Biologist ___________________________
Date ______________
35-1 Infectious Diseases PowerPoint Notes
Causes of Infectious Disease
During the mid-nineteenth century, Louis Pasteur and Robert Koch established a ___________
explanation for infectious disease.
Pasteur’s and Koch’s observations and experiments led them to conclude that infectious diseases
are caused by ___________.
Microorganisms were commonly called “___________,” so this conclusion was called the germ theory
of disease.
Agents of Disease
Infectious diseases are caused by pathogens—organisms that invade the body and disrupt its
___________ functions.
Examples of pathogens are viruses, bacteria, single-celled eukaryotes, fungi, and ___________.
Viruses are nonliving particles that replicate by inserting their genetic material into a host cell and
taking over many of the host cell’s ___________.
Viruses cause the common cold, ___________, chicken pox, and warts.
Bacteria cause disease by breaking down the tissues of an infected organism for food, or by
releasing ___________ that interfere with normal activity in the host.
Bacteria cause streptococcus infections, diphtheria, botulism, and ___________.
Different types of fungus may infect the surface of the skin, mouth, throat, fingernails and
___________. Dangerous infections may spread from the lungs to other ___________.
The ___________ Trichophyton interdigitale causes athlete’s foot.
The single-celled ___________ Plasmodium causes malaria, a very damaging infectious disease.
The single-celled ___________ Trypanosoma brucei feeds off nutrients in its host’s blood and
causes African sleeping sickness.
Both Plasmodium and Trypanosoma brucei are spread to human by ___________.
Giardia intestinalis causes infection of the digestive tract and is transmitted in infected
__________.
People may be infected with the roundworm Trichinella spiralis from eating infected ___________.
The flatworm Schistosoma mansoni can be contracted by people working in ___________ paddies.
Other parasitic ___________ include tapeworms and hookworms.
Koch’s Postulates
Koch’s studies with bacteria led him to develop rules for identifying the microorganism that
causes a ___________ disease. These rules are known as Koch’s postulates.
1. The pathogen must always be found in the body of a ___________ organism and
should not be found in a healthy one.
2. The pathogen must be isolated and grown in the laboratory in ___________ culture.
3. When the cultured pathogens are introduced into a ___________ host, they should cause
the same disease that infected the original host.
4. The injected pathogen must be ___________ from the second host. It should be identical to
the original pathogen.
Although there are exceptions to these rules, they remain important guidelines for identifying the
causes of new and ___________ diseases.
Symbionts vs. Pathogens
Most microorganisms that live and grow in the human body are ___________ that are either
harmless or actually beneficial.
Yeast and bacteria grow in the mouth and throat without causing ___________.
Bacteria in the large intestine help with digestion and produce ___________.
What’s the difference between harmless microorganisms and pathogens that cause disease?
The “good guys” obtain nutrients, grow, and reproduce ___________ disturbing normal body
functions.
The “bad guys” cause ___________ in various ways (toxin, disruption, obtaining nutrients, etc.)
How Diseases Spread
Pathogens are often spread by symptoms of disease, such as sneezing, coughing, or ___________.
In many cases, these symptoms are changes in host behavior that help pathogens spread and
infect new ___________.
If a virus infects only one host, that virus will die when the host’s immune system kills it or when
the host dies. For that reason, ___________ selection favors pathogens with adaptations that help them
spread from host to host.
Coughing, Sneezing, and Physical Contact
Many bacteria and viruses that infect the nose, throat, or respiratory tract are spread by
___________ contact.
Coughing and sneezing releases thousands of tiny droplets that can be inhaled by other
___________.
Other pathogens, including drug-resistant staphylococci that cause skin infections, can be
transferred by almost any kind of body-to-body ___________.
They can also be transferred by contact with towels or certain kinds of ___________ equipment.
The most important means of infection control is thorough and frequent hand ___________.
If you have a cold or flu, cover your mouth with a ___________ when you cough or sneeze, and
wash your hands regularly.
Exchange of Body Fluids
Some pathogens require specific kinds of direct contact to be transmitted from host to
___________.
A wide range of diseases, including herpes, gonorrhea, syphilis, and chlamydia, are transmitted by
___________ activity. Therefore, these diseases are called sexually transmitted diseases.
Sexually transmitted diseases can only be completely prevented by ___________ sexual activity.
Other diseases, including certain forms of hepatitis, can be transmitted among users of injected
drugs through blood from shared ___________.
___________ can be transmitted through blood or sexual contact.
Contaminated Water or Food
Many pathogens that infect the digestive tract are spread through ___________ contaminated
with feces from infected people or other animals.
Contaminated water may be ___________, or it may carry pathogens onto fruits or vegetables. If
those foods are eaten without being washed thoroughly, infection can result.
Symptoms of these diseases often include ___________ diarrhea, another adaptation that helps
pathogens spread from one host to another, especially in places with poor sanitation.
Bacteria of several kinds are commonly present in seafood and ___________ meat, especially ground
meat.
If meats and seafood are not stored and cooked properly, ___________ can result.
Zoonoses: The Animal Connection
Any disease that can be transmitted from animals to humans is called a ___________.
Mad cow disease, severe acute respiratory syndrome (SARS), West Nile virus, ___________ disease,
Ebola, and bird flu are all zoonoses.
Sometimes an animal carries, or transfers, zoonotic diseases from an animal host to a ___________
host.
These carriers, called ___________, transport the pathogen but usually do not get sick themselves.
Mosquitos can transfer West Nile virus between ___________ and humans.
In other cases, infection may occur when a person is bitten by an ___________ animal, consumes
the meat of an infected animal, or comes in close contact with an infected animal’s wastes or secretions.