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According to research by Professor Kenny of the Department of Veterinary Medicine at Ohio State University, the virusMeeting overflow usually follows five steps:

1. Virus source accumulation: The virus replicates within the primary host species without compromising the viability of the species, thereby making the species a “storage pool” for the virus.

   
   

2. Exposure: The secondary species host is exposed to the virus through close contact with the primary species.

   
   

3. Breakthrough: The virus overcomes natural barriers in new host species, such as species incompatibility and immune responses.

   
   

4. Propagation: The virus is effectively spread from one host to another.

   
   

5. Tipping point: The incidence of disease and the rate of infection of new hosts have risen sharply.

   
   
   

   The most important step in the whole process is the completion of the “breakthrough” to enable the virus to transform from animal virus to zoonotic virus. Coronaviruses, as RNA viruses, have a stronger ability to recombine and obtain point mutations than other virus families, and can overcome obstacles between species more quickly through evolution.

   Thomas Gillespie, a disease ecologist at Emory University, pointed to a common place where “breakthroughs” occur-the game market. Because a series of species from completely different environments interact in a closed environment, “exposure” is very easy to achieve, so the game market “is enough to set off a storm of cross-species transmission of pathogens.

   Take many markets in West and Central Africa as examples. They sell monkeys, bats, mice, and dozens of slaughtered birds, mammals, insects, and rodents. They are sold near open dumps without drainage facilities. . There are many similar environments in the world, and they provide a hotbed for virus spillage.

   From animal viruses to zoonotic diseases Source: CDC
   

   Since 1980, zoonotic infectious diseases caused by spillover effects (eg Ebola, SARS, Avian Influenza, New Coronavirus) The outbreak is becoming more and more.

   The US Centers for Disease Control and Prevention estimates that three-quarters of new or emerging human infections originate from animals. Spillover effects are not new in human history. Both rabies and plague have completed “breakthroughs” from animal hosts centuries ago.

   But whether it is MERS from the Middle East, LASSA Fever found in Nigeria, Nipah from Malaysia, or Ebola in Africa, Zika and West Nile virus have only spilled into humans in recent decades Social.

   Kate Jones, chair of the Department of Ecology and Biodiversity at University College London (Kate Jones) said that the new Of infectious diseases are “growing threats to global health, safety and economy”.

   What we have to ask is, what makes virus spilling into human society easier and more frequent?

   Humans and viruses, an accidental encounter

   Ten years ago, it was generally believed that tropical forests and intact natural environments are full of wild animals and plants. The viruses and pathogens they carry can cause new human diseases such as Ebola virus, AIDS and dengue fever. But today’s scientific research more and more clearly reveals that species diversity itself will not cause virus spillage, it is precisely for the destruction of biodiversity to create conditions for spillover. A new discipline called (planetary health) is emerging, trying to say goodbye to the fragmented perspective and focusing on the organic environment of the earth and human diseases contact.

   David Kwaman, author of “Overflow: Animal Infections and the Next Pandemic” (David Quammen) recently wrote in the New York Times: “When we cut trees, kill wild animals or put them in cages, and then send them to the market. We destroyed the ecosystem and freed the virus Its natural host. When they need a new host, who else can we be? “

   This theory has also been verified by more and more scientific empirical data in recent years.

   Kate Jones ’s research team counted 335 diseases that occurred between 1960 and 2004, and found that at least 60% of them were from animals. More importantly, these zoonotic diseases are increasingly associated with environmental changes caused by human behavior. Factors such as logging, mining, road construction in remote areas, rapid urbanization, and population growth have driven the destruction of virgin forests, bringing people closer to animal species that have never been exposed to it before. Because simple ecosystems have an amplification effect, the virus spillage of species in degraded habitats will also be amplified.

   A study on April 7, 2020 at the University of California, Davis found that when the number of animal populations decreased due to hunting, wildlife trade, and habitat quality decline, compared to non- For populations with reduced human factors, the former (human) the zoonotic virus carried is the latter (Non-human) twice, it can be seen that there is a significant correlation between environmental degradation caused by human activities and virus spillage.

   In order to study the overflow of Ebola virus, the researchers used high-resolution satellite forest data to draw the 2000 (angles a and c below) ) and 2014 (below corners b and d) land use coverage rate change map, and marked on it From 2004 to 2014, the location of the first center of 11 Ebola infections was (yellow triangle) . They found that the spread of Ebola virus from wildlife to humans is more likely to occur in fragmented areas caused by forest degradation. Specifically, of the 11 infections, 8 occurred in highly fragmented forest areas.

