Flashcards - Pathogens and Infectious Diseases

Pathogen

A disease-causing organism

The ability of a pathogen to cause harmful effects

Virulence

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

Host

Requires oxygen

Aerobic

Does not require oxygen

Anaerobic

Toxin present inside a bacterial cell

Endotoxin

Infectious form of a virus

Virion

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

Opportunistic pathogen

Microbes found on the human body that normally cause no harm

Normal Flora

Pathogenic or beneficial single-celled organisms with cell walls

Bacteria

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

Viruses

Infectious proteins with no DNA; difficult to destroy

Prions

Unicellular, often waterborne organisms, some are pathogenic

Protozoa

Yeasts and molds; can be pathogenic in immunocompromised hosts

Fungi

Parasitic worms with complex life cycles

Helminths

Stain purple, simpler cell wall

Gram-positive bacteria

Stain red/pink, complex wall

Gram-negative bacteria

Method of bacterial reproduction (splitting)

Binary fission

Slow growth, searching for food/environment

Lag phase

Rapid exponential growth of bacteria

Log phase

Resources deplete, metabolic rate decreases

Stationary phase

Bacteria die off due to lack of nutrients

Death phase

Permanent change in bacterial DNA

Mutation

Tough, dormant form that helps bacteria survive harsh conditions

Endospore

Virus binds to host cell using protein spikes

Adsorption

Virus enters host via endocytosis or fusion

Penetration

Virus sheds capsid and envelope, releasing genetic material

Uncoating

Host machinery copies viral DNA/RNA and makes proteins

Synthesis

New viruses are put together

Assembly

New virions exit the cell via lysis or budding

Release

Uses host cell for transcription/translation of DNA

DNA virus

Uses RNA to make proteins directly

RNA virus

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

Retrovirus

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

Candida albicans

Fungal infection; can be superficial to systemic

Mycosis

Protective layer around protozoa, helps survive harsh environments

Protozoa cysts

Two hosts (one for larva, one for adult)

Helminth life cycle

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

Ectoparasites

Study of how diseases spread in populations

Epidemiology

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

Reservoir

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

Portal of exit

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

Portal of entry

Direct or indirect contact between hosts or fomites

Contact transmission

Large droplets carry pathogens short distances (cough/sneeze)

Droplet transmission

Pathogens spread via air >1 meter

Airborne transmission

Pathogens in water (e.g. Giardia)

Water-borne transmission

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

Vector transmission

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

Mechanical vector

Insect carries disease in its body and bites host

Biological vector

Caused by normally harmless organisms during host vulnerability

Opportunistic infection

Two organisms living in close interaction

Symbiosis

Both organisms benefit

Mutualism

One benefits, other unaffected

Commensalism

One benefits, host harmed

Parasitism

Microbes that temporarily reside on the body

Transient flora

Originates from the host's own flora

Endogenous infection

Comes from external environment

Exogenous infection

Passed from mother to fetus

Congenital infection

Multiplication of microbes causing disease

Infection

Harmful change in host physiology due to infection

Disease

Measurable changes (e.g. fever, rash)

Signs

Felt by the patient (e.g. dizziness)

Symptoms

Time from exposure to first symptom

Incubation period

Mild symptoms begin, microbe multiplying

Prodromal phase

Severe symptoms, peak microbe invasion

Acute phase

Microbes decrease, recovery begins

Decline phase

Host repairs damage

Convalescence

Microbes resist being eaten by immune cells

Escape from phagocytes

Microbes change surface proteins to evade detection

Antigenic variation

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

Concealment