World on the border of life
Viruses - World Travelers
When does flu season start?
The flu is a true seasonal disease that occurs in the colder part of the year. In the northern hemisphere, the flu season lasts approximately from November to March, and in the south from May to September.
Why is flu more common during the colder part of the year?
Influenza viral particles are more stable at low humidity. Since cold air possesses less moisture than warm air, viral particles are more stable and they can be transmitted over longer distances. The infection can be transmitted between persons who are approximately 2 meters away!
Besides, people spend more time indoors in the winter, so the risk of infection is higher.
You can find out more about the effect of humidity on viral particle stability.
Is there flu in warmer regions?
Although you might not think so, you can get the flu even in the tropics, throughout the year! Temperatures and humidity in the tropics are high, which doesn’t favor viral particle stability. As the temperature rises, so does the activity of the viral proteins and the nucleic acids that build them up reduces. However, due to the high humidity, there is less evaporation and so the droplets containing the viral particles are larger. Larger droplets stay longer on surfaces, thus increasing the risk of flu viral infection.
Viruses - the travelers
When the Spanish conquistadors came to present-day Mexico in the 16th century, they clashed with Native Americans there. Then, Montezuma, the Aztec Emperor, was killed. In the coming years, many Aztecs died because they were not resistant to the pathogens brought by the Europeans (pathogens of smallpox, influenza, hepatitis, etc.). However, the Spaniards also suffered the same fate - they suffered from severe diarrhea, called "Montezuma's Revenge", which was caused by local microbes.
Pandemics, epidemics?
Unlike the "ordinary" seasonal epidemics caused by viral variants, with which people have already been in contact, drastic changes in viral glycoproteins almost always lead to global epidemics - the so-called pandemics which lead to many casualties. As pandemic variants are generated by mixing parts of the genome of the virus from different hosts, all pandemics are caused solely by type A influenza virus. Several influenza pandemics with many casualties have had a huge impact on human history. It is estimated that the viruses have taken four times as many lives during the 20th century as World War I and WWII combined!
How did viruses lead us to the Renaissance?
At the end of the Middle Ages, many diseases caused by microbes spread across Europe, including the influenza virus. Without exception, the rich and the poor, kings and serfs, sinless and sinners became sick. Their appearance prompted people to start questioning religious dogmas and socially imposed hierarchies, thus contributing to a change in the way they understand the world. Therefore, some say that without the virus and other pathogenic microbes there would be no renaissance.
The most famous influenza pandemic
The largest number of victims is attributed to the so-called Spanish flu (subtype H1N1) that appeared during World War I. Because of the fear of lowering the morale of the soldiers, in many countries, it was forbidden to talk about the high mortality caused by influenza. Consequently, the lack of information and the departure of soldiers to distant battlefields made contagion spread even easier!
Spanish Smurfs
During the famous Spanish flu epidemic in 1918, the skin of many patients had turned blue! This happened due to the lack of oxygen in the tissues. Namely, because of the severe inflammation, their lungs had filled with too much fluid causing them to lose their function and people would drown "in their own fluids".
Be a virus - travel the world!
Although we consider that globalization is a modern phenomenon, the Spanish flu had already "traveled" the world in 1918 thanks to soldiers from various countries who often traveled to very distant battlefields. Those who managed to survive the war would often return home with a "viral souvenir"...
Why was it called Spanish flu?
The name Spanish flu for the known pandemic is incorrect. Since Spain was neutral during World War I, the Spanish press was not subject to censorship. Therefore, the Spanish newspaper was the first to report the consequences of the pandemic. At the same time, to avoid panic among the soldiers, the allies were trying to cover up such news. Besides, King Alfonso XIII of Spain became reportedly ill with the flu and frequent reports on his medical condition further fueled the false assumption that the influenza started to spread from Spain. In Japan, for example, the Spanish flu was known as a "sumo-disease" because the epidemic erupted/broke out after the sumo-fighters fought.
A flu in Spain and other countries
In Spain at that time, the flu was known as the "Naples soldier", according to the aria from a musical operetta entitled La canción del olvido (The Song of Forgetting). Federico Romero, one of the librettists, reportedly said that the song was as catchy as the flu.
Interestingly, during the pandemic, some governments banned handshaking (in Arizona) or spitting in public places (in France)!
Here is some advice given by the US government:
1. Do not inhale someone else's exhaled breath.
2. Take care of the hygiene of your mouth and teeth.
3. Avoid persons who cough and sneeze.
4. Do not visit poorly ventilated areas.
5. Protect yourself from the cold, expose yourself to sunlight and inhale fresh air.
6. Do not drink from the same glasses, use common towels, etc.
7. When you cough or sneeze, cover your mouth.
8. Avoid worry, fear and fatigue.
9. If you feel sick, stay home.
10. Go to work on foot.
11. Wear a gauze mask in the areas where there are sick persons.
What leads to the end of a pandemic?
The Spanish flu ended in the summer of 1919 when most patients died and others acquired immunity against the pandemic H1N1 virus subtype. Some pandemics that occurred later, such as Asian flu, Hong Kong flu, or swine flu, ended the same year that they occurred due to the rapid development and administration of the vaccine.
