Where to from here with Infectious Diseases?

Updated: 4 days ago

Victor Luca, 12-Jun-20.

The Beacon 17-Jun-20

The COVID-19 pandemic has given us a baptism of fire in infectious disease and pandemics and how they can take and upend lives. Yet infectious disease pandemics are nothing new; they have plagued human civilizations for thousands of years. Over the millennia, we have had more than just the odd close shave with infectious diseases.

In New Zealand, thanks to relatively prompt and concerted action by our government, we have come out of the COVID-19 pandemic relatively unscathed, at least in terms of direct physical health impacts. Personally, I would have put us into lockdown as soon as it became obvious that we were dealing with a pandemic involving a novel influenza virus to which the population, in general, had no immunity. However, the “small window of opportunity” that Jacinda mentioned when she announced the lockdown thankfully has turned out to have been enough.

Below is a table of the more important pandemics that we know about.

Most of the pandemics in the table are caused by zoonotic viruses meaning that they are viruses that are transmitted between animals and humans.

You may be surprised to know that although infectious diseases have been with us for a long time, they weren’t always with us. Infectious diseases emerged about 10,000 years ago when there were less than five million humans on the planet. The question arises therefore, from where did infectious diseases emerge?

In the figure below are shown just some of the common zoonotic infectious diseases and the animals from which they came.

The main thing to notice from the figure is that most of the animals you see are those that have been domesticated by us humans. When we brought animals into the barnyard, they brought their diseases with them.

If we look at the history of pandemics in the table we should also note that they are coming with increasing frequency. As the human population grows exponentially and we increasingly encroach on animal habitats and come into closer contact with them, and as we intensify farming practices, then the chances increase that animal virus reservoirs will cause us increasing problems. Chinese wet markets where live and butchered animals are sold in open settings are not the places to be if you want to avoid zoonotic diseases.

Climate change will also cause increasing problems because as warming occurs vector-borne diseases such as malaria, dengue and Zika that are transmitted by mosquitos will become more prevalent in places that previously never had them.

What has made COVID-19 so problematic? My answer to this question centers on its combination of transmissibility or infectiousness and clinical severity, or the fatality rate. In a previous article I made the case that in addition to contact and droplet transmission modes, airborne transmission could be an important mode of transmission of SARS-CoV-2, the virus that causes COVID-19 disease. It is now well recognized that aerosols produced by coughing, sneezing, breathing or even speaking are important in the transmission of diseases such as Influenza, Chickenpox, Measles, Smallpox and Tuberculosis. Aerosols are very small liquid droplets carrying virus particles that can float in the air for up to 30 minutes and travel large distances.

The virus particles responsible for these diseases are similar in size to the SARS-CoV-2 virus responsible for COVID-19. Simple physical-chemical principles suggest that a similar transmission mechanism would also be important for COVID-19.

Given continued growth of human populations, consumption, waste generation and the intensity of farming practices all over the world, there is a high probability that the COVID-19 pandemic will not be the only pandemic to which the present generation we will be subjected. Yes, we in New Zealand came out of COVID-19 relatively unscathed in terms of the loss of life, but we may not be so lucky when the next inevitable pandemic hits.

Although there were plenty of warnings that a global pandemic would hit soon or later, almost all global healthcare systems were caught unprepared for the COVID-19 pandemic. Even first-world countries with sophisticated public healthcare systems like Italy, France and the UK were unprepared for the ferocity of the spread of COVID-19. Deficiencies and inequities in the private US healthcare system are still playing out and it remains to be seen where it ends in terms of the ultimate death count. Make no mistake, had strong countermeasures not been mounted by most countries the number of fatalities would have been astronomical.

As far as infectious diseases go COVID-19 has only moderate lethality and transmissibility and is probably most comparable to the 1957 influenza pandemic that killed upwards of one million people. Countermeasures such as social-distancing have done a good job of limiting the numbers of COVID-19 deaths compared to what they might have been in the absence of such draconian measured.

Measles has a far higher transmissibility than COVID-19. It is much more easily spread from human-to-human and smallpox is far more lethal. I dread to think how we would cope were a virus to evolve that had the transmissibility of measles combined with the lethality of small-pox. It is my opinion that were COVID-19 been allowed to propagate unchecked, a more virulent strain might have evolved. We should not therefore be complacent.

When something like a pandemic hits we begin to understand the value of a properly functioning and well prepared healthcare system. That is, one that prioritizes health outcomes over economics. In NZ we have a public healthcare system and economic rationalization has caused privatization of parts of the system. Economic rationalization provides strong disincentives for redundancies and the stockpiling of equipment such as ventilators and consumables such as PPE. We must change this mentality if we are to be better prepared for what undoubtedly will be coming down the pike in the future.

We know that we can expect more pandemics because as the world population grows, and there is an increasing need to feed more people, farming intensification will increase and animals will come under increasing stress and be more susceptible to disease. Factory farming practices that have been adopted to feed increasing populations are perfect places for viruses to thrive. In such high density environments viruses will have bigger reservoirs in which to vary and multiply and certain mutations will be able to better express themselves and reach threshold values.

In addition to pandemics due to viruses and bacteria we should also keep a close watch on those diseases that are attributed to pathogens known as prions. Unlike a virus which consists of nucleic acid genome enveloped in a protein sheath, a prion is a proteinaceous infectious particle consisting of protein having no genetic material. The term prion was a term first used to describe the mysterious infectious agent supposedly responsible for several neurodegenerative diseases found in mammals, including Creutzfeldt-Jakob disease (CJD), kuru and Gerstmann-Sträussler-Scheinker (GSS) disease in humans. In animals prions are thought to be responsible for the condition known as Chronic Wasting Disease (CWD). A common prion disease in cattle is Bovine Spongiform Encephalopathy (BSE), more dramatically known as mad cow disease. Fortunately, thus far, none of these prion-based diseases have caused pandemics, that we know of.

Get ready folks this is not the end of pandemics but merely the beginning. And let’s not forget climate change which represents perhaps the most important global existential threat of all. In this case also, we have missed the opportunity to act pre-emptively. But we must act now or forever hold our peace.

Animal infected with CWD. Source: Team Surra Outdoors

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