Disease: Infectious and Noninfectious Disease

Disease Overview

• Definition: A condition that prevents the body, or any of its parts, from functioning normally.
• Classification: Diseases are classified into two main categories: Infectious and Non-infectious.

Glossary of Terms

• Organism: Living thing, plant, or animal.
• Micro-organism: An organism so small that it can only be seen with a microscope.
• Pathogen: Anything that causes disease.
• Host: The organism being affected by the agent.
• Vector: An organism that carries a pathogen and transmits it to the host, but is not affected by it.
• Parasite: An agent that uses the host for food or shelter.
• Infection: Invasion of the body by foreign organisms.
• Infectious: The invading agent can multiply easily in the host and be passed onto other host organisms. Examples are chicken pox or the common cold.
• Virulence: Measures how much damage a disease does to the host.
• Endemic: A disease that regularly affects a small number of people in the population.
• Epidemic: Higher than normal numbers of people are affected by a particular disease in a certain place.
• Outbreak: A disease that suddenly gets out of control.
• Pandemic: An outbreak that goes global, placing everyone on the planet at risk.

Infectious vs. Non-Infectious Diseases

• Infectious Disease
  • Can be transmitted from one person to another.
  • Can be contagious (spread by contact).
  • Can be infected via food and/or water.
  • Can involve a vector.
  • Caused by a pathogenic agent.
  • Causes include: Prions, Viruses, Bacteria, Fungi, protozoans, and macro parasites.
  • Examples include: CJD, COVID-19, Meningococcal, Thrush, Malaria, Hydatid disease.
• Non-Infectious Disease
  • Cannot be transmitted from one person to another.
  • It is not contagious and cannot be spread by contact.
  • No pathogens involved.
  • Causes include: Nutritional, physiological malfunctions, cancer, genetic, mental disorders, chemical deficiencies, and environmental factors.
  • Examples include: Mesothelioma, Down Syndrome, Scurvy, Melanoma.

Infectious Diseases

• A disease is classified as infectious if it is caused by a pathogen.
• A pathogen is a disease-causing organism.

Types of Pathogens

• Cellular (Living)
  • Parasites (e.g. helminthes) → Tapeworm
  • Protozoa (e.g. plasmodia) → Malaria
  • Fungi (e.g. tinea) → Athlete's foot
  • Prokaryote (i.e. bacteria) → Leprosy
• Acellular (Non-Living)
  • Virus (e.g. HIV) → AIDS
  • Prion → CJD

Disease-Causing Organisms (Pathogens)

• Bacteria
• Fungi
• Protozoa
• Virus

How Pathogens Cause Illness

• Toxins: Harmful substances produced by the pathogen that poison the body’s tissue and enzymes.
• Reproduction: A rise in the number of pathogens can damage a cell, even causing it to burst. Some pathogens hijack resources that the cell needs to survive.
• Immune Response: Sites of infection often become swollen, sore, and hot as a result of increased blood flow.

Types of Microbes

• Bacteria
• Viruses
• Fungi

Bacteria Fact File

• Size: $1/1000$ mm (very small).
• Structure: Single-celled organisms without a complete nucleus.
• Harmful: Produce toxic substances to the host.
• Useful: Breakdown dead matter in soil, make cheese and wine.
• Reproduction: Reproduce very quickly (e.g., two can become four, then eight, and so on).
• Examples: Salmonella and Streptococcus, pimples, and mastitis in cattle.

Viruses Fact File

• Size: $1/1,000,000$ mm (very small).
• Living or Non-living Debate:
  • Living characteristic: DNA.
  • Non-living characteristics: Cannot grow and reproduce on their own without a host cell.
• Reproduce: By invading a host cell, hijacking the cell, and reprogramming it to make more viruses, then breaking open and destroying the host and surrounding cells.
• Dormant: Some viruses invade cells and remain inactive for long periods.
• Examples: Flu virus, HIV (the AIDS virus), herpes (cold sores), measles, warts, and rubella.

Fungi Fact File

• Size: Some fungi can be seen with the naked eye; others are slightly bigger than bacterial cells (e.g., mushrooms, toadstools, and molds).
• Structure: Complex structures.
• Opportunistic Pathogen: Infect a person when their immune system is down (e.g., HIV/AIDS, cancer treatments, and after organ transplants).
• Examples: Penicillin, yeast, tinea (athlete’s foot), ringworm (skin), thrush (mouth/vagina).

Diseases Caused by Microbes

• Viruses: Influenza (flu), mumps, chickenpox, smallpox, polio, rabies, German measles.

• Bacteria: Food poisoning, sore throats, tuberculosis (TB), tetanus, cholera, typhoid, whooping cough.

• Fungi: Fungal sinusitis, athlete’s foot, Onychomycosis (discolored toenails).

