Generally human disease transmission spreads in one of three ways. Direct contact, touching something contaminated by someone else, or by getting too close and breathing a floating germ from someone else via the air.
History of infectious disease transmission
Generally human disease transmission spreads in one of three ways. Direct contact, touching something contaminated by someone else, or by getting too close and breathing a floating germ from someone else via the air. Throughout history humans have had to deal with many large pandemics like the current corona19 virus and many of those past pandemics were devastating to the human population.
Prior to the agricultural revolution 10,000 years ago the hunter gatherer societies of the previous 2 million years rarely had to worry about transmitted diseases. This was because with a wandering nomadic lifestyle and small groups of people numbering less than 150 there just wasn’t the chance to transmit any illness to enough other people at the time.
As communities grew in the agricultural era this became more easily achieved as people started travelling between larger groups of people.
Back in 430 BC Athens was devastated by a plague whilst besieged by the Roman army. Two thirds of the city state population died. Similar types of “local” disaster occurred periodically throughout the last two thousand years.
In 541 AD the Justinian Plague which spread throughout the Mediterranean area causing to weaken the Roman empire just when they were attempting to regain their earlier historical strength in the region. This plague kept recurring for the next 200 hundred years.
The big one that everyone has heard about occurred in 1350-the Bubonic Plague caused the loss of an estimated one third of the world’s population at the time.
The data from the Bubonic Plague in London around 1665 shows the following.
This graph shows the typical disease curve associated with pandemics. As the disease spreads to more and more of the population, less and less people remain to become infected so the transmission rate drops and the disease finds it harder to meet new people. Many new civilizations were severely affected when introduced
diseases arrived as evident by the South American Tribes, and the First
Australians here in Australia.
History also shows us that these plagues often returned in subsequent times with usually less affect in the communities due to many now having resistance to the disease.
In today’s era, people travel the world in enormous numbers so any new disease that emerges is quickly able to be transmitted around the whole world in weeks rather than centuries as occurred in the past when the faster movement was generally at the speed of a walking human rather than a supersonic jet.
But the transmission graphs still look like they did in 1665 in London because that’s the way infectious diseases spread. How can we mitigate these facts? Well reducing interactions between people, cleaning, and quarantining work just as good now as they did in the past.
Countries have attacked the Virus quite differently and inside America even States have dealt with the problem in a multitude of ways-just like they did in 1918 when the “Spanish Flu” arrived. Those Countries and States that acted quickly have had the most success and the least affected populations.
If every person was able to be kept within their own homes for a 4 weeks period and assuming that once infected survivors were not able to infect another after 4 weeks later, then the disease would completely die out. As measures take effect to reduce the transmission rate there gets a point where the numbers getting affected are less than those affected at an earlier rate and then the numbers of current infectious people reduce until the disease seems to go away.
Of course, it hasn’t gone away if anyone infected spreads it to others so that is why we get second and third waves over time. As herd immunity develops the disease has a harder time getting transmitted so its affect also reduces over time within the population.
In the end, a vaccine is the goal to prevent further infections.
Many countries are now showing data graphs appearing to reach a peak and this would mean an estimate could be made as to when the worst of it was past. However, even when that were to occur, an easily transmitted disease with a high rate of mortality would return as soon as people started to interact again. Measures will need to remain in place.
This chart from Spain shows an expected trend to the peak
level and the reduced numbers of people affected due to social distancing
measures introduced That should give reassurance to those Countries and
communities that started such a strategy early.
Based on observations from many of the other Country charts
a 3 months window appears to be the time for the start to the later stages of
the spread. Of course, you must remember that even when the numbers reduce to
lower levels any relaxation of prevention measures will likely produce a second
wave.
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