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