Chapter 2 Basic Concepts of Infectious Disease

adhesions, environmental factors, and susceptibility of pathogens

3 means of colonization

Nutrition and Exercise

Good nutrition and moderate exercise enhances immune system

Info

Illness may also be spread during the prodromal phase

Reservoir of Infection

an animal or an environment that normally harbors the pathogen Rocky Mountain spotted fever: Tick is both reservoir and vector Eastern equine encephalitis (EEE): Bird is the reservoir and mosquito is the vector

Pandemic

an epidemic that spreads worldwide influenza virus bubonic plague HIV

Pathogen

any bacterium, virus, fungus, protozoan, or worm (helminth) that causes disease. Basically, it's a disease causing microbe.

Parasite

any organism that colonizes and harms its host

To cause a pandemic, the organism must:

be easily transmitted from person to person; not kill host too rapidly; cause an extended prodromal period

Broad

can infect many different animals in addition to humans; salmonella enteric server Typhimurium

Narrow

can only infect humans; Salmonella enterica serovar Typhi

Opportunistic Pathogens

cause disease only in a compromised host

Normal Microbiota

collection of bacteria, archaea, and eukaryotic microbes usually colonizing our bodies

Syndrome

collection of signs and symptoms that occur together and signify a particular disease or infection fever and rash together signify something

Incubation Period

depends on many factors, such as the infectious dose, the host's health status, and the pathogenicity of the microbe

The infection cycle can be _____ or ______

direct or indirect

Disease

disruption of the normal structure or function of any body part, organ, or system that can be recognized by a characteristic set of symptoms and signs (Does not imply it is from bacteria or a virus)

Morbidity

existence of a disease state and the rate of incidence of the disease; death is not required for these stats, only illness

Group IV

extremely dangerous pathogens for which no treatments or vaccines are available

Secondary Infection

follows a primary infection (Haemophilus influenza after viral influenza infection)

Underlying Non-Infectious Diseases or Conditions

genetic defects in immune system, chronic infections, diabetes, alcohol use, vascular insufficiency, caner

Group II

greater pathogenic potential but vaccines and treatments are readily available

Age

greatest susceptibility amongst the very young (under 3) and very old (over 60)

Host Hygiene and Behavior

hand washing/hand sanitizers proper cooking of food sexual activity

Occupation

health care workers, laboratory personnel, agricultural workers, hunters, prostitutes

Host genetic makeup

host receptors to which bacteria and viruses bind

Immune Status and Immunopathogensis

immune response to pathogen, immunosuppressant drugs

Nosocomial Infection

infection acquired during a hospital stay (MRSA - Methicillin-resistant Staphylococcus aureus) Refer to Table 2.1 for more information

Primary Infection

infection in a previously healthy individual (syphilis)

Iatrogenic Infection

infection transmitted from a health care worker to a patient (some Staphylococcal septicemias)

Zoonotic Disease

infections that normally afflict animals but can be transmitted to humans; typically contracted after encountering the animal reservoir bubonic plague (Yersinia pestis) Lyme Disease (Borrelia burgorferi) Rocky Mountain Spotted Fever (Rickettsia Rickettsii)

Ectoparasite

insects such as fleas or lice that lie on the surface of the body, or fungal parasites like T. rubrum. Athlete's foot is caused by ectoparasite fungus Trichophyton rubrum. T rubrum lives on the surface of the host. It does not have the molecular tools that would allow it to grow inside of a host.

Group I

little to no pathogenic potential

Epidemic

many cases developing in a community in a short time; unusual not necessarily a large population

Sequelae

pathological consequences that occur after the infectious disease has resolved

Convalescence

period after symptoms disappear and patient recovers

Septicemia

presence and replication of bacteria in blood (bubonic plague)

Bacteremia

presence of bacteria in blood, usually transient, no replication (streptococcus mutans during dental procedure)

Toxemia

presence of toxins in the blood (diphtheria, toxic shock syndrome)

Viremia

presence of viruses in the blood (HIV)

The Centers for Disease Control (CDC)

publishes a weekly report called the Morbidity and Mortality Weekly Report that discusses current outbreaks, statistics, and other health topics

Biosafety Groups

ranked by the severity of disease and ease of transmission

Mutualism

relationship in which community members and host both benefit

Group III

serious or lethal human disease for which vaccines and treatments may be available

Prodromal Phase

short period of vague symptoms and malaise; can serve as a warning of more symptoms to come but may not be noticed

Symptom

something that can be felt only by the patient ((pain and malaise(general tired feeling))

Sign

something that can be observed by a person examining a patient (runny nose or rash)

serovar

subclass within a species

Chronic

symptoms develop gradually over weeks or months and are slow to resolve (TB)

Acute

symptoms develop rapidly/generally go away pretty quickly (step throat)

Sub-acute

symptoms take longer to develop than acute but arise more quickly than chronic (bacterial endocarditis)

Information

After the initial infection, the numbers of organisms (or virus particles) rise in the body until the immune system recognizes that an invader is present. This is the prodromal phase. Symptoms start to develop at the same time the immune system begins attacking the organism or virus. During the illness phase, the pathogen reaches peak numbers. Once the immune system becomes more efficient at killing the pathogen, its numbers decrease (decline phase). The immune system remains ready during convalescence but the ability to attack the same invader will wane over time.

