Ch. 6 (Viruses)

Viroids

(1/10 the size of an average virus), naked strand of RNA with no capsid or coating. Infects tomatoes, potatoes, cucumbers, citrus and flowers

About how many genes do viruses have? Which virus is an exception?

Apx. 900 genes, exception is Hep. B: only about 4

Orthomyxoviridae

*8 segments of RNA • Influenza virus

Coronaviridae

*Looks like a crown Infectious bronchitis virus (bronchitis) Enteric corona virus (enteritis) SARS virus (severe acute respiratory syndrome) *transferred by an animal called the civet

Retroviridae

*becomes a provirus *is lysogenic because it can hide in the DNA NOTE: approximately 40 million people with aids, and ½ a million people have died • Lentivirus (HIV, types1 and 2, cause AIDS) • Human T-cell leukemia virus (HTLV)

Reoviridae

*double stranded with 11 segments of RNA • Rotavirus (gastroenteritis) • Colorado tick river virus

Lysogeny

*induced by temperate phages in certain bacterial species - Occurs in Corynebacterium diphteriae. Its toxin responsible for the deadly nature of the disease if a bacteriophage product. These bacteria without their prophage are totally harmless! - Same in Vibrio cholera and Clostridium botulinum.

Paramyxoviridae

*mimics the flu virus • Mumps virus (mumps) • Parainfluenza virus (parainfluenza) • Measles virus (measles) • Respiratory syncytial virus (common cold syndrome)

The International Committee on the Taxonomy (ICTV) of Viruses has reported how many orders, families, and genera?

1. 3 orders 2. 63 families (viridae) 3. 263 genera (virus) *all written in italics

What are the 6 steps in viral penetration?

1. Adsorption (Fig. 6.12) 2. Penetration (Fig. 6.13) 3. Uncoating 4. Replication or synthesis 5. Assembly 6. Release (Fig. 6.15)

What are the 4 components of a virus?

1. Capsid 2. Central core (nucleocapsid) 3. Envelope 4. Spikes or peplomers

Name the 3 viruses with double stranded RNA?

1. Criptovirus 2. Cystovirus 3. Reovirus *cant cry reo

What are the 6 DNA viruses?

1. HERPESviridae 2. POXviridae (pox=blister) 3. ADENOviridae 4. PAPOvaviridae 5. HEPADnaviridae 6. PARVOviridae (parvo=small) *red cheeks

Name the 5 viruses with single stranded DNA?

1. Inovirus 2. Microvirus 3. Plectrovirus 4. Parvovirus 5. Geminivirus *I make peach pie good

List the 13 RNA viruses:

1. Picornaviridae 2. Calicivirus 3. Togaviridae 4. Flaviviridae 5. Bunyaviridae 6. Filoviridae 7. Reoviridae 8. Orthomyxoviridae *8 segments of RNA 9. Paramyxoviridae *mimics the flu virus 10. Rhabdoviridae (rhabdo=little rod) - looks like a bullet 11. Retroviridae *becomes a provirus *is lysogenic because it can hide in the DNA 12. Arenaviridae 13. Coronaviridae *Looks like a crown

What are the 2 complex viruses?

1. poxvirus: A large DNA virus 2. flexible tailed bacteriophage

Virion

A fully-formed extracellular virus particle that is able to establish infection in a host

Who coined the word virus?

Pasteur

What is the length for viral penetration?

from 8 hours in polioviruses to 36 hours in herpesviruses

What are the 4 enveloped viruses (2 helical / 2 icosahedral)?

helical = 1. mumps 2. rhabdovirus icosahedral= 1. herpesvirus 2. HIV (AIDS)

What are the 3 naked viruses (1 helical / 2 icosahedral?

helical = 1. plum poxvirus icosahedral= 1. poliovirus 2. papillomavirus

Where do DNA viruses multiply and what is the 1 exception?

in the nucleus of cells except for poxviridae

What is the difference between the lytic cycle and the lysogenic cycle?

lytic cycle: involves full completion of viral infection through lysis and release of virions lysogenic state or lysogeny: a condition in which viral DNA is inserted into the bacterial chromosome and remains inactive for an extended period of time.

