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Microbiology Infection and Disease I: Morbidity and Pathogenesis

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