Around the world, scientists are venturing into the habitats of wild animals to study the viruses circulating in their bodies. In this regard, governments and institutions allocate millions of dollars to this research with which they try to predict what will be the next pathogen with the potential to cause a pandemic, but some scientists think that this strategy is too expensive and inefficient.
The origin of SARS-CoV-2 has not been clarified, but scientific evidence continues to point to the spillover theory, in which an animal virus managed to jump to humans and spread uncontrollably. Most pathogens come from animals and the spill theory is the basis of multiple surveillance and prevention investigations.
But for scientist Gregory Gray, pouring so many resources into this idea is like “looking for a needle in a haystack. Spills happen all the time and very few manage to become a pandemic”, this epidemiologist from the University of Texas in the United States tells BBC Mundo. Gray and other experts propose an alternative way to monitor and prevent pandemics; it somehow challenges how we think about its origins and how we deal with them.
What does it consist of?
These scientists assume that researching thousands of animal viruses is expensive and often inefficient. “Interesting from a scientific point of view, but I really do not think we can predict which ones will become pandemics”, biologist Stephen Goldstein, from the University of Utah in the United States, tells BBC Mundo. Goldstein, like Gray, insists that spills happen all the time. “But most do not get past the first receiver”, Goldstein explains.
This is because, although a virus is capable of adapting to a human, it usually takes time -many times years- and multiple other spills for a variant to emerge that spreads efficiently and becomes a pandemic. And it is in this space of time that these scientists recommend focusing.
“If we monitor and study people in frequent contact with animals, such as agricultural workers or live animal dealers, especially when they get sick, we could identify the agents that are making them sick”, Goldstein gives as an example. “Instead of looking for thousands of viruses in animals, here we look at what is already spilling. It brings us closer to worrying viruses because we would already know that they can infect people”, he complements.
“It is the basis of our argument. Reduce data and detect pathogens in their early stages that have already caused disease. From here we can take intervention measures against the most threatening ones”, says Gray.
There are not many studies in recent decades that have looked at strokes inside people to determine how common they are. And when patients with mysterious pneumonia arrive in emergency rooms, doctors look for known pathogens. They cannot detect viruses that have not been discovered; that is to say, it is the type of cases that these scientists ask to study more.
Tightening the noose
Through a videoconference, Gray shows a graph of the viruses that have caused the most deaths in the last century. Most of them are respiratory. The Spanish flu in 1918, the SARS of 2003, the H1N1 influenza of 2009, and the SARS-Cov-2 of 2020 are just some of these examples.
For this reason, Gray thinks that the siege on the most threatening viruses can be narrowed if we focus more research on respiratory viruses. “These spread many times without symptoms and we cannot control them very well. They are transmitted before we can isolate the patients”, says the expert. “When surveillance of the human-animal interface is not possible, an efficient option is to monitor novel respiratory viruses in pneumonia patients in regions of frequent animal contact. If they are discovered, their human risk can be assessed and, if indicated, mitigation strategies can be initiated”, Gray defends in a study.
Lineage of decades
Gray argues that the extensive study of animals was not able to prevent the Covid-19 pandemic. Neither was influenza A of 2009. When the variants that spread throughout the world emerged, it was already too late. But there are studies that suggest that, in the case of SARS-CoV-2, it could have waited for decades in the body of an animal before the fatal variant emerged.
Research published in the journal Nature in 2020 suggests that the lineage that gave rise to SARS-CoV-2 may have been circulating unnoticed among bats since around 1969. “If so, it took a long time to become highly transmissible to humans”. says Gray. “Some virologists would say that among the thousands of coronaviruses, it seems that a few do spill over to humans, but if we monitor humans exposed to animals and come up with new viruses, based on their biological evolution we can do something before they run over us in emergency apartments”, insists the expert.
Advantages and disadvantages
Gray acknowledges that the theory he is betting on carries risks. “If we put all our resources into respiratory-type viruses, we could ignore other threats. That is why we also advocate developing other technologies such as massively parallel sequencing”, he explains.
David Heymann, an epidemiologist at the London School of Hygiene and Tropical Medicine, agrees that databases created from studying animal viruses are not very effective at predicting pandemics. But he points out that if “a new virus emerges, you can compare its sequence with this database, identify which animals carry this virus and perhaps make a list of animals where it could have originated”, Heymann explains to BBC Mundo.
Goldstein, of the University of Utah, also warns of challenges to the theory he defends if it were to be further implemented. “You still need resources; it is expensive, and it requires logistics and global coordination. And even if you identify viruses that are spreading, deciding what to do about it is not so easy”, he says. After all, it would require manufacturing vaccines for infections whose scope remains hypothetical. “To make vaccines you need human clinical trials, and it is a challenge to do them for viruses that, while worrying, have not caused epidemics”, says Goldstein.
On the other hand, Konstans Wells, a bioscientist at Swansea University in the UK, cautions that it is just as important to assess how different human behaviors and human-animal interactions contribute to animal virus infections in different contexts. “For example, tourists or urban populations may be exposed to bats in a different way than hunters or guano collectors. It remains relevant to see how these variations of environments and interactions affect the circulation of the virus”, he explains.
Without detracting from the fact that efforts are being made to focus research on the most threatening viruses, Wells recalls the complexity of these interactions. He thinks it is “equally important to work on identifying so-called ‘blind spots’: unknown species and environments that may facilitate pathogen spills”. He summarizes that any pathogen emergence “needs to be evaluated from many different perspectives”.
