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Diseases and pathogens

What is a disease? It is any state of being in which one’s health is disrupted.

It’s very hard to come up with an exact definition for “disease.”

… a look through any medical dictionary soon shows that articulating a satisfactory definition of disease is surprisingly difficult. And it is not much help defining disease as the opposite of health, given that definitions of health are equally tricky…. Why is it important to know what a disease or disability is? One reason is practical: because today’s medicine has an unprecedented ability to actually do things, it matters a great deal what we decide to tackle. The ability to make powerful, effective interventions into people’s health brings with it new ethical responsibilities.

What is a disease? Jackie Leach Scully. EMBO Reports 2004 Jul; 5(7): 650–653
From Brief Review in the Living Environment, Topic 2, Disease
Causes of disease small

What are pathogens?

from http://www.ck12.org/book/CK-12-Biology-Concepts/section/13.48/


How do we fight pathogens?

antibiotics – Only kill bacteria. Useless against all other pathogens.

anti-virals – Only kill viruses. Useless against all other pathogens.

anti-fungals – Only kill fungi. Useless against all other pathogens.

anti-protozoal – Only kill some protists. Useless against all other pathogens.

anti-helminthic – Only kill parasitic worms (helminths) . Useless against all other pathogens.

Flash animation: Fighting the common cold


How do viruses infect cells?

Viruses are not alive, like bacteria are. So how can a virus replicate?

{Images from http://www.bbc.co.uk/science/0/21143412 }

Virsus structure

Virus Lifecycle

Your skin is a barrier to disease

{ image from https://classconnection.s3.amazonaws.com/38/flashcards/1293038/png/inflammatory_response1336076941784.png }

Pin skin histamines inflammatory_response




AIDS (acquired immune deficiency syndrome) isn’t a disease in itself:
AIDS is a condition that develops when a person’s body has been weakened by HIV
HIV (the human immunodeficiency virus) is found in blood and sexual fluids
HIV spreads mainly through unprotected sexual contact, and the sharing of hypodermic needles and equipment.

When a person becomes infected with HIV,  it damages his or her immune system
-> leading to immunodeficiency; the immune system can no longer fight off common germs and pathogens.
So a person infected with HIV becomes ill from diseases that don’t usually affect someone without HIV.

HIV Life Cycle

It can take HIV many years to damage the immune system enough to make the person vulnerable to these diseases, called opportunistic infections. These infections, including Kaposi’s sarcoma, a form of skin cancer, take the opportunity to invade because they don’t encounter resistance. When doctors see someone with one of these diseases, they know that HIV is probably responsible, and the person may be diagnosed with AIDS.

Influenza (“the flu”)


Influenza  is a highly contagious viral infection of the respiratory tract.
It affects all age groups, though kids tend to get it more often than adults.

In the United States, flu season runs from October to May.
The flu is often confused with the common cold, but flu symptoms usually are more severe than the typical sneezing and stuffiness of a cold.

Symptoms, which usually begin about 2 days after exposure to the virus, can include:

muscle aches
loss of appetite
sore throat
runny nose
nausea or vomiting
ear pain

Infants with the flu also may seem fussy all of a sudden or just “not look right.”

Duration: After 5 days, fever and other symptoms have usually disappeared, but a cough and weakness may continue.

All symptoms are usually gone within a week or two. However, it’s important to treat the flu seriously because it can lead to pneumonia and other life-threatening complications, particularly in babies, senior citizens, and people with long-term health problems.

Auto-immune diseases

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Viral Attack (comic book)

Story Behind the Scenes    Click here to read the comic: “Viral attack!”

For Teachers


Mental illnesses

Psychiatry is a medical field devoted to the diagnosis, study, and treatment of mental disorders.  Psychiatry


Many pop psychologists now are claiming that drug and alcohol addictions are a disease. However, many scientists disagree. In this article  A neuroscientist argues that it’s time to change our minds on the roots of substance abuse.

Learning Standards

College Board Standards for College Success: Science

LSH-PE.5.4.3 Give examples, using evidence gathered from print and electronic resources, of genetic diseases (e.g., cystic fibrosis, sicklecell anemia, Tay-Sachs disease or phenylketonuria) that result from mutations to a single gene. Identify, for each example,
the specific type of mutation that causes the change in amino acid sequence and ultimately the change in the protein that is produced.

LSH-PE.5.4.4 Give examples, using evidence gathered from print and electronic resources, of instances when viruses are linked to cancer. Explain, based on knowledge of viral gene insertions and of the relationship among DNA, proteins and traits, how a viral insertion into DNA can cause cancer.

LSH-PE.5.4.5 Give examples, using evidence gathered from print and electronic resources, of the potential of using viruses for curing genetic diseases via gene therapy. Make a claim about, and justify, based on knowledge of viral DNA and viral insertions, why some viruses are appropriate for this application.

Massachusetts Comprehensive Health Curriculum Framework

Students will gain the knowledge and skills to select a diet that supports
health and reduces the risk of illness and future chronic diseases. PreK–12 Standard 4

Through the study of Prevention students will
8.1 Describe how the body fights germs and disease naturally and with medicines and
Through the study of Signs, Causes, and Treatment students will
8.2: Identify the common symptoms of illness and recognize that being responsible for individual
health means alerting caretakers to any symptoms of illness

8.5 Identify ways individuals can reduce risk factors related to communicable and chronic diseases
8.6 Describe the importance of early detection in preventing the progression of disease
Through the study of Signs, Causes, and Treatment students will
8.7 Explain the need to follow prescribed health care procedures given by parents and health care providers
8.8: Describe how to demonstrate safe care and concern toward ill and disabled persons in the family, school, and community

8.13 Explain how the immune system functions to prevent and combat disease

Interdisciplinary Learning Objectives: Disease Prevention and Control
8.a. (Law & Policy. Connects with History & Social Science: Geography and Civics &
Government) Analyze the influence of factors (such as social and economic) on the treatment and management of illness.

Benchmarks for Science Literacy, AAAS

The immune system functions to protect against microscopic organisms and foreign substances that enter from outside the body and against some cancer cells that arise within. 6C/H1*

Some allergic reactions are caused by the body’s immune responses to usually harmless environmental substances. Sometimes the immune system may attack some of the body’s own cells. 6E/H1

Some viral diseases, such as AIDS, destroy critical cells of the immune system, leaving the body unable to deal with multiple infection agents and cancerous cells. 6E/H4

Vaccines induce the body to build immunity to a disease without actually causing the disease itself. 6E/M7** (BSL)

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