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VET140- Microbiology
Viruses and Prions
| Term | Definition |
|---|---|
| "Virus" | latin for poison |
| Viruses | unique infectious agents, extremely small 20-300 nm, contain only one type of nucleic acid (DNA or RNA), depend on host cells for replication, some have affinity for paricular cell types, some stable in environment, many labile. |
| Labile | viruses sensitive to hear, desiccation ,and disinfectants. |
| Virus Morphology | morph: fully assembled infective virus, has a nucleic acid core, core enclosed within a shell o proteins called a Capsid, some have envelopes covering the nucleocapsid from host cell. |
| Double stranded DNA, enveloped | belong to the families Poxviridae |
| Double stranded DNA, non-enveloped | belong to the families Adenoviridae |
| Single stranded DNA, non-enveloped | belong to the families Parvoviridae |
| Single stranded RNA, enveloped | belong to the families Paramyxoviridae |
| Single stranded RNA, non-enveloped | belong to the families Calciviridae |
| Double stranded RNA, non-enveloped | belong to the families Reoviridae |
| Virus Replication | replication: multiply ONLY in host cells and not on still media like bacteria. Utilize host cell organelle, enzymes, and other macromolecules. Effects on host cells range from minor changes in cellular metabolism to host cytolysis |
| Cytolysis | the dissolution or disruption of cells, especially by an external agent. |
| Stages of Replication | attachment > entry > uncoating > replication > assembly > release from host cell |
| Attachment Stage | stage where virus attaches to a surface receptor on a susceptible host cell, random event, related to number of virus particles and availability of appropriate receptor molecules. |
| Replication Stage | stage that is an energy dependent process that can occur in a number of ways: -endocytosis with fusion of viron in endosome w/ a lysosome. -fusion of viral envelope with the plasma membrane. -direct introduction of genomes into cytoplasm via channels |
| Endocytosis | the taking in of matter by a living cell by invagination (turn inside out) of its membrane to form a vacuole. |
| Uncoating and Replication Stage | stage where viral nuclei acid is uncoated and released in a form suitable or transcription. Replication of viral nucleic acid and synthesis of virus-encoded proteins, usually occurs in nucleus for DNA viruses / cytoplasm for RNA viruses. |
| Assembly and Release Stage | stage where newly-formed virus particles are assembled and released from host cell by exocytosis or cytolysis. Some don't breach the membrane and is non-cytopathic, can result in persistent infections. Other budding viruses can cause cell death. |
| Exocytosis | process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane. |
| Cytopathic | producing damage to living cells |
| How a virus kills a cell | 1) virus enters cell 2) virus duplicates itself 3) cell explodes, releasing thousands of brand new virus particles |
| Non-cytopathic enveloped viruses are associated with...? | persistent infections |
| Viral Disease Diagnoses | Dx: clinical signs, postmortem findings (gross necropsy), histopathological findings. Confirmation requires special lab procedures: virus isolation, serology, electron microscopy, detection of nucleic acid. |
| Surveillance for Viruses | -more than 200 major important vet viral diseases -important in valuable animals (bulls, rams, stallions) -certification of health needed for interstate and international trade -protection and eradication of exotic viral diseases and for human health |
| Sample Collection | -check w/ diagnostic lab -if exotic/reportable dz, notify authorities -get sample early before secondary bacterial or fungal overgrowth. -take samples from apparently normal live animals that are actively shedding the virus. |
| Sample Collection Sites | -respiratory diseases: mucosal scrapings of oropharynx/nasopharyngeal aspirates. -enteric diseases: feces/mucosal scrapings -viremia: blood (check buffy coat of WBC's) -serology: serum -tissue samples in formalin |
| Preservation/Transportation of Samples | transport in a buffered isotonic saline with protein, antibacterial and antifungal drugs, do not use w/ urine samples (urine in only a sterile container), refrigerate but not freeze, submitted ASAP. |
| Air Dried Smears | these are used for fluorescent antibody (FA) staining for testing . This should be fixed in methanol or acetone for 10 minutes when preserving. |
| Virus Isolation | -cell cultures -standard for comparison against other dx methods -labor intensive, slow and expensive -different types of cell damage is used in dx -family level often requires additional tests |
| Cell Culture | culture method used for viruses. The virus needs live cells to grow so fertile eggs or different animal cell types are used (same as host animal). |
| Diagnostic Serology | used retrospective (post mortem) dx and for epidemiological surveys. Automated and diagnostic reagents available commercially for many pathogens, single blood sample for establishing dz prevalence. |
| How serology tests work | -detects/measures antibodies or antigens -detection depends on binding of antibodies and antigens -binding is invisible so requires secondary events to detect the union. |
| ELISA (Enzyme Linked Immunosorbent Assay) | test that can detect antigens or antibodies, kits available for heartworms/FIV/FeLV/K9 parvo/progesterone etc. |
| ELISA Technique | the microwell has monoclonal antibody bound to its walls, serum sample is added to well and if antigen is present in the sample it will bind with the antibody. Color producing substrate added that will react with the enzyme to produce a specific color. |
| Latex Agglutination | small spherical latex particles coated w/ antigen suspended in water, if the serum added contains corresponding antibodies the antigen-antibody complexes formed cause agglutination or clumping. Smooth to clumpy. |
| Immunodiffusion | a technique used for detecting or measuring antibodies ad antigens by their precipitation when diffused together through a gel or other medium. |
| Fluorescent Antibody Testing | direct and/or indirect antibody testing, detects presence of specific antibody or antigen in a sample. Send to reference labs to verify tentative diagnosis. (+) results is fluorescent dyd-conjugation and then examined with a special fluorescent microscope |
| tentative | unconfirmed, indefinite, uncertain. |
| Detection of Nucleic Acid | this is done through molecular diagnostics, becoming the method of choice for virus ID, can detect latent infections in which the infectious virus is not present, can be used for inactivated virus specimens. |
| Molecular Diagnostic uses | used to: -identify viruses/fungi/bacteria, find genetic defects, determining sex, verify animal pedigrees, classify cancers. It analyzes samples for DNA or RNA of microbe |
| Molecular Diagnostics (advantages) | -increased sensitivity and specificity -only require very small samples -safe -age, condition, and growth requirement factors are not as crucial -testing can be accomplished in hours versus days |
| Molecular Diagnostics (disadvantages) | -contamination can lead to false positive results -takes a high level of technical expertise -high costs Many of these problems are being solved w/ commercial kits now available. |
| PCR Test (Polymerase Chain Reaction) | small amount of DNA segment detected is amplified to produce many copies of small select region of DNA, is a very complicated process. Microbe may be present in sample but not causing the disease. |
| Reverse Transcriptase Polymerase Chain Reaction | Test used for RNA viruses, concerts the single stranded RNA virus to double stranded DNA before PCR process. |
| Interpretation of Test Results | in young animals, passively acquired maternal antibodies can persist for months (can lead to false +), false (+)&(-) results can occur. |
| Sensitivity of a test | a % of the ability of a test to correctly identify all animals that are truly positive. |
| Specificity of a test | a test that measures the % of the numbers of false positives produced. |
| High sensitivity tests | these tests should be used to detect all animals with an important viral infection (flocks, herds). |
| High specificity tests | these tests should be used to confirm viral infections in individual animals. |
Created by:
Riley.Scherf
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