   Ebola outbreaks mostly occur in forest degradation areas Source: Nature
   

   The same phenomenon can be observed in many places in the world. An infectious disease in India, abbreviated as KFD (Kyasanur Forest Disease) , was found to have surged in the past few years. The areas are highly consistent. Even in developed countries, although the ecological protection is better, the phenomenon of overflow cannot be avoided.

   A common example is Lyme disease, which occurs in North America, Europe and Asia, and is caused by the spread of bacteria through the bite of infected lice. According to a 2018 study, the incidence of Lyme disease in the United States is also increasing as forests become fragmented due to increased human settlements.

   Let ’s go back to Professor Kenny ’s five-step decomposition. When human beings are pressing and stepping forward, the original virus accumulation pool in step 1 “> (First level host) is constantly being requisitioned or consumed by human activities, making the virus have a need to overflow. The exposure of step two continues to increase during this process, which gives the virus more opportunities to achieve the breakthrough of step three.

   What can we do now? What should I do?

   Next time, are we ready?

   Being in front of us is still the difficult balance between environmental health and development. On the one hand, experts in the field of infectious diseases have repeatedly emphasized the dangers of traditional markets selling game meat, and Kate Jones likens it to “a nuclear bomb waiting to explode.” On the other hand, she bluntly said: “It is unfair to demonize a place without a refrigeratorof. These traditional markets provide a lot of necessary food for Africa and Asia. “

   In addition, Delia Grace, a senior epidemiologist at the International Livestock Research Institute in Nairobi, Kenya, (Delia Grace) pointed out The blind prohibition of wildlife trading will give rise to underground gray trade, and the black market will not pay attention to hygiene.

   If the environmental problem is behind the disease problem, the development problem is behind the environmental problem. Only by providing practical alternatives to the vast population in underdeveloped areas can they not be caught in the dilemma of “health or livelihood”.

   At the same time, we ca n’t wait until all the supporting plans are in place, then it may be really too late. As Jones said, even if we cannot fully control the ecological damage caused by the demand for wood, minerals and resources, at least, “we must consider global biosecurity, identify weaknesses and strengthen health care in developing countries.

   Experts are also advocating the use of a multidisciplinary coordinated “One Health” (One Health) method to effectively respond to zoonotic diseases Global emergence. The so-called “one health” is to regard human health and environmental health as a whole, and our health is closely related. As of now, nearly 50 countries have signed the Global Health and Safety Agenda (GHSA) One Health is promoted among countries to prevent, detect and respond to disease threats.

   A health picture source: Lancet
   

   But there are still challenges in implementing “one-stop medical services,” especially in developing countries.

   New York-based non-profit EcoHealth alliance disease ecologist Jonathan Epstein (Jonathan Epstein) said that from a de facto perspective , Most government departments (Human Health, Veterinary / Agricultural and Environmental Institutions) perform tasks and budget independently, as required by “One Health” The cross-sector and cross-country cooperation has many problems in practice. Institutions need to work within the framework of common issues, but “the resources allocated to each institution are usually very different, and the level of technical training around health care is different.” Consistency of goals and differences in resource capabilities The balance between them is another huge challenge .

   Eric Fevre, director of the Department of Veterinary Infectious Diseases, University of Liverpool ’s Institute of Infection and Global Health, (Eric Fevre) advocates reconsidering cities planning. “The focus of short-term efforts is to curb the spread of disease.” He said, “Considering that new infectious diseases may continue to spread rapidly within and between cities, in the long run, this will require current urban planning and development Comprehensive reform. “

   Reference article link:

   1. https://insights.osu.edu/food/coronavirus-spillover
   

   2. https://www.theguardian.com/environment/2020/mar/18/tip-of-the-iceberg-is-our-destruction-of-nature -responsible-for-covid-19-aoe
   

   3.https: //www.sciencedaily.com / releases / 2020/04 / 200407215653.htm
   

   4.https: //www.ncbi.nlm.nih.gov/pmc/articles/PMC5214842/
   

   5. https://india.mongabay.com/2020/02/spillover-encroachment-into-forests-increases-risk-of-contracting-diseases-from-animals /
   

   6. https://edition.cnn.com/2020/04/07/health/mammal-human-virus-spillover-coronavirus-scn-wellness/index.html
   

   7. https://www.theguardian.com/environment/2020/apr/08/human-impact-on-wildlife-to-blame-for-spread-of -viruses-says-study-aoe
   

   8. https://e360.yale.edu/features/spillover-warning-how-we-can-prevent-the-next-pandemic-david-quammen

   9. https://mp.weixin.qq.com/s?__biz=MzI3NzUyMTE3NA==&mid=2247496167&idx=1&sn=712cad1e496adaaa3ef47fb46d31b160&chksm=eb66479edc11ce88ba37c30