topic 8; Viruses pt1: Key Concepts, Classification, and Laboratory Techniques

What does the term Contagium vivum fluidum refer to?

An early term used for infectious, filterable agents (like those causing plant disease).

When did the word 'virus' come into use and what is its origin?

The word 'virus' was used in the 1930s; it comes from Latin virus meaning 'poison'.

What invention made it possible to see viruses for the first time?

The electron microscope.

Who first described tobacco mosaic disease and in what year?

Adolf Mayer, 1886.

What key observation did Dmitri Ivanovsky make in 1892?

He showed infected sap remained infectious after filtration through the finest Chamberland filters and suggested the agent was smaller than bacteria.

What did Martinus Beijerinck demonstrate in 1898?

Filterability of the agent, serial transmission with no loss of potency, and helped define the idea of a new type of infectious agent (virus).

Which two scientists identified the first filterable animal agent and what disease was it?

Loeffler and Frosch in 1898 — identified the virus of Foot-and-Mouth Disease (FMD).

What are the typical size characteristics of viruses?

Small (filterable), about 20 to 300 nm.

What does it mean that viruses are obligate intracellular parasites?

They absolutely require living host cells to multiply.

Do viruses have their own metabolic enzymes?

They have few or no enzymes of their own for metabolism and take over host cell metabolic machinery to multiply.

What is a core characteristic A of viruses (genetic material)?

Viruses contain a single type of nucleic acid: either DNA or RNA, never both.

What is core characteristic B of viruses (coat and envelope)?

Viruses have a protein coat (capsid) surrounding the nucleic acid and sometimes an envelope of lipids, proteins, and carbohydrates.

What is core characteristic C of viruses (replication)?

Viruses replicate inside living cells using the host's synthesizing machinery.

What is core characteristic D of viruses (specialized structures)?

Viruses cause synthesis of specialized structures that transfer viral nucleic acid to other cells.

How do viruses differ from bacteria in cellular organization?

Viruses are acellular; bacteria are unicellular prokaryotes.

Do viruses have a plasma membrane?

No — viruses do not have a plasma membrane; bacteria do.

Do viruses contain ribosomes?

No — viruses do not possess ribosomes; bacteria do (for protein synthesis).

Can viruses contain both DNA and RNA?

No — viruses contain either DNA or RNA; bacteria contain both DNA and RNA.

Do viruses reproduce by binary fission?

No — viruses do not undergo binary fission; bacteria reproduce by binary fission.

Do viruses generate ATP via metabolism?

No — viruses do not have ATP-generating metabolism; bacteria are capable of ATP production.

Can viruses multiply independently outside living host cells?

No — viruses are obligatory intracellular parasites and can only multiply inside living host cells; bacteria can often live and reproduce independently.

How do viruses and bacteria compare in filterability?

Viruses pass through bacteriological filters; bacteria generally do not.

Are viruses sensitive to antibiotics?

No — viruses are not sensitive to antibiotics; bacteria usually are.

Are viruses affected by interferons?

Yes — viruses are sensitive to interferons; bacteria are not affected by interferons.

What is the Baltimore classification based on?

It organizes viruses by type of nucleic acid and replication strategy (developed by David Baltimore).

Name a nonenveloped dsDNA family and its size.

Adenoviridae — size: 70 to 90 nm.

What is an important genus in Adenoviridae and clinical features?

Mastadenovirus; causes various respiratory infections in humans and some cause tumors in animals.

Name Papovaviridae size and important genera.

Size: 40 to 57 nm. Important genera: Papillomavirus (human wart virus) and Polyomavirus.

Clinical features of Papovaviridae?

Small viruses that cause warts and can cause cervical and anal cancer in humans.

Name an enveloped dsDNA family that is the largest animal virus and its size.

Poxviridae — size: 200 to 350 nm (largest animal virus).

Important genera of Poxviridae and clinical features?

Orthopoxvirus (vaccinia and smallpox), Molluscipoxvirus; very large, complex, brick-shaped viruses causing smallpox (variola), molluscum contagiosum, cowpox.

Size and genera of Herpesviridae?

Size: 150 to 200 nm. Genera/human herpesviruses: Simplexvirus (HHV-1, HHV-2), Varicellovirus (HHV-3), Lymphocryptovirus (HHV-4), Cytomegalovirus (HHV-5), Roseolovirus (HHV-6, HHV-7), Rhadinovirus (HHV-8).

Clinical features of Herpesviridae?

Medium-sized viruses causing fever blisters, chickenpox, shingles, infectious mononucleosis; some cause human cancers such as Burkitt's lymphoma.

Which family causes African Swine Fever?

Asfarviridae.

What does Iridoviridae infect?

Infect fishes, amphibians, and insects.

Name a nonenveloped ssDNA family and its size.

Parvoviridae — size: 18 to 25 nm.

Important virus in Parvoviridae and clinical features?

Human parvovirus B19 — causes fifth disease and anemia in immunocompromised patients.

Which family includes the smallest known virus and what hosts?

Circoviridae (smallest known virus); genera include Porcine circovirus infecting pigs — Type 1 and Type 2 exist; Type 2 is pathogenic causing multisystemic disease in pigs.

Name a nonenveloped dsRNA family and its size.

Reoviridae — size: 60 to 80 nm.

Important genera and clinical features of Reoviridae?

Genera: Reovirus, Rotavirus; generally cause mild respiratory infections, often transmitted by arthropods; Colorado tick fever is an example.

