Microbiology 7: Evolution and emergence of new viruses Flashcards
Define Zoonosis
The crossing of an animal pathogen into humans is called zoonosis
Define host range
The range of host species or cell types which a particular virus, bacteria, or parasite is able to infect or parasitise.
Define host range barrier
A host range barrier means that most viruses that are able to infect animal hosts are compramised in their ability to replicate and spread in humans due to genetic differences between host factors the virus needs.
Define antigenic shift
Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. due to gene reassortment this change allows the influenza virus to jump from one species to another
What process enables an avian virus to jump the species barrier and adapt for replication in human hosts? Hint: this process results in the creation of new virons that can contain mixture of genes from each of the parental viruses
Reassortment
Define antigenic drift
The emergence of a new virus from first one Antigenic drift is due to mutation and selction. NOT REASSORTMENT.
Describe how the HIV virus emerged.
HIV emerged as a human pathogen in the mid 20th century. We can see from sequence analysis of related viruses of apes that HIV is derived from a simian retrovirus that was found in chimpanzees.
Describe how west nile virus emerged
Before 1999 West Nile Virus was not seen in the American continent. The replication cycle involves infection of mosquitoes and birds. The virus has spread across the USA in less than a decade. Belongs to Japanese encephalitis group of flaviviruses - cause disease by going to the brain
Describe the emergence of Norovirus
Norovirus is a small RNA virus that causes diarrhoea and vomiting. A new genotype of virus has emerged that appears to use a new receptor for host cell entry that is particularly widespread in humans.
Describe the emergence of SARs
The virus is normally found in bats. Farmed civet cats were an intermediate host in China for the evolution of a strain of virus that could attach to a receptor on human cells
Why are RNA viruses more prone to mutations?
RNA viruses are particularly prone to generate many errors during their replication because their RNA dependant RNA polymerase lack proof reading capacity.
define quasispecies
A viral quasispecies is a group of viruses related by a similar mutation or mutations, competing within a highly mutagenic environment
