How are viruses different than bacteria?
-size: 10-500nm (much smaller than bacteria)
-replication: multiply only within a living cell
-nucleic acid: DNA or RNA - never both
-enzymes: few if any enzymes
-lack ribosomes and enzymes for harvesting energy
How do classify viruses?
Naked - outer coat consists only of the protein capsid
Enveloped - have additional covering over the capsid protein
Name some virus shapes
-Isometric
-Helical
-Complex (Isometric head with long, helical sheath or tail)
How would we culture viruses?
-Use of animal cell cultures
-fertilized chicken eggs
-living animals
What types of nucleic acids do they contain?
DNA or RNA -
DNA may be linear or circular, either double-stranded or single stranded.
RNA is usually single stranded but a few viruses contain double -stranded RNA.
What s a bacteriophage?
A virus that attacks bacteria
Define "host range
The number of different bacteria that phage can infect. (usually limited to single bacterial species for a single phage)
What are the steps involved in Bacteriophage replication?
1-Adsorption/Attachment
2-Penetration
3-Transcription/Translation
4-DNA/Protein Synthesis
5-Assembly/Maturation
6-Release
Explain the difference between lytic and lysogenic cycles
Lytic Cycle - phage multiply inside cell, producing numerous progeny (aka productive cycle)-phage lyse cell.
Lysogenic Cycle- phage integrate into host genome (aka Lysogenic state)
What is a "prophage" ("temperate infection")
Phage DNA that is integrated into the genome of a host.
Some bacteria must be infected with a phage before they develop toxins. Name some examples.
corynebacterium diphtheriae - causes diptheria
Clostridium botulinim - causes botulism
Streptococcus pyogenes - causes scarlet fever
Salmonella - causes food poisoning
Vibrio cholerae - causes cholera
Caused by Lysogenic Conversion - the change in propert
Animal viruses have some differences in comparison to bacterial viruses. List some.
...
What is an "envelope"?
a lipid bilayer that covers the capsid - similar to the plasma membrane of the host.
What is a "capsid"?
the protein coat surrounding the nucleic acid of viruses
What is a prion?
An infectious agent that causes neurodegenerative disease; consists of protein similar in amino acid sequence to a normal protein in the body. Consists of protein and no nucleic acid.
Animal viruses penetrate cells differently than bacteriophage. How do they accomplish this?
The entire virus (not just DNA or RNA) enters cell through endocytosis -
Bacteriaphage will land on bacteria & inject the DNA (Fusion Protein)
What does a "fusion protein" on viruses do?
The envelope of the virus fuses with the plasma membrane of the host after attachment - it then releases the nucleocapsid directly into the cell
Persistent infections
An infection in which the virion or its genome is continually present with or without disease.
Chronic Infection
A persistent infection in which the virion can be demonstrated at all times, with or without symptoms. (ex. Hepatitis B)
Latent Infection
A persistent infection in which the infectious agent is present but not active. The agent can reactivate and then cause symptoms. (ex. Herpes Simplex Virus 1 & 2)
Acute Infections
Infection in which the symptoms appear soon after the pathogen is introduced. Symptoms are short lived. (ex. measles)
Zoonotic Infection
Transmitted from animal to human via animal vector
What is a vector?
any living organism that can carry a disease-causing microbe; most commonly arthropods such as mosquitoes and ticks.
Ecosystem
an environment and the organisms that inhabit it
Symbiosis
the living together of two dissimilar organisms or symbionts
Parasitism
an association in which one organism, the parasite, derives benefit at the expense of the other organism, the host. (one way - causes harm)
Mutualism
an association in which both partners benefit. (two way - both benefit)
Commensalism
an association in which one partner benefits but the other remains unharmed. (one way, but don't cause harm)
Normal Microbiota
the population of microorganisms routinely found growing on the body surfaces of healthy individuals
Transient flora
microbes that inhabit the body temporarily (usually picked up from a surface ex. tissue, door knob)
Opportunistic pathogens
a microorganism or virus that causes disease only when introduced into an unusual location or into an immunocompromised host. (a microbe able to cause disease only when the body's innate or adaptive defenses are compromised or when introduced in an unusua
Infection
colonization by a pathogen on or within the body (when microbe enters body and starts to cause harm)
Secondary Infection
an additional infection that occurs as a result of the primary infection
Sign
objective evidence of disease such as rash, pus formation and swelling (measurable)
Symptom
subjective effects experienced by patient such as pain & nausea, weakness, achiness etc.
Subclinical Infection
symptoms either do not appear or are mild enough to go unnoticed
Focal Infection
infection is localized or limited to a small area (ex: boil)
Incubation Period
the interval between introduction f an organism to a susceptible host and the onset of illness
Hemolysin
membrane damaging toxin that lyse red blood cells (toxin that destroys RBC's)
Compromised Host
a host with weaknesses or defects in the innate adaptive defenses
What causes antibiotic-associated colitis?
treatment with antibiotic that supresses normal intestinal microbiota and allows overgrowth of toxin producing strains of clostridium difficile
What is the lipid A part of the bacterial cell wall responsible for?
toxicity of Gram-Negative (responsible for the adverse effects of LPS (lipopolysaccharide - endotoxin)
What factors would influence the outcome of an infection?
Various characterisitics of the host
-Health
-Age
-Sex
-Lifestyle
-Ethnicity
What mechanisms do viruses and bacteria use to avoid host defenses?
-killing complement
-inhibit formation of MAC
-Avoid phagocytosis
--avoid the phagocyte
--destroy the phagocyte
--destroy the ability of attraction
--live inside phagocytes
Epidemiology
Study of the spread, control and prevention of disease in populations
Pathology
study of the disease
Communicable Disease & Examples
disease that spreads from one host to another. (contagious disease) ex: colds, measles
Non-Communicable Disease & Examples
disease that is not caught from another host (diabetes)
Incidence
number of new cases in a specific time period in a given population at risk
Pandemic
a worldwide epidemic
Epidemic
a disease or other occurrence that has a much higher incidence than usual (peak in a short time frame)
Endemic
a disease or other occurrence that is constantly present in a population
Prevalent
total number of existing cases both old and new in a given population at tisk
Reservoirs - Examples
The natural habitat of a pathogen; sum of the potential sources of an infectious agent. (ex. humans, animals, soil or water)
Droplet Transmission
inhaling respiratory droplets (ie close proximity when someone sneezes or coughs)
Direct Contact
When a person physically touches another (ex. handshake or sexual intercourse)
Fomites
non-living method of communication of disease - kleenex, door knob, dirty syringe, clothing (indirect transmission)
Carriers
individual that may harbor infectious agents for months or years and continue to spread pathogens , even though they show no signs or symptoms of the disease
Nosocomial Infection
hospital acquired infection
When is a physician required to report a disease to the US Center for Disease Control?
immediately if they ever see a case of a notifiable/reportable disease
Notifiable/Reportable Diseases
List of disease that require a physician to notify CDC - typically diseases are of relatively high incidence or otherwise a potential danger to public health.