virology Flashcards
size range of viruses
18 nm to 300 nm
families of DNA viruses (7)
1) poxviridae: smallpox virus, monkeypox virus
2) herpesviridae: herpes simplex virus (types 1 and 2), epstein-barr virus, cytomegalo virus, human herpes virus 6,7,8
3) adenoviridae - adenovirus
4) hepadnaviridae - hep B virus
5) polyoma viridae - BK virus
6) papilloma viridae - papilloma virus
7) parvoviridae - parovirus B19
capsids
protein; environmentally stable to temperature, acid, proteases, detergents drying; release from cell by lysis;
consequences: can be spread easily, can dry out and retain infectivity; can survive the adverse acidic conditions of the gut; antibody may be sufficient for immunoprotection
enveloped virus
membrane; lipid; proteinl glycoproteins
environmentally labile - is disrupted by acid, detergents, drying, heat; modifies cell membrane during replication; is released by budding and cell lysis
consequences: must stay wet; cannot survive the gastrointestinal tract; spreads in large droplets, secretions; does not need to kill the cell to spread; may need antibody and cell-mediated immune response for protection and control; elicits hypersensitivity and inflammation to cause immunopathogenesis
how do hemagglutin glycoprotein trimers of influenza virus help in the rapid infection of various human cell types?
sialic acid binding domain - attachment region of influenza virus binds to sialic acid domains expressed in various types of cells; this facilitates the binding of influenza with several cell types
how does the antibody molecules, nucleoside analogues and protease inhibitors help combat the spread of an infecting virus?
antibody - before entering the cell binds to viral proteins
nucleoside analogs - inhibit the replication, DNA synthesis
protease inhibitors - inhibit assembly of virus from a polyprotein segment
families of RNA viruses
1) paramyxoviridae - measles virus, mumps, virus, metapneumovirus
2) orthomyxoviridae - influenze virus types A, B, C
3) coronaviridae - coronavirus, SARS
4) rhabdoviridae - rabies virus
5) retrovirdiae - human T-cell leukemia virus types I and II< HIV
6) picornaviridae - poliovirus, hep A
7) togaviridae - rubella virus
8) flaviviridae - yellow fever virus, west nile virus, hep C
DNA viruses
DNA is not transient or labile
viral genomes remain in the infected cell
many DNA viruses establish persistent infecitons
DNA genomes reside in the nucleus
viral genome resembles host DNA for transcription and replication
viral genes must interact with host transcriptional machinery (except for pox viruses)
viral gene transcription is temporarily regulated (early genes and late genes)
RNA viruses
RNA is labile and transient replicate in the cytoplasm cells cannot replicate RNA RNA viruses must encode an RNA dependent RNA polymerase prone to mutation
what are the probes as well as the material being tested during in situ hybridization?
DNA probes can be used to detect specific genetic sequences in biopsy specimens
what are the probes as well as the material being tested during northern blot?
DNA probe hybridization of RNA electrophoretically separated and blotted onto a nitrocellulose filter
what are the probes as well as the material being tested during southern blot?
DNA probe hybridization of DNA separated in gel electrophoresis and transferred onto a nitrocellulose paper
what are the probes as well as the material being tested during western blot hybridizations?
electropohoretically separated proteins can be identified using antibodies
what are the probes as well as the material being tested during PCR?
Amplified single copies of viral DNA millions of times over; can be used to detect even few viruses lying dormant in infected cells; most sensitive, recent and preffered method to detect a few DNA molecules
what are the probes as well as the material being tested during RT-PCR?
involves the use of revere transcriptase enzyme of retroviruses; viral RNAs are first converted to DNA by reverse transcriptase enzyme and then PCR amplified
Prodrome
non specific early symptoms
Tropism
a particular disease caused by several viruses that have a common tissue preference - hepatitis (liver), common cold (upper respiratory tract)
Viremia
presence of virus in the blood circulation
What are acyclovir and AZT? How do they influence the viral spread?
Acyclovir is a nucleoside analogues inhibit viral DNA polymerase selectively and there by inhibit viral DNA polymerase selectively and thereby inhibit viral replication
AZT was originally developed as anticancer drug. It si 100 fold more sensitive to viral reverse transcriptase than to the host cell DNA polymerase. AZT is the first useful therapy for HIV infection
some viruses do not cause any cytopathological effects (CPE) on tissues. How can these viruses be detected and identified?
cells infected with influenze virus, parainfluenza virus, mumps virus and togavirus do not exhibit classic CPEs; these cells expressive viral glycoprotein - hemagglutinin can bind to erythrocytes (hemadsorption) of a given species and cause hemagglutination; antibodies against specific viruses can prevent the hemagglutination caused by that specific viruses (against which the antibodies have been raised); this demonstration of hemagglutination and inhibition of hemagglutination is a major tool to detect and identify a specific virus without a CPE
What is a PFU?
plaque forming units
viruses can be quantitated by determining the greatest dilution that retains the following titers: TCD50, LD50, ID50
TCD50
tissue culture dose - titer of virus that cause cytopathologic effects in half the tissue
LD50
lethal dose; titer of virus that kills 50% of a set of test animals
ID50
infectious dose; titer of virus that initiates a detectable symptom, antibody or other response in 50% of a set of test animals
