Microbiology Chapter 14

Pathology

study of a disease

Etiology

cause of a disease

Pathogenesis

the manner in which the disease develops

Infection

establishment and multiplication of a pathogenic microorganism on or within a host, which may or may not lead to overt disease

Infectious disease

occurs when an infection results in any change in the state of health

• May exist in the absence of a detectable disease

• Disease may result when a particular type of microorganism locates in a aprt of the body where it is not normally found

Human Microbiome Project

analyzes relationships between microbial communities on the body and human health

Normal microbiota (normal flora)

permanently colonize the host and do not cause disease under normal conditions

Normal microbiota protect host by

1. Competing with invading microbes for nutrients and space

2. Producing substances harmful to invading microbes

3. Affecting pH and available oxygen

Microbial antagonism (competitive exclusion)

• is a competition between microbes

• Normal microbiota play a role in the development of the immune system

Transient microbiota

may be present for days, weeks, or months, and then disappear

Factors influencing Normal Microbiota

1. Nutrients

2. Physical and chemical factors

3. Body’s defenses against microbes

4. Age, diet, nutritional status, geography, personal hygiene, living conditions, occupation, lifestyle 

Symbiosis

relationship between microorganisms and the host

Commensalism

the microorganism benefits and the host is unaffected

Mutualism

Both the microorganism and the host benefit

Parasitism

one organism benefits at the expense of the host, typically causing harm

Koch’s Postulates

Helps determine etiology (cause) of the disease

• pathogen is present in every case

• isolated and grown in pure culture

• must cause disease into laboratory animal

• isolated from incoulated animal and shown to be the original organism

Exceptions of Koch’s postulates

1. some pathogens can cause several diseases

2. some pathogens can cause disease only in humans

3. some microbes have never been cultured

4. several pathogens may cause the same signs and symptoms

Symptoms

 subjective changes in body function that are felt by a patient as a result of disease

• Not apparent to an observer

Signs

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

Syndrome

 a specific group of signs and symptoms that accompany a disease

Communicable disease

a disease that is spread from one host to another

Contagious diseases

diseases that are easily and rapidly spread from one host to another

Noncommunicable disease

a disease that is not spread from one host to another

• Tetanus, legionallosis, valley fever

Sporadic disease

diseases that occurs only occasionally

Endemic disease

disease constantly present in a population

• Expected

Epidemic disease

disease acquired by many people in a given area in a short time

• Flu, excess

Pandemic disease

worldwide epidemic

Herd Immunity

Immunity in most of the population

• When established, the disease is limited to sporadic cases among the small number of susceptible individuals in the population

• 95% of people need to be vaccinated, other 5% will be protected 

Incidence

number of people who develop a disease during a particular time period; new cases

Prevalence

number of people who have disease at a specified time, regardless of when it first happened

• Takes into account both old and new cases

Severity

the presence and extensiveness of a disease in the body and its ability to cause death

Duration

average time that individuals that have a disease from diagnosis until they are either cured or die

Acute disease

symptoms develop rapidly but has a short duration

Chronic disease

symptoms develop slowly, likely to last for a long period

Subacute disease

intermediate between acute and chronic

Latent disease

causative agent is inactive for a time but then activates and produces symptoms

Local infection

pathogens are limited to a small area of the body

Systemic (generalized)  infection

 an infection spread throughout the body, often via the blood and lymph

Sepsis

 toxic inflammatory condition/response arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection

Bacteremia

bacteria in the blood; can be temporary or harmless

Septicemia

also known as blood poisoning, growth of bacteria in the blood; bacteria are proliferating in the blood

Toxemia

toxins in the blood

Viremia

viruses in the blood

Primary infection

 acute infection that causes the initial illness

Secondary infection

 opportunistic infection after a primary (predisposing) infection

• Not the same as coinfection (two organisms at the same time)

Subclinical infection

 no noticeable signs or symptoms (inapparent infection, asymptomatic infection)

