PBL Week 5 Flashcards
How can viruses invade and harm human cells?
First, viruses attach themselves to specific receptors on the surfaces of our cells. Then, they penetrate and enter the cells, at which point the capsid breaks down and the genetic material inside the virus breaks free. This is called receptor-mediated endocytosis. Then, the virus can replicate:
For DNA viruses, the viral DNA begins to replicate and creates messenger RNA, which codes for capsid proteins. The replicated viral DNA and the new formed capsids now combine to make many new viruses, leaving the cell. Usually uses viral DNA polymerase for replication.
For RNA viruses, the RNA enters the nucleus where it is replicated using viral RNA polymerase. The RNA then makes capsid proteins, which combine with the new RNA molecules to make new viruses, leaving the cell.
What do the terms zoonosis and spillover mean (providing examples) and why are these increasing?
A zoonosis is an infectious disease that has moved from animals to humans. A spillover is when an infectious disease moves from a reservoir population to a new host population. Examples include HIV, SARS, Ebola, Rabies and COVID-19.
These have increased in recent years due to human influence; as we disrupt the environment and expand our populations, animals are pushed out of their habitats and come into more contact with humans, increasing the chances of a spillover event occuring. Certain cultural practices, such as the chinese live animal markets, also cause spillover events, in this case the covid-19 pandemic.
What is the biochemical structure of a virus?
Viruses are not living, as they cannot reproduce on their own. In a virus, the genetic information is encased in a protective protein coat (known as a capsid). They are not cells and are metabolically inert on their own. The capsid comes in a variety of shapes and some viruses have a membrane around the outside. This membrane has various proteins projecting from the outside.
The genetic material can be single stranded DNA, single stranded RNA, double stranded DNA or double stranded RNA.
What is the immunological response to viral infections?
When a virus infects a cell, it is invisible to the immune system. To combat this, cells use MHC class 1 molecules to display proteins from inside the cell on the cell surface; if a virus is present, this will include viral proteins. Cytotoxic T-cells have T-cell receptors which are all specific to a certain viral protein. If it detects it’s specific protein, the cell release cytotoxic factors to kill the infected cell, alongside the virus within it.
Sometimes, viruses combat this by interrupting MHC molecules. NK cells, however, can detect if there is a reduced number of MHC molecules on a cell surface and will also release cytotoxic factors to kill the cell.
These cytotoxic factors are stored in granules and are released by granulation. They include perforin, which creates holes in the cell membrane and granzymes, which enter these holes and trigger apoptosis.
What is an emerging disease and what are some examples?
Emerging infectious diseases are diseases whose incidence in humans has increased in the past few decades or which threaten to in the near feature. They can also be outbreaks of previously unknown diseases. Examples include HIV, SARS, E.Coli and Zika virus.
Why can a newly emerging disease have an impact on health, society and the economy that is hard to predict?
Because epidemics and pandemics happening are random occurences and are nearly impossible to predict with any degree of accuracy. Although WHO has certain diseases on a watch list to prepare the world in case one causes a pandemic, this doesn’t always work; the covid-19 pandemic caused the biggest recession since the great depression, shut down businesses for over a year and has caused the deaths of over 3 million people, yet we had no way of predicting that the spillover event was going to happen.
How can viral diseases by diagnosed in a lab?
Electronic microscopes can be used to identify the family of virus present by just looking at the virus after a negative stain has been applied.
Nucleic acids can also be used to identify specific viruses in a culture, using complementary sequences as probes. This is done using PCR.
Viral isolation from a tissue can be done using a microscope and considerable expertise, looking at the cell layers and detecting degenerative changes. Can be used to analyse genotypic and phynotopic changes in viral populations.
What is the one health approach and why is it important?
One health is the collaborative effort to achieve optimal health for people, animals and our environment. It is important as the health of animals and the environment directly affects our health, too. For example, spillover events due to us disrupting animal habitats and global warming is occuring due to the effects we are having on the environment. Therefore, it’s mutually beneficial for us to not only look after our own health, but the health of animals and the environment, too.
What can be done on a global scale to prevent the next pandemic?
Learn from the covid-19 pandemic, have specific plans in place now that we know what a pandemic in our modern world looks like. A more in-depth watch list for certain diseases. More money put into study of these diseases. An effort to reduce incursions into animal’s habitats and a reduction in climate change in order to avoid spillover events.
