigens directly and help control the immune response. They also release chemicals, known as cytokines, which control the entire immune response.
   • Adaptive or Acquired Immunity:
   • Immunity that develops with exposure to various antigens (substance capable of triggering immune response).
   • Immune system builds a memory and tailored defense that is specific to each antigen.
   • Artificial Immunity:
     • Immunity that is acquired through vaccination.
•  Passive immunity:
  • Developed immunity by antibodies that are produced in a body other than your own.
  • Infants have passive immunity because they are they are born with antibodies that are transferred through the placenta from their mother.
  • These antibodies disappear between 6 and 12 months of age.
    • Passive immunization may also be due to injection of antiserum, which contains antibodies that are formed by another person or animal. It provides immediate protection against an antigen, but does not provide long-lasting protection. Immune serum globulin (given for hepatitis exposure) and tetanus antitoxin are examples of passive immunization.
6. Vaccines, When the Body Needs Help:
   • Vaccines help develop immunity by imitating an infection, but this "imitation" infection does not cause illness.
     • A dead or weakened form of the the disease germ or pathogen is injected into the body.
   • The imitation infection will cause the immune system to develop the same response as it does to a real infection so the body can recognize and fight the vaccine-preventable disease in the future.
   • Some vaccines can cause minor symptoms (such as fever), which are normal and should be expected as the body builds immunity.
   • Scientists take many approaches to designing vaccines which are based on
     • Information about the germs (viruses or bacteria) the vaccine will prevent
     • How it infects cells
     • How the immune system responds to it
     • Regions of the world where the vaccine would be used, are also important because the strain of a virus and environmental conditions, such as temperature and risk of exposure, may be different in various parts of the world.
   • Some Vaccines present a lifetime of immunity, where others need to be re-administered each year.
     • Flu viruses are always changing or drift to create new viruses, meaning specific immunity is no longer present.

7. Specific Infectious Diseases and Disorders:
   • For detailed information concerning specific Infectious Diseases or Disorders refer to the sites below:
     • Centers for Disease Control and Prevention
     • National Institute for Allergy and Infectious Diseases
8. Sexually Transmitted Infections and Disease:
   • Sexually Transmitted Infection:
     • Infection or invasion of body tissue by a microorganism (bacteria, virus, protozoa) that can be passed from one person to another during intimate bodily contact.
     • Infection has the potential to cause disease or illness, but the infected individual is asymptomatic (not experiencing symptoms) and may not feel sick.
     • Someone with an STI can unknowing pass on an infection as they are often unaware they are carrying an infection and may not take the proper precautions toward protecting their partner.
   • Sexually Transmitted Disease:
     • Disease (damage) resulting from a Sexually Transmitted Infection (above).
       • An infection with symptoms
   • Common Sexually Transmitted Infections and Diseases (click on title below to read)
     • Bacterial Vaginosis (BV)
     • Chlamydia
     • Gonorrhea
     • Genital Herpes
     • HIV/AIDS & STDs
     • Human Papillomavirus (HPV)
     • Pelvic Inflammatory Disease (PID)
     • Syphilis
     • Trichomoniasis
     • Viral Hepatitis

Did You Know?

• Each year, roughly one in six Americans (48 million people) gets sick, 128,000 are hospitalized and 3,000 die of foodborne diseases. Reducing foodborne illness by 10 percent would keep about 5 million Americans from getting sick each year.
• Most food poisoning is caused by bacteria, viruses and parasites, rather than toxic substances in the food.
• Raw foods are the most common source of foodborne illnesses because they are not sterile.
• When food is cooked and left out for more than two hours at room temperature, bacteria can multiply quickly.
• Some people are at greater risk for bacterial infections because of their age or an unhealthy immune system. Young children, pregnant women and older adults are at the greatest risk.
• Hand-washing and wearing gowns and gloves in hospitals cuts the number of infections of methicillin-resistant staphylococcus aureus, also known as (MRSA), and other hospital-acquired infections.
• Vaccination is the only medical intervention that has ever completely eliminated an illness in humans.
• One in nine people who contract a meningococcal disease, such as meningitis, will die from it, even if they are diagnosed and treated quickly.46• Cases and deaths from the most vaccine-preventable diseases targeted since 1980, such as chickenpox, have declined by 80 percent or more because of widespread immunization.
• The Centers for Disease Control and Prevention recommends vaccinations from birth through adulthood to provide a lifetime of protection against many diseases and infections, such as influenza, pneumococcal disease, human papillomavirus and hepatitis A and B.

Above Statistics from National Public Health Week, Communicable Disease Fact Sheet; www.nphw.org