Incubation period

 interval between initial infection and first signs and symptoms

• Can still spread

Prodromal period

short period after incubation; early, mild nonspecific symptoms

• Symptoms begin

Period of illness

disease is most severe

Period of decline

signs and symptoms subside

Period of convalescence

body returns to its prediseased state; recovery

Reservoirs

continual sources of infection

Human reservoir

People with signs and symptoms OR

Carriers: individual who harbor an infectious agent w/o having any observable signs or symptoms

Animal Reservoirs

Zoonoses: diseases primarily in wild and domestic animals that can be transmitted to humans

• Ex. rabies, lyme disease

Nonliving or environment reservoirs

Soil and water

• Ex. naturally harbor fungi, Clostridium botulinum, C. tetani

Direct contact transmission

requires close association between the infected and susceptible host

Congenital transmission

transmission from mother to fetus or newborn at birth

Indirect contact transmission

spreads to a host by a nonliving object called a fomite

• Ex. door knob (not a reservoir because you can’t replicate)

Direct Droplet Deposition

transmission through infectious respiratory particles which travel a short distance and land directly on a person’s eyes, nose, or mouth

Vehicle transmission

transmission by an inanimate reservoir

• airborne

• waterborne

• foodborne

Vector transmission

animals that carry pathogens from one host to another

Mechanical Transmission: arthropods carries pathogen on its feet

Biological Transmission: pathogen reproduces in the vector; transmitted via bites or feces

Healthcare-Associated Infections (HAIs) or nocosomial infection

acquired while recieving treatment in a health care facility

• Microorganisms in the hospital

• Weakened status of the host

• chain of transmission in a hospital

• Ex. Catheters, ventilators, bloodstream, surgical site, gastrointestinal

Compromised host

an individual whose resistance to infection is impaired by disease, therapy, or burns

1. Broken skin or mucous membranes

2. Suppressed immune system

3. Invasive procedures and devices

Universal precautions

• Assumes all human blood, body fluids, and tissues are potentially infectious

• Designed to reduce the transmission of microbes in healthcare and long-term care settings

• Protects patients, residents, staff, visitors from contact with pathogens

Emerging Infectious diseases

diseases that are new or changing, increasing in incidence, or showing a potential to increase in the near future

• Most (75%) are zoonotic, primarily of viral origin, and likely to be vector-borne

Contributing factors to emerging infectious diseases

• Generic recombination between organisms

• Evolution of existing organisms

• Widespread use of antibiotics and pesticides

• Inherent genetic instability of some microbes

• Changes in global climate and weather patterns

• Modern transportation

• Insect vectors transported to new areas

• Ecological disaster, war, expanidng human settlement

• Public health failure

• Bioterrorism

Epidemiology

 the study of where and when diseases occur and how they are transmitted in populations

• Determined etiology of a disease

• Identify other important factors and patterns concerning the spread of disease

• Assemble data and graphs to outline incidence of disease

• Predict the probability than an infection will spread through a population

• Explore various methods for controlling a disease

John Snow (1848-1849)

mapped in occurrence of cholera; identified that contaminated water from a specific pump was the source

Ignaz Semmelweis (1846-1848

handwashing decreases incidence of puerperal sepsis

Florence Nightingale (1858)

collected and organized data on patterns of epidemic typhus, mortality rates, and living conditions; showed that improved sanitation decreases the incidence of the disease

Descriptive epidemiology

collection and analysis of data

• focuses on identifying patterns of disease distribution by time, place, and person, without delving into causation

Analytical epidemiology

analyzes a particular disease to determine its probable cause or risk factors

Clinical trial

test and control group; placebo vs drug

Morbidity

occurrence of a specific notifiable disease

• Morbidity rate: number of people affected 

Mortality

deaths from notifiable disease

• Mortality rate: number of deaths

Notifiable infectious disease

diseases in which physicians are required to report occurence

CDC

Collects and analyzes epidemiological information in the US