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 ______Trichophytoninterdigitalecauses athlete’s foot.
The single-celled ______Plasmodium causes malaria, a very damaging infectious disease.
The single-celled ______Trypanosomabruceifeeds off nutrients in its host’s blood and causes African sleeping sickness.
Both Plasmodium and Trypanosomabrucei 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 Trichinellaspiralis from eating infected ______.
The flatworm Schistosomamansonican 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.
- The pathogen must always be found in the body of a ______organism and should not be found in a healthy one.
- 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.