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Patho Merrimack College


A state of tissue destruction resulting from the invasion of microbes that destroy cells, interfere with metabolism, and produce toxins


Spread from person to person often through the exchange of fluids


Noncontagious, usually a chronic disorder


The ability to cause disease


Potency of pathogen

- Ratio of # cases : # exposed to the microbe
- More Virulence = More People Affected


The # of exposures needed to cause an infection by entering and surviving


The ability of the pathogen to produce harmful toxins that damage the host

- Increase in toxigenicity = Increase in damage


Level of foreign that the body sees the pathogen as

- More Antigenic = more of an immune response

Pathogenic Defense

Ways to avoid destruction by host

- capsules


Hosting two or more pathogens

- Ex: Chlamydia & Gonorrhea


When an infection arises in addition to the one present, then host is compromised

- Proliferation of flora

Obligate Parasites

Require a host for metabolism & reproduction

Facultative Parasites

May live on host but can survive on own as well


Single-cell microbe has a cell wall, cytoplasm, ribosomes, and DNA

Antibotics are aimed to inhibit the growth of cell walls when bacteria reproduce in order for the body to fight the infection

Antibotics and Fighting Bacteria With Cell Walls

1. Independent Survival
2. Stimulation of Inflam. Response
3. Capsule to Resist Phagocytosis
4. Endotoxin
5. Endospores

5 Factors that Increase Pathogenicity

Gram - complex of phosolipid polysaccharides form in cell walls cause inflammatory mediators to release and turns into septic shock

How can endotoxins make a microbe more pathogenic?

Washing & antibotics in tears

Natural Antimicrobial Mech: Eyes

Phagocytosis by Natural Killer Cells

Natural Antimicrobial Mech: Lymph Nodes

Acts as a physical barrier

Natural Antimicrobial Mech: Skin

Trapped in mucous, phagocytosis by macrophages

Natural Antimicrobial Mech: Respiratory Tract

Phagocytosis by macrophages and granulocytes, attack of complement proteins

Natural Antimicrobial Mech: Blood

Phagocytosis by macrocytes and granulocytes, attack by natural killer cells

Natural Antimicrobial Mech: Bone Marrow

Phagocytosis of Kupffer cells (macrophages)

Natural Antimicrobial Mech: Liver

Phagocytosis by macrophages and granulocytes, attack by natural killer cells

Natural Antimicrobial Mech: Spleen

Destruction by gastric acid, bile, and enzymes

Natural Antimicrobial Mech: Digestive System

Flushing and acidity of urine

Natural Antimicrobial Mech: Urinogential Tract

Prions - simply protein disease causing agents

Smallest Agent of Infection

Herpes, Influzena, and Polo

Examples of Viruses

From Bacilli or Cocci

Examples of Bacteria

Ameba, Glardia, Paramecium, Plasmodium in RBC's

Examples of Protozoan

Yeast & Mold

Examples of Fungi

Tick or lice (Visible)

Examples of Ectoparasites

Tapeworm, round worm, liver fluke = all lay eggs in host (Visible)

Examples of Multicellular Parasites

Neisseria meningitidis & Meningitis

The brain is the site of infection for_____________ to cause______________.

Streptococcus pneumoniae & pneumonia

The lungs are the site of infection for_____________ to cause______________.

Streptococcus pygenes & septicema (blood poisoning by bacteria), myositis (inflam. & degeneration of muscle), necrotizing fasciitis

The blood is the site of infection for_____________ to cause______________.

Streptococcus aureus & endocarditis (Gram + large dark red globules and white nuclei)

The heart is the site of infection for_____________ to cause______________.

Escherichia coli & UTI, diarrhea (Gram - bacilli)

The large intestine is the site of infection for_____________ to cause______________.

Salmonella typi & entercolitis (inflam. of intestine & colon), typhoid

The small intestine is the site of infection for_____________ to cause______________.

Pseudomonas aeruginosa & UI, wound infection

The bladder is the site of infection for_____________ to cause______________.