The biggest viral pandemics
1918 – The World
So-called Spanish flu
Responsible: subtype H1N1
Origin of the virus: birds + humans
Beginning point: still unknown, most likely Kansas (US)
Number of deaths: about 50 - 100 million people
1957 - China, the US, and the UK
So-called Asian flu
Responsible: subtype H2N2
The origin of the virus: birds + humans
Beginning point: Eastern Asia
Number of deaths: 1 - 2 million people
1968 - Hong Kong, the United States, Western and Eastern Europe, South America, Australia and Japan
So-called Hong Kong flu
Responsible: subtype H3N2
Origin of the virus: bird + humans, altered Asian influenza virus
Beginning point: Hong Kong
Number of deaths: 1 - 4 million people
2009 - Mexico, the United States, Spain, Germany, Austria, UK, Israel, New Zealand and in Canada
So-called swine flu
Responsible: subtype H1N1
Origin of the virus: Pigs + birds + humans
Beginning point: small town La Gloria (Veracruz, Mexico)
Number of deaths: 284,500 – 575,400 people
Viruses from the depths of the sea
Viruses are omnipresent. They can be found in air, water, soil, but also in less accessible places like deserts, hydrothermal vents, ice or salt lakes.
Hydrothermal vent in Yellowstone National Park.
Dead Sea coast, i.e. salt lake in Israel, Palestine and Jordan.
Did you know that even 10 million viral particles can be found in one teaspoon of seawater, which is ten times more compared with bacteria?
Don't worry, these viruses mostly infect microbes that live in the sea. These include, for example, algae, bacteria, archaea, and protozoans such as amoebae, slipper animalcules and euglena.
Slipper animalcule
Cyclops
Daphnia magna
Euglena
Amoeba
By infecting bacteria, it releases around 10 trillion tonnes of carbon a day!
A viral infection can affect synthesis of certain bacterial proteins.
Viral DNA can serve as source of new host genes.
Why are marine viruses important?
Marine microbes, such as bacteria and algae, play an important role in the decomposition of dead marine organisms and the circulation of biogenic elements in nature. Since viruses can infect microbes, they play a significant role in maintaining ecosystem balance and biodiversity.
For example: Red tide is the result of increased reproduction of algae under favorable environmental conditions. By infecting microbes, viruses reduce their abundance. By reducing the number of algae on the surface of the sea, this allows light and oxygen to reach other organisms to which the supply is necessary for their life.
Red tide at Hermanus, South Africa - as a result of a massive bloom of dinoflagellate.
Learn more about marine viruses and their role
Unusual inhabitants
Some of the largest and most diverse virus specimens have been found in the sea. Although viruses are sub-microscopic (their sizes are expressed in nanometers!), among them there are exceptions known as giant viruses. Their diameters are 0.6 - 1.5 µm. For comparison, the average bacterial size is about 1 µm! Did you know that viruses, due to their small size, can only be seen under an electron microscope? However, the giant viruses, due to their extreme size, can be observed even under a light microscope!
Light microscope
Electron microscope
Besides the size of their particle, giant viruses also stand out with the size of their DNA genome. Unlike the usual DNA viruses, whose genomes consist of 3 - 200,000 pairs of nitrogenous bases, the genome of giant viruses has more than one million pairs!
The hosts of these large viruses are protozoans (most commonly amoebae), algae, fungi and bacteria.
The first giant viruses discovered were:
Mimivirus (year 2003.)
Mamavirus (year 2008.)
Megavirus chilensis (year 2011.)
Pandoravirus (year 2013.)
Phitovirus (year 2014.)
Mollivirus (year 2015.)
Medusavirus (year 2019.)
The first giant virus found in the sea was Megavirus chilensis (about 0,680 µm in diameter) near the coast of Chile. Later, a larger virus was found in the same area - Pandoravirus salinus (about 1 µm in diameter).
What makes Mimivirus special?
Mimivirus is an abbreviation of the denotation microbe mimicking virus, that is, a virus that by its size and particle structure mimics microbes such as bacteria. Its official name is Acanthamoeba polyphaga mimivirus because it’s a host is the amoeba Acanthamoeba polyphaga. It is round-shaped and on the surface has filaments like cilia. Its 0.6 µm diameter is even 35 times larger than the smallest detected virus of 17 nm in diameter!
Apart from their size, viruses can also vary in shape, where we can distinguish archaea viruses as particularly interesting. These viruses have unique and interesting forms. Some have filaments that are claw, lemon, droplet or bottle-shaped.
Which viruses have interesting forms?
Bicaudaviridae
Acidianus two-tailed virus from the family Bicaudaviridae (lat. Bi-cauda, two tails) is lemon-shaped. Their hosts are archaea from the genus Acidianus that live at a temperature of 85 oC°!
Guttaviridae
Aeropyrum pernix ovoid virus 1 and Sulfolobus newzealandicus droplet-shaped virus from the viral family Guttaviridae (lat. gutta, droplet) are droplet-shaped. Their hosts are archaea from New Zeland named Sulfolobus newzealandicus.
Ampullaviridae
Acidianus bottle-shaped virus from the viral family Ampullaviridae (lat. ampulla, bottle) is bottle-shaped. Their hosts are archaea from the genus Acidianus from Italy.
Rudiviridae
Sulfolobus islandicus rod-shaped virus 2, Acidianus rod-shaped virus 1 and Sulfolobus islandicus rod-shaped virus 1 from the family Rudiviridae (lat. rudi, small rod) are rod-shaped viruses with filaments that look like claws. Their hosts are thermophilic archaea Sulfolobus islandicus from Iceland.
Studies on archaeal viruses are very expensive due to the specific localities on which archeae reside. Therefore, only a small number of scientists are researching that matter, so our knowledge of these interesting viruses is modest.
The site was co-financed by the European Union, from the European Social Fund.