• Microbes can cause viral meningitis and bacterial meningitis.

Infectious Disease Transmission

• Different pathogens have different transmission routes:
  • Direct contact
  • Indirect contact
  • Food and water
  • Airborne droplets
  • Insect bites

Disease Transmission Modes

• Direct Transmission: Occurs when a disease is passed directly from one infected person or animal to another person or animal.
  • Examples: Kissing (herpes simplex virus), touching, sexual contact (Human papillomavirus), droplet spread through coughing, sneezing, and talking (influenza, whooping cough).
• Indirect Transmission: Occurs when a disease is passed from an infected person to another person, even though they have not had direct contact.
  • Examples: Airborne transmission (measles), food (Salmonella), water (Cholera), surfaces (common cold, influenza).
• Vector Transmission: Requires another organism to transmit the disease from person to person.
  • Examples: Mosquitos (malaria, dengue fever, Ross River fever, and Japanese encephalitis), ticks (Lyme disease), fleas (plague), rats (leptospirosis).

Infection

• The invasion and growth of pathogens in the body.
• The pathogens may be bacteria, viruses, yeast, fungi, or other microorganisms.
• Infections can begin anywhere in the body and may spread all through it.
• An infection can cause symptoms such as fever and other health problems, depending on where it occurs in the body.

Endemic Disease

• Caused by an organism that is restricted or peculiar to a locality or region.
• The disease is typically present in a particular region or population at all times.
• Example: Malaria in South-East Asia.

Epidemic

• An epidemic disease spreads quickly and affects many individuals at the same time.
• Sometimes referred to as an outbreak.
• There is sudden rapid spread, growth, or development of the disease in a short time frame.
• Example: Measles outbreak in Siem Reap, Cambodia.

Pandemic

• A pandemic is the worldwide spread of a new disease. A pandemic is not the same as an epidemic.
• Viral respiratory diseases, such as those caused by a new influenza virus or the coronavirus COVID-19, are the most likely to turn into a pandemic.

Secondary Source Reliability, Accuracy, and Validity

• Reliability: Refers to the consistency of information with other reliable sources.
• Accuracy: The information presented is correct, with information we know to be true.
• Validity: Evaluates the appropriateness of the information for the topic under investigation.

The Immune System

• The immune system's role is to protect against foreign bodies by physically stopping them from entering the body, and then identifying and neutralizing them if they manage to bypass initial defenses.
• It utilizes three lines of defense, each playing a unique role in protecting against disease.

First Line of Defense - Barriers

• The body's initial line of defense is intended to block invading pathogens from entering.
• This includes physical barriers like skin, coughing, sneezing, cilia, and nasal hairs, as well as chemical barriers such as saliva, tears, stomach acid, and acidic vaginal mucus.
• Nasal Hairs: Sweep pathogens out of the body.
• Mucous Membranes: Line the openings of the body such as mouth, nose, throat. Microbes become trapped in the mucus.
• The Skin: Is the main barrier which is thick, waterproof, and difficult to damage.

Second Line of Defense - Inflammatory Response

• When pathogens bypass the first line of defense, the second line of defense, inflammation, takes action.
• Infections cause redness, warmth, and swelling as blood flow increases and vessels become more permeable.
• White blood cells, including phagocytes, move to the infection site to combat the pathogens.
• Fever: To heat up the body and destroy pathogens that cannot survive in extreme heat.
• Blood clotting: To stop additional infection through the skin (scabs).
• Inflammation: To increase the amount of blood - carrying white blood cells to the infected areas.
• Phagocytosis: Large white blood cells envelop pathogens and destroy them via enzymes.

Third Line of Defense - Immune Response

• The immune response includes a specialized white blood cell known as a lymphocyte. There are two primary types of lymphocytes: B cells and T cells.
• T Lymphocyte - (Memory cells):
  • Memory cells remember the antigen which remains in the blood. If it occurs again the body will be quicker at fighting it and may have an immunity.
  • Vaccinations assist with immunity.
• B Lymphocyte:
  • White blood cells divide to produce plasma cells that produce antibodies (proteins that bind with particular antigens).
  • Antibody is specific to a particular antigen.

How do vaccinations work?

• Vaccines stimulate the body to produce antibodies without causing the disease.

Defining Endemic, Epidemic, and Pandemic

• Endemic: A disease that persists in a community at a consistent level over time.
• Epidemic: A temporary occurrence of a disease which spreads rapidly and extensively within a specific population, community, or region, typically affecting a significantly higher number of individuals than expected.
• Pandemic: An epidemic that has spread over several countries or continents and affects a very large number of people.

