BSL-4 Lab Worker - Photo Credit –USAMRIID
Every few months we seem to learn of a new virus, previously unrecognized, circulating in a non-human species but with the potential to infect humans. Over the past three decades, we’ve seen dozens of these zoonotic pathogens identified.
The question is, just how deep is this viral pool, and how many more viruses wait to be identified?
Researchers at Columbia University's Mailman School of Public Health, EcoHealth Alliance, the NIH, and universities and research centers around the world have worked out a strategy to estimate the number of viruses in the wild, awaiting discovery.
Their findings are published today in the open access journal mBio. The good news is, the estimated number of viruses out there is finite, the bad news is, we are talking 6 figures.
First a link to the research article, then a excerpts from a couple of press releases.
Simon J. Anthony, Jonathan H. Epstein, Kris A. Murray, Isamara Navarrete-Macias, Carlos M. Zambrana-Torrelio, Alexander Solovyov, Rafael Ojeda-Flores, Nicole C. Arrigo, Ariful Islam, Shahneaz Ali Khan, Parviez Hosseini, Tiffany L. Bogich, Kevin J. Olival, Maria D. Sanchez-Leon, William B. Karesh, Tracey Goldstein, Stephen P. Luby, Stephen S. Morse, Jonna A. K. Mazet, Peter Daszak, W. Ian Lipkin
The majority of emerging zoonoses originate in wildlife, and many are caused by viruses. However, there are no rigorous estimates of total viral diversity (here termed “virodiversity”) for any wildlife species, despite the utility of this to future surveillance and control of emerging zoonoses.
In this case study, we repeatedly sampled a mammalian wildlife host known to harbor emerging zoonotic pathogens (the Indian Flying Fox, Pteropus giganteus) and used PCR with degenerate viral family-level primers to discover and analyze the occurrence patterns of 55 viruses from nine viral families. We then adapted statistical techniques used to estimate biodiversity in vertebrates and plants and estimated the total viral richness of these nine families in P. giganteus to be 58 viruses.
Our analyses demonstrate proof-of-concept of a strategy for estimating viral richness and provide the first statistically supported estimate of the number of undiscovered viruses in a mammalian host.
We used a simple extrapolation to estimate that there are a minimum of 320,000 mammalian viruses awaiting discovery within these nine families, assuming all species harbor a similar number of viruses, with minimal turnover between host species. We estimate the cost of discovering these viruses to be ~$6.3 billion (or ~$1.4 billion for 85% of the total diversity), which if annualized over a 10-year study time frame would represent a small fraction of the cost of many pandemic zoonoses.
IMPORTANCE Recent years have seen a dramatic increase in viral discovery efforts. However, most lack rigorous systematic design, which limits our ability to understand viral diversity and its ecological drivers and reduces their value to public health intervention. Here, we present a new framework for the discovery of novel viruses in wildlife and use it to make the first-ever estimate of the number of viruses that exist in a mammalian host. As pathogens continue to emerge from wildlife, this estimate allows us to put preliminary bounds around the potential size of the total zoonotic pool and facilitates a better understanding of where best to allocate resources for the subsequent discovery of global viral diversity.
From EcoHealth Alliance we get the following press release:
September 3, 2013
Scientists Determine New Strategy to Estimate Total Viral Diversity in Mammals
NEW YORK - September 3, 2013 - EcoHealth Alliance, a nonprofit organization that focuses on local conservation and global health issues, and the Center for Infection and Immunity (CII) at Columbia University's Mailman School of Public Health announced a new strategy to identify the total number of wildlife viruses that could potentially cause emerging disease outbreaks that threaten both public and wildlife health.
Combining field investigations with a new statistical approach, scientists estimate that there may exist a minimum of 320,000 viruses awaiting discovery from mammals alone. With over three-quarters of the emerging infectious diseases originating from wildlife this research gives scientists an estimate of the number of viral agents that may eventually cause a pandemic.
Diseases such as SARS, West Nile virus, HIV/AIDS, Ebola and Avian influenza are all examples of a zoonotic diseases - those that originate in wildlife and are spread to humans. "For decades, we've faced the threat of future pandemics without knowing how many viruses are lurking in the environment, in wildlife, waiting to emerge. Finally we have a breakthrough - there aren't millions of unknown virus, just a few hundred thousand, and given the technology we have it's possible that in my lifetime, we'll know the identity of every unknown virus on the planet," says Peter Daszak, PhD, corresponding author and president of EcoHealth Alliance.
From Columbia University's Mailman School of Public Health we get the following press summary.
Minimum of 320,000 viruses; identifying them could help mitigate disease outbreaks; total cost less than a single pandemic
Scientists estimate that there is a minimum of 320,000 viruses in mammals awaiting discovery. Collecting evidence of these viruses, or even a majority of them, they say, could provide information critical to early detection and mitigation of disease outbreaks in humans. This undertaking would cost approximately $6.3 billion, or $1.4 billion if limited to 85% of total viral diversity -- a fraction of the economic impact of a major pandemic like SARS.
Close to 70% of emerging viral diseases such as HIV/AIDS, West Nile, Ebola, SARS, and influenza, are zoonoses -- infections of animals that cross into humans. Yet until now, there has been no good estimate of the actual number of viruses that exist in any wildlife species.
More than 40 years ago, in the movie The Graduate, Dustin Hoffman was cornered at his graduation party and famously offered the following career advice:
Mr. McGuire: I just want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Plastics.
Given the explosive growth in molecular biology and virology, and the apparent ocean of viruses still yet to be discovered, I would amend this advice just slightly for this 21st century.
I just want to say one word to you. Just one word.