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Any deviation from the normal functioning
of the body (healthy)

Disease Cont'd

An abnormal or unhealthy state


a diseased state or condition

A Morbid state

Signs and Symptoms
Damage to host cells
Decrease cell function
Increased immune response
Suppression of the immune system


the study of how diseases are caused

Infectious disease (or infection)

Disease caused by microbes/pathogens
2 categories

(1.) Communicable

Disease that is spread from one host to another (i.e. from person to person).

Contagious (Infectious)

disease that is very easily spread from one person to another.


not spread from one host to another.


Infections caused by normal flora
Often occurs when microbe is introduced into a sterile area of the body or is moved from its normal location in the body.


exposure to toxins


Pre-formed Toxins


Toxin produced as a result of infection

Nosocomial Infections

Infectious diseases that are acquired and/or develop in hospitals

Nosocomial Infections (Cont'd)

Usually refers to infections acquired by patients during hospitalization
But also refers to infections acquired by medical personnel

(1) Genetic/Inherited

genetic disorders passed from parent to child

(2) Congenital diseases

structural and functional defects present at birth
*Microbial exception: several microbes (bacteria, protozoa, viruses) can cause congenital diseases

(3) Degenerative diseases

disorders affecting one or more body systems that develop as a patient ages
*Microbial exception: Infection with prions

(4) Nutritional deficiencies

diseases that result from the lack of specific nutrients; may be due to poor diet or may be inherited as a genetic defect.
*Microbial exception: helminths and parasite load

(5) Endocrine diseases

due to excesses or deficiency in hormones
*Microbes respond to hormones

(6) Mental diseases

mostly due to emotional or psychological factors, including biochemical imbalance.
*Microbial exception: herpes and schizophrenia

(7) Immunological diseases

diseases of the immune system; include allergies, autoimmune disease, immunodeficiency,
*Microbial exception: HIV infection and AIDS

(8) Neoplastic diseases

abnormal cell growth that leads to the formation of tumors (benign or malignant)
*Microbial exception: HPV and cervical cancer; EBV and Burkitt's lymphoma

(9) Iatrogenic disease

caused by medical procedures or treatments, surgical errors, and/or drug interactions;
*Microbial exception: nosocomial infections

(10) Idiopathic diseases

cause of disease is unknown


The study of how diseases are spread.
Examines the frequency and distribution of disease and other health-related problems within human populations


The study of diseased states
The study of the structural and functional manifestations of disease

Pathology (Cont'd)

A branch of medicine that examines the nature of disease, how the disease is manifested, and changes to the body that occur as a result of disease

Morbidity Signs

objective evidence of disease
characteristics of a disease that can be observed by someone else; objective

Morbidity Sign Examples

runny nose
pus formation

Morbidity Symptoms

subjective evidence of disease
characteristics of disease that can only be determined [experienced] by the patient

Morbidity Symptoms Examples

Shortness of breath
Sore throat
Malaise (discomfort)


combination of signs and symptoms that occur together and are indicative of a disease or abnormal condition

Syndrome (Cont'd)

A complex of symptoms indicative of a morbid state


permanent damage to tissues as a result of infection and disease

Signs of Inflammation

Pain (soreness)
Edema (swelling)
Granulomas (small mass or nodule of inflamed tissue)
Abscesses (A collection of pus in a tissue, cavity or confined area)


The process of determining the cause of the disease
Commonly involves the use of chemical or immunological tests


The projected outcome of a disease
The prospect of recovery from a disease
The recovery success (or a lack thereof) is based on the nature (pathology) of the disease


any organism that obtains its nutrients from another living organism.
Often an obligate relationship


any organism that provides an ecological niche for a parasite or contributes to its survival.

The actions of the parasite and the actions of the immune system both

Contribute to the disease.


the parasite is not free-living and is metabolically dependent on the host for survival.


the parasite lives within the host cell


the parasite lives in the extracellular spaces between cells, on the cell surface, etc.

