Viral classification, structure and replication of DNA Viruses: Adenoviridae, Poxviridae Flashcards

Question

What are the laboratory methods of confirming a viral diagnosis?

Answer 1

Isolation and growth of the virus Cytopathic studies on cells in culture Electron microscopy Detection of viral components (Proteins, enzymes, nucleic acids) Evaluation of patients immune response (Serology)

Answer 2

Depends on the virus: Cell death and lysis Transformation of host cell into cancerous phenotype Fusion of membranes of adjacent cells (synctia) - Feature of cells that have been infected with virus that have F protein Development of inclusion bodies in cells - HSV causes Cowdry type A and Rabies causes negri bodies

Answer 3

Live cultivation Use serial dilution end point method to determine: Plaque formation (Viral lysis of cells in culture) Focal Cytopathic changes in tissue culture Focal proliferation of cells in tissue culture Pock formation in membranes of chicken embryonated egg Infection in experimental animals

Answer 4

Electron microscopy Hemagglutinin Immunological testing via Complement fixation or direct fluorescent antibody Western Blot ELISA PCR

Answer 5

Complement fixation Hemagglutination inhibition Latex agglutination ELISA Indirect fluorescent antibody Western immunoblot

Answer 6

Viral neutralization by antibodies Cell-mediated immunity Interferon production - Interferons inhibit viral multiplication and may provide temporary, localized protection for nearby cells NK cells - Kill virally infected cells

Answer 7

Virally-infected cells process endogenously produced viral antigens and present them to cytotoxic T cells Cytotoxic T cells are activated and are then produce cytotoxic substances

Answer 8

Antibodies bind to virus (Opsonize) Endocytosis / phagocytosis is blocked Uncoating is blocked via capsid stabilization and fusion interference Virus is destroyed

Answer 9

Type 1 interferons (alpha and beta) The synthesis of the Type I interferons is induced in a cell by viral infection This induction may be induced by active and inactivated virus, by ds RNA and other compounds Interferons are host specific but not virus specific

Answer 10

After Type I interferons are released from a cell, they bind to other cells A protein transcription factor is activated inside the cell that then turns on a set of genes The products o f these genes inhibit viral protein synthesis, degrade viral mRNA, and promote apoptosis in virally infected cells

Answer 11

**_Localized infections_**: Viral multiplication and cell damage localized near the site of entry **_Disseminated infection_**: Local multiplication at the site of entry, spread through the lymphatics to blood stream and circulation, multiplication at secondary sites, secondary viremia, infection of the target organ

Answer 12

This is an asymptomatic period where infection is not apperant.

Answer 13

**_Day 0_**: Infection via eye conjunctiva and/or upper respiratory tract Replication in primary lymph nodes **_Day 4-6_**: Primary viremia; replication in liver, spleen, and other organs **_Day 14_**: Secondary viremia; infection of skin. Appearance of a rash. Infection of sensory ganglia and establishment of latent infection.

Answer 14

These are asymptomatic viral infections Very common; may result from infection by attenuated virus or from effective host defense mechanisms These are important medically because they represent an often unrecognized source for the dissemination of a virus. This may confer immunity on a host.

Answer 15

The virus infects the host and shortly after, disease ensues. After a defined but short period of time, the host recovers. The virus may be totally eliminated from the body or it can hide within the body and will result in a latent infection.

Answer 16

Latent Infections Chronic Infections

Answer 17

Viral particles are not detectable but they will reappear during recurrences of the disease. Viral nucleic acids are detectable between recurrences. Herpesvirus infections are the best example of this.

Answer 18

The virus is always detectable and often shed. Infected cells produce and release virus but cellular metobolism is little affected and the infected cells can grow and divide.

Answer 19

Prevention of transmission Public health surveillance Education Isolation of disease cases Passive immunization Active immunization - Live attenuated, inactivated, or subunit vaccines

Answer 20

Live tissue culture Some genetically engineered vaccines are now being used Viral DNA vaccines are an active area of research. DNA is engulfed by dendritic cells and protein antigen is presented to T cells. This elicits cell mediated immunity.

Answer 21

Offer many years of immunity IgA and IgG antibodies are produced Stimulates good cell-mediated response Vaccine rarely reverts to virulence

Answer 22

Immunity does not last a lifetime IgG antibody produced Poor cell-mediated response elicited No reversion to virulence

Answer 23

No animal reservoir Good vaccine Few or no subclinical cases (Latent infections ensure that virus will survive in population) One antigenic type or only a few (No antigenic switching)

Answer 24

Person must be symptomatic Immune serum is best if given early in infection, before exposure or during incubation period A limited number of drugs are available for treatment of viral diseases

Answer 25

Large, brick-shaped complex particles Replication of DNA much like that for cellular DNA but uses mainly virus-coded enzymes Propensity to infect epidermal cells Viral DNA replicates in cytoplasm of infected cells

Answer 26

Large DNA virus Dumbbell shaped core Has a complex membrane Humans are the only known host in nature Major health issue until immunization became wide-spread (vaccinia-live virus vaccine) No naturally occuring cases since 1977 and declared extinct on Friday, Oct. 28, 1979

Answer 27

Virus is inhaled and replicates in upper respiratory tract Internal and dermal tissues are seeded with virus after two rounds of viremia Hallmark "pox" forms (Lesions that are seen) Two varients of small pox: Variola major (15-40% mortality) and Variola minor (1% mortality)

Answer 28

If patient has suspect rash, isolate patient in negative air pressure room Rule out chickenpox Obtain specimen from lesion pustules Contact state public health lab for further guidance

Answer 29

Rashes have vesicles that appear in a centrifugal pattern All lesions are at the same stage of debvelopment Patients appear moribund

Answer 30

This is a pox virus Transmitted by direct contact or fomites Virus infects the basal cell layer and replicates Molluscum contagiosum leaves benign epidermal tumors that can occur in people given vaccinia based vaccines (esp. in people with HIV) Lesions are smooth, firm, shiny flesh colored to pearly white hemispheric papules with umbilicated centers confined to the skin and mucous membranes Children, people that live in tropical climates and HIV+ are most at risk

Answer 31

Adenoviruses are medium sized (90-100 nm), ds DNA 49 immunologically/serologically distinct types organized into six subgenera called A through F. All of these can cause human infections. This is a frequent cause of the common cold. They have naked icosahedral nucleocapsids These are very stable to chemical and physical agents as well as adverse pH. This allows for prolonged survival outside of the body. There is a fiber with a terminal knob that projects from each penton.

Answer 32

Most commonly cause respiratory illness Depending on the infecting serotype, they may also cause various other illness such as gastroenteritis, conjunctivities, cystitis, and rash. Respiratory symptoms range from common cold to pneumonia, croup, and bronchitis. Patients with compromised immune systems are especially at risk. Acute respiratory disease was first recognized among military recruits during WW II. Can be caused by adenovirus infections during conditions of crowding and stress.