An infection of the intestines by a protozoan called Entamoeba histolytica

What's Amebiasis?

1. Mostly asymptomatic
2. 3rd most fatal disease after malaria
3. Acquired by eating contamenated food by human feces containing amebic cysts

What is associated with Amebiasis? How is it caused?

An inactive form of a protozoan (like and endospore for bacteria)

What is a cysts?

When an infection overwhelms the body leading to extremely low blood pressure & huge inflammatory response (hypotension)

What is septic shock?

1. Cannot replicate outside host
2. Bind to host and taken inside
3. Cause acute or chronic infections

* Release virions or genetic material agents to nearby cells when losing function in order to increase survival

What are the characteristics associated with intracellular parasites or viruses?

1. Size of the virus
2. Process of viral replication
3. Viral genotype
4. Host susceptibility

What are the 4 elements that determine the degree of chronic viral infection?

Latency or dormancy

(stays within cell but causes little to no damage aka hiding- activates when immunocompromised or under stress)

What is a common characteristic of a viral infection?

1. Host cell lysis releasing virus or budding releases enveloped viruses
2. Attachment & Absorption
3. Penetration into host
4. Uncoating of Capsid & DNA
5. Viral replication
6. Cycle repeats (Or Latency can cause tumor or protein coat synthesis or malignancy)

Cycle of Viral Infection

1. Rickettsiae
2. Mycoplasms
3. Chlamydiae

Name 3 infections that are both bacterial & viral

Transmitted by fleas or ticks to causes infection through blood to epithelial tissues... Cannot replicate outside of host but produces energy like a bacteria

What is Rickettsiae?

Lack a cell wall and survive on host but do not use host for replication ... can cause lung or urinary/gential infection & lack of cell wall makes them not good for the use antibotics (get from cough or STD)

What are mycoplasms?

An STD that cause genital tract infections and acts as a parasite but reproduces like a bacteria through binary fission

What is Chlamydiae?

Metabotically inactive stage in life cycle where it attaches and internalizes in host

What is an elemental body?

Metabolically active stage in life cycle where the microbe takes over the host cell

What is a reticulate body?


Chlamydia Growth Cycle

Attach to host and internalize through phagocytosis

First, Inactive elemental bodies...

Reticulate bodies

Then, the activation of elemental bodies to...

undergo binary fission

Next, reticulate bodies...

Host DNA synthesis declines, & RB's produce RNA, DNA, and protein

Now, binary fission of reticulate bodies...

Reorganization of RB's to EB's

Continued Multiplication and then...

Inclusion forms contains EB's and RB's (mostly EB's)

Infectivity increases as...

48 Hour Growth Cycle can now repeat

Lysis of epithelial cells...

Unicellular parasites that deprive the host and kills it ... Transmits through a vector

What is a protozoa?

Water, food, or sexual contact

What is a vector?

A Eukaryote such as yeast or mold that are resistant and usually inhabit skin or mucous

What is a fungus?

Causes disease in a host when the immune system is compromised

What is an opportunistic pathogen?

Candidias = yeast that cause white growth on the mouth "thrush"

Examples of an opportunistic pathogen?

Yeast is unicellular & produces by budding in long chains called Pseudohyphae

Mold is multicellular and have tubules hyphae (form clusters = mycelium)

What is the difference between yeast & mold?

Softening or breakdown of tissues

What is maceration?

Infectious agent > Reservoirs > Portal of Exit > Means of Transmission > Portal of Entry > Suspectible Host

Chain of infection?


