Wild origins of the flu in animals around us

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Jonathan Runstadler, Tufts University

(THE CONVERSATION) At the beginning of the 20th century, infectious diseases were the leading cause of death. Epidemics broke out with little warning, apparently unannounced. When the "Great Flu" hit in 1918, it killed thousands of people every week in American cities and spread like wildfire around the world. My great aunt, still a teenager and living in the San Francisco area, was one of her 50 to 100 million victims worldwide.

Neither the public health authorities nor the medical researchers realized that it was a virus that caused the 1918 pandemic – most of the world at that time did not even know what a virus was. A century later, deaths from infection are much less common, thanks to public health efforts and improvements in technology and medical skills. Common diseases are now rare. Nevertheless, 100 years later, infectious disease specialists like me still fear the appearance of viral diseases that we will not be able to control, particularly influenza.

My laboratory, as well as others around the world, is struggling to understand how and why new influenza viruses can attack us again. To do this, we need to go well beyond men's hospitals and in the wild, where viruses persist in animal populations. As disease ecologists, our goal is to understand the dynamics of pathogens in the environment and their interactions with hosts. By better understanding what is happening with viruses in animals, we think we can be better prepared to assess, predict and react if an infection spreads to humans, making people sick.

Identify the invisible, infectious virus

Until the 1930s, it was mistakenly thought that the "Spanish flu" was a bacterial infection, with the joint responsibility of Haemophilus influenzae. This bacterium is a pathogen in its own right and may have contributed significantly to the number of victims of the 1918 pandemic – but it was a secondary infection in many serious cases, not the original cause of the disease of the victims.

Researchers only identified viral particles for the first time less than 30 years before the peak of the flu pandemic, and the nascent field of virology was just beginning to identify them as causes of disease in plants and animals . Scientists were the first to be able to visualize a virus, the tobacco mosaic virus, after the invention of the electron microscope in 1931. Although the technology, knowledge and pace of research were different at the beginning of the twentieth century, why was the discovery of the flu virus so long?

The answer, it seems, lies at least in part in the naivety of people about the relationship between animals, the environment and human disease. In 1918, veterinarian J.S. Koen noted a disease very similar to influenza in pigs. However, it was not until 1931 that researcher Richard Shope identified a filtering agent, smaller than the bacteria, as the cause of the disease in pigs and demonstrated the transmission of an influenza virus. This work led to the description of the human influenza virus in 1933.

The tools of molecular biology, including nucleic acid sequencing, developed in the second half of the 20th century, ultimately helped to pave the way for the destruction of the origins of the 1918 pandemic. In 2005, Jeffrey Taubenberger and a team of researchers reconstructed the genetic sequence of the 1918 deadly virus by combining sequencing and sequencing of the viral genome. died during the pandemic.

They were able to relate the origins and evolution of the 1918 pandemic to viruses circulating in other animals, particularly those from birds and swine examined by Dr. Koen. As in more recent outbreaks of new influenza viruses, the 1918 pandemic traced its origins to circulating strains of virus.

The natural world, reservoir of human diseases

The critical insight that led to the reconstruction work of the 1918 virus came in the 1970s. Under the impulse of virologist Rob Webster, the researchers realized that influenza viruses are endemic in the natural world , especially in waterfowl. In birds and possibly other animals, influenza viruses can replicate and spread to new hosts without causing serious illness. On rare occasions, under the right circumstances, this new host is a different species. This cycle, common in many pathogens, plays an important role in maintaining the virus in nature and explains how animals can be a reservoir of new influenza viruses that can cause human diseases.

While researchers sequenced the influenza viruses found in ducks and other birds, as well as in humans, pigs and other animals, we looked at an image of viral ecology based on nature. Birds serve as a reservoir for a wide range of influenza viruses to which all major human pandemics have been caused. People were largely unaware that at the same time as the 1918 influenza pandemic, the pigs were suffering from the disease and that influenza viruses also caused outbreaks of bird flu. Exactly how and where the 1918 virus entered the human population remains controversial. But the realization that the influenza virus happily exists in a reservoir of wild animals has influenced the way scientists study influenza – and in addition, emerging diseases of all kinds.

This understanding is also part of what drives the One Health movement – the concept that human health is intimately linked to the health of animals and the environment. The One Health and Evolutionary Medicine Initiatives establish collaborations between physicians, veterinarians, ecologists, environmental researchers and many other fields to describe the links between environmental change, animals and human health.

Watch the Wild World to Protect Human Health

We now know that 60% of human infectious diseases are transmitted by animals. Over the last 20 years, this awareness has intensified influenza surveillance efforts around the world and identified several other influenza viruses that threaten public health. In the work of my laboratory, we strive to describe the ecology and natural history of the influenza virus in animals to understand how new viruses develop and what is the risk of overflowing on new ones. hosts where they could cause illness.

For example, human activities – such as the existence of open dumps, habitat destruction or agricultural practices – may attract or force animals to invade spaces that they can not normally . When interactions between species and the environment are so disrupted, how does this affect the circulation, evolution and movement of influenza viruses or other pathogens than these animals? host? Changes in the ecology of pathogens in the wild are what most often leads to spillover into human populations and an epidemic.

Following an outbreak of seal deaths in 2011 in New England, our large group of collaborators spent cold days in winter sampling seals, uncovering evidence of the persistence of influenza viruses in circulation. These results lead us to explore the effects of the flu on seals, but also the impact of the rapid increase in the seal population on the virus. If seals are a mammalian reservoir more commonly infected than we knew, their populations can affect the ecology of the flu.

Surveillance and research work such as that on influenza and its animal hosts has led to more aggressive efforts to eliminate emerging infections before they turn into human pandemics. It gives biomedical researchers a long way to characterize potential pandemic viruses to understand their potential impact. And public health workers gain new knowledge about infection prevention and control.

This information may be crucial to identify and contain the next pandemic virus. The One Health community's experience with influenza has shown how scientists are trying to understand and prevent the spread of other diseases, including SARS, Ebola and Zika. Researchers quickly ran after the SARS animal source and are still working to identify reservoir hosts and understand the ecology of the disease, Zika and Ebola viruses.

One hundred years after the "Great Influenza", there is still much to learn to reduce the risk of recidivism in 1918. Over the last 10 years, thanks to the efforts of many researchers around the world, including renewed efforts funded by national institutes American health, the sequencing rhythm of influenza viruses has leapt forward. Scientists are beginning to understand the true diversity of the flu virus, not only in birds, but also in other animals.

Efforts to produce a universal vaccine to prevent influenza infection in humans are promising. However, the ability to test these vaccines and to prepare and predict emerging strains will not be complete without a deep understanding of the origins, motions, and risk of virus transmission in animals and in animals. environment around us. With a better understanding of these ecological links resulting from ongoing research, we hope to be better prepared for the next pandemic.

This article is republished from The Conversation under a Creative Commons license. Read the original article here: http://theconversation.com/influenzas-wild-origins-in-the-animals-around-us-91058.

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