Name a nonenveloped + ssRNA family and its size.

Picornaviridae — size: 28 to 30 nm.

Important genera/viruses in Picornaviridae and clinical features?

Enterovirus, Rhinovirus, Hepatitis A virus; includes polio, coxsackie, echoviruses, hand-foot-mouth disease; rhinoviruses are the most common cause of colds (over 100 rhinoviruses).

Size and clinical features of Caliciviridae?

Size: 35 to 40 nm; includes viruses that cause gastroenteritis and hepatitis E.

Name an enveloped + ssRNA family and size.

Togaviridae — size: 60 to 70 nm.

Important genera in Togaviridae and clinical features?

Alphavirus, Rubivirus (rubella); many are arboviruses — cause EEE, WEE, Chikungunya; Rubella transmitted by respiratory route.

Size and genera of Flaviviridae and clinical features?

Size: 40 to 50 nm. Genera: Flavivirus, Pestivirus, Hepatitis C virus. Can replicate in arthropods (vectors) and cause yellow fever, dengue, Zika, West Nile encephalitis.

Size and key features of Coronaviridae?

Size: 80 to 160 nm. Important genus: Coronavirus. Associated with upper respiratory tract infections, common cold, includes SARS and MERS CoV.

Name a family in enveloped − ssRNA viruses and its size.

Rhabdoviridae — size: 70 to 180 nm.

Important genera and clinical features of Rhabdoviridae?

Genera: Vesiculovirus (vesicular stomatitis virus), Lyssavirus (rabies virus). Bullet-shaped viruses with spiked envelope; cause rabies and numerous animal diseases.

Describe Filoviridae size and clinical importance.

Size: 80 to 14,000 nm (note broad/large range). Enveloped, helical viruses including Ebola and Marburg viruses.

Size and genera of Paramyxoviridae and clinical features?

Size: 150 to 300 nm. Genera: Paramyxovirus, Morbillivirus (measles).

What is the size range of Paramyxovirus?

150 to 300 nm.

What viruses are included in the Deltaviridae family?

Hepatitis D virus.

What does it mean when single-stranded RNA has multiple segments?

The genome is segmented; different segments encode different viral proteins.

What are the important viruses in the Orthomyxoviridae family?

Influenza A, B, C.

What is the size range of Bunyaviridae?

90 to 120 nm.

What diseases are caused by Hantaviruses?

Hemorrhagic fevers and Hantavirus pulmonary syndrome.

What is the size range of Arenaviridae?

110 to 130 nm.

What diseases are caused by Arenaviruses?

Lymphocytic choriomeningitis, Venezuelan hemorrhagic fever, Lassa fever.

What family do retroviruses belong to?

Retroviridae.

What are the key features of retroviruses?

Enveloped, single-stranded RNA that use reverse transcriptase.

What is the size of Hepadnaviridae?

42 nm.

What is unusual about Hepadnaviridae replication?

It produces its DNA from mRNA using reverse transcriptase.

What is the host range?

The spectrum of host cells a virus can infect.

What types of hosts can viruses infect?

Invertebrates, vertebrates, plants, protists, fungi, and bacteria.

What does specificity refer to with viruses?

Most viruses infect specific types of cells, usually in only one host species.

What is a bacteriophage?

A virus that infects bacteria.

What determines a virus's host range?

Virus requirements, especially the presence of specific receptors on the host cell surface.

Where are receptor sites located for animal viruses?

On the plasma membranes of host cells.

What is a virion?

A complete, fully developed viral particle composed of nucleic acid surrounded by a coat.

What types of genetic material can a virus contain?

Either DNA or RNA — never both.

What is a capsid?

The protein coat surrounding the viral nucleic acid.

What are capsomeres?

Subunits that make up the capsid.

On what bases are viruses classified?

Type of nucleic acid and replication strategy.

What is the naming rule for virus family names?

Family names end in '-viridae'.

What is the naming rule for virus genus names?

Genus names end in '-virus'.

What is the general rule for growing viruses?

Viruses must be grown in living cells.

Which viruses are the easiest to grow?

Bacteriophages.

How can bacteriophages be grown in the laboratory?

In suspensions of bacteria in liquid media and in bacterial cultures on solid media using the plaque method.

What is a plaque?

A clearing on a bacterial lawn on agar where bacteria have been destroyed by phage.

What are the main methods for growing animal viruses in the lab?

Using living animals, embryonated eggs, or cell cultures.

Which animals are commonly used for in vivo viral growth?

Mice, rabbits, and guinea pigs.

What are advantages of using embryonated eggs?

Convenient and inexpensive for growing certain viruses.

Which viruses grow on the chorioallantoic membrane of eggs?

Herpes simplex virus, Poxvirus, Rous sarcoma virus.

What is Western Blotting?

An antibody-based viral protein detection test.

What is PCR in virology?

A method that amplifies viral genetic material for detection.

What is the size of the largest animal viruses?

Poxviridae.

What family contains the smallest viruses?

Circoviridae.

Can positive-strand RNA function directly as mRNA?

Yes.

What must negative-strand RNA do before it can be translated?

It must synthesize a new positive strand.

What do interferons do in viral infections?

They protect cells from viral infections.

What are three animal diseases under Herpesviridae?

Aujeszky's disease, Infectious laryngotracheitis, Marek's disease.

Which porcine virus type is pathogenic?

Porcine circovirus Type 2.