Animal viruses Flashcards
what is a virus?
obligate intracellular parasites that require a host to replicate. absolute dependence on host cell, can infect all types of life. Most ubiquitous and diverse group of organisms on the planet
disadvantage of virus’
invasion of living organisms in order to reproduce, resulting in disease/death of the host
selective adavantage they give the host
can aid immune system’s maturation, aid development of resistance to similar viral infections, can destroy bacteria and other viruses causing infections. aid evolution by transferrin genomic sequence among different species
where do viruses come from
the progressive (escape) hypothesis- mobile genetic elements that become autonomous and can move between cells- transposons The regressive (reduction) hypothesis- derived from a more complex progenitor- a complex virus, or a type of mitochondrion The virus- first hypothesis- viruses predate cells- exist as self-replicating units. this would make the viruses the "first form of life" on earth
common viral properties
- are small particles of genetic material, surrounded by a protein coat
- are build de novo in each generation
- don’t have any cellular components
- don’t have homeostasis
- lack response to environmental stimuli
- cannot be culture
- they can only reproduce within living organisms
genome structure
a virus can have a DNA, or RNA genome and sometimes both. but only one type is present at any given time
- RNA viruses carry own polymerases and usually replicate in the host-cell cytoplasm
- DNA viruses replicate in the host cell nucleus
- Their diversity complicates their classification
- there is a classification based on the nature of the viral genomes and their modes of replication
The baltimore scheme classification
Class I&VII- DNA virus- transcription of minus strand
Class II- DNA virus- synthesis of the minus strand
Class III- RNA (ssRNA+)- transcription of minus strand
Class IV- RNA (ssRNA-)- used directly as mRNA
Class V- RNA(ssRNA+)- transcription of minus strand
Class VI- RNA(ssRNA+)- reverse transcription
viral symmetry
Helical- Rod
Isometric- spherical
life cycle
host recognition and attachment penetration gene expression and viral replication further processing and assembly of new viruses cell lysis
virus replication
eclipse: genome replicated and proteins translated
Maturation: packaging of nucleic acids in capsids
Latent period: eclipse+maturation
Release: cell lysis, number of virions released
stages of viral infection
1) infection
2) incubation period- time between infection + symptoms
3) acute period - the disease at its height
4) decline period- disease symptoms are subsiding
5) convalescent period- patient regains strength and returns to normal
types of viral infections
no permissive- virus is not allowed cell entry
permissive- virus gains entry
- acute, or lysis- virus replicates, progeny is released and cell dies
- persistent- virus replicates- progeny is released by cell survives
-latent, or chronic- virus present in cell, may replicate
- transformation- virus causes cell immortalisation
- abortive- virus enters the cell, but fails to replicate
Reservoirs
species in which infectious agents remain viable and from which individuals can become infected. BAts are an example of a reservoir of “zoonotic” diseases
Carriers
pathogen-infected indiviudals with no disease symptoms, individuals in the incubation period of the disease, or convalescing. typhoid mary is an example of a carrier
co-evolution and co-adaption
host develops resitance to pathogen, pathogen develops countermeasure evasion mechanisms. a well adapted parasite must ensure survival of its resources
