Will virus hunting programs prevent the next pandemic?

An essay by Rachel Stadler

Deadly pandemics have massively impacted human life throughout history. As a result, humans have attempted to prevent?fatal?diseases caused by pathogens. One of the most successful disease prevention methods is immunization against pathogens. In 1796, English physician Edward Jenner developed the first reliable and successful vaccine where he collected a cowpox sore from a milkmaid and inoculated James Philpps, an 8-year-old boy, to cowpox. Afterward, when Jenner exposed Philpps to smallpox, the boy did not develop the disease.?

?The development of vaccines enabled humans to prevent infections. However, to create vaccines, the causative agent must first be identified. But what if scientists could determine which virus would become the next pandemic before the virus started to infect humans? Virus hunting seeks to do just that by discovering novel pathogens capable of causing pandemics in animal reservoirs. Once the pathogen is identified, the development of vaccines can occur, and a potential pandemic due to a spillover event avoided. But is virus hunting a practical pandemic prevention program?

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Spillover Events

Just as cowpox can infect humans, numerous animal pathogens – called zoonotic diseases – can spread to humans. These spillover events occur through any human contact with domestic, agricultural, or wild animals – including direct contact with infectious body fluids, indirect?contact in the environment, foodborne, and vector-borne methods of contact. As humans increase close interactions with animals– from catching wildlife or bushmeat for food, clearing forests to grow crops, or creating roads through previously uninhabited areas – we increase the likelihood of contracting a novel animal pathogen. Of known human diseases, approximately two-thirds are the result of a spillover – including HIV, West Nile virus, SARS, MERS, and Ebola. Spillover events are estimated to?cause?3 out of 4 novel or emerging human infectious diseases. From 1963 to 2019, spillover events increased exponentially and?are predicted?to continue to increase due to human-driven climate and environmental change.

?The late 20th century and the beginning of the 21st century saw the start of the global spread of bird flu. In 1997, a spillover of H5N1 avian influenza from a Hong Kong live animal market infected 18 people and killed six people – leading to Hong Kong slaughtering all 1.3 million chickens in their territory to stop the outbreak. However, another H5N1 avian influenza outbreak started in 2004. This time, the spillover event started in Southeast Asia before spreading to multiple countries?and resulting?in 142 people infected and millions of birds killed to prevent the spread of the disease.?

?In response to the H5N1 spillover events, the United States government created programs to limit animal and human infections?as well as?prepare for a possible pandemic. At the U.S. Agency for International Development (USAID), infectious disease specialist Dennis Carroll led the agency response - including working with animal experts to teach farmers and animal sellers methods to reduce and prevent exposures.?

?The global efforts controlled the outbreak and prevented a pandemic-level outbreak of H5N1 bird flu in humans. However, the risk for an H5N1 global pandemic is not over, especially since H5N1 circulates in wild avian species that migrate across the globe and could infect domestic poultry. But what if scientists could predict potential outbreak locations by identifying infected flocks and their migration patterns? This line of thought led Dennis Carroll and others to wonder about what knowledge could be gained about other potential viral threats circulating in animal populations beyond influenza.

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Virus Hunting Policy and Programs

In 2009?as?a response to the 2005 H5N1 avian influenza outbreak, Dennis Carroll designed and oversaw the PREDICT project – a part of USAID’s Emerging Pandemic Threats (EPT) program. The project was led by UC Davis’ One Health Institute and partnered with EcoHealth Alliance, Metabiota, the Wildlife Conservation Society, and Smithsonian Institution Conservation Biology.?The PREDICT project objective was to prepare the world to detect, identify, prevent, and respond to viral threats and act as an early detection system for future epidemics and pandemics. In addition to training individuals at more than 60 laboratories, the PREDICT project increases the global surveillance and testing capabilities of known and new viruses. From 2009 to 2019, PREDICT tested over 164,000 animals and people for zoonotic diseases, found 217 known viruses, and detected 949 novel viruses, including Bombali ebolavirus, Zaire ebolavirus, Marburg virus, and MERS- and SARS-related coronaviruses.?

?In September 2019, PREDICT’s second five-year contract expired, resulting in the end of fieldwork. The Trump administration had previously informed Congress of its plan to end the project?along with?other global health programs. In November 2019, Senator Angus King wrote to USAID about his concerns about ending the PREDICT program. With the beginning of the COVID-19 pandemic, Senators Angus King and Elizabeth Warren stated their concerns to the Trump administration over ending projects like PREDICT in February 2020. On April 1st, 2020, the USAID granted PREDICT an emergency six-month extension?that focused?on detecting COVID-19.

?In 2021, a follow-up USAID project – the Discovery and Exploration of Emerging Pathogen-Viral Zoonoses (DEEP VZN) – began and was set to run through 2026. The?goal was similar to the objective of PREDICT in collecting wildlife samples but at a larger scale. The aim was to collect almost half a million biological wildlife samples and detect at least 12,000 novel viruses for future research. However, with?the COVID-19 pandemic and the previous results from the PREDICT project, DEEP VZN became a controversial program. Supporters of virus hunting stated the need existed to provide an early warning on wildlife pathogens with spillover capabilities.?Additionally, supporters pointed to the COVID-19 pandemic that scientists believed evolved from bat coronavirus. However, while PREDICT detected novel viruses, including new coronaviruses, the project did not predict or prevent the COVID-19 pandemic. Opponents of DEEP VZN also argued that the project was just as likely to lead to an outbreak as to prevent one?since?collecting the samples requires humans to come into close contact with potential pandemic-causing viruses. By September 2023, the program?was halted?by the Biden administration.?

?The COVID-19 pandemic has forced the reevaluation of how best to prevent the next pandemic. Virus hunting programs could prevent pandemics if the virus?is discovered?before infecting humans. However, determining which virus will become the next pandemic has proven challenging.?Currently, programs for pandemic prevention have shifted from finding novel pathogens to quickly detecting, identifying, and responding to pandemic-level threats. This shift occurred in part due to the unproved ability of virus hunting programs to prevent pandemics and the increased exposure potential to scientists collecting wildlife samples as well as the increasingly politicized landscape of infectious disease research. While virus hunting may not prevent pandemics, valuable information was gained by the PREDICT program. The goals of virus hunting programs may need to change to further our understanding of viruses circulating in the wild while increasing protection measures to further decrease the risk of potential exposures to scientists. However, for the goal of pandemic prevention, proven methods – such as global surveillance and accurate testing – should be the focus for now.

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