What are the smallest viruses?

parvoviruses (20 nm or 0.02 µm) in length

What are the largest viruses?

poxviruses (up to 450 nm or 0.450 µm) in length

Proghage

replicates right along with the chromosome every time the bacterium divides

Synthetic viruses

• A similar virus to poliovirus was created at the State University of New York in 2002 • A bacteriophage (phi X) was created in Rockville, Maryland, in 2003

ADENOviridae

• Adenovirus infections

Treatment of Viral Diseases

• Antibiotics do not work on viruses • No cure for patients with viral disease. • Drugs reduce effects and alleviate symptoms 1. Antiviral drugs block replication (severe side effects) 2. Azidothymidine (AZT) • Acyclovir (herpes) • Naturally-occurring cellular interferon • Vaccines (to stimulate host immunity) ** delta agent it's a defective virus that only replicates during hepatitis

Adsorption

• Attachment to specific receptors (some animal cells up to 100,000 per cell) - Rabies virus attaches to acetyl-choline receptors of nerve cells - HIV attaches to a CD4 protein on certain white blood cells • Enveloped viruses use their spikes to attach to cell receptors • Naked viruses use molecules on their capsids to adhere to cell membrane receptors

Central core (nucleocapsid)

• Contain DNA or RNA, some enzymes, no ribosomes

Bunyaviridae

• Crimean-Congo hemorrhagic fever virus *makes you bleed • Rift Valley fever virus • Sin Nombre virus • Bunyamwera virus (California encephalitis) • Hantavirus (Korean hemorrhagic fever) *spread by white footed mouse

Flaviviridae

• Dengue fever virus • West Nile virus • Yellow fever virus • Hepatitis C virus *only transmitted by blood

Togaviridae

• Eastern equine encephalitis virus • Western equine encephalitis virus • St. Louis encephalitis virus • Rubella virus *can affect child

Filoviridae

• Ebola virus (ebola fever) • Marburg virus (a type of ebola fever)

HERPESviridae

• HSV Type I (cold sores) • HSV Type II (genital) • Epstein-Barr (EBV) mononucleosis, o Varicella-Zoster (VZR), rash (Chicken Pox or Shingles) ** Lysogenic - provirus

HEPADnaviridae

• Hepatitis B virus ONLY (serum hepatitis)

PAPOvaviridae

• Human Papillomavirus (warts)

What is In vivo cultivation

• Inoculation of lab-bred animals • Embryonic (fertilized) bird tissues of chicken, turkey, ducks • Strains of white mice, rats, hamsters, guinea pigs, rabbits • Primates (non-humans) • Insects

Complex viruses

• No capsid but several layers of lipoproteins Bacteriophages have polyhedral head, helical tail and fibers for attachment to bacteria • Includes poxviruses and some bacteriophages

Calicivirus

• Norwalk virus (Norwalk virus syndrome) *spreads in food

Prions

(Proteinaceous infectious particles) • Group of infectious agents that are not viruses • Do not have any type of nucleic acid • Alter adjacent normal protein inducing spontaneous abnormal folding • Proteins display extreme resistance to environmental factors - Survive disinfectants, radiation, and the usual sterilization techniques - Destroyed by very high temperatures and high alkaline chemicals • Cause transmissible spongiform encephalopathies - Mad cow disease, kuru, fatal familial insomnia, CJS

Rhabdoviridae

(rhabdo=little rod) - looks like a bullet • Lyssavirus (rabies virus)

Who discovered the foot and mouth disease in cattle?

F. Loeffler and P. Frosch

Which virus has both single stranded DNA & double stranded RNA?

Hepatitis B

Who showed that the tobacco disease was caused by tobacco mosaic virus?

Ivanovski and M. Beijerinck

Arenaviridae

Lassa virus (Lassa fever)

Oncogenic viruses

Viruses that are capable to enter a cell and permanently alter its genetic material, leading to abnormal growth resulting in tumors (cancer)

Which enzyme converts RNA to DNA

Retroviridae = reverse transcriptase

What is x-ray crystallography?

