Zoonotic Disease Pathways
#16,110
The overriding theme of this blog over the past 15+ years has been that Nature's laboratory is open 24/7 - and that it operates without budgetary constraints, ethical considerations, or oversight - and it is continually creating or modifying an untold number of viruses, bacteria, and fungi.
The primary limiting factor on emerging pathogens is their `Biological fitness'; essentially their ability to survive their environment, and to replicate (either inside or outside a host).
To become a pathogenic threat, it must also be able to infect one or more species, and ideally replicate, adapt to its new host, and be transmitted onward efficiently. Luckily this is a high bar, and one that most random evolutionary experiments fail to clear.
But the more rolls of the genetic dice taken, the greater the chances that a random mutation will turn a mediocre or underperforming pathogen into a contender.
This is why we watch avian viruses like H5N1, H5N8, H7N9, and H9N2 closely, because they have all demonstrated the ability to infect humans, but they (so far) are unable to transmit efficiently from human-to-human.
But with each new host they infect, they get to roll the genetic dice again (antigenic drift) - or have an opportunity to reassort with another flu virus (antigenic shift) - giving them the possibility of overcoming this barrier to becoming a pandemic strain.
While there are some `human' pathogens that don't appear to affect other species (smallpox being an example), most of the infectious diseases that affect humans originated in other animals, and spilled over into humans; what are called zoonotic infections.
Tuberculosis probably jumped to humans when we began to domesticate goats and cattle around 5000 years ago. Measles appears to have evolved from canine distemper and/or the Rinderpest virus of cattle.And Influenza, which is native to aquatic birds, became much more of a threat after humans domesticated ducks, geese, and chickens.
In 2014, in Emerging zoonotic viral diseases L.-F. Wang (1, 2) * & G. Crameri wrote:
The last 30 years have seen a rise in emerging infectious diseases in humans and of these over 70% are zoonotic (2, 3). Zoonotic infections are not new. They have always featured among the wide range of human diseases and most, e.g. anthrax, tuberculosis, plague, yellow fever and influenza, have come from domestic animals, poultry and livestock. However, with changes in the environment, human behaviour and habitat, increasingly these infections are emerging from wildlife species.
We explored some of the reasons behind this dramatic shift more than a decade ago in The Third Epidemiological Transition - which focused on the work of anthropologist and researcher George Armelagos (May 22, 1936 - May 15, 2014) - of Emory University.
Emerging infectious diseases are considered such an important public health threat that the CDC maintains as special division – NCEZID (National Center for Emerging and Zoonotic Infectious Diseases) – to deal with them, and 26 years ago the CDC established the EID Journal dedicated to research on emerging infectious diseases.
Yet, despite all the examples we've seen, we still mostly react to pandemic threats after they emerge, rather than seriously trying to preempt them. Worse, we were caught massively unprepared for the COVID-19 pandemic, despite ample warnings (see here, here, and here) that we were overdue.
And we somehow continue to delude ourselves into thinking the next public health crisis either won't affect us, or won't happen for years to come.
One movement towards a more unified and cohesive approach to zoonotic threats is called One Health. The AVMA (American Veterinary Medical Association) defines One Health as:
One Health refers to two related ideas: First, it is the concept that humans, animals, and the world we live in are inextricably linked. Second, it refers to the collaborative effort of multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment.
Although this concept has been around for many years, and it is growing in acceptance, as the AVMA points out:
But even today studies in the areas of human, animal, and environmental science are largely conducted independently, and obvious connections may be missed. As the human population continues to grow and our relationships with animals continue to evolve, understanding the interdependencies of people, animals, and the environment becomes even more critical to our collective health and safety.
All of which brings us to a new commentary, published this week in the Journal of the Royal Society of Medicine, which calls for greater collaboration and coordination between veterinary medicine and global health security.
First, a link and some excerpts from the report (you'll want to read it in its entirety), followed by a link to a press release. I'll have a postscript when you return.
