HESI Science Portion (Biology): Infectious Diseases

What is Cycle of Infection?

Starts with the presence of a pathogen (a disease causing organism) and an environment that allows it to grow and multiply. Conditions must allow it to be passed on (transmission) from one organism (host) to another.

What is Direct Transmission?

Occurs when the infection is passed from one infected host to another.

What is Indirect Transmission?

Its when an infection is passed on through an infected object or when the person touches a contaminated object.

What is a Fomite?

An inanimate object that can spread a pathogen from one person to the next.

What must occur in order for any mode transmission to happen?

There must be a way for the pathogen to enter the new host, and the host must be susceptible to the infection.

What factors must occur in order for an infection transpire?

Infectious Agent;

(1st) Reservoir Host, (2nd) Portal of Exit, (3rd) Method of Transmission, (4th) Route of Entrance, and (5th) Susceptible Host.

What is a Reservoir Host?

An kind of living host. They are carriers of the disease and are oblivious that they have been infected.

Ex. Humans, insects, or even an animal

What is a Portal of Exit?

Describes a method in which the microorganism leaves the reservoir host to continue on to infect another organism, which is known as susceptible host.

Ex. Mouth, Nose, Blood, Urine, Vaginal or Seminal Fluid, Feces, and even the Eyes

Describe how Droplets are a Mode of Transmission?

Droplets (mucous) particles may be transmitted when the reservoir host sneezes or coughs. Reservoir host does not need to be in close proximity to the susceptible host as droplet particles can travel several feet in the air

Describe how Direct Contact is a Mode of Transmission?

Bloodborne transmission may occur by direct mode if blood from the infected reservoir host comes with the susceptible host’s mucous membranes or when the integrity of the skin is compromise.

Most common bloodborne pathogen transmitted in healthcare setting: Hepatitis B (HBV), Hepatitis C (HCV), and Human Immunodeficiency Virus (HIV)

Describe how Airborne Transmission is a Mode of Transmission?

The spread of microorganisms can take place when miniscule particles are dispersed from the respiratory system of the reservoir host and inhaled by another individual.

Ex. Influenza, Tuberculosis, or even Chickenpox when spread. People may also become ill after the inhalation of bacteria or fungi within water that is contaminated.

Describe how Vehicle-Borne Fomite is Mode of Transmission?

Contaminated or Infectious inanimate objects can transfer multiple diseases to other people.

Example of Fomites: Doorknobs, Drinking Fountains, Water Glasses, Pens, Toys, Books, and Shopping Carts

Example of Vehicle-Borne Fomites (medical setting): Instruments used in clinical care settings such as tools for surgical procedures or patient care. Also Blood, Biopsy specimens, or Organs and Tissues used for transplants or grafting material

Describe how Vector-Borne (Mechanical or Biological) Transmission is a Mode of Transmission?

This transmission occurs when pathogens are spread from one living organism to another. Vectors are commonly insects that act as couriers that transport bacteria and other common organism from one individual to the next.

Ex. Mosquitos, Flies, Ticks, and Fleas

What is Portal of Entry?

As microorganisms exits the reservoir host, it must have an entrance portal to infect the susceptible host.

Ex. Similar to exit routes and include any Mucous Membrane such as Nose, Mouth, Eyes, Rectum, or Vagina

What is a Susceptible Host?

An individual that is unable to fight off an infection and will enable a cycle to continue when this individual passes the pathogen onto another person.

Examples how they get infected: Strength of the immune system, Overall health, Level of nourishment, Age, Hygiene practices, and Living conditions

What is Gram-positive or Gram-negative status?

Most Bacteria are Gram-negative stains (red) or Gram-positive (purple) although a few cannot be identified by staining.

• Common Gram-positive cocci (round) bacteria: Streptococcus pneumoniae, Staphylococcus aureus, Enterococcus

• Common Gram-positive bacilli (rods) bacteria: Corynebacterium diphtheriae, Listeria monocytogenes, Bacillus anthracis

• Common Gram-negative cocci (round) bacteria: Neisseria gonorrhoeae, Neisseria meningitides, Moraxella catarrhalis

• Common Gram-negative bacilli (rods) bacteria: Haemophilus influenzae, Legionella pneumophila, Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori

What is Taxonomic status?

Taxonomy is based on the genera and species of a bacterium, but this can be confusing because some names have changed or two are used. Genome sequencing should standardize identification.

What is Anaerobic/aerobic status?

Some bacteria are strictly anaerobic, but very few are strictly aerobic. Those that have flexibility and can grow in either aerobic or anaerobic conditions are called facultative.

What is Usual environment?

Bacteria are classified according to where they usually reside as flora or where they usually cause infection.

What is Virulence Factor?

Bacteria vary widely in virulence. Some are actively invasive but others only cause opportunistic infections.

What are the 4 phases of bacterial Growth

Lag Phase, Log Phase, Stationary Phase, and Death Phase.

What happens during the Lag phase of bacterial growth.

Microorganisms become accustomed to their new environment. Little to no growth

What happens during the Log phase of bacterial growth.

Bacteria logarithmic, or exponential, growth begins; multiplication is the most rapid and constant

What happens during the Stationary phase of bacterial growth.

Rate of Multiplication slows down due to the lack of nutrients and build up of toxins. Bacteria are constantly dying so the numbers actually remain constant.

What happens during the Death phase of bacterial growth.

Cells numbers decrease as growth stops and existing cells die off

What is Viruses?

Sub-microscopic and generally considered non-living because they lack cell structures. They consist of nucleic acid, single or double-stranded DNA and/or RNA (the genome), encapsulated in a protein coating called capsid.

What is the purpose of Viruses?

Is to reproduce, but they require a host cell with a protein receptor to which a virus must bind to penetrate the cell membrane

What happens to viruses during the Lytic Cycle?

The virus forces the cell to manufacture proteins and new genomes. After new viral particles form, the cell ruptures, releasing the viruses.

What happens to viruses during the Lysogenic Cycle?

The virus integrates the DNA of the host and as the cell replicates, the virus replicates with it. The virus remains dormant until it activates and begins the lytic cycle.

What are Fungi?

They vary widely from one-celled microorganisms to multi-celled chains that are miles long. Fungi are used to make antibiotics, but they can also cause infection and disease.

What are the 2 common classifications of Fungi?

Molds (including mushrooms) and Yeast

As microorganisms, how does fungal infections invade the body?

Through sinuses, the mouth, the respiratory system, and the vagina

What do fungal infections include?

Histoplasmosis, Blastomycosis, and Coccidioidomycosis