BIOL 271 Module 6

Biology 271 Microbiology

viruses

small, non-cellular particles that cannot replicate unless inside a living host cell.

cannot replicate on their own.

obligate intracellular parasites.

neither prokaryotic nor eukaryotic.

all viruses have two basic components:

genomic material.

capsid.

genomic material

comprised of either DNA or RNA

capsid

a membrane-like protective structure that contains the genetic material, similar to the nucleus of a eukaryotic cell

prokaryotic and eukaryotic genomes

contain a double-stranded DNA genome

viral genomes

either double or single-stranded.

found in circular or linear arrangements.

pandoravirus

houses the largest known viral genome

large genome exceptions

pandoravirus (about 2.5 million).

megavirus (about 1.25 million).

mimivirus (about 1.2 million).

envelope

additional membrane.

surrounds the capsid.

derived from the host cell membrane and serves as an additional barrier to the external environment.

naked or non-enveloped virus

surrounded by the protein capsid.

animal viruses

are enveloped

plant or bacteria-infecting viruses

are non-enveloped

virion composition

influence the shape and appearance of the virus

differences can be observed using

electron microscope (EM)

paramyxoviruses

causative agent of measles and mumps.

contain a single-stranded linear genome and fuse with the host cell membrane to initiate entry and viral replication.

enveloped.

spherical.

and about 100-150 nm in diameter.

orthomyxoviruses

causative agent of the flu.

contain eight segments of RNA and enter the host cell via endocytosis.

enveloped.

spherical.

and about 100-150 nm in diameter.

viruses require

host cell enzymes in order to successfully replicate

outside of a host

no metabolism.

dormant.

dormant

virus takes up neither energy nor nutrients

viral envelope

interact with and promote successful entry into the host cell

nucleocapsid enters the cytoplasm

uncoats (unravels) and releases the viral genome into the cell

bacteriophage (or phage)

virus that infects bacteria.

possess an icosahedral (20-sided polygon) capsid head group, containing the viral genome, and a helical tail.

tail fibers

fibrous extensions or legs that aid in binding host cells

attached to the tail are tail fibers

viruses that infect either animals or plants

two forms of replication:

lytic.

lysogenic.

lytic

bacteriophages replicate within the host bacteria until it lyses, or ruptures, effectively destroying the host bacterial cell

viral titer

quantitative amount of virus present in the culture.

allows researchers to carefully and effectively plan infectious experiments.

too much virus will cause it

immediately overwhelm and kill the host cells

too little virus will cause it

too long to generate detectable levels of newly produced virus

lysogenic (or temperate) bacteriophages

exist in a non-replicative state such that its viral genome is integrated into the host genome

prophage

upon integration into the host genome, the phage is referred to as.

host cell replicates its DNA, it also replicates the viral DNA.

2 types of immunity:

active immunity.

passive immunity.

active immunity

body is exposed to a disease (or antigen) and the immune system produces antibodies to fight the infection.

process results in immune cells "remembering" the antigen for a time in case there is re-infection.

acquired naturally when someone is infected with a pathogen (natural immunity).

vaccine-induced (or artificial) immunity, when antigen is introduced via vaccination (also known as immunization).

passive immunity

receives antibodies to fight the infection without their own immune system developing them.

newborn acquires antibodies from the mother via the placenta or breast milk.

individual can gain passive immunity from injection of antibodies gathered from donated blood or produced recombinantly. 

measles (rubeola)

virus: paramyxoviridae.

enveloped, singl-stranded RNA virus.

epidemiology: extremely contagious.

transmission: respiratory droplets.

signs/symptoms: fever, sore throat, cough, koplik’s spots, maculopapular rash.

treatment/prevention: MMR (measles, mumps, rubella) vaccine.

mumps (epidemic parotitis)

virus: paramyxovivrus.

enveloped, linear, single-stranded RNA.

epidemiology: endemic in areas with low MMR vaccination (Africa, South Asia, and Middle East).

transmission: respiratory droplets and saliva.

signs/symptoms: non-specific vital symptoms, swelling of parotid salivary glands, orchitis, and meningitis.

treatment/prevention: MMR (measles, mumps, rubella) vaccine.

rubella (German measles)

virus: togaviridae.

enveloped, single-stranded RNA.

transmission: aerosols from respiratory tract 1 week before and after the rash appears.

signs/symptoms: pink maculopapular rash starts at face and travels downward lasting 3-7 days, fever, swollen lymph nodes, muscle/joint aches, runny/stuffy nose.

treatment/prevention: MMR (Measles, Mumps, Rubella) vaccine.

major complication: congenital rubella syndrome (CRS)

chickenpox (varicella virus or zoster virus)

virus: herpesviruses.

enveloped, linear, double-stranded DNA.

transmission: airborne droplets (sneezing/coughs) or contact with blisters of an infected individual.

signs/symptoms: small, itchy, fluid-filled blisters that can form anywhere on the body.

diagnosis and treatment/prevention: supportive (itchy relief) perscribed an antiviral medication.

shingles (herpes zoster)

virus: varicella-zoster virus (VZV).

enveloped, linear, double-stranded DNA virus.

epidemiology: exposed to developing chickenpox during the contagious stage.

signs/symptoms: severe pain, tingling, or burning localized when the rash will later present.

treatment/prevention: over-the-counter pain medications, anti-viral drug, acyclovir.

smallpox (variola virus)

virus: orthopoxvirus: variola major and minor.

enveloped, linear, double-stranded DNA virus.

epidemiology: highly contagious with 30% death rate; eradicated in 1980.

transmission: respiratory droplets or contact with formites (contaminated objects).

signs/symptoms: fever, fatigue, rash (vesicles to pustules that feel solid, and looked domed-shaped with a dimple) on face that spreads to limbs then the trunk.

diagnosis and treatment/prevention: vaccination.

polio (also known as poliomyelitis)

virus: picornaviridae.

non-enveloped, single-stranded RNA virus.

most significant small virus (30 nm).

epidemiology: endemic in Afghanistan and pakistan.

transmission: respiratory droplets and fecal-oral route.

signs/symptoms: flu-like symptoms (sore throat, fever, fatigue, nausea/stomach pain, headache), small portion have paresthesia, meningitis, and paralysis.

influenza

virus: orthomyxoviridae family (influenza A, B, and C).

enveloped, single-stranded RNA.

epidemiology: endemic, can lead to epidemics and pandemics; seasonality (late fall to spring).

transmission: respiratory droplets and fomites.

signs/symptoms: fever/chills, body aches, coughing/sneezing.

treatment/prevention: antivrals in high-rise patients and vaccination.

coronaviruses (SARS-CoV-2 COVID-19)

virus: coronavirdae family.

enveloped, single-stranded RNA.

epidemiology: originated in wuhan, China and started a global pandemic in late 2019.

transmission: respiratory droplets.

signs/symptoms: asymptomatic, flu-like symptoms, lossof taste or smell, nausea/vomiting, diarrhea, life-threatening acute respiratory distress syndrome (ARDS), respiratory failure, or cytokine stolm.

human immunodeficiency virus (also known simply as HIV)

virus: retroviridae.

enveloped, linear, single-stranded RNA.