The threat of a new infectious world

Are we rapidly approaching a new age of infectious disease? Despite more than a century of prevention and control, infectious diseases have not disappeared and remain a critical global problem for our public health causing hundreds of millions of deaths every year around the world. 

Changes in our behaviour and technology as well as climate change and a rapid rise in human mobility has transformed our world. We now live in a borderless world where more people than ever before now cross national and international borders every day. In many cases infectious disease accompanies such movements recognising no border constraints.

Added to this we seem to believe that we are the dominant species on earth and that we can simply level magic bullets at infectious disease agents and come out on top. Nothing could be further from the truth.

We continue to underestimate the microbial world’s ability to change and mutate and adapt to the specific measures that we develop to help prevent their spread. In addition our attempts at disease control have often accelerated the emergence of so called “new” diseases as well as the re-emergence of diseases once thought to have been defeated or under control. 

Our failure to recognise that microbes are the dominant species on our earth possessing the ability to mutate change and adapt to anything we might level at them remains a major hurdle. Our belief that infectious disease is a part of our past history and that our life is now dominated by diseases like cancer, heart disease and stroke is fast becoming a mis-conception.

More than 50 years ago the US Surgeon-General proudly announced to all America that the threat of infectious disease had passed and that we could now devote our attention to dealing with chronic diseases such as cancer and heart disease enjoying a new infection-free age.

Nothing could have been further from the truth and the last 50 years have not only seen a seemingly endless parade of infections such as SARS, Avian and Swine Flu, Zika, Chikungunya Virus and Ebola but also the re-emergence of a host of more common infections such as dengue, influenza, measles, malaria and a wide range of childhood infectious diseases. The recent spread of measles throughout the developed world including Australia plus a significant influenza season this year illustrates what now confronts us.

So just how secure are we? Perhaps not very secure at all. Despite remarkable breakthroughs in medical research infectious diseases are undergoing a global resurgence that threatens our health. This allied to the rise and spread of anti-microbial resistance threatens our health. The measles and influenza outbreaks over the last few months indicate a measure of our susceptibility and the role that human behaviour plays in the spread of infections and the erosion of our health security.

Vaccination hesitancy has played an important role in the spread of measles. But what about a host of mosquito-borne infections that have plagued Australia for generations? Dengue outbreaks have become a frequent visitor to parts of Northern Queensland and outbreaks of Ross River Virus and Barmah Forrest virus often occur further south. Ironically, we seem to have developed a health philosophy that if an infectious disease does not threaten to kill us but simply offers a few weeks of infective illness then we live with it, otherwise we would have had specific cures for such infections decades ago.

Dengue in particular remains an important threat to our health. Australia has a long history of major dengue outbreaks and while the disease is not endemic in Australia the mosquito vector aedes aegypti has a widespread distribution over parts of Australia. Look back in history for a moment. In 1925-26 Australia suffered it greatest dengue disaster when more than 560,000 cases of the disease occurred and the disease spread all over the eastern coast of Australia almost reaching Sydney  and while the epidemic only caused 147 deaths it caused extraordinary panic and disruption to all sectors of Australian society.

Dengue of course remains a major threat around the world and is rapidly spreading.  Today roughly 3.9 Billion people worldwide are at risk of infection.

And let us also remember the 1919 Flu pandemic which caused 1.5 million causes of flu and 15,000 deaths standing as perhaps our greatest health crisis. But then Australian society is littered with infectious disease disasters ranging from measles and smallpox in the 19^th century to bubonic plague, smallpox, influenza, polio and a host of childhood infections in the 20^th century. Finally we would all remember SARS and Avian and Swine Flu and the impact that they had on our society.

So what sort of health circumstances are we likely to face over the next 20-30 years? There is little doubt that chronic diseases such as cancer and heart disease will continue to play an important part particularly as our population continues to age but there is also a strong likelihood that “old” infections will re-emerge as well as so-called “new” infections both of which will have a considerable impact on our health. Travel and trade will continue to play an important role in helping the spread of infectious disease as well as increasing anti-microbial resistance.

In all of this human behaviour reigns supreme whether it be by moving around our world carrying infectious disease, declining vaccination, interfering with the natural environment through deforestation and/or irrigation and dam projects or extending the built environment of urban areas.  All in all it is a disturbing scenario.