Immune Avoidance

Altered surface antigens (serve as markers); some bacteria can change those antigens so immune system cannot recognize it Secretion of "all is well" signals; Tells immune system to relax Apoptosis signals; tells body to kill off own cells

Info

An organism need not be endemic to an area to cause an epidemic The Third Pandemic of plague (1855-1959) started in China and spread to many other areas of the globe (carried by people and rats as they traveled). In India alone, an estimated 12 million people died of plague over 30 years spanning the late 19th and early 20th centuries. Surprisingly few organisms are capable of causing pandemics. Influenza virus, Yersinia pestis, and HIV are some that are able (See Table 2.3)

Modes of Transmission

Cycles of infection can be simple or complex

Info on Groups

Examples (refer to Table 2.4) Group I: Bacillus subtilis, Escherichia coli K-12, Saccharomyces spp. Group II: Bordetella pertussis, Clostridium spp., Helicobacter pylori, Staphylococcus aureus Group III: Bacillus anthracis, Francisella tularensis, Mycobacterium tuberculosis Group IV: Ebola virus, Hantavirus, Marburg virus

Illness phase

Fever is a sign often seen during the illness phase. It is a protective mechanism to fight infection. High temperatures help the immune system function better and can inhibit microbial growth

Latent

Infection occurs after an acute episode. Organism is present but symptoms are not. (Cold sores due to Herpes Virus) Refer to Table 2.1 for more information

Information

Infectious agents can be transmitted horizontally from one member of a species to another by a variety of means: direct contact between people indirect transmission by fomites or insect vectors vehicle transmission by air, food, water Vertical transmission is passage from parent to offspring during birth.

Obtaining nutrients from the host

Iron uptake (lactoferrin, transferrin); if iron is bound up, bacteria cannot get to it; but bacteria has the ability to take the iron

Info

Many infections never progress to the active disease state bed case the host immune response disables the pathogen before it can cause signs and symptoms

Are all infectious diseases known to us?

New diseases are continually emerging or re-emerging Malaria spread in South America due to deforestation Pig farms built next to fruit bat habitat led to spillover of Nipah virus from bats to pigs and then to humans SARS virus was intorduced to Asia due to hunting of civet cats

Endemic

always present in a community and seen at a low rate; often harbored in an animal reservoir

Latent State

Organism is within a host but cannot be detected by culture

Direct Contact Transmission

Organisms may spread directly from person to person touching, kissing, sexual intercourse aerosol

Indirect Transmission

Organisms may spread indirectly through an intermediary, which may be living or non-living fomites (inanimate objects: door knob, desk, pencils, anything lying around) food and water vector (ticks, mosquitos)

Endoparasite

Organisms that live inside the body. Filariasis (elephantiasis) is caused by the worm Wuchereia bancrofti, which enters the lymphatic system and blocks lymphatic circulation.

How are diseases spread?

Pathogens must pass from one person or non-human animal to another if a disease is to spread

Info

Reservoirs are crucial for the survival of a pathogen and serve as a source of infection Reservoirs do not necessarily exhibit disease A carrier is a special type of reservoir Example: Neisseria meningitidis is maintained in a population by infecting the nasopharynx of unsuspecting hosts whose immune systems keep the bacterium out of the bloodstream A simple sneeze from a carrier can aerosolize the pathogen and transfer it to a susceptible host.

Direct Contact

Rhinovirus (common cold) can be passed from person to person through an aerosol of secretion particles called droplet nuclei

Host Range

Some organisms can infect only certain animals (hosts) and produce disease

Decline

Symptoms begin to subside; fever resolves

End and echo parasite

Two types of parasites?

Illness Phase

Typical symptoms and signs of the disease appear and fever may be present; acme is the point where disease is most severe

Infectious Disease

a disease caused by a microorganism (bacterial, viral, or parasitic) that can be transferred from one host to another

Mortality

a measure of how many patients have died from a disease

Virulence

a measure of the degree of severity of disease

Infection

a pathogen or parasite enters or begins to grow in/on a host. Does not imply overt disease (just began to grow in or on you). May go unnoticed and is often temporary.

Carrier

a person who harbors a potential disease agent but does not have signs or symptoms of disease

Colonization

ability of a microbe to stay affixed to a body surface and replicate

Invasion

ability of some pathogens to actually enter and live inside a host cell

Primary Pathogens

able to breach defenses of a healthy host. If you are a good, strong, and healthy person, it can still cause problems.

Attachment

adhesions and their specific receptors

Incubation Period

organisms can be transmitted to others during this time, even though there are no signs or symptoms

Pathogenicity

the ability of an organism to cause disease. This can be the genetic makeup of a host and pathogen, location in/on the host's body (some are perfectly happy and healthy where they are, but can be harmful if moved somewhere else), or host immune system (if it can overcome our immune system, it is pathogenic).

Lethal Dose 50% (LD50)

the number of bacteria or virus particles (visions) required to kill 50% of an experimental group of animal hosts

Infectious Dose 50% (ID50)

the number of bacteria or visions needed to cause disease symptoms in 50% of an experimental group of hosts

Infection cycle

the route of transmission an organism takes infect additional hosts

Skin

through epithelial surfaces

Parenteral

through injection into the bloodstream insect bits or wound/needle sticks

Fecal-oral

through mucosal surfaces of gastrointestinal tract

Urogenital

through mucosal surfaces of genital and urinary tracts

Respiratory

through mucosal surfaces of respiratory tract

Incubation Period

time after the microbe first infects a host but before the first signs of disease