As more people around the world are getting vaccinated, one can almost hear the collective sigh of relief. But the next pandemic threat is likely already making its way through the population right now.
There is a simple strategy to mitigate emerging outbreaks: proactive, real-time surveillance in settings where animal-to-human disease spillover is most likely to occur.
In other words, don’t wait for sick people to show up at a hospital. Instead, monitor populations where disease spillover actually happens.
In 1947, the World Health Organization established a global network of hospitals to detect pandemic threats through a process called syndromic surveillance. The process relies on standardized symptom checklists to look for signals of emerging or reemerging diseases of pandemic potential among patient populations with symptoms that can’t be easily diagnosed.
This clinical strategy relies both on infected individuals coming to sentinel hospitals and medical authorities who are influential and persistent enough to raise the alarm.
Sentinel surveillance recruits select health institutions and groups to monitor potential disease outbreaks.
There’s only one hitch: By the time someone sick shows up at a hospital, an outbreak has already occurred. In the case of SARS-CoV-2, the virus that causes COVID-19, it was likely widespread long before it was detected. This time, the clinical strategy alone failed us.
A more proactive approach is currently gaining prominence in the world of pandemic prevention: viral evolutionary theory. This theory suggests that animal viruses become dangerous human viruses incrementally over time through frequent zoonotic spillover.
It’s not a one-time deal: An “intermediary” animal such as a civet cat, pangolin or pig might be required to mutate the virus so it can make initial jumps to people. But the final host that allows a variant to become fully adapted to humans might be humans themselves.
Viral evolutionary theory is playing out in real time with the rapid development of COVID-19 variants. In fact, an international team of scientists has proposed that undetected human-to-human transmission after an animal-to-human jump is the likely origin of SARS-CoV-2.
Viruses jump species through a process of random mutations that allow them to successfully infect their hosts.
When novel zoonotic viral disease outbreaks such as Ebola first came to the world’s attention in the 1970s, research on the extent of disease transmission relied on antibody assays, blood tests to identify people who have already been infected.
Antibody surveillance, also called serosurveys, test blood samples from target populations to identify how many people have been infected. Serosurveys help determine whether diseases such as Ebola are circulating undetected.
Turns out they were: Ebola antibodies were found in more than 5% of people tested in Liberia in 1982, decades before the West African epidemic in 2014. These results support viral evolutionary theory: It takes time – sometimes a lot of time – to make an animal virus dangerous and transmissible between humans.
What this also means is that scientists have a chance to intervene.
One way to take advantage of the lead time for animal viruses to fully adapt to humans is long-term, repeated surveillance. Setting up a pandemic threats warning system with this strategy in mind could help detect pre-pandemic viruses before they become harmful to humans. And the best place to start is directly at the source.
The lion’s share of pandemic prevention funding and effort over the past two decades has focused on discovering wildlife pathogens and predicting pandemics before animal viruses can infect humans. But this approach has not predicted any major zoonotic disease outbreaks — including H1N1 influenza in 2009, MERS in 2012, the West African Ebola epidemic in 2014 or the current COVID-19 pandemic.
Predictive modeling has, however, provided robust heat maps of the global “hot spots” where zoonotic spillover is most likely to occur.
Long-term, regular surveillance at these “hot spots” could detect spillover signals, as well as any changes that occur over time. These could include an uptick in antibody-positive individuals, increased levels of illness and demographic changes among infected people.
As with any proactive disease surveillance, if a signal is detected, an outbreak investigation would follow. People identified with symptoms that can’t be easily diagnosed can then be screened using genetic sequencing to characterize and identify new viruses.
The good news is that surveillance infrastructure in global “hot spots” already exists. The Connecting Organisations for Regional Disease Surveillance program links six regional disease surveillance networks in 28 countries. They pioneered “participant surveillance,” partnering with communities at high risk for both initial zoonotic spillover and the gravest health outcomes to contribute to prevention efforts.
It is easy to miss warning signals when global and local priorities are tentative. The same mistake need not happen again.
Maureen Miller is adjunct associate professor of epidemiology at Columbia University. Distributed by theconversation.com.