Infectious Diseases

What is the relationship between humans and microorganisms?

Humans and microorganisms live in a delicate balance

What is symbiosis?

A close relationship between two different organisms

What is mutualism?

A relationship in which both organisms benefit

What is commensalism?

A relationship in which one organism benefits and the other is not significantly affected

What is parasitism?

A relationship in which one organism benefits while harming the host

What is an obligate relationship?

A relationship in which an organism depends on another organism for survival or reproduction

What is a facultative relationship?

A relationship in which an organism can live independently or in a particular relationship

What is normal microbiota?

Microorganisms that normally live on or in the human body

What is another name for normal microbiota?

Normal flora

What is colonization?

The presence and growth of microorganisms on or in the body without necessarily causing disease

Does colonization always cause disease?

No

What is an infection?

When a microorganism invades or establishes itself in host cells or tissues and triggers a host response

What does infection include besides the microorganism itself?

The host reaction and reactions to substances the microorganism produces or secretes

What is the chain of infection?

The sequence of steps that allows an infectious agent to spread to a susceptible host

What are the steps in the chain of infection?

1. Infectious agent

2. Reservoir

3. Portal of exit

4. Mode of Transmission

5. Portal of Entry

6. Susceptible Host

What are infectious agents?

Micro-organisms capable of causing disease or illness

What are examples of infectious agents?

• Bacteria

• Fungi

• Parasites

• Prions

What are reservoirs?

Place in which infectious agents live, grow, and reproduce

What are example of reservoirs?

• People

• Water

• Food

What are portals of exit?

Ways in which infectious agents leaves the reservoir

What are examples of portals of exit?

• Blood

• Secretions

• Excretions

• Skin

What are modes of transmission?

Ways in which the infectious agent is spread from the reservoir to a susceptible host

What are examples of modes of transmission?

• Physical

• Contact

• Droplets

• Airborne

What are portals of entry?

Ways in which the infectious agent enters the susceptible host

What are examples of portals of entry?

• Mucous membrane

• Respiratory system

• Digestive system

• Broken skin

What are susceptible hosts?

Individuals that may have traits that affect their susceptibility and severity of the disease

What are examples of susceptible hosts?

• Immune deficiency

• Diabetes

• Burns

• Surgery

• Age

What is an infectious disease?

A disease caused by an infectious microorganism

What is an acute infection?

An infection that develops quickly and usually lasts a relatively short time

What is a chronic infection?

An infection that persists for a long time

What is a subacute infection?

An infection that develops or progresses more slowly than an acute infection

What is a primary infection?

The initial infection caused by a pathogen

What is a secondary infection?

An infection that develops after or because of another infection or condition

What is an example of a secondary infection after influenza?

Haemophilus influenzae pneumonia following influenza

How can a burn lead to a secondary infection?

Damage to the skin barrier allows microorganisms to enter the body

What is a latent infection?

An infection in which the infectious agent persists without causing ongoing noticeable symptoms

What is pathogenicity?

The ability of a microorganism to cause disease

What is pathogenesis?

The process by which a disease develops

What is a primary pathogen?

A microorganism that can cause disease in a healthy person

What is another name for a primary pathogen?

An overt or true pathogen

What is an opportunistic pathogen?

A microorganism that causes disease when host defenses are weakened or conditions allow it

Where can opportunistic pathogens come from?

Normal microbiota or environmental organisms

What is a nonpathogen?

A microorganism that does not normally cause disease

What is virulence?

The degree of harm or severity of disease a pathogen can cause

What are examples of virulence factors?

• Capsules

• Toxins

• Adhesions

• Enzymes

What are the five stages of infection?

• Incubation

• Prodromal

• Illness

• Decline

• Convalescence

What is the incubation stage?

The period between infection and the appearance of symptoms

What is the prodromal stage?

The early warning period of an illness or condition that happens right before the main, obvious symptoms show

What is the illness stage?

The stage when characteristic symptoms are most noticeable

What is the decline stage?

The stage when symptoms begin to decrease

What is the convalescence stage?

The recovery period when the body returns toward normal

What is a carrier?

A person who harbors an infectious agent and can spread it to others

When can a person become a carrier during disease?

