Researchers have developed a new catalog of viruses to identify pathogens that have the greatest capacity to initiate future global public health crises. According to the authors, this survey serves as assistance for scientists to promptly assess the risk of new viruses detected in patients and even anticipate the characteristics of the next agent capable of causing a pandemic.
Viral Discovery Trend
The study indicates that, in a standard annual period, between two and three novel viruses are discovered in humans. Although this quantity may vary, the trend has remained relatively stable since the 1960s. Many of these viruses receive little attention from the scientific community, forcing researchers to consult old medical articles to find references, while others simply disappear from scientific literature.
Historical Pandemic Cases
The identification of HIV-1 in 1983 and SARS-CoV-2 in 2020 preceded two of the biggest pandemics in recent history: AIDS and Covid-19, which together resulted in tens of millions of deaths.
Focus of the Concern Catalog
The research was conducted by a group from the University of Edinburgh, Scotland, aiming to provide a tool to measure the pandemic potential of new viruses immediately after their discovery. The researchers point out that the most severe pandemics of recent decades were mainly caused by viruses whose genome is composed of RNA, not DNA. Despite thousands of species of RNA viruses being identified—and possibly millions in nature—only 239 are known to infect humans. It was on this set of viruses that the scientists elaborated the catalog to highlight the highest risks.
Decisive Factor: Human Transmission
The researchers emphasize that the severity and type of disease are not sufficient to cause a pandemic. For a virus to become a global threat, it must be able to spread among people, whether through physical contact, aerosols, blood, feces, or via vectors such as mosquitoes and ticks. The survey showed that approximately two-thirds of the cataloged viruses have a low chance of transmission from one individual to another. These pathogens are classified as zoonotic, meaning they generally pass from animals to humans but do not persist in human circulation. Rabies is mentioned as an example of this. However, the authors observe that viruses evolve rapidly, which raises concerns that some zoonotic virus might acquire the capacity for continuous transmission between humans. This possibility explains part of the concern over avian flu, although the researchers state there is no documented record of an RNA virus acquiring such capacity after circulating only in animals. Rabies, for instance, has never spread among people, even with thousands of annual cases.
Greater Risk in Adapted Viruses
Scientists consider that the most substantial danger lies in viruses that can already spread among humans. Such agents can increase their transmissibility over time, as seen in several variants of SARS-CoV-2, but they had already crossed the species barrier, possessing the capacity for interpersonal transmission. Researchers suggest that, in the distant past, this was probably the path of emergence for viruses causing diseases such as measles, mumps, and rubella, as well as numerous viruses related to colds and gastrointestinal infections.
Limited Outbreaks Also Deserve Attention
The catalog also covers viruses that transmit between people but have so far only caused limited outbreaks. This occurs because the R number, a metric that measures the average number of people infected by each case, remains low, causing transmission chains to naturally cease. However, this indicator can change depending on conditions. One cited case is the Ebola Zaire virus, which caused a major epidemