Lecture 6 pt 2 Flashcards
Viruses and bacteria need hosts, how do they get them
Droplet transmission
Airborne transmission
Waterborne transmission
Vector transmission
what is Droplet transmission —
for example, being passed along when one host accidentally sneezes on another. The flu is transmitted this way
what is Airborne transmission —
for example, being exhaled by one host and inhaled by another. Tuberculosis is transmitted this way.
what is Waterborne transmission —
leaving one host (e.g., in feces), infecting the water supply, and being taken up (e.g., in drinking water) by a new host. Cholera is transmitted this way
what is Vector transmission —
getting picked up by a carrier (the vector — e.g., a mosquito) and carried to a new host. Malaria and Zika are transmitted this way
what influences how “virulent” a virus or bacteria is
The form of transmission will influence how “virulent” a virus or bacteria is
what is Virulence
is how much the virus/bacteria affects the host
We can think of virulence as the reproductive output of the virus:
highly virulent strains have created more offspring than less virulent ones BUT strains that are too virulent risk losing their host before being transmitted
what is transmissibility
how easily they move from host to host
what does natural selection favour
We predict that Natural Selection will favor viruses and bacteria that achieve a balance between their virulence (their reproductive output, how sick they make you) and their transmissibility (how easily they move from host to host)
are sexually transmitted viruses more or less virulent
Thus, sexually transmitted viruses, for example, are generally less virulent because their hosts need to be reasonably active to transmit the virus
what are examples of Flu viruses
H1N1 and the 1918 spanish flu
what are examples of Filamentous viruses
hemorraghic fever viruses like marburg and ebola
what are two major kinds of viruses
Filamentous viruses
Flu viruses
what is an epidemic
is when new cases of a disease exceed expectation based on recent experience
what is a pandemic
is a epidemic that has spread through a large region, for example multiple continents or even worldwide
what else can we do with virus’s
We use them as tools: for gene therapy, for implanting false memories into mice, etc
how hav viral infections have influenced human evolution
Our interactions with them over millions of years has resulted in additions and translocations to human DNA
are viruses adaptable
XTREMELY
What makes viruses so adaptable
Relatively simple construction
short generation time
(one virus can quickly replicate, become many viruses)
High mutation rates
how are virus’s simple to construct
1) Made up of two or three parts:
Nucleic acid (can be RNA or DNA, we’ll discuss both)
Protein coat or capsid (contains the DNA/RNA)
Some have a lipid membrane or “envelope” covering the capsid
2) Viruses don’t replicate (copy themselves) on their own, they use the machinery from the host cell
3) DNA/RNA isn’t long and tied up with histones (like ours), but comes in small packets that are easily picked up and transcribed or incorporated into the host genome
what is High mutation rates especially high in
RNA virus’s
why is High mutation rates especially high in RNA virus’s
Because viral RNA polymerases lack proof-reading ability so there are just more frequent errors during copying
This can make it difficult to develop vaccines (because the genetic sequence is always changing)
Influenza A viruses are divided into subtypes based on two surface proteins
the hemagglutinin (H) and the neuraminidase (N).
what is Hemagglutinin
is important for binding and selectivity, it is the “key” to the cell’s “lock” from the video
what is Neuraminidase is
important to let new copies of the virus out of the cell so they can infect other cells
In their host species viruses often undergo ____ or ____ evolution, gradually changing through a process called antigenic drift
In their host species viruses often undergo slow or limited evolution, gradually changing through a process called antigenic drift
what is Antigenic drift
: small changes in the virus that occur gradually through the accumulation of mutations
Over time, antibodies to a virus may not recognize new strains of the virus that result from this drift
how is Antigenic drift different from genetic drift
unlike genetic drift, these are small, positive adaptations of the virus not small, random changes in allele frequency
when viruses infect a new host they show ___ evolution
when viruses infect a new host they show rapid evolution
what is Antigenic Shift:
Large, abrupt changes that occur, often because a cell has been infected by multiple viruses, for example viruses from more than one species
Such a “shift” occurred in the spring of 2009, when a new H1N1 virus with a new combination of genes emerged to infect people and quickly spread, causing a pandemic
what happens to the people when such a shift occurs
When a shift happens, most people have little or no protection against the new virus
what is H1N1 also caled
swine flu
The H1N1 virus associated with the 2009 pandemic is an example of an _____
The H1N1 virus associated with the 2009 pandemic is an example of an antigenic shift involving viruses to three species (pig, bird, human)
the H1N1 was a virus with parts of a viruses from multiple species such as:
the H1N1 was a virus with parts of a viruses from multiple species
1) A pig contracted a bird virus and a human virus
2) Bird and human viruses combined with swine virus that was in the pig
3) New bird-human-pig virus was transmitted from pig to human
4) New virus was then transmitted from human to human
The H1N1 virus associated with the 2009 pandemic turned out to be ________
Highly transmissible but Not highly virulent
That is, it was easily passed from host to host (transmissible)
But most people just felt a little sick and then recovered, few people died (not very virulent).
That time, we were lucky But that’s not always the case…
H1N1 2009 Pandemic
There was a lot of worry about this virus,
WHY?
H1N1 2009 Pandemic
There was a lot of worry about this virus,
WHY?
Because viruses from antigenic shifts result from such large, rapid changes, immune systems will be unable to recognize them
Humans have some immunity to other human viruses, but do not have immunity to viruses from other species
Shifted viruses can be highly virulent
It is also unpredictable how transmissible they will be
1918 Spanish Flu devestation
Infected 500 million people and killed 50-100 million people (~2.5% of the population)
This virus was strange for a few reasons (1918 spanish flu)
1) There were three waves of infection, very close together in time.
The SECOND wave was the most deadly
especially strange since you expect greater immunity during the second wave
2) Healthy, young adults had surprisingly high death rates
By comparison, seasonal flu kills <0.1% of the population annually
almost entirely very young or very old individuals (e.g. black line below) with weak or compromised immune systems
3.) Effects of the virus were really rapid
Virus activates the hosts inflammatory response
Triggers a tremendous immune response that destroys the hosts own cells
This could be why it’s so deadly in young adults, people 20-40 years old, because they have strong, active immune systems!
was the 1918 spanish fee highly transmissible or virulent
the disease was both highly transmissible AND highly virulent