How to Break the Chain of Infection


1. Infectious Agents... Bacteria, fungi, virus, etc.

Sanitizing environment & Antimicrobial drugs

2. Reservoirs ... People, equipment, Water, etc.

Handwashing, cover secretions, & disposal

3. Portal of Exit ...Excretions, secretions, skin, droplets, etc.

Handwashing, sterilization, universal precautions, airflow control, food handling, isolation

4. Means of Transmission... Direct contact, ingestion, airborne, etc.

Treatment of underlying diseases & recognition of high risk patients

5. Portal of Entry... Mucous membrane, GI tract, broken skin, burns, surgery, immunosupressed, elderly

1. Exposure
2. Incubation
3. Prodrome
4. Clinical Illness
5. Convalescence Recovery

5 Phases of Acute Infection

Pathogen enters host (immunity & inflam. activated)

1. Exposure

1. Direct Contact
2. Droplet transmission (up to 3 feet)
3. Airborne transmission (suspended in air)
4. Vector transmission

Modes of Contact

Disease present but not visible

2. Incubation

Subclinical Illness - disease present but few nonspecific symptoms "under the weather = something not right"

3. Prodrome

Signs easily seen

4. Acute Illness

Over the whole body...
1. Fever
2. Weakness
3. Fatigue
4. Headache
5. Nausea
6. Pain

Systemic Manifestations

Site Specific...
1. Site pain
2. Swelling / Edema
3. Redness
4. Pus or Purulent Exudate
5. Loss of Function
6. Heat on spot
7. Inflamed Lymph Nodes

Local Manifestations

Goes to full recovery usually with fatigue

5. Convalescence


True or False. Septicemia can cause shock.

1. Either stays at surface or penetrates the epithelial and basement layers
2. Penetration goes through lymphatic system
3. Then gets into blood stream
4. Travels to a specific tissue
5. Infection of other people (contagion)

Spread of Infections

Its involves...
1. Massive Vasodilation
2. Fluid Loss
3. Low Blood Pressure
4. Perfusion Failure to Vital Organs
(Often Gram - Rods)

What is septic shock?

Can't get rid of
Examples... HIV, Hepatisis B, Typhoid

Chronic Infections in Carrier State

Gram - bacteria builds up endotoxins and bacteria lysis... or LPS

What is involved in endotoxic shock?

Binds to Protein complexes and formation of LPS-LPB complex in blood

Then What?

Engulfed by macrohages

This complex is then...

Tumor Necrosis Factor

What is TNF?

Kills endothelial cells

So then Tumor Necrosis Factor alpha is released by the macrophages &...

Makes cells more permeable

TNF alpha receptor on endothelial cells...

Loss of fluids to interstitial space

This leads to...

The lowering of blood pressure, blood volume and perfusion

This causes...

& ends in recovery or death

This in turns triggers septic shock...

Decrease in WBC count= may indicate infection by suppression of WBC production

What is Leukopenia?

Elevation in WBC count, indicates presence of infection

What is Leukocytosis?

1. White Blood Cell Count
2. Serum Antibody Levels
3. Cultures
4. Sensitivities (2 Antibotics)

Types of diagnostic tests?

5,000 - 10,000 cells/ml

What is a normal WBC count?

Acute = neutrophils
Chronic = monocytes & lymphocytes

If the differential count is off, determines the nature of the infection

Target cell wall & DNA/RNA synthesis

Antibotics or Antimicrobial Drugs

ONLY for fungi... target membrane


Targets Preentry, entry, synthesis, assembly, & release


Tylenol = V pain & fever
Ibuprofen = inflammation & pain (NSAIDS)

Symptoms Reduction



D. Mode of Transmission

1. You are looking to break the chain of infection by washing your hands frequently as you provide care for patients. Will of the following links have you broken?

A. Reservoir
B. Host
C. Portal of Entry
D. Mode of Transmission

C. Finals Exam Week

2. Which of the following may make a person more suspectible to getting an infection?

A. Age between 6 and 46 Years old
B. Surgery cut healing by primary intention
C. Finals Exam Week
D. A functioning immune system

C. Prodrome

The feeling that "something is not quite right" is considered which stage of infection?

A. Point of infection
B. Incubation
C. Prodrome
D. Acute Symptoms

B. Chronic Infection

5. A white blood cell differential shows an increase in the number of monocytes and macrophages in the blood. This typically means that it is...

