Deadly encounters: are we prepared?

Polio, once thought to be well under control and close to disappearing, has re-emerged in a new form. And what about Bubonic Plague? Today Plague is more geographically widespread around our world that ever before and is nurtured in permanent animal reservoirs which defy control or eradication.

Mosquito-borne infections also continue to dominate our world including Australia. Dengue, Ross River Virus and Barmah Forrest virus cause hundreds of cases every so many years. In Australia since 1870 dengue has been responsible for almost 1000 deaths and more than one million cases of illness.

Ebola and Zika also show us just how quickly new viral infections can emerge and wreck human havoc. Finally, a wide range of childhood infections linger on. Measles is a case in point. In 2018 there were at least 41,000 cases of measles in Europe as well as a number in Australia, all presumably originating from people's inability to seek vaccination for their children.

So what have we learned from our past pandemic experience? The answer is in some respects very little.

SARS, Avian and Swine Flu revealed just how devoid our arsenal of response was and how we were forced to reach back into the past for control measures such as quarantine, cleansing, closures, fumigation, isolation and avoidance. Our real problem is that we continue to believe that we are the dominant species in our world and we continue to underestimate the power and significance of the biophysical environment and the role it plays in our lives.

The biophysical environment is a powerful, ever-changing force and we have severely under-estimated the role it plays in our lives and in particular its significance with respect to infectious disease. We need to appreciate that the microbial world reveals a dynamism that confirms the strength of evolution and adaptation.

Many infectious diseases continually change and mutate in ways that make it difficult for our immune system to adapt or for medical science to provide a satisfactory cure. We are also living in a highly mobile world where tens of millions of people move across national borders most by air in journeys that are far less than the incubation time of most infectious diseases.

Infections now recognise no borders and move at will around our world. Add this to the way we continue to modify our natural environment and intrude on natural disease reservoirs such as Plague and Ebola continually placing ourselves at risk.

There are some things that we have learned however.

Firstly, that pandemics of flu behave unpredictably with some being far more virulent than others generally targeting the very young and the old, although not in the case of the 1918-19 pandemic where people aged between 20 and 39 were most at risk. The reasons why this was the case still remain unclear.

Secondly, that pandemics follow what is known as an "epidemic curve" with a gradual onset, followed by a surge of cases and then a gradual decline.

Thirdly, that flu pandemics tend to unfold in a series of waves, with the second wave often being far more virulent than the first. The 1918-19 flu pandemic came in three or four waves with the first being moderately mild.