NERD as a Pandemic (Claim-Evidence-Reasoning)

• Claim: NERD is a pandemic.
• Evidence: NERD has been reported in 73 countries across six continents. The total number of cases worldwide exceeds 260,000, with some countries experiencing 5,000–15,000 new cases daily. Hospitals operating at 120% and workforce operating with 40% absences.
• Reasoning: Its global reach across many countries and continents demonstrates widespread transmission. The 260,000 total cases and the rapid daily increases show its potential for exponential growth, a hallmark of pandemics. The strain on healthcare systems and the economic disruption further show the impact on society.

Comparing Endemics, Epidemics, and Pandemics

• Endemic:
  • Geographic spread: Continuous presence of a disease in a specific area.
  • Duration: Long-term, persistent over years.
  • Scale: Generally low numbers.
  • Behavior: Number of cases is stable or consistent over time.
  • Public health impact: Routine health policies manage the disease.
  • Example: Malaria is endemic in 85 countries (WHO, 2022).
• Epidemics:
  • Geographic spread: Limited to a region or population.
  • Duration: Usually short term, typically weeks to months.
  • Scale: Can affect a significant number of people in a particular region (contained geographically).
  • Behavior: Sudden or rapid rise of infections in a particular region or population.
  • Public health impact: May overwhelm local health care systems.
  • Example: Ebola in West Africa 2014–2016.
• Pandemic:
  • Geographic spread: Widespread across the world.
  • Duration: Temporary but may last months or years.
  • Scale: Affects significant portions of the world’s population.
  • Behavior: Sudden or rapid rise of infections across countries/continents.
  • Public health impact: Disrupts healthcare on a global scale.
  • Example: Spanish flu 1918-1919, COVID19 2020-2023.

Checkpoint: Compare epidemics, endemics, and pandemics including an example of each

• Epidemics, endemics, and pandemics all involve spreading infectious diseases but differ in duration and spread.
• An epidemic refers to a sudden, localized increase in disease cases within a specific region, such as the Ebola outbreak in West Africa (2014–2016), where the spread is rapid but geographically limited.
• In contrast, an endemic is a disease consistently present in a specific region or population over time, like malaria in sub-Saharan Africa, where case numbers remain stable and predictable.
• A pandemic, like COVID-19 (2020–2023), is a global outbreak, spreading across multiple countries or continents and affecting large populations over an extended period.
• While epidemics are short-term and confined to a particular area, endemics are ongoing and geographically limited, and pandemics have a broad, global reach.

Describing how vaccines can reduce the incidence and severity of diseases

• Vaccinations limit the incidence and severity of diseases.

Investigating vaccine effectiveness

• Analyzing how misconceptions about vaccines could negatively impact public health efforts.

National Immunisation Program Schedule

• Identifying the disease and the name of the vaccine.
• Understanding the purpose of having information written in different colors.
• Knowing when children are vaccinated for diphtheria, tetanus, and pertussis (whooping cough).

Measles Case Study Data

• Trend from 1995 = Exponential decrease
• The rate of measles in the Australian population since 1991 by Australian Institute of Health and Welfare licensed under CC BY 4.0

Interpolate and extrapolate

• Interpolate: Using a graph to estimate a value between data points that have been collected. Indicated by the red dot in the graph.
• To interpolate within a graph, read up from the x-axis at the data point given and then across to the vertical axis to find the new value.
• Extrapolate: Using a graph to predict a data point outside the given graph. Indicated by the green dot on the graph.
• To extrapolate a graph, you may first extend the line. Then, read up from the x-axis to the line and across to the y-axis to find the new value.

Assessing strategies used to reduce the spread and number of cases of infectious diseases

• Describe a range of strategies used to reduce the incidence and spread of infectious diseases.
• Make a judgment about the success of strategies in reducing the incidence and spread of a selected infectious disease.
• Relate the success of the strategies to the pathogen and mode of transmission.

Strategies for reducing the incidence and spread of infectious diseases

• Hygiene practices such as handwashing, regularly cleaning surfaces, safe food handling.
• Reducing contact with vector.
• Vaccination.
• Social distancing.
• Personal Protective Equipment (PPE) such as masks, condoms.
• Medication (antibiotics and antivirals).
• Quarantine.
• Water treatment.
• Contact tracing.
• Public health education.

Infectious disease examples

• Chickenpox
• Whooping cough
• Athlete’s foot
• Pinworms
• Flu
• Gastroenteritis
• Covid-19
• Malaria
• Chlamydia
• Variant Creutzfeldt-Jakob disease (CJD)

Aboriginal and Torres Strait Islander Peoples’ use of plants

• Describe how plants were used by Aboriginal and Torres Strait Islander Peoples for disease management.
• Identify plants used by First Nations Peoples to prevent or control diseases.
• Describe how the plants are prepared for use as a medicine.
• Describe how plants were used to prevent or control diseases.