ch 13

Avenue of departure for pathogens to exit the host

Secretion

Excretion

Discharge

Sloughed tissue

Respiratory

Salvatory

Skin

The outer layer of skin and scalp is constantly being shed

Anal (fecal)

Some intestinal pathogens cause irritation in the intestinal mucosa that increases the motility of the bowel.

Resulting diarrhea provides a rapid exit for the pathogen

Helminth worms and eggs release eggs and cysts through the stool

Feces containing pathogens creates a public health problem

Urogenital

Agents involved in STIs leave the host in vaginal discharge or semen.

Source of neonatal infections that infect the infant as it passes through the birth canal.

Herpes simplex

Chlamydia

Candida albicans

Blood

portal of exit when it is removed or released through vascular puncture.

Blood-feeding animals are the most common transmitters of pathogens:

Ticks

Fleas

Mosquitoes

Exogenous

originating from outside of the body

enviornment

another person

animal

Endogenous

already existing in the body

normal biota

previously silent infection

skin

sites of entry

Nicks

abrasions

punctures

tiny

inapparent

conjunctiva

Gastrointestinal

Entry through food, drink, or other ingested substances.

Adapted to survive digestive enzymes and abrupt pH changes

Respiratory

gateways

oral cavity

nasal cavity

Continuous mucous membrane covering the upper respiratory tract, sinuses, and auditory tubes

Microbes often transferred from one site to another

Urogenital

Sexually transmitted infections (STI's)

Entry points through the skin or mucosa of:

Penis

external genitalia

vagina

cervix

urethra

Placenta (TORCH)

exchange organ

Formed by maternal and fetal tissues–Separates the blood between mother/fetus

Permits diffusion of dissolved nutrients and gases

A few microbes cross the placenta and are spread by the umbilical vein into the fetal tissues.

Other infections are transmitted perinatally as the child passes through the birth canal.

TORCH: common infections of the fetus and neonate.

Toxoplasmosis

Other diseases:

syphilis

coxsackievirus

varicella-zoster virus

AIDS

chlamydia

Rubella

Cytomegalovirus

Herpes simplex virus

Exoenzymes

Secreted by pathogenic bacteria, fungi, protozoa, and worms

Break down & inflict damage on tissues

Dissolve host’s defense barriers

promote the spread of microbes into deeper tissues

Toxins

Specific chemical product that is poisonous to other organisms

Endotoxin

Not actively secreted

Shed from the outer membrane

Only found in gram-negative bacteria

Exotoxin

Secreted by a living bacterial cell to the infected tissues

Many types

Phagocytes

White blood cells that engulf and destroy pathogens using enzymes and antimicrobial chemicals

Antiphagocitic factors

Virulence factor used by pathogens to avoid phagocytes

Circumvent some part of the phagocytic process

Virulence factors

Structures, products, or capabilities

allow a pathogen to cause infection in the host

Adaptations that a microbe uses

invade

establish itself in a host

Determine the degree of tissue damage that occurs

Vertical transmission

Transmission from parent to offspring

ovum

sperm

placenta

milk

Horizontal transmission

Spread from one infected individual to another

Vehicle

Any inanimate material commonly used by humans that can transmit infectious agents

Fomite

An inanimate object that harbors and transmits pathogens

Not a continuous source of infection

Communicable

Infected host can transmit the agent and establish infection in another host

Direct

Kissing

Droplets

Peripheral

Indirect

Fomite

Food

Water

Waste

Air

Contagious

Highly communicable

Noncommunicable

Does not arise through transmission from host to host

Vectors

live animal that transmits an infectious agent from one host to another

Majority of vectors are arthropods (insects)

Biological

Actively participates in a pathogen’s life cycle

Site of multiplication or end of life cycle

Mechanical

Not necessary to the life cycle of an infectious agent

Merely transport it without being infected

Fimbrae

Capsule

Subtopic

Spikes

Patterns of Infection

Localized

Microbe enters the body and remains confined to a specific tissue

Boils

Fungal skin infections

Warts

systemic

When an infection spreads to several sites and tissue fluids, usually in the bloodstream.

Viral:

measles

rubella

chickenpox

AIDS

Bacterial:

brucellosis

anthrax

typhoid fever

syphilis

Fungal:

histoplasmosis

cryptococcosis

Infectious agents can travel by means of nerves or cerebrospinal fluid

Focal

Exists when the infectious agent breaks loose from a local infection and is carried to other tissues

Examples:

Tuberculosis

Streptococcal pharyngitis:

scarlet fever

Toxemia:

infection remains localized, toxins are carried through the blood to the target tissue

Mixed

Several agents establish themselves simultaneously at the infection site

synergistic infections

microbes cooperate in breaking down tissue

other mixed infections

one microbe creates an environment that enables another microbe to invade

Polymicrobial diseases:

gas gangrene

wound infections

dental caries

human bite infections

Primary

initial infection

Secondary

Primary infection is complicated by another infection caused by a different microbe

Acute

Come on rapidly

Have short-lived effects

Chronic

Progress and persist over a long period of time

Disease signals

Signs

Any objective evidence of disease as noted by an observer

Symptoms

Subjective evidence of disease as sensed by the patient

Syndrome

A disease identified or defined by a certain complex of signs and symptoms

Infections that go unnoticed:

Asymptomatic

Subclinical

Patient experiences no symptoms or disease and does not seek medical attention

Inapparent

Host is infected -> no disease

Inflammation

Earliest symptom of disease

Edema

Accumulation of fluid in afflicted tissue

Granuloma

Abscess

Blood Infection Signs

Leukocytosis

Increase in white blood cells

Leukopenia

Decrease in white blood cells

Septicemia

General state

microbes are multiplying in the blood and are present in large numbers

Bacteremia

Small numbers of bacteria are present in the blood

not multiplying

Viremia

Presence of viruses in the blood, maybe actively multiplying

Persistence of Pathogen

Reservoir

A permanent place for agent to reside

Source

Distinct from a reservoir

Carrier

An individual who inconspicuously shelters a pathogen and can spread it to others without knowing

Latency

A dormant state

microbe can periodically become active and produce recurrent disease

Sequelae

Types of Carriers

Asymptomatic

infected but shows no symptoms of disease

Incubating

infected but shows no symptoms of disease

microbes are multiplying

Convalescent

recuperating patients without symptoms

they continue to shed viable microbes and convey the infection to others

Chronic

individuals who shelter the infectious agent for a long period after recovery from latency of the infectious agent

Passive

medical and dental personnel who must constantly handle contaminated materials and risk picking up pathogens mechanically and accidentally transferring them to other patients

Stages of Infection

Incubation

Initial contact appearance of first symptoms

Prodromal

earliest notable symptoms of infection appear

Invasion

Agent multiplies at high levels and exhibits greatest virulence

Convalescent

Patient responds to infection and symptoms decline