Microbiology Chapter 7 Infection and Disease (Part 3)

Reservoir > transmission >penetration /entry portal > colonization /attachment > persistence > reproduction > invasion /toxigenicity >dissemination; portals of exit

1. Maintain a reservoir

2. Leave the reservoir and be transported to the host (transmission)

3. Enter the host (penetration; portals of entry)

4. Establish a site of reproduction and growth within the host (colonization)Adhere to the surface of the host (attachment) invade the body of the host

5. Evade the host defenses (persistence)

6. Multiply within the host (reproduction)

7. Damage the host (invasion and toxigenicity)

8. Leave the host and return to the reservoir or find a new host (dissemination; portals of exit)

Reservoir: a place to live before and after infecting a host.

• -Three types of reservoirs
• 1. Animal (non-human)
• 2. Human
• 3. Environmental

Zoonosis: a disease spread from animals to humans

Symptomatic -those who are sick

Asymptomatic carriers-those who are infected but not sick

Incubatory carriers: people who are infected with a pathogen but appear healthy; will get sick soon.

chronic carriers: people who are infected with a pathogen but do not become sick for months or years.

Latent/Dormant carriers: people who are infected with a pathogen that undergoes latency.

Arthropods - insects , Arachnids 

Fomites - (objects) & Surfaces

Soil, Water , Food , Air , House ,Dust

Transmission=

-The spread of a pathogen from one organism to another

-The transfer of disease from one organism to another

Vertical: mother to child; parent to off-spring-

Lateral: person to person, environment to person, etc.

If a disease is transmissible (capable of being spread from one organism to another) then the disease can be termed

Direct contact -Physical touch between individuals,handshake,kissing,sexual intercourse

Indirect contact-Individuals contract pathogen via fomites , inanimate objects involved in the spread of a pathogen e.g. fork, doorknob, stair rails, etc.

• Vectors -Living organisms that transmit diseases to humans
• -Most common vectors are arthropods Ticks ,Fleas,Mites,Flies,Lice,Mosquitoes

They are important because most of this vectors involve animals.

Mechanical Vectors-The pathogen is on the external surfaces of the vector-Organism is not involved in the life cycle of the pathogen

Biological Vectors-Pathogen lives within the body of the vector; often serves as the definitive host-Vector transmits the pathogen by biting, sucking, aerosol formation

Types of Mechanical Vectors :common housefly, cockroach

Types of Biological Vectors :biting and blood sucking vectors,Flies (sand flies, tsetse flies), mosquitoes, lice, tick, mites, fleas

Mosquito -Penetrate the skin and inject saliva infected with the pathogen directly into the blood.

Fleas-Penetrate the skin and defecate around the wound, thereby introducing pathogen into the host.

Tsetse Fly -Penetrate the skin and regurgitate infected blood into the wound.

the pathogen is deposited directly into the blood stream, into tissue below the skin or into mucous membranes

Enteric Bacteria

Water (water-borne) -Consuming contaminated drinking water; bathing or swimming in contaminated water.

Food (Food-borne) -Consumption of contaminated food products.

Infected feces of one host enters a new host via ingestion

Direct contact with feces

Indirect contact with fomites contaminated with fecal matter.

Contaminated food and contaminated water.

Animal to human and human to human transmission

Infection cycle: the route an organism takes to pass from one person (or animal or plant) to another.

-Simple infection cycle:Pathogen is spread directly from person to person

-Complex infection cycle : Vector

Blood: usually sterile; contains most pathogens; microbes use the circulatory system for dissemination.

Urine: usually sterile

Saliva: often via spit

Respiratory secretions: sneezing, coughing (sputum)

Sweat

• Feces
• Fingers
• Flies
• Fomites (e.g., fields, floors etc.)
• Fluids
• Food
• Fornication (STI)

Yes ,

urogenital tract

digestive tract 

respiratory tract

conjunctiva (mucosal lining of the eye)

• Alimentary Tract
• Mouth: enter via ingestion of contaminated food, drink, etc.Ingested pathogens can survive stomach pH and enzyme activity

e.g., Salmonella, poliovirus, hepatitis A virus

Respiratory TractNose: pathogen enters the body through inhaled droplets or aerosols inhaled particles can be deeply inhaled bacteria: sore throat (strep throat)

• E.g.(streptococci), meningitis, diphtheria, pneumonia .
• viruses: measles, mumps, chickenpox, cold

• Genitourinary (also Urogenital) Tract
• Vagina, urethra ,sexually transmitted diseases (STDs)

e.g., syphilis, gonorrhea, chlamydia, herpes, AIDS, yeast infection

Trans-Placental and Birth Canal Infections.Pathogens can cross the placenta.Fetus can become infected during pregnancy and parturition (the act of giving birth)

e.g. Listerosis

Clostridium tetani and tetanus, Herpes simplex type 1 and cold sores/fever blisters

The establishment of the pathogen at the appropriate portal of entry.

The establishment of a site of microbial reproduction on or within a host.

The presence of microorganisms in a site of the body that may lead to tissue damage and signs of disease.

The first stage 

Surfaces external to the environment

Structures involved in colonization are considered virulence factors

Structures used in attachment

• -Fimbriae
• -Flagella
• -Adhesive slimes layers or capsules
• Adhesins
• -Specialized receptors on viral surfaces (glycoprotein spikes)
• -Suckers, hooks, barbs (important for parasitic worms)

Produce lytic enzymes that alter the host tissue.Destroy the extra cellular matrix or basement membranes.Degrade carbohydrate-protein complexes between cells.Disrupt cell surface molecules and their function

Passive mechanisms:Pre-existing tissue damage; e.g burns, ulcerations.Existing internalization methods; e.g endocytosis, phagocytosis

Yes

Yes, 

• -To hide from the immune system.
• -To avoid destruction by immune cells.
• -To persist and multiply within the host.
• -The immune response becomes stronger as the microbial population increases

Cytotoxins

• Cytopathic: resulting in cell death.
• Lysis/Necrosis
• Apoptosis/programmed cell death

• Oncogenic: cancer causing
• Teratogenic: damage to the fetus

Respiratory and salivary: sneezing, coughing and spitting

• Skin: sweating
• Fecal: defecation
• Urogenital: urination
• Blood and bleeding