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Diseases and pathogens

What is a disease?

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




Viral Attack (comic book)

Story Behind the Scenes

For Teachershttp://askabiologist.asu.edu/viral-attackhttp://askabiologist.asu.edu/body-depot/viral-attack_teachers
Click here to read the comic: “Viral attack!”



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