Extracellular Parasites

Parasites can directly damage host cells.


will ingest and digest host cells, resulting in cellular damage to organs and tissues

Intracellular Parasites

Parasites can indirectly result in damage to host cells

Nutrient Depletion

Parasite load within the cell causes cell death

Immune Cells Destroy

infected host cells


any substance or agent that is toxic to the cell; often results in cell death


death of a cell by lysis; often a result of osmotic changes


damage to cells


Any disease causing microorganism

True or Primary Pathogens

can cause infection and disease in healthy people

Opportunistic Pathogens

can infect host only when immune defense is weakened


The ability of a microbe to cause disease

Pathogenicity depends on

Physical/structural factors
e.g. capsule, outer membrane
Biochemical factors
Proteins (toxins)
Genetic factors
e.g. resistance genes

Pathogenicity (Cont'd)

Is related to virulence


The capacity of a pathogen to invade and harm a host

Virulence Factors

determined by factors associated with the pathogen

Virulence (Cont'd)

Is an important indicator of disease progression after infection by a pathogen

Virulence factors


Exogenous (pathogen sources)

Exogenously acquired infections results from encounters with pathogens in the environment

Endogenous (pathogen sources)

Endogenously acquired infections are caused by pathogens or potential pathogens in or on the body.


The process whereby microbes invade and multiply within cells of the host

Infection Alternate Definition

Deviation from a healthy state that is caused and maintained by microorganisms

Infections can be



patient actively exhibits signs and symptoms

Clinical infections have

Two Main Infections

Acute infection

is severe and short
symptoms present abruptly

Chronic infection

Signs and symptoms (S/S) make take a long time to develop
S/S are persistent and lasts over long periods


The microbe persists in host tissues for long periods of time; the disease alternates between an acute and a subclinical state.


the patient lacks signs or symptoms.

Subclinical (Cont'd)

May not be observed by clinical examination, although laboratory tests may confirm the presence of pathogens.
May not be detectable by laboratory tests

Subclinical (other names)

Also called asymptomatic, subvert or inapparent.

Local Infection

infection of specific tissues (e.g. warts)

Focal infection

spread from one localized area to other localized areas (e.g. tuberculosis)

Systemic (generalized) Infection

microorganism circulates throughout body and infect many different tissues; e.g., measles, typhoid


Signs of Infection in the blood

Septicemia (also called blood poisoning)

multiplying microbes in the blood; presence of toxins


the presence of bacteria in the blood; may be actively multiplying


the presence of viruses in the blood; may be actively multiplying


the presence of fungi or fungal spores in the blood; may be actively multiplying


the presence of toxins in the blood

Signs of Infection On Skin

Lesions (sores)
Pus formation (purulence)
Discoloration (hypo- or hyper- pigmentation)
Itchiness (pruritus)
Bruising (ecchymosis)

Signs Of Infection Systemic

Vomiting (emesis)
Vision loss (blindness)
Double vision (diplopia)


Infection resulting in pus formation


Infection resulting in fever; fever-inducing


pathogen that induces fever


infection resulting in congenital defects


pathogen that damages the developing fetus


developing in utero or soon after birth

The Progress of an Acute Infection


Incubation period

Time from the first exposure to the pathogen to the time symptoms become apparent
Length of incubation period varies considerably for some microorganisms

length of the incubation stage

Pathogenicity of the infecting microbe
Infective dose
Health of the patient
Generation time of the pathogen
Site of infection

Prodromal stage

A short period before specific symptoms set in where the patient feels general discomfort (headache, joint pain, muscle ache)
Not all illnesses have a prodromal period

Period of Invasion

Pathogen multiplying, producing toxins, etc.
Signs and symptoms can include cough, rash, diarrhea, etc.
Immune system is responding to pathogen


The gradual return to a normal or healthy state
The patient's immune system, over time, has been able to contain and eliminate the infective agent

Signs of disease subside

High level of immunological molecules, e.g. antibodies
The patient either recovers or the disease is fatal

Convalescent period (Recovery)

Signs and symptoms abate and patient starts to feel better
Affected tissues and systems are repaired


the amount of damage the infecting microbe did to the body
The condition of the patient's immune system before and during infection
The nature of the pathogen

Primary (initial) infection

host is colonized by pathogens

Secondary infection

once host is infected, other pathogens will colonize the host

Polymicrobial infection

also referred to as a mixed infection

Polymicrobial infection (Cont'd)

simultaneous establishment of infection by several different microbes
e.g. bacteria and fungal spores in a puncture wound

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