11 Microbial Diversity - Viruses Flashcards
Pandemic Phases
Phases 1-3 (predominantly animal infections - few human infections)
Phase 4 (sustained human-to-human transmission)
Phase 5-6 (widespread human infection
Post peak (possibility of recurrent events
Post pandemic (disease activity at seasonal levels)
Examples of eradicated diseases
Small pox
Small pox
Smallpox alone in the 20th century, has killed an estimated 300million individuals, about 3x as many people killed due to all of the wars during this century.
Rabies
More than 55,000 people die of rabies per year (most human deaths follow a bite from an infected dog)
30-60% of the victims are children under the age of 15
Once the signs and symptoms of rabies start to appear, the disease is almost always fatal
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The most cost effective strategy for preventing rabies in people is by eliminating rabies in dogs through animal vaccinations
Africa spends US $560 million each year mostly on post-exposure prophylaxis
Foot and mouth (2001 UK outbreak)
Example of animal virus —> resulted in the slaughter of 4 million animals
Cost to UK up to £4 billion (lost tourism / compensation / cost of control)
History of viruses
Idea of viruses was hypothesised in 1892 by Dimitri Ivanovsky
The same of leave infected with tobacco mosaic disease retains its infectious properties even after filtration through chamber land filter candles
Martinus Willem Beijerinck- discovered viruses in 1898 proving in filtration experiments that the tobacco mosaic disease is cause it something smaller than a bacterium - named the new pathogen virus
Virus definition
obligative intracellural parasite of translation
Viral taxonomy
15 ranks —> standardised taxonomy system (same linnaeus tructure)
Viral classification is based on the genome (RNA or DNA) / number and sense of RNA/DNA strands / morphology / ecology / genome sequence similarity
Structure of viruses
ONE NOTE IMAGE
Membrane - glycoprotein
Lipid envelope
Matrix
Capsid
Internal genetic material
Classification of capsid symmetry
- Icosahedral
- Helical
- Complex
Anomaly —> poxvirus (complex symmetry)
Baltimore characterisation method
viruses can be grouped into 1 of 7 groups depending on the viral DNA structure
Virus - Positive sense RNA
mRNA is positive sense (5”-3”) - codes for protein
In host cell the positive sense strand is directly translated into proteins by the host ribosome
Production of proteins is necessary for viral progen, starts straight away - no need for functional proteins to be packaged in the capsid
- Eg. Foot and mouth disease
Virus - Negative sense RNA
Negative sense (3”-5”) RNA is not readable by the host ribosome
First the strand must be converted into positive sense RNA by virus RNA dependant RNA polymerase (made in the previous host and packaged with the genomic content) —> ribosomes then translate this to produce viral proteins
- Eg. Influenza / Rabies
Host range varies
Very narrow - swine vesicular disease - pigs
Some wide - foot and mouth disease - cloven hoofed animals
Others zoonotic - rabies - wild animal reservoirs
Lytic cycle
Viral DNA remains separate from host DNA
Takes over the host cell replicating itself —> host cell lysis/death —> virulence/ symptoms
Rapid / Enables dissemination
Lysogenic cycle
Viral DNA is incorporated into host DNA —> prophage
Replicated during host cell division —> daughter cells
Dormant until lytic cycle is triggered
Bacteriophage – virulence genes (toxins, resistance)
Control of virus diseases
Antimicrobials
Vaccination is the main approach - live or killed vaccines
Eradication in some cases (FMD / Rabies)
Biosecurity - important to minimise contact between virus and host —> lockdown
Edward Jenner and smallpox
1976 - human experimentation (James Phipps 8 years old)
Pus from a cowpox put into an incision, then infected him with smallpox - no development of disease (immune)
Needed more proof, Jenner experimented on several other children, includin his own 11 month old son
1978 - results published and Jenner coined the word vaccine from the latin word for cow
