Emerging viruses
/If you are not sure what viruses are, please read the blog post “What are viruses?” first before reading this one.
What are emerging viruses?
Emerging viruses are those that appear suddenly or suddenly come to the attention of scientists. New or novel human viral diseases are usually caused by already existing viruses that have expanded their host range. For example, instead of being specific to birds, the avian influenza virus H1N1 expanded its host range from just birds to include humans.
Image of Coronavirus MERS-CoV. Coronaviruses get their name from the crown-like spikes on their surface. (Photo by CDC on Unsplash)
Emerging viruses can also be caused by a viral strain the host cell had previously not been exposed to. For example, the Ebola virus, one of the deadliest viruses known, is thought to have been around long before the first case was reported.
Once it has infected its first host, the new emerging viruses can go on to infect many people at the same time, spreading from person to person in a locality where the disease is not permanently prevalent. With travel, these emerging viruses can then spread to other locations around the world through infected individuals.
There are many examples of emerging viruses such as Human Immunodeficiency Virus (HIV) which first appeared in the 1980s in the USA, the deadly Ebola virus which was first reported in 1976 near the Ebola river in Central Africa, and Severe Acute Respiratory Syndrome (SARS) which appeared in China in 2003. Most recently, in January of this year (2020) the novel Coronavirus COVID-19 was first detected in Wuchan City, China before spreading to other countries as people traveled around the world.
What causes a virus to suddenly emerge?
Emerging outbreaks of ‘new’ viral diseases in humans can be due to three main processes.
One process is through the mutation of existing viruses generating new strains; RNA viruses particularly have a high rate of mutations. These new strains of the virus may be better at infecting their host cell leading to disease. A good example is the influenza virus that causes seasonal outbreaks of flu due to the virus mutating every year, becoming different from the year before; this is why each year we need a new flu vaccine.
Other existing viruses can mutate to produce a new strain of the virus that is able to expand its host territory and so move from one species to the next. Coronaviruses are a good example of zoonotic viruses - viruses that have spread from animals to humans. A mutation in a coronavirus strain previously found only in animals, such as bats, cats, and camels, has allowed the virus to expand its host range to humans. Once this happened, the coronavirus is able to spread from person to person. The large family of coronaviruses can cause a range of symptoms from the common cold to the more serious respiratory illnesses as seen with SARS, Middle East Respiratory Syndrome (MERS) and COVID-19.
Finally, some viruses may be initially confined to an isolated population, but then spread globally, as was the case of HIV. Acquired Immunodeficiency Syndrome (AIDS), caused by HIV, went initially unnoticed for decades as this disease began to spread around the world through blood transfusions, sharing of intravenous needles, sexual promiscuity and travel.
How do viruses spread?
Viruses are infectious and they do not discriminate! As long as you are the right species it will infect your cells.
Human viruses can spread easily from person to person. They are very good at high jacking our mechanisms such as sneezing and coughing to help them spread to other people. As you sneeze or cough you release tiny droplets. If these droplets then fall on the nose, mouth or eye of another uninfected individual, the virus can then enter the host and find a cell to infect. Other viruses spread via bodily fluids, for example HIV can spread by blood transfusions or from an infected mother to her child during pregnancy.
The coronavirus that causes SARS, SARS-CoV, is known to have originated in bats and the MERS coronavirus, MERS-CoV, from camels. Both viruses then expanded into humans that were in close proximity and working with the animals already infected with the virus. It is still not known where COVID-19 originates from, but you can keep up to date with the latest news on COVID-19 on the WHO website.
What is the difference between an endemic, epidemic and pandemic?
An endemic is when a disease is confined to a specific area, for example, malaria in some parts of Africa or chickenpox among school children. An epidemic is a general outbreak of a disease like the flu, and a pandemic is when an epidemic becomes global. One of the worst pandemics was the flu pandemic of 1918 which started in the USA and quickly spread across the world resulting in approximately 50 million deaths. The last pandemic was in 2009 with 100,000 to 400,000 deaths in the first year, caused by Swine flu, a new influenza A H1N1 virus (WHO statistics).
How can we protect ourselves against viruses?
There are a lot of viruses out there, not all are able to infect humans, and most are harmless. Vaccines are available against some viruses, such as measles, and this helps reduce the incidence of the disease and chances of an outbreak. In other cases, antiviral drugs are used to slow the progression of viral infections, as with HIV.
Our skin is a pretty good barrier against most infections. However, the easiest and best way to avoid catching and spreading viruses, as well as other types of germs is by washing your hands regularly (CDC has a good guide to when and how to wash your hands).
Other basic hygienic steps (which everyone should be doing anyway) to help protect you and stop a virus (as well as other germs) from infecting others include using a tissue when you sneeze or cough and then throwing it away. Avoid close contact with people who are visibly sick and showing symptoms, and please stay home when you are sick to avoid spreading the illness to others. Also avoid touching your eyes, nose, and mouth when you are out and touching common surfaces. A good tip, and something I do, is to press buttons for lifts (elevators) and ATMs, etc with your knuckles instead of fingertips in case you do touch your face or forget to wash your hands before you eat – after all you don’t eat with your knuckles!
With the recent rapid spread of the coronavirus COVID-19, it is important more so than ever to listen to the warnings issued by WHO and local governments. Social distancing, that is being at least 2 meters away from anyone at any time (unless you live in the same house), is very important to help avoid the spread of the disease. It is becoming clear that those with underlining health issues should self-isolate. This is because as their body is already compromised, it will be harder for them to fight the COVID-19 viral infection and so are more at risk of developing severe symptoms that could lead to death. Young and middle-aged adults are also at risk of serious illness form this disease. During this pandemic, it is important for us to all work together to slow the progression of the disease.
Remember viruses do not discriminate!
If you enjoyed reading this, please like, share or leave a comment.