Flashcards - Pathogens and Infectious Diseases

Pathogen

A disease-causing organism

Virulence

The ability of a pathogen to cause harmful effects

Host

An organism that harbours/nourishes another (e.g. human)

Aerobic

Requires oxygen

Anaerobic

Does not require oxygen

Endotoxin

Toxin present inside a bacterial cell

Virion

Infectious form of a virus

Opportunistic pathogen

Only causes disease under favourable conditions (e.g. low immunity)

Normal Flora

Microbes found on the human body that normally cause no harm

Bacteria

Pathogenic or beneficial single-celled organisms with cell walls

Viruses

Non-living particles that infect host cells and require them to replicate

Prions

Infectious proteins with no DNA; difficult to destroy

Protozoa

Unicellular, often waterborne organisms, some are pathogenic

Fungi

Yeasts and molds; can be pathogenic in immunocompromised hosts

Helminths

Parasitic worms with complex life cycles

Gram-positive bacteria

Stain purple, simpler cell wall

Gram-negative bacteria

Stain red/pink, complex wall

Binary fission

Method of bacterial reproduction (splitting)

Lag phase

Slow growth, searching for food/environment

Log phase

Rapid exponential growth of bacteria

Stationary phase

Resources deplete, metabolic rate decreases

Death phase

Bacteria die off due to lack of nutrients

Mutation

Permanent change in bacterial DNA

Endospore

Tough, dormant form that helps bacteria survive harsh conditions

Adsorption

Virus binds to host cell using protein spikes

Penetration

Virus enters host via endocytosis or fusion

Uncoating

Virus sheds capsid and envelope, releasing genetic material

Synthesis

Host machinery copies viral DNA/RNA and makes proteins

Assembly

New viruses are put together

Release

New virions exit the cell via lysis or budding

DNA virus

Uses host cell for transcription/translation of DNA

RNA virus

Uses RNA to make proteins directly

Retrovirus

Uses reverse transcription (RNA → DNA → proteins), e.g. HIV

Candida albicans

A yeast that can cause oral/vaginal thrush (opportunistic)

Mycosis

Fungal infection; can be superficial to systemic

Protozoa cysts

Protective layer around protozoa, helps survive harsh environments

Helminth life cycle

Two hosts (one for larva, one for adult)

Ectoparasites

Insects on body surface (e.g. fleas, ticks, mites)

Epidemiology

Study of how diseases spread in populations

Reservoir

Where a microorganism normally lives (e.g. humans, animals, water)

Portal of exit

How pathogen leaves host (e.g. cough, blood)

Portal of entry

Route pathogen uses to infect new host (e.g. skin, respiratory tract)

Contact transmission

Direct or indirect contact between hosts or fomites

Droplet transmission

Large droplets carry pathogens short distances (cough/sneeze)

Airborne transmission

Pathogens spread via air >1 meter

Water-borne transmission

Pathogens in water (e.g. Giardia)

Vector transmission

Spread via insects (e.g. mosquitoes, fleas)

Mechanical vector

Surface transmission (e.g. fly landing on food)

Biological vector

Insect carries disease in its body and bites host

Opportunistic infection

Caused by normally harmless organisms during host vulnerability

Symbiosis

Two organisms living in close interaction

Mutualism

Both organisms benefit

Commensalism

One benefits, other unaffected

Parasitism

One benefits, host harmed

Transient flora

Microbes that temporarily reside on the body

Endogenous infection

Originates from the host's own flora

Exogenous infection

Comes from external environment

Congenital infection

Passed from mother to fetus

Infection

Multiplication of microbes causing disease

Disease

Harmful change in host physiology due to infection

Signs

Measurable changes (e.g. fever, rash)

Symptoms

Felt by the patient (e.g. dizziness)

Incubation period

Time from exposure to first symptom

Prodromal phase

Mild symptoms begin, microbe multiplying

Acute phase

Severe symptoms, peak microbe invasion

Decline phase

Microbes decrease, recovery begins

Convalescence

Host repairs damage

Escape from phagocytes

Microbes resist being eaten by immune cells

Antigenic variation

Microbes change surface proteins to evade detection

Concealment

Microbes hide inside cells or tissues (e.g. CNS, cysts)