During the early stage of disease or during recovery

What is a chronic carrier?

A person who continues to harbor and potentially transmit an infectious agent over a long period

Which organisms or infections are examples of chronic carriage in the notes?

• Staphylococcus aureus including MRSA

• HBV

• HCV

• Typhoid fever

What is a reservoir of infection?

A place or host where an infectious agent normally lives and is maintained

What are the main types of infectious disease reservoirs?

• Humans

• Animals (zoonotic)

• Insects (arthropods)

• Nonliving — water, soil, food

What is a zoonosis?

An infectious disease that can be transmitted from animals to humans

What is a fomite?

An object that can carry infectious agents and help spread them

What are examples of fomites?

• Facial tissues

• Drinking glasses

• Doorknobs

How can fomite transmission be reduced?

Appropriate disinfection and cleaning

How do respiratory aerosols and droplets spread infection?

Infectious particles are released into the air and reach another person's respiratory tract

What can help reduce respiratory transmission?

Appropriate face masks and other infection-control measures

What is fecal-oral transmission?

Spread of pathogens from feces to the mouth

How can fecal-oral transmission be reduced?

Handwashing and proper food and water hygiene

How can direct contact spread infection?

Through contact with infected secretions and mucous membranes

What are examples of direct-contact transmission?

• Sexual contact

• Body fluid splashes

• Childbirth

What is parenteral transmission?

Transmission through routes that bypass the body's usual barriers

What are examples of parenteral transmission?

• Blood transfusion

• Organ transplant

• Dialysis

What does percutaneous transmission mean?

Transmission through the skin

What is transplacental transmission?

Transmission of an infectious agent across the placenta from mother to fetus

What can transplacental transmission cause?

Congenital infection

What is a vector?

An organism that carries and transmits an infectious agent

What is a mechanical vector?

A vector that physically carries a pathogen without the pathogen developing or multiplying inside it

What are examples of mechanical vectors?

House flies and cockroaches

What is a biological vector?

A vector in which the infectious agent develops or multiplies as part of its transmission cycle

What are examples of biological vectors?

Mosquitoes, ticks, fleas

What are arboviruses?

Viruses transmitted by arthropods

Which viruses are examples of arboviruses in the notes?

Yellow fever virus, Dengue virus, West Nile virus

How can zoonoses spread from animals to humans?

Through bites

What is epidemiology?

The study of infectious disease patterns and spread in populations

How does epidemiology differ from studying an individual infection?

It focuses on disease in populations rather than only in one person

What determines whether an infectious agent persists in a community?

The availability of susceptible people who lack immunity

What does immunologically naïve mean?

Having no previous immune protection against a particular infectious agent

What does seronegative mean in this context?

Having no detectable antibodies against the infectious agent being tested

How can vaccination help create herd immunity?

It increases the number of immune people and reduces opportunities for transmission

What is herd immunity?

Population-level protection that reduces the spread of an infectious agent

What are incidence and prevalence used to measure?

The occurrence of infection in a population and the speed of spread

What is incidence?

The number of new cases occurring in a population during a specified period

What is prevalence?

The total number of existing cases in a population at a given time or during a period

How does the route of infection affect disease spread?

It affects how the agent enters the body and how easily it can be transmitted

How can the number of infectious particles shed affect transmission?

Shedding more infectious particles can increase the chance of transmission

How does the incubation period affect the spread of infection?

It affects how long it takes symptoms to appear and how transmission may occur before diagnosis

What is communicability?

The ability of an infected person or organism to transmit an infectious agent to others

What factors can cause infections to be concentrated in a geographic area?

• Vectors

• Location of resevoirs

• Proximity and crowding

• Poor sanitation

What is an outbreak?

An increase or occurrence of disease linked to a particular area or population

What are examples of outbreaks listed in the notes?

• Hepatitis A

• Mpox

• Ebola

• Marburg

What is an endemic disease?

A disease that is regularly present in a particular population or geographic region

What are examples of endemic diseases listed in the notes?

Malaria and rhinovirus infections

What is an epidemic?

A large abrupt outbreak that occurs over a larger population and geographic area for a short period of time