Pathology

Study of disease

Etiology

Study of the cause of disease

Pathogenesis

Development of disease

Infection

Colonization of the body by pathogens

Disease

An abnormal state in which body is not functioning normally

Normal flora

Microorganisms that inhabit us but do not cause disease in or on an organism under normal conditions

Microbial antagonism

Competition between microbes

Three ways normal flora protect the host

• Occupying niches that pathogens might occupy
• Producing acids
• Producing bacteriocins

Probiotics

Live microbes applied to or ingested into the body

Intended to exert a beneficial effect

Symbiosis

The relationship between normal microbiota and the host

Three types of symbiosis

• Commensalism
• Mutualism
• Parasitism

Commensalism

One organism benefits, one organism unaffected

Mutualism

Both organisms benefit

Parasitism

One organism benefits at expense of another

Koch's Postulates

• Certain organisms cause certain diseases
• Same microorganism must be present in every case of the disease
• Must isolate the microorganism from the diseased host and grow in pure culture
• The microorganism must produce the same disease when inoculated into susceptible host
• The microorganism must be recovered from the inoculated host again in pure culture

Symptom

Change in body function that is felt by a patient

Sign

Change in a body that can be measured or observed as a result of a disease

Syndrome

A specific group of signs and symptoms that accompany a disease

Communicable disease

Spread from one host to another

Contagious disease

Easily spread from one host to another

Noncommunicable disease

Is not transmitted from one host to another

Incidence

Fraction of a population that contracts a disease during a specific time

Prevalence

Fraction of a population having a specific disease at a given time

Sporadic disease

Disease that occurs occasionally in a population

Endemic disease

Disease that is constant in a population

Epidemic disease

Disease that is acquired by many hosts in a short amount of time

Pandemic disease

Worldwide epidemic

Acute disease

Symptoms develop rapidly

Chronic disease

Disease develops slowly

Subacute disease

Symptoms between acute and chronic

Latent disease

Disease with period of no symptoms when patient is inactive

Herd immunity

Immunity in most of a population

Local infection

Pathogens limited to a small area of the body

Systemic infection

An infection throughout the body

Focal infection

System infection that began as a local infection

Bacteremia

Bacteria in the blood

Septicemia

Growth of bacteria in the blood

Toxemia

Toxins in the blood

Viremia

Viruses in the blood

Primary infection

Acute infection that causes initial illness

Secondary infection

Opportunist infection after a primary infection

Subclinical diseases

No noticeable sign or symptom

Predisposing factors for infection

• Climate and weather
• Chemotherapy
• Inherited traits
• Fatigue
• Age
• Lifestyle

Incubation period

Microorganism is present but host is not showing any sign of disease

Prodromal period

Short period of mild symptoms

Period of illness

Acute disease process

Period of decline

Signs and symptoms subside

Period of covalescence

Person regains strength and body returns to the pre-diseased state

Reservoirs of infection

Continual sources of infection

Ways to transmit a disease

• Contact
• Vehicle
• Vector

Transmission of disease through contact

• Direct: requires close association between infected and susceptible host
• Indirect: spread by formites
• Droplet: airborne

Transmission of disease through vehicle

• Transmission via an inanimate object:
• Food
• Water
• Air

Transmission of disease through vector

• Arthropods: fleas, ticks, mosquitos
• Mechanical: arthropod carries disease on feet
• Biological: pathogen reproduces in vector

Nosocomial infection

• Acquired as result of hospital stay
• MO in environment
• Compromised status of host
• Chain of transmission in hospital

How to control a nosocomial infection

• Cleanliness
• Hand washing
• Disinfection

Epidemiology

Study of when and where diseases occur and how they are transmitted

Morbidity

Incidence of a specific, notifiable disease

Mortality

Deaths from notifiable disease