Veterinary intelligence: integrating zoonotic threats into global health security
Gemma Bowsher, Tracey McNamara, Rose Bernard, ...
First Published August 5, 2021 Article Commentary
https://doi.org/10.1177/01410768211035355
Animal diseases are human diseases
Zoonotic diseases are leading threats to public health globally. The recent G7 meeting of world leaders made strong political commitments to strengthening One Health approaches at the human–animal interface as an integral element of the global health security architecture. Repeated epidemics and pandemics from Ebola to COVID-19 have demonstrated the systematic disregard of zoonotic disease within what still remains a predominantly human-centric public health approach. In particular, commitments to the expansion of pathogen surveillance and health intelligence require the development of novel approaches to improve and strengthen our domestic capabilities for species neutral monitoring, which requires the sustained involvement of veterinary colleagues.
The belief that medical and veterinarian communities should be synergistic collaborators in outbreak response has been largely neglected.1 At present, there is a dearth of systems capable of providing indicators and warnings for zoonotic diseases beyond livestock management (e.g. bovine TB, foot and mouth, etc.). Companion (e.g. domesticated dogs and cats), zoo and shelter animals exist in close proximity to human populations and with limited syndromic monitoring in place, remain an under-evaluated, but potentially high-risk disease reservoir for potential zoonoses.
SARS-CoV-2 virus with its ability to move in and out of multiple mammalian species including humans has shown us that new approaches are necessary to detect high consequence pathogens in the zoonotic space. Health security intelligence requires the integration of veterinary analysts within a multi-source threat intelligence framework that incorporates an ‘all-species’ approach.
Furthermore, domesticated animals in high-income countries are as much a potential reservoir of high-threat zoonoses as the oft-cited wildlife in wet markets or equatorial rainforests. Veterinary intelligence thus needs to cover a complex global ecosystem from the very remote to the local high street and zoo.
The press release:
Zoonotic threats must be integrated into global health security planning, say experts
While most people believe that the biggest risk of a zoonotic spillover resulting in a pandemic would come from a bat, or a rodent, in Asia, or Africa (both realistic possibilities), the 2009 H1N1 swine flu pandemic virus evolved and emerged from North American domesticated swine.
Last year, we saw SARS-CoV-2 infect dozens of mink farms around the world, which in turn resulted in the creation - and spread in humans - of a mutated COVID variant (see SSI Study: Denmark's Cluster-5 mink Variant Had Increased Antibody Resistance).The CDC's IRAT (Influenza Risk Assessment Tool) lists 3 additional North American swine viruses as having at least some pandemic potential (2 added in 2019), and in February, the CDC added China's EA H1N1 `G4' swine virus, assigning it with the highest emergence score (n=7.5) to date.
In late 2016, the New York City Health Department issued an unusual Statement On Avian H7N2 In Cats at a Manhattan animal shelter. Hundreds of cats, across multiple shelters, were infected with a novel avian flu virus, which resulted in at least 1 human infection (see J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016).
Dogs, cats, horses, marine mammals, even many small peridomestic animals (rodents, rabbits, raccoons, etc.) are susceptible to a variety of influenza viruses, and - as we continue to learn - to novel coronaviruses as well (see USDA/APHIS: White-Tailed Deer Exposed To SARS-CoV-2 Detected In 4 States and EID Journal: Peridomestic Mammal Susceptibility to SARS-CoV-2 Infection).
Pandemic threats are, in all likelihood, only going to increase in frequency over the next couple of decades, simply due to way we produce and ship our food, our continued incursion into previously wild and undeveloped environments, and our ability to cross continents or oceans, in a matter of hours.
We either have to get a lot better at identifying, monitoring, and sharing infectious disease information from the animal world, and find ways to prevent their spillover into humans, or we are destined to repeat the pain and sorrow of our current COVID pandemic again and again.
