Bacti Lecture 4

Pathology

Study of disease

Etiology

Cause or origin of a disease

Pathogenesis

Development and progression of a disease

Infection

Invasion/colonization of the body by a pathogen

Disease

Abnormal body state where normal functions are impaired

Does infection always cause disease?

No

Are all microbes pathogenic?

No

Microbiome

Community of microorganisms living in a specific environment

When does the microbiome begin developing?

Immediately after birth

Sources of microbiota acquisition (how are microbes acquired)

microbiota can be acquired from the food an animal eats and from contact with other animals or humans.

Resident microbiota

Microbes that remain on the host for life

Transient microbiota

Microbes present temporarily for days weeks or months

When can normal microbiota cause disease?

When in abnormal body sites or when the host is immunocompromised

Microbial antagonism

Good microbes outcompete pathogens

How does microbiota protect the host?

Compete for nutrients produce harmful substances to pathogens and alter pH/oxygen

Symbiosis

Relationship between host and microbiota

Commensalism

One organism benefits and the other is unaffected

Mutualism

Both organisms benefit

Parasitism

One organism benefits at the host's expense

Opportunistic pathogen

Normally harmless microbe that causes disease in weakened hosts

Purpose of Koch's postulates

Associate a specific microbe with a specific disease

Exception to Koch's postulates

Some pathogens cause multiple diseases

Another exception to Koch's postulates

Some pathogens infect only humans

Why are some bacteria exceptions to Koch's postulates?

Some cannot be cultured in the lab

Symptoms

Subjective changes felt by the patient

Examples of symptoms

Pain fatigue inappetence

Signs

Objective observable changes caused by disease

Examples of signs

Fever swelling paralysis

Syndrome

Group of signs and symptoms accompanying a disease

Communicable disease

Disease spread from one host to another

Contagious disease

Disease that spreads easily and rapidly

Non-communicable disease

Disease not spread between hosts

Incidence

Number of new cases during a given time period

Prevalence

Total number of cases at a specified time

Sporadic disease

Disease occurring occasionally

Endemic/enzootic disease

Disease constantly present in a population

Epidemic/epizootic disease

Disease affecting many individuals in a short time in one area

Pandemic/panzootic disease

Worldwide disease outbreak

Acute disease

Rapid onset short duration

Chronic disease

Slow development long duration

Latent disease

Inactive period followed by symptom activation

Localized infection

Infection confined to one tissue/site

Systemic infection

Infection spreads through tissues or bloodstream

Focal infection

Local infection spreads to other tissues

Sepsis

Toxic inflammatory condition from spread of microbes/toxins

Bacteremia

Bacteria in the blood

Septicemia

Growth of bacteria in the blood

Toxemia

Toxins in the blood

Viremia

Viruses in the blood

Primary infection

Initial acute infection

Secondary infection

Opportunistic infection following a primary infection

Subclinical infection

Infection without noticeable signs or symptoms

Predisposing factors for disease

Factors increasing susceptibility to infection

Examples of predisposing factors

Age nutrition fatigue genetics climate lack of vaccination gender

Incubation period

Time between infection and first signs/symptoms

Prodromal period

Early mild vague symptoms after incubation

Period of illness

Stage where disease is most severe

Period of decline

Symptoms decrease as immune system overcomes infection

Convalescence period

Recovery stage where body returns to normal

Reservoir of infection

Continual source of infectious agents

Animal reservoir

Infected animals that transmit disease

Carrier animal

Animal with inapparent or latent infection

Human reservoir

Humans that transmit zoonotic diseases

Fomite reservoir

Non-living reservoirs like soil water or feed

Direct contact transmission

Spread through close contact between infected and susceptible host

Vertical transmission

Mother to fetus/newborn transmission

Indirect contact transmission

Spread through fomites/non-living objects

Direct droplet transmission

Spread through airborne droplets directly to host

Indirect droplet transmission

Infection from lingering airborne particles

Vehicle transmission

Transmission through inanimate reservoirs

Examples of vehicle transmission

Waterborne foodborne airborne

Vector transmission

Spread of pathogens by arthropods

Mechanical vector transmission

Passive carriage of pathogens on vector body

Biological vector transmission

Pathogen reproduces in vector before transmission

Nosocomial infection

Infection acquired in a healthcare facility

Causes of nosocomial infections

Hospital microbes (microbes found in hospitals, weakened host, chain of transmission (lots of germ spread)

Compromised host

Host with weakened resistance due to disease therapy or burns

How can nosocomial infections be controlled?

Hand washing aseptic technique limiting hospital stay

Iatrogenic infection

Infection acquired during medical treatment