Lecture 5: Viruses

(Viruses) Lecture 5 Viruses · space ship analogy · viruses require a host cell · often take a membrane coat from the host cell · viruses are infectious particles, but not living cells · Many forms of transmission: ↳ blood transfusion, mucus droplets, aerosols, fomites, air (airborne), water, food, vectors · Must be treated in different ways than other microorganisms because of different in makeup/structure Virus Bacteria · multiply only in host cells · most are free living and can multiply out of host cells · few enzymes · contain many enzymes · smaller 10-500nm · Larger 500-2000nm · contain DNA OR RNA · contain DNA AND RNA · no ribosomes or enzymes · contain both ribosomes and enzymes Virus Shapes and Sizes · Bullet · Icosahedral · filamentous · complex Viral Structure virion: complete infections viral particle with nucleic acid surrounded by a protein coat ↳ capsid: protein coat made of capsomeres that protect the DNA/RNA · complete unit: nucleocapsid · Some viruses have lipid envelopes outside of nucleocapsid · glycoproteins or spikes inserted in envelopes or capsid (attachment) Host Range · Different viruses can infect every life form ↳ bacteria, fungi, plants, animals, humans · USUALLY specific host range ↳ bacteriophage infects bacteria Classifying Viruses Bacteriophages · viruses that infect bacterial cells and can transfer new genes from one bacteria to another · can be used for genetic engineering ↳ insulin · can transfer genes for production of toxin ↳ lysogeny · Based on DNA or RNA composition · RNA viruses are known for their ability to mutate quickly DNA viruses: · Papillomaviridae (HPV) RNA Viruses: · Hepadnaviridae (hepatitus B virus) · Orthomyxoviridae (Influenza A, B, C) · Poxviridae (smallpox, monkeypox etc. ) · Coronavirus · Retroviridae (HIV) · Adenoviridae (adenovirus) · Flaviviridae (Yellow fever virus, west nile virus) · Herpesviridae (HSV-1, HSV-2, HHV-3... ) · Picornoviridae (Enterovirus) · Parvoviridae (B-19) Events in Viral Infection (3 steps) ① Attachment and penetration into host cell ↳ must attach to host cell, usually to receptors ↳ (1)Fusion (with envelope) or (2)Pinocytosis (without envelope) ② Replication of the Genome Fusion ↳ a DNA virus hijacks the host cell DNA polymerase to produce viral DNA ↳ a RNA virus must bring its own enzyme into the host cell because it needs to produce RNA from RNA to make a new virus Pinocytosis DNA virus, RNA virus, RNA retrovirus, reverse transcriptase Memorize: ③ Assembly and Release of New Virus ↳ new replicated RNA or DNA with new viral proteins results in new nucleocaspids ↳ if enveloped virus: envelope components are produced and inserted into the host cell plasma membrane and buds through Antiviral Drugs · Fuzeon - stops entry (fusion) of HIV into cells · Acyclovir - stops replication of herpes viruses by interfering with the viral DNA polymerase Treats herpes · Tamiflu (oseltamivir) - Stops budding/release of influenza virus from host cell Host-virus interactions · Acute/Productive infection Acute - the common cold ↳ virus replicates, produces many virions ↳ lytic infection: host cell is killed (adenovirus, poliovirus) · Latent infection ↳ viral genome persists in host cell but does not replicate ↳ "provirus" (herpesviridae, HPV) Latent - Epstein-Barr · Chronic infection ↳ virus replicates without causing host cell lysis and can persist for long periods of time (hepatitus (and B) Chronic - AIDS/HIV Chickenpox: Acute vs. Latent Acute: · fever and rash (5 days) · rash primarly on head on trunk, less on arms and legs · airborne virus · skin vesicles always present in different stages of formation · When healed, virus travels up nerve ganglion where it remains latent Latent: · virus is present but is not replicating until triggered by external factors, then travels down nerve to skin and reactivates · In Human Herpes virus 3 this is known as shingles/zoster Chickenpox Complications · Secondary bacterial infection ↳ common in immunocompromised ↳ flesh-eating disease in children (chicken pox parties) · CNS disease: encephalitis, meningitis, myelitis (uncommon) ↳ encephalitis: inflammation of active tissues of the brain ↳ meningitis: inflammation of the meninges ↳ myelitis: inflammation of the spinal cord ↳ hemorrhagic complications (RARE) ↳ primary varicella pneumonia (VERY RARE) Shingles/Zoster · reactivation of the virus as it travels back down the nerve to the skin from the site of latency · begins as local skin rash · confluent rash and pain · untreated rash lasts 2-5 weeks and is infectious Zoster Complications · PHN (Post Herpetic Neuralgia)* ↳ 25-50% of patients >50 years ↳ severe chronic pain for months or years ↳ important to get treatment within 48-72 hours Prevention of Chickenpox Active immunization: Zoster · Live attenuated vaccine, highly protective, memory cells produced · Now included with MMR (MMRV) Passive immunization: · Effective up to 3 days post-exposure · VZIG: varicella-zoster immunoglobulin (antibodies to the virus) ↳ used for immunocompromised exposed children and neonates born to mothers with varicella Chickenpox - lesions are in different stages of development Smallpox - lesions are all in the same stage of development Oncogenic Viruses · Some viruses can "transform" normal host cells to cancer cells ↳ not all transformed cells become cancerous · Cancer-producing viruses can be RNA or DNA viruses Viral Diagnosis · PCR: polymerase chain reaction ↳ a fast, highly effective way to detect infectious diseases · Cell Culture ↳ cells are grown under controlled conditions and then observed ↳ very labour intensive and slow Prions (infectious proteins) Human Prion Disease · Protein misfolding disease · ALWAYS FATAL ↳ become changed and nonfunctional Signs: · 1982 Stanley Prusihet -ataxia · often not treatable · Examples: -cortical visual symptoms -Mad Cow disease (BSE, bovine spongiform encephalitis) -Scrapie (in sheep) -Kuru (transmitted by cannibalism N. Guinea) -CJD, vCJD in humans (crentzfeldt-Jakob) -Fatal familial insomnia -progressive dementia -myoclonus -akinetic mutism · Average time of death after onset: 4 months Spongiform encephalitis