DANIEL CLINTON (L6)
If you were to go back in time and ask what caused a particular ailment, the responses you would get would be nothing short of bizarre. People used to believe diseases were caused by anything from bad air to curses hence the common victorian tradition of carrying about flowers to ward off foul-smelling air. Fortunately, owing to the pinnacle of modern science that is the microscope, we now know that this is far from the truth, as what really causes disease is pathogens. Bacteria, fungi and viruses are the three main types of organisms which could be classed as pathogenic (able to cause disease). However, the way in which they operate and the mechanisms through which they cause disease differs greatly between the three
Viruses
Since the start of the Covid-19 pandemic, through social distancing and scandal, one fearsome phrase has remained in the limelight, standing at the forefront of it all: Mortality Rate. Covid, like the vast majority of other viruses, has a high spread rate with, thankfully, a relatively low mortality rate. However, there is indeed a reason these buzzwords like “r-number” and “mortality rate” are so morbidly prevalent in the start of any new pandemic and whilst its sole purpose isn’t for the creation of clickbait, but it is instead due to the high levels of variability that come with any virus.
So why hasn’t a virus like Covid succeeded in wiping our frail population off the face of the earth? Some scientists believe it all comes down to energy…To begin with, viruses, like all organisms have a myriad of traits specific to them that have been evolving for centuries for the sole purpose of their survival and reproduction; strains with more successful traits to allow for their survival, such as rapid reproduction - synonymous with having a higher r-rate - are usually the ones which are able to survive for longer and pass on those successful traits to their offspring. However, this seemingly iron-clad system which has been around since the dawn of time has one major issue, that being it relies on energy.
In the covid pandemic, one notable trend was as variants mutated and gained a higher rate of transmission, their mortality rate had a tendency to decrease, this being seen with many viruses around the world, so the question remained, why does this happen? In many ways, viruses are analogous to a video game character, accessing certain abilities only when equipped with a high enough level of experience. In a similar vein, viruses like all organisms require a base level of energy for growth and maintenance, known as a dynamic energy budget.
As a result, despite the fact that viruses aren’t technically living organisms, the dynamic energy budget theory has also been applied to the covid situation, as the principle remains the same, viruses have a limited amount of energy, therefore having to carefully balance how that energy is used, whether that be into causing more damage to the host organism, or simply into creating more efficient ways to reproduce.
Bacteria
Bacteria have a similar mechanism through which they evolve and adapt traits. However, their method of pathogenesis is extremely different. In short, they can either secrete toxins or directly destroy cells by feeding off of cell content (effectively making them the pac-man of the microbial world), both of which cause harm to body tissues. In addition to this, they can also cause harm through the body’s own immune system, as infected cells have to be gotten rid of. This is often done through autolysis, which is the immune system signaling to cells to release hydrolytic enzymes in order to break themselves down. Whilst this is a normal process, occurring at the end of all cells’ life cycles, it is done more quickly to infected cells as a response to prevent them from multiplying.
Fungi
Fungal infections on the other hand are a dime a dozen, with the World Health Organisation listing them as being the most common of any type of infection. For the most part, fungal infections in humans such as dandruff and athlete’s foot aren’t too dangerous, usually ranging from relatively harmless to mildly annoying. What’s more interesting though is the impact of fungi on much smaller organisms, such as plants and insects.
Plants are vulnerable to a variety of fungal diseases, such as rose black spot and the tobacco mosaic virus. Rose black spot, as the name suggests, causes black spots to appear on the surface of rose leaves. This doesn’t only affect their colour, but also their ability to grow as it reduces the area of the leaf able to undergo photosynthesis. Whilst this may seem minor at first glance, they work to devastating effect, as it means infected plants have to be either treated with fungicides or destroyed entirely to
Resultantly, one could say fungal infections in plants are seemingly harmless, in insects however, their effects are nothing short of terrifying and to see that, we need to look no further than the cordyceps fungus. This is a fungus predominantly affecting ants, effectively turning them into zombies by causing them to decay and climb to the top of tall trees, in order to spread the fungus’ spores to other unsuspecting victims. This however, is a far cry from the walking dead, as this fungus doesn’t affect humans, due to the simple fact that whilst the defense systems in an ant are complex on their small scale, it is nothing compared to those of humans, meaning we won’t need to worry about a rogue zombie fungus spelling the end of mankind anytime soon.