Lecture 7- Evolution and emergence of new viruses Flashcards
Why is viral evolution very fast?
- replicate fast
- large progeny numbers
- Hugh mutation rates
What is a quasispecies?
the viral genomes within a single infected patient which are slightly different ti the genome in other patients because of evolution specific to that host
What happens when a virus encounters a bottleneck is encountered?
Only one or two quasi species survive
what is the purpose of combination therapy in HIV infected patients?
- monotherapy increases the risk of a single nucleotide change creating resistant strains
- In combo therapy virus needs 5/ more simultaneous mutations mutations= unlikely
What is the name of the treatment against HIV?
HAART highly active anti-retroviral therapy
What is antigenic drift?
Antigens gradually change over a period of time due to pressure exerted by antibodies
How do new viruses emerge?
- zoonosis
- genetic variation
- increased exposure- Tavel/ world population
- increased exposure- spread of vector
- new discoveries
Name some viruses which were recently discovered
Hepatitis C
HPV 16 and 18
HHV8 - causes kapok’s sarcoma
Merkel cell polyoma virus
What influences the emergence of infections?
- Environmental modification
- world population
- climate change
- travel
- farming practice (monoculture)
- immunosuppression
- Medical progress
What are arboviruses?
Viruses transmitted to humans by arthropods such as mosquitoes and ticks
Name some arboviruses
- what sort of virus do they tend to be?
- what is their host?
Yellow fever Dengue West Nile Chikingunya - Flaviviruses= single strand positive- sense RNA genomes - Mosquitoes
What causes the levels of arboviruses to increase
- global waring= increased distribution of mosquitoes
- Decrease in mosquito control
- imports
- stagnant water (dams)
Which animals are dead end hosts for the west Nile virus?
Horses
Humans
What group of viruses does the West Nile virus belong to?
The Japanese encephalitis group of flaviruses- disease goes to the brain
Which group of people were most affected by WNV in New York?
The elderly
What is Antibody dependent enhancement of Infection? Which viral infection does this apply to?
Dengue Haemorrhagic Fever
- 4 serotypes
- 1st infection you develop antibodies against this serotype
- 2nd infection- antibodies from first serotype make you more sick
What are the risk factors for Dengue Haemorrhagic Fever?
- Virus strain
- Pre-eisting anti-dengue antibody (from previous infection, maternal antibodies in infant)
- Age
- Higher risk in secondary infections
- Higher risk in locations with two or more serotypes circulating simultaneously at high levels
Why is it that dengue antibodies cause opposite reactions (neutralise or enhance infection)?
NEUTRALISE: homologous antibodies bind tightly to vision and stop it entering the cell
ENHANCE: non-homologous = low affinity binding but doesn’t block. Antibodies can bind to Fc receptors on immune cells and enter easily
What are the symptoms of Zika virus?
Headache Pale skin, rash Fever Muscle pain, athralgia diarrhoea red eyes
Define the term Zoonosis. What is a potential consequence of Zoonosis
A disease which can be transmitted from animals to humans. Can cause a pandemic but don’t spread easily
What was the animal source of ebola
Fruit bats or monkey species
How was the spread of Ebola managed?
- Protective ebola suit worn
- Contact tracing and containment
- isolation of infected individuals
Where did Severe Acute Respiratory Syndrome originate and spread to? and which animal did it drift from?
- from bats and civets
- started in China
- spread to Vietnam, Singapore
How is SARS spread?
Through respiratory droplets
especially through nebulisers in hospitals
Which age group doe sit particularly affects
High mortality rate in the elderly
Why was the epidemic overcome so quickly?
Long period of time between symptoms and infectious stage so you can isolate the symptomatic individuals
Which virus causes SARS? Which receptor does the virus bind to? and with which molecule does it bind?
- Coronavirus (largest RNA virus 30kb and +ve sense RNA)
- envelop spike protein highly plastic can adapt to bind to different receptors
- receptor is ACE-2 protein
What is MERS, which virus causes it and which animal species did it originate from?
MIDDLE EASTERN RESPIRATORY SYNDROME
- coronavirus
- fruit bats –> camels –> humans
What does MERS cornovirus cause in older infected persons?
- ARDS (acute respiratory distress syndrome)
Which receptor does coronavirus bind to?
DPP4 in the lungs
Give an example of virus recombination
Swine Flu H1N1- Human flu and Avian flu mix in pigs forming a new virus
What is antigenic drift?
where a virus circulates in humans and slowly changes over years.
What is H7N9? Where does it originate from?
Bird Flu
China
