IMMUNOLOGYIMMUNOLOGY

THE NATURE THE NATURE

OFOF

INFECTIOUS DISEASEINFECTIOUS DISEASE

How Are Diseases Caused?How Are Diseases Caused? Infectious diseases are caused by disease-Infectious diseases are caused by disease-

producing agents called producing agents called PathogensPathogens.. Bacteria, Protists, Fungi, and VirusesBacteria, Protists, Fungi, and Viruses Not all microorganism are pathogenicNot all microorganism are pathogenic

Infectious disease – Any disease caused by Infectious disease – Any disease caused by the presence of pathogens in the body.the presence of pathogens in the body.

Where do diseases come from?Where do diseases come from?

The main source of human disease The main source of human disease pathogens is the human body itself.pathogens is the human body itself.

People can be carriers.People can be carriers. They do not have the disease but act as a They do not have the disease but act as a

reservoir and can spread the disease.reservoir and can spread the disease.

CarriersCarriers

Carriers can pass on the disease during Carriers can pass on the disease during the incubation period.the incubation period.

Incubation period – A symptom-free Incubation period – A symptom-free period, while cells are multiplying within period, while cells are multiplying within the body. the body. Ex. Common cold, HIVEx. Common cold, HIV

Other ReservoirsOther Reservoirs Animals can also serve as reservoirs for Animals can also serve as reservoirs for

microorganisms that cause disease in microorganisms that cause disease in humans.humans. RabiesRabies

Soil and Water can be reservoirs for Soil and Water can be reservoirs for infectious disease. infectious disease. Soils can contain pathogens such as fungi Soils can contain pathogens such as fungi

and a type of bacterium that causes botulism.and a type of bacterium that causes botulism. Water may be contaminated by fecesWater may be contaminated by feces

TransmissionTransmission 4 ways for pathogens can be transmitted 4 ways for pathogens can be transmitted

from reservoirs to humans.from reservoirs to humans. Direct contact, by an object, through air or by Direct contact, by an object, through air or by

a vector a vector

1. Direct contact – Common cold, Flu, 1. Direct contact – Common cold, Flu, STDs and HIVSTDs and HIV

2. An object – Food poisoning, food is 2. An object – Food poisoning, food is contaminated by a food handlercontaminated by a food handler

TransmissionTransmission

3. Vectors – An intermediate organism3. Vectors – An intermediate organism Insects and ticks:Insects and ticks:

Malaria is transmitted by mosquitoesMalaria is transmitted by mosquitoes

Lyme disease is transmitted by ticksLyme disease is transmitted by ticks

Fleas helped transmit the bubonic plague Fleas helped transmit the bubonic plague from rats to humans.from rats to humans.

Causes of Symptoms of DiseaseCauses of Symptoms of Disease Viruses take over a host cell’s genetic Viruses take over a host cell’s genetic

material and may cause death to the cells material and may cause death to the cells they invadethey invade

Bacteria release toxins, which cause damage Bacteria release toxins, which cause damage to the host.to the host. Toxins can produce fever, inhibit protein Toxins can produce fever, inhibit protein

synthesis, destroy blood cells, or cause spasmssynthesis, destroy blood cells, or cause spasms Some toxins can be deadly.Some toxins can be deadly. What makes us FEEL sick (fever, sore throat) What makes us FEEL sick (fever, sore throat)

are symptoms from our fight against the disease!are symptoms from our fight against the disease!

Patterns of DiseasePatterns of Disease Diseases are able to spread rapidly in Diseases are able to spread rapidly in

today’s highly mobile world. today’s highly mobile world. Endemic – a disease that is always Endemic – a disease that is always

present in a population. Ex. Common Coldpresent in a population. Ex. Common Cold Epidemic – occurs when many people in a Epidemic – occurs when many people in a

given area are afflicted with the same given area are afflicted with the same disease at the same time.disease at the same time. Ex. Flu, PolioEx. Flu, Polio

Treating DiseaseTreating Disease

Antibiotics are often used to kill or inhibit Antibiotics are often used to kill or inhibit the growth and reproduction of bacteriathe growth and reproduction of bacteria

Produced naturally by various species of Produced naturally by various species of bacteria and fungi.bacteria and fungi.

Do not affect viruses. Do not affect viruses.

Problems with AntibioticsProblems with Antibiotics

Bacteria can often become genetically resistant Bacteria can often become genetically resistant to antibiotics. (This involves plasmid transfer)to antibiotics. (This involves plasmid transfer)

Resistance is caused by continued use of Resistance is caused by continued use of antibiotics.antibiotics.

Penicillin first used in the 1940s but now after Penicillin first used in the 1940s but now after about 60 years of use, types of bacteria have about 60 years of use, types of bacteria have evolved a resistance.evolved a resistance. The bacteria produce an enzyme that breaks down The bacteria produce an enzyme that breaks down

the antibiotic. Ex. Gonorrheathe antibiotic. Ex. Gonorrhea