1.1 Bacteria and Diseases

Disease

• Result of an undesirable relationship b/w host and pathogen

• Interruption on the normal functioning of body part/s

Infection

Invasion of the body by pathogenic microorganisms

Symbiosis

Prolonged and close interaction b/w organisms of different species

Mutualism

Both organisms benefits from the relationship

Commensalism

One organism benefits from another organism without causing harm to it

Parasitism

One organism benefits from another organism and at the same time causes harm to others

Pathogenicity

Ability of an organism to produce disease “pathogenic”

Virulence

Describes the degree of pathogenicity of an organism or the degree to which an organism can produce disease

Contamination

Presence of unwanted materials where they should not be or at concentrations above the normal

Pollution

Presence of contaminants that can cause adverse biological effects to humans and communities

Bacteremia

Presence of bacteria in the blood

Septicemia

• Presence of actively multiplying bacteria in the blood

• Usually from a source of infection

• The condition is called sepsis

Pyemia

Presence of pus-producing bacteria in the bloodstream

Viremia

Presence of virus in the blood

Toxemia

Presence of toxins in the blood

Robert Koch

Most well-known contribution was providing that certain microorganisms caused specific diseases

Koch’s Postulates

the ability of the pathogen to grown in the laboratory using artificial culture media

Viruses

are obligate intracellular parasites that need to be grown in living cells

Chain of Infection

The development of an infectious disease is a consequence of the interaction among three components: etiologic agent, the host, and the environment

Transmission starts when the pathogenic organisms leaves it host or a reservoir through a portal of exit

A susceptible organism acquires the infection through a given mode of transmission, entering the body of the susceptible host through a portal of entry

Reservoir

Continual source of disease-producing microorganisms

Site where infectious agent normally resides and multiplies

• Animal

• Human

• Carriers

• Environment

Reservoirs of Infection

Animal Reservoir

zoonotic infections: from animal to humans

(ex. plague, and rabies)

Human Reservoir

from one individual to another

(ex. Respiratory pathogens & sexually transmitted infections)

Carrier

developed the disease, got well but still harbor the organism thereby transmitting them to others

• Asymptomatic or Healthy Carriers

• Incubatory Carriers

• Chronic Carriers

• Convalescent Carriers

Forms of Carriers

Asymptomatic or Healthy Carriers

those who are infected but do not manifest symptoms

Incubatory Carriers

transmit causative agents during incubation period of illness

Chronic Carriers

harbor organisms for months or longer after the patient developed the initial infection

Convalescent Carriers

develop disease, recovered but remain capable of transmitting causative agent

Environmental Reservoirs

Water, soil, and plants

Portal of Exit

Route by which an infectious agent exits its hosts and the site where infectious agent is commonly located or localized

• Direct Contact

• Indirect Contact

Mode of Transmission

• Person-to-person contact

• Droplet Spread

Direct Contact

Droplet Spread

pt. with respiratory tract infections Differentiated from aerosols by its larger size (> 5 microns)

• Airborne Transmission

• Vehicle Transmission

• Vector Transmission

Indirect Contact

Airborne Transmission

through dust or aerosols (ex. measles)

Vehicle Transmission

through media such as food, water, milk, or biologic substances such as blood and body secretions

Vector Transmission

insects that can transmit an infectious agent

• Mechanical Transmission

• Biological Transmission

Vector Transmission

Mechanical Transmission

passive transport of organism on the insect’s feet or other body parts

Biological Transmission

active transport of organisms as it enters the insect vector after the insect vector bites an infected person

Portal of Entry

• How infectious agents enters a susceptible host

• Provides access to tissue where the infectious agent can multiply

• More commonly, portal of exit is also the portal of entry

Host

Final link

• Constitutional or Genetic

• Immune Status

The host’s susceptibility is affected by several factors: