Viruses

virus

submicroscopic particles whose genomes are elements of nucleic acid that replicate inside living cells using the cellular synthetic machinery for production of progeny virions (either RNA or DNA, never both)

The professor does not think that viruses are alive

The professor's old buddy John henry thought viruses were the most evolved living life form

host range

range of animal species and tissue cells that virus can infect (can be broad or limited)

capsomeres

morphological subunits from which virus capsid is built

the professor thinks of capsomeres as Legos or building blocks

capsid

protein shell or coat that encloses nucleic acid genome

envelope

lipid-containing membrane that surrounds some viruses

naked virus

virus without an envelope

nucelocapsid

capsid together with enclosed nucleic acid

virion

complete infective virus particle (synonym)

incomplete virion

virion without nucelic acid (empty capsid)

pseudovirion

during viral replication, capsid sometimes encloses host nucleic acid rather than viral nucleic acid; looks like ordinary virus particles when observed by electron microscope, but do not replicate

provirus

viral DNA that is integrated into host cell chromosome in latent state and must be activated before it is transcribed, leading to production of progeny virions; transmissible from parent cell to daughter cells

Virion or virus (bacteriophage)

Consist of nucleic acid surrounded by protective protein coat (capsid)

virions are very small in size

Smallest virus = 20nm

Largest virus = 300nm

E.coli = 1000nm

Contain very few genes due to small size (4 up to 200 vs. 3000 for E.coli)

Contain either DNA or RNA, never both.

DNA can be either single-stranded or double-stranded

RNA can be either single-stranded or double-stranded

Most DNA viruses contain all their genetic information in a single linear molecule

RNA viruses can be linear or contain segmented genomes, which have several different RNA molecules in their capsid. Each one carries the same or different genetic information

Viruses lack cellular components necessary to generate energy and synthesize proteins

Contain few enzymes. Only those involved with entry into cells and replication of their own nucleic acid. Therefore, viruses can only multiply inside living cells

viruses contain a minimum amount of genetic information

Info to make its special protein coat

Info to assure replication of its own chromosome

Info to move the virions in and out of the host cell

helical (column) or spherical

Shape of virus is determined by shape of capsid:

capsomeres

Each capsid is composed of many identical units:

Some viruses have an additional lipid membrane - envelope

Usually acquired from the cytoplasmic membrane of an infected cell. The structure is similar. Double layer of lipids

Just inside the lipid envelope is the protein matrix

Spikes project from the envelope and attach the virion to the host cell. Protein and glycoprotein

Papovaviridae, Adenoviridae, and Iridoviridae

classification of DNA viruses that infect vertebrates ((like humans and animals) are:

Papovaviridae

Naked virion structure

1 molecule, circular double-stranded DNA

human papillomavirus associated with genital and oral carcinomas

Adenoviridae

Naked virion structure

1 molecule, double-stranded DNA

causes tumors in animals

Iridoviridae

Naked virion structure

1 molecule, double-stranded DNA

no known human pathogens; only animal pathogens

zika virus

is a single stranded RNA virus

microcephaly where the baby's head is much smaller than it should be

If a pregnant woman gets bitten by an infected mosquito, it can impact the baby and cause:

very warm mosquitoes and typically do not show up in Indiana

The mosquitoes that carry the Zika Virus are:

attachment, penetration, transcription or translation, replication, assembly, and release

Viral replication includes:

attachment

Phages attach to host cell receptors

phage = viral

Penetration

Viral nucleic acid enters the host cell

Lysozyme (located on the tip of the tail) lyses the cell wall

The tip of the tail opens, and linear DNA in the head passes through the channel and is injected through the cell wall into the interior of the cell

Only the nucleic acid, not the entire Virion enters

transcription or translation

Phage DNA is transcribed, leading to the production of specific proteins

Part of DNA is transcribed into mRNA

mRNA is translated into proteins that are specific for infecting the cell (phage-induced proteins). One such protein is a nuclease that degrades the DNA of the host cell. Host DNA is not transcribed, only phage DNA

replication

Phage DNA copies itself and structural proteins are synthesized

Assembly

Phage DNA and protein assemble to form mature virions

Some steps involve a self-assembly process

Release

Virions are released from the host cell

Lysozyme is coded by phage DNA. Lysozyme digests the host cell wall from within. Cell lysis and release of phage virions (up to 200)

Laboratory Diagnosis of Viral Infections

Cell culture - Living cells (ex. chick embryos)

Serological techniques - Detecting antigens and antibodies

Direct detection of antigen from the specimen - Polymerase chain reaction (PCR)

Molecular methods - Live or dead viruses

Viral Specimens types

Upper respiratory- n/p swabs, nasal, throat

Lower respiratory- endo trach asp., bronch washes, BAL (bronchioalveolar lavage), lung washes, lung and bronchial biopsies

Eye swabs

Stools or rectal swabs

Body fluids - cerebrospinal fluid, bone marrow, serum, blood, and saliva

Viral Specimens collection and storage

Virus isolation and direct detection must be collected within the first few days of the onset of the illness

Specimens should not be held at ambient temperature. Should be delivered to the lab on ice and stored at 4°-8°C (refrigerator) for no more than 1-3 days before excessive loss of infectivity

Freezing at -70°C or below will preserve indefinitely

refrig-freezer back and forth will cause loss of infectivity rapidly because of temperature recycling