A. Acute Infection
B. Chronic Infection
C. Viral Infection
D. Not useful

Key Word: Mode of Transmission = sterilize, handwashing, airflow control

Also influenza spread by coughing droplets

D. Wear a mask (control airflow)

6. Given the mode of transmission for influenza how would you break the chain of infection and prevent spread?

A. Antibotics
B. Wash hands
C. Disinfect the room
D. Wear a mask

A. Hepatitis B surface antigen (HBsAg)

7. What aspects of bacterial activity would be effective targets for pharmacologic treatment? Indicates Carrier State?

A. Hepatitis B surface antigen (HBsAg)
B. Hepatitis B core antigen (HBcAg)
C. Prothrombin time (PTT)
D. No way to distinguish the different forms of Hepatitis B

B. Pyelonephritis (Inflammation of the kidneys by bacteria)

8. What is the most likely complication of an untreated UTI?

A. Glomerulonephritis (acute inflammation of kidney by immune response)
B. Pyelonephritis
C. Fulminant UTI (sudden onset)
D. Urethritis (Inflammation of the urethra)

A. Oral antifungals

9. Treatment for tinea unguium must include

A. Oral antifungals
B. Topical antifungals
C. Both topical and oral antifungals
D. Nail removal and topical antifungals

A. CSF has high neutrophil count and high protein count

Neutrophils & HIGH protein

10. Which of the following scenarios is most likely i the CSF of a patient with bacterial meningitis>

A. CSF has high neutrophil count and high protein count
B. CSF has a high glucose level and high RBC
C. CSF has high neutrophil count and low protein count

C. Septic Shock (result of septicema)

11. What is a complication of infections where pathogens gain access to blood?

A. Septicemia (bacteria infection of the blood)
B. Bacteremia (the bacteria that causes septicema)
C. Septic Shock (result of septicema)
D. Chronic Infection

A. Inability to bind to host receptor cell

12. Which characteristics explains why some pathogens do not cause disease in humans?

A. Inability to bind to host receptor cell
B. High level of pathogenicity
C. Invasiveness
D. Potency

A. Fever

13. A specific type of Gram - bacteria contains endotoxins. What is likely the clinical manifestation if these bacteria become pathogenic?

A. Fever
B. Constipation
C. Leukopenia
D. Vomiting

Universal Precautions

14. This is a standard of health care that recognizes all blood and body fluids as potentially infected.

B. Antibacterial meds are not effective against fungi

15. With athlete's foot you use an antibotic cream for 3 days, why isn't it working?

A. Topicals take at least 7 days to work
B. Antibacterial meds are not effective against fungi
C. This requires oral antibotics
D. You are immunocompromised

D. Body aches, cough, sore throat

16. Which of the following sets of clinical manifestations is most characteristic of influenza?

A. Diarrhea, stomach cramping, vomit
B. Nasal congest., sneezing, watery eyes
C. Headache, sinus pressure, fever
D. Body aches, cough, sore throat

B. Sterilization of the room

17. Your room mate has influenza. All the following are appropriate measures to avoid infection except:

A. Immunization
B. Sterilization of the room
C. Hand washing
D. Avoid close contact

A. Fat emulsification & absorption are impaired during liver disease

18. Which of the following explains why a low fat diet is recommended for those with hepatitis?

A. Fat emulsification & absorption are impaired during liver disease
B. Weight gain will exacerbate hepatocyte destruction
C. With hep. are more vulnerable to the development of atherosclerosis
D. Ascites, a common complication of liver disease, can be alleviated by moderate weight loss


19. Which of the following types of viral hepatitis is not associated with transmission through contact of infected blood?

A, B, C, or D

D. Communicable disease are caused by infectious agents that live and reproduce in a human host

Infectious means it spreads!

20. All of the following describe communicable disease except...

A. All infectious disease are communicable
B. Communicable diseases spread person to person
C. Blood is a common carrier of communicable disease
D. Communicable disease are caused by infectious agents that live and reproduce in a human host

C. Pathogen recognized by host immune system

21. Which is not a mechanism by which a pathogen causes disease in humans?

A. Direct destruction of host cell
B. Interference with the host cell's metabolism
C. Pathogen recognized by host immune system
D. Exposure of host cell to toxins

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