Epidemiology: Disease Patterns

Epidemiology

• Epidemiology studies how diseases spread, affect populations, and how they can be controlled.
• It examines the patterns, causes, and effects of health and disease conditions in specific populations.

Sporadic Disease

• This is a disease that occurs infrequently and irregularly in a population.
• A sporadic disease does not follow a predictable pattern.

Outbreak

• A sudden increase occurs in the number of cases of a particular disease in a specific area.
• Outbreaks often occur in a short period.
• Outbreaks are typically more localized than epidemics.

Epidemic

• A sudden increase occurs in the number of disease cases above normal expectations in a specific area or region.
• Epidemics are usually larger and more widespread than outbreaks.

Endemic

• A disease or condition is regularly found and consistently present in a particular geographic area or population.
• Malaria in certain tropical regions is an example.

Pandemic

• This is a global disease outbreak that spreads across countries or continents.
• Pandemics drastically affect a large proportion of the population.
• Pandemics are usually caused by a new infectious agent, like COVID-19.

Nosocomial Infection

• An infection acquired in a hospital or healthcare setting.
• It typically occurs during treatment for another condition.
• These infections can result from bacteria, viruses, or fungi.

Infection

• This is the invasion and multiplication of microorganisms (bacteria, viruses, or fungi) in the body.
• Infections can cause disease.

Disease

• A condition occurs when the body’s normal functioning is disrupted.
• Infections or other factors like genetics or environmental issues can cause diseases.
• Symptoms result from diseases.

Host

• An organism supports the growth and reproduction of a pathogen.
• In humans, a host is a person infected by a microorganism.

Pathogens

• Microorganisms cause disease.
• Bacteria, viruses, fungi, and parasites are pathogens.

Normal Microbiota

• These microorganisms naturally live in or on the human body without causing harm.
• Includes bacteria, fungi, and viruses.
• Normal microbiota helps protect the body against harmful pathogens.

Prions

• Infectious agents are composed of proteins.
• Prions cause neurological diseases.
• They induce abnormal folding of normal proteins in the brain.
• Creutzfeldt-Jakob disease is an example.

Viruses

• Small infectious agents can only reproduce inside living host cells.
• Viruses can cause various diseases, like influenza or HIV.

Bacteria

• Single-celled microorganisms can exist independently or as parasites.
• Some bacteria are beneficial, like those in the gut.
• Other bacteria can cause diseases, such as tuberculosis or cholera.

Protists

• A diverse group of eukaryotic microorganisms exists.
• Some protists can cause diseases like malaria or amoebic dysentery.
• Plasmodium species is an example.

Fungi

• Eukaryotic organisms include yeasts, molds, and mushrooms.
• Some fungi can cause infections in humans, especially in immunocompromised individuals.
• Candidiasis is an example.

Helminths

• Parasitic worms infect the human body.
• Tapeworms and roundworms are examples.
• They often lead to gastrointestinal symptoms or other systemic problems.

Innate Immunity

• The body’s first line of defense against pathogens occurs from birth.
• It includes physical barriers (like skin), chemical barriers (like stomach acid), and immune cells (like macrophages).
• Innate immunity provides rapid, nonspecific protection.

Acquired Immunity

• A more specific immune response develops after exposure to a pathogen.
• It involves memory cells that recognize and fight the pathogen more effectively upon re-exposure.
• Acquired immunity can be active (developed after infection or vaccination) or passive (from receiving antibodies, like from mother to baby).

T Cells

• A type of white blood cell plays a crucial role in the immune response.
• T cells can destroy infected host cells and help regulate other immune responses.
• Helper T cells and cytotoxic T cells are different types of T cells.

B Cells

• Another type of white blood cell is responsible for producing antibodies.
• B cells mature into plasma cells upon encountering an antigen.
• Plasma cells secrete antibodies to neutralize pathogens.

Antibodies

• Proteins produced by B cells recognize and bind to specific antigens on pathogens.
• Antibodies mark pathogens for destruction or neutralization.

Antigens

• Foreign molecules or parts of pathogens (e.g., proteins, sugars) trigger an immune response.
• The immune system identifies antigens as threats.
• Antibodies are produced to attack antigens.

Chain of Infection

• The sequence of events allows a disease to spread from one host to another.
• Agent: The microorganism that causes the disease.
• Reservoir: The habitat where the pathogen lives (e.g., humans, animals, environment).
• Portal of Exit: The route by which the pathogen leaves the host (e.g., respiratory droplets).
• Mode of Transmission: How the pathogen is transferred (e.g., air, contact, vectors).
• Portal of Entry: The route through which the pathogen enters a new host (e.g., respiratory tract, skin, mucous membranes).
• Susceptible Host: An individual vulnerable to the pathogen, often due to factors like age, immunity, or health conditions.