Age of Uncertainty

A report in the New York Times yesterday suggests that there is now evidence of Covid-19 transmitting faster in cold, dry climates and slower in warm, humid climates.

Warmer Weather May Slow, but Not Halt Coronavirus by Knvul Sheikh and Ernesto Londono, dated March 22, 2020, discusses a study conducted by researchers at Massachusetts Institute of Technology which found that regions with average temperatures above 18C account for fewer than 6% of global cases so far.  Differences in transmission rates have been noted across different climatic regions within both China and the USA, as well as between European regions.  However, it is also considered too early to make any certain conclusions.  Only time will tell.

Without a laboratory test to identify the cause, someone suffering from symptoms of an upper respiratory tract infection will never know what they have.  Multiple viruses can cause the common cold, including but not limited to Rhinoviruses, Adenoviruses and Respiratory Syncytial Virus (RSV).  Four known serotypes of Coronavirus circulate among humans, causing symptoms of the common cold and sometimes leading to lower respiratory tract infections such as bronchitis or pneumonia.  They tend to occur mostly in cooler seasons.  Whether this seasonality becomes a feature of Covid-19 remains unknown for now, but evidence is starting to mount that perhaps it will.

Reasons for this climatic pattern appear to be at least in part, related to the structure of the virus.  As this diagram shows, Coronaviruses are surrounded by a lipid envelope (the red layer) which protects the viral genetic material (RNA and N protein) inside. Without all of these parts, including the lipid envelope, the virus can neither replicate nor survive.

Coronavirus 02
https://www.scientificanimations.com, CC BY-SA 4.0,

Viruses can only infect human cells when they are structurally intact.  They can survive for periods of time outside the cells of the host animals that they infect as long as their components remain complete and undamaged.  A human respiratory virus may survive on human hands or surfaces such as door handles and benchtops, doing no harm to anyone.  When the virus is transported to a nose or mouth, for example by infected hands, or via droplets coughed out by an infected host which are then breathed in by another, this can present the virus to respiratory cells of a new host allowing the virus to invade those cells and replicate.  Unlike bacteria, the only way that viruses can reproduce is by “stealing” parts from it’s host cells that the virus does not have, but that it needs in order to replicate. It is this process which damages host cells and causes illness.

The lipid envelope encasing Coronaviruses appears to be fragile to heat, humidity and UV light.  In warmer, more humid climates, it may be easily damaged, rendering the virus less efficient at transmitting between people than it is in cooler climates.

The situation of Covid-19 in Cambodia so far, seems to suggest that perhaps the virus is not easily transmitting in their environment.  This is the hottest, most humid time of year in Cambodia.  In addition, due to fears of the pandemic, normally bustling streets are deathly quiet as people hide away hoping to protect themselves.  So the very limited evidence of local transmission (of 86 cases as at yesterday, only 6 were transmitted locally, and all had very close contact with an imported case/s) may be as much due to the self isolation taking place, as any climatic conditions rendering the virus unviable.

Meanwhile businesses are closed, staff have been laid off, vendors have no customers and a much larger pandemic, of hunger and starvation seems to loom.  Where the Australian government are releasing multi billion dollar stimulus packages to keep our national economy afloat and protect our newly-unemployed and vulnerable, no such back up exists in poor countries, where survival is never guaranteed.  For places like Cambodia this is not a stand-alone public health crisis, and will have far reaching impacts for perhaps years to come.  It seems sadly ironic when the virus that started it all may not even spread easily amongst this population!

Nevertheless, it’s important to understand that:

WHO Fact Climate

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