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11 Cards in this Set
- Front
- Back
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Viruses
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Obligate intracellular parasites
–Completely dependent on the host • Acellular infectious agents –Also prions • Do not produce energy • Can infect any living organism |
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Viruses cont.
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Do not divide
–Replicate genome and make new proteins all within the host • Very small – ultramicroscopic –Only orthopoxviridae (all -poxes except chickenpox) are large enough to see. |
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Structure
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Virus particle = virion
• Small genomes –Smallest = 3 proteins –Largest = 100 proteins –E. coli = 4300 proteins , Ebola = 7 proteins, most deadly virus • Nucleic acid – RNA or DNA –Surrounded by a capsid • Nucleocapsid (capsid + protein) |
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Classification
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Genome=RNA/DNA, Continuous/segmented
Replication-Tropism (usually narrow for viruses) • Subdivisions: –Immunology –Cytopathology –Epidemiology |
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Viral Replication
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Lack many necessary genes
• Lack ribosomes - they steal them • Host cell replicates • Death of cell –Lytic replication |
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5 Stages of Replication
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•Attachment- surface protein of virus interact w/ specific receptors on cell surface
•Entry -penetration- enveloped viruses penetrate -membrane fusion-broad tropism, fusion of viral envelope w/ cell membrane -endocytosis- naked virus, cytoplasmic membrane of host engulfs virus •Synthesis( Uncoating)-replication of genome and proteins, depends on genome (DNA-nucleus RNA- cytoplasm) •Assembly- forms nucleic acid structure •Release- lyse or bursts cell |
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Defective Viruses
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Cannot replicate autonomously
• Require co-infection • Hepatitis delta virus – HBV |
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Infection
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Acute infection
• Chronic infection (herpes). low and stead for a long time. Hides out in neurons, T-cells, something that the immune system thinks is one of theirs • Latent infection –Reactivation –Transformation |
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Transmission
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Horizontal
–Acutely infected persons –Chronic carriers • Respiratory • GI • Transcutaneous • Sexual • Vertical –Mother – fetus • Almost always exogenous with endogenous reactivation • Viremia - virus in blood |
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Spread
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Neuronal spread
• Viremia –Associated with cells –Free • Lymphatics |
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Diagnosis
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• Antivirals are not broad-spectrum
–Need to identify • Ribavirin • Isolate –Culture • Cytopathic Effect (CPE); syncytia • Antibody titer • Nucleic acid – PCR • Immunological staining • Hemagglutination |
