Infectious disease: nature bites back

Twenty-one years ago, Thomas Eisner and Paul Erlich published a short satirical piece in the journal Science on the resurgence of infectious disease. They claimed that their comment was based on a recently received document from the World Convention of the Pathogen Association entitled "Our Infective Future: The New Agenda". In it the President of the Pathogen Association, appropriately named President Prion, stated in his opening address to delegates, the following:-

" must inform the infective community, that most of our natural hosts are disappearing. Never has our future been bleaker, threatened as it is by a reality that was unthinkable 5,000 years ago. Our food supplies are being displaced by a single species – Homo Sapiens … Action is called for. Indeed in this disaster there is a germ of an opportunity and an opportunity for the germs. In our evolutionary tradition, we must prepare ourselves to change our tastes, shift hosts, and take advantage of the single most appealing and available addition to our menu. Homophagia is the way of the future. Some congratulations are in order. To HIV for making the big leap most recently and for killing slowly enough to share the host with many of the rest of us. To the TB bacillus for its unexpected renewed success. To the viruses – Ebola, Hanta, Lassa and Marburg – for their gallant efforts. To Legionella for its stealth [ and had he been speaking today he would have added – SARS, Bird Flu, Swine Flu, Ebola and Covid as well]. There are many factors that give us hope. Homo is remarkably hospitable to us. In extraordinary numbers they are undernourished and immunodeficient, have a penchant for keeping on the move and they misuse antibiotics, blind to our evolutionary capacity to develop resistance. They pay little attention to our ability to evolve new levels of virulence, and they are recklessly changing the climate releasing many of us from our historical geographical constraints…

How true and how relevant all this sounds today, when barely a week goes by without the emergence or re-emergence of a new or old microbiological threat to human health and wellbeing particularly at a time when our world seems totally consumed by the threat of Covid. Some years earlier the US Surgeon-General had proudly announced to the American Nation that infectious diseases had been conquered and that we should now move on to address a wide range of chronic diseases like Cancer and Heart Disease. As many people indulged visions of a new infectious disease-free age, new infections were already appearing throughout parts of Africa and Asia.

In fact the 1950s saw a wide range of infectious diseases wreck havoc throughout parts of the world. West Nile Virus burst forth in Israel in a series of epidemics between 1950 and 1954, Korean Hemorrhagic Fever appeared in 1951, Dengue Hemorrhagic Fever appeared a year or so later, while Junin Virus wrecked havoc in parts of Argentina in 1953, as did a range of other exotic infections in India, Brazil and Uganda. Although many of us just ignored such developments, by the 1970s a wide range of infectious diseases struck. The next few decades would witness an endless parade of so called "new infections" from La Cross Encephalitis, Lassa Fever, Hantaan Virus, Lyme Disease, Ebola, Legionnaires Disease, Toxic Shock Syndrome, AIDS, Mad Cow Disease and more recently West Nile Virus, SARS, Ebola, Monkeypox, Bird and Swine Flu and now Coronavirus. Our hope of an infectious free age so triumphantly proclaimed 50 years ago has proved to be illusionary. Over the last twenty-two years infectious disease has returned to our agenda with so-called "new infections" triggering global epidemics, while older infections reappeared.

One of the crucial messages to emerge from the resurgence of infectious disease is that the bio-physical environment remains a powerful, ever-changing force which we continue to under-estimate. The microbial world, without any doubt, has also revealed a dynamism that confirms the importance of evolution in our natural world. We continue to believe that we are the dominant species in the world and that we can simply place our confidence in anti-biotic and anti-viral drugs when confronted by infectious disease. There is an alternative view which simply sees humans as just one of a series of competing species in a world where many processes are cyclical, waxing, waning and evolving. Our anthropocentric quest to control and eradicate all infectious diseases has proved to be utopian.

The emergence and persistence of infectious disease over the last 200 years underscores the reality that mutation and change are facts of life and that the microbial world changes in accord with changes in their environment as well as their host's environment. We certainly appear to have under-estimated such things and placed too much reliance on anti-bacterial drugs and lockdowns to protect us. We also tend to overlook the fact that our continuing interference with the natural environment such as deforestation, road construction, dam building, mining and residential expansion can initiate a wave of factors aiding and encouraging infections to emerge and change.

There are a host of critical factors that help explain the persistance of infectious disease in countries like Australia.

In the first place we tend to overlook the fact that infectious disease emergence is a complex process requiring a number of factors to change simultaneously or sequentially.

Secondly, we tend to ignore the fact that infectious diseases are dynamic, often involving a complex interplay between the disease agent, vectors, animal hosts and natural reservoirs.

Thirdly, most so-called "new Infections" are not new. Many are zoonoses or animal diseases long present in our environment often circulating among their animal hosts without affecting humans until perhaps their host's environment is in some way disturbed.

Fourthly, our medical intervention to control infections can paradoxically increase the burden of disease. This is often seen in our over- use of anti-microbial drugs.

Fifthly, Over the last 60 or so years our vulnerability to infectious disease has increased reflecting a variety of factors such as ageing, increasing marginality, avoidance of vaccination, environmental intrusions and modifications and increased human mobility. To this end national borders have lost their significance and no longer offer protection as infectious disease moves across the world almost at will.

Sixthly, our complacency when confronting infectious disease outbreaks and our government and medical fraternity's inability to understand how ordinary people regard risk and exposure in their lives also adds an important variable. Our history of official response to major outbreaks of infectious disease is simply littered with examples of lack of cooperation, of self-interest, over-reaction and outright antagonisms. Our response to many disease outbreaks demonstrates how vested interests and State-Commonwealth rivalries intersected with matters of health and made infectious disease control a difficult undertaking.

Finally, the way we tend to ignore infectious diseases that cause few deaths but incapacitate many people for a few weeks has long- term implications. Mosquito-borne infections in Australia such as Dengue provide a good example. Dengue epidemics have been a familiar part of Australian life since the 1870s particularly in parts of Northern New South Wales and Queensland. The 1925-26 Epidemic which almost reached Sydney is a case in point where 560,000 cases of Dengue occurred but only 147 deaths. Dengue and a variety of other mosquito-borne infections continue to affect Australians every year but very few die. Perhaps the low death rate is the reason we have lived with and continue to live with Dengue.

Threats from the microbial world are not new. Australia's history is simply littered with outbreaks of infectious disease. Australia has been swept up in at least 22 Pandemics and more than 30 major Epidemics since the early days of settlement including Smallpox in 1881-82 and 1913-17, Influenza in 1891 and 1919, Bubonic Plague in 1900-23, Dengue in 1925-26, Polio in 1903-56, HIV/AIDS in 1982-2011, SARS in 2003, Avian Flu - and now Covid. Many of these produced extraordinary scenes as the Government struggled to come to grips with the outbreaks as well as widespread fear and panic among Australia's population.

In the final analysis major outbreaks of infectious disease present formidable challenges to everyday life and to our Health System. Infectious disease and the associated fear and anxiety acknowledge no borders and the internationalisation of risks have made us all vulnerable. There is much that we have to learn about the emergence/re-emergence and spread of infectious disease, how ordinary people react, and how our Government continues to struggle in its attempt to control such outbreaks.