Study of how viruses work

Assembly

Virus particles are put together starting with the capsid

Describe the properties of viruses:

• Obligate parasites of bacteria, protozoa, fungi, algae, plants, and animals • Ultramicroscopic size (20 to 450 nm in diameter) • Not cellular in nature: structure is compact an economic • Do not independently fulfill the characteristics of life • Inactive particles (made of macromolecules) outside the host cell and active only inside the host cells • Basic structure consists of protein shell (capsid) surrounding nucleic acid • Nucleic acid can be DNA or RNA but not both • Molecules on viral surface impart high specificity for attachment to host cell • Multiply by taking control of host cell's genetic material and regulating the synthesis and assembly of new viruses • Lack enzymes for most metabolic processes • Lack machinery for synthesizing proteins • Viral replication inside host cell usually causes its death or loss of function

Release

• Once cycle completes viral particles will exit cell • Naked and complex viruses are released when cell ruptures or lyses • Enveloped viruses are liberated by budding or exocytosis from membranes of the cytoplasm, nucleus, ER, or vesicles • Cell dies or apoptosis occurs at later stage Some viruses are able to spread by the fusion of multiple host cells into single large cells containing multiple nuclei. As a result a syncytium (pl. syncytia) is formed. Typical in respiratory syncytial virus. Some viruses are capable of lying 'dormant or latent' in their host cells, becoming active at some time later (herpesvirus, HIV).

PARVOviridae *red cheeks

• Parvovirus B-19 (Erythema infectiosum)

Satellite viruses

• Perhaps are defective forms of viruses • AAV (Adeno Associated Virus) only replicate in cells affected by Adenovirus • The Delta Agent is a naked strand of RNA expressed only in the presence of hepatitis B virus! **Its presence worsen the severity of liver damage

Picornaviridae

• Poliovirus (poliomyelitis) • Coxsackievirus (hand-foot-mouth disease) Hepatitis A virus (short-term hepatitis) • Rhinovirus (common cold, bronchitis)

In vitro cultivation

• Polymerase Chain Reaction (PCR) - Detects and amplifies minute amount of DNA. Hantavirus, Four Corners, New Mexico, 1993. • Serology - Presence of specific antibodies - Main test for HIV • Electron Microscope • Immunofluorescence Microscopy • Labeled fluorescent antibodies and UV light

Capsid

• Protective outer shell made of protein • Capsomer and protomer subunits • Icosahedral (polygon of 20 faces or equilateral triangles)

Spikes or peplomers

• Protruding glycoprotein molecules for attachment to cell. • Parts of capsids and envelopes stimulate immunological system

Uncoating

• Release of the nucleic acid in the cytoplasm of host cell • The exact manner varies with the virus • Virus fuses with the wall of the vesicle and breaks it

POXviridae

• Smallpox • Cowpox (chickenpox not included) - ** new one > molluscus contagiosum

Enveloped viruses

• Some bud off the cell membrane; others leave via the nuclear membrane, the Golgi apparatus or the endoplasmatic reticulum • More sensitive to environmental factors • With helical nucleocapsid (mumps virus, rabies virus) • With icosahedral nucleocapsid (herpesviruses, HIV)

How are viruses classified?

• Structure • Chemical composition • Similarities in genetic make-up • System is based on host and the disease they cause • There are two super-families of animal viruses based on nucleic acid composition • Total of 19 families affecting humans, 6 contain DNA and 13 RNA (Table 6.3)

Genome

• The sum of the genetic information carried by an organism or a virus • Contain only the necessary genes needed to invade the host and redirect their activity *can be linear (fragmented or non-fragmented) or circular • RNA can be positive-sense or negative-sense

Replication or synthesis

• The synthetic and replicative phases of animal viruses are highly regulated and extremely complex at the molecular level • Use cell metabolic pool for chemical components • Free viral nucleic acid exerts control over the host's synthetic and metabolic machinery • Most DNA viruses replicate and assemble in the nucleus of the cell • All known RNA viruses in the cytoplasm

Envelope

• Viruses having a modified host's membrane are called 'Enveloped viruses' and those lacking it are called 'Naked viruses'. *tobacco mosaic virus • Viruses with an envelope differ from naked ones in the way they enter and leave a host cell *influenza

Penetration

• Whole virus or just DNA or RNA penetrates the cell. • Engulfment of entire virus by the cell and enclosement into a vacuole (endocytosis) • (rubella, herpesviruses) • Direct fusion of the viral envelope with the host cell membrane (influenza, mumps)