IÂ spoke with Jonna Mazet, PhD, UC Davis School of Veterinary Medicine, about emerging pathogen surveillance and public health. Dr. Mazet is the Principal Investigator and Global Director of the novel viral emergence early warning project, PREDICT, that has been developed with the US Agency for International Development’s (USAID) Emerging Pandemic Threats Program.Â Recorded at the Emerging Infectious Diseases A to Z (EIDA2Z) conference hosted by the National Emerging Infectious Diseases LaboratoriesÂ (NEIDL).
Ian Lipkin, Columbia University, New York, andÂ Lyle Petersen, Centers for Disease Control and Prevention, Fort Collins, Colorado, discuss recently emergedÂ pathogens, and how to prepare should their range expand. When asked if MERS-coronavirus would cause the next pandemic, Ian Lipkin responded ‘I don’t have a crystal ball’.
Recorded at the Annual Meeting of the American Society for Microbiology, Boston, MA on 19 May 2014.
On episode #283 of the science show This Week in Virology,Â Jens Kuhn speaks with the TWiV team about filoviruses, including the recent Ebola virus outbreak in Guinea.
You can find TWiV #283 at www.microbe.tv/twiv.
My colleague Ian Lipkin has developed new methods to rapidly identify pathogens. At Pop!Tech 2008, he explained how an increased understanding of zoonotic diseases, together with advancements in diagnostic technology, are helping to detect the next emerging virus.
The term emerging virus was coined by scientists in the 1990s to describe the agent of a new or previously unrecognized infection. The term implies that emerging viruses are new; however this assumption is incorrect. New virus infections have been emerging for thousands of years, at least since the rise of agriculture 11,000 years ago. The development of agriculture and commerce provided the large populations needed to sustain human infections such as measles and smallpox.
Viruses probably (although we do not know for sure) appeared when living cells evolved, possibly even before. They subsequently infected multicellular forms of life and then mammals, which were present on the globe before humans. Humans then acquired virus infections from animalsÂ (an infection transmitted from animals to humans is aÂ zoonosis). At some point the number of virus genomes and virion structures became established, and for the next millions of years, viruses evolved. It is unlikely that new viruses emerge de novo; rather they evolve from existing viruses.
Some examples serve to illustrate the origins of viruses. Comparisons of genome sequences of today’s members of the herpesvirus family has lead to the suggestion that these viruses arose 180-220 milllion years ago, possibly from ancestors of similar viruses that infect oysters and fish today. Smallpox virus may have emerged after an infection of humans with a gerbil poxvirus. Measles virus may have originated from infection of humans with an ancestor of a virus that today infects cows, rinderpest virus. It has been suggested that the virus ‘jumped’ from cows to humans about 5,000 years ago, when humans first began to domesticate cattle. Measles virus then spread throughout the Middle East and was then brought to the Americas by colonization and migration, where it had lethal effects on the Native Americans.
It is safe to say that all of the human viruses that exist today originated from a zoonotic infection. In some cases, related viruses still infect animals (e.g. measles and rinderpest virus). However, often the human virus has no knownÂ counterpartÂ in animals. An example is the human pathogen, poliovirus. The ancestral poliovirus is not known, and there are currently no hosts for the virus other than humans. However, other members of the picornavirus family, of which poliovirus is a member, infect a variety of animals, and ancient versions of these viruses may have made the jump from animals to humans.
Two simple facts ensure that new human virus infections will continue to emerge from animal hosts. The first is the ability of viruses to produce huge numbers of progeny (billions and billions!) with a high level of diversity (mutation). The second is the fact that human and non-human animal populations continue to grow and interact. Put another way, humans are always finding new ways to acquire novel virus infections!
Viral evolution is a fascinating subject. A good place to start reading about it would be Principles of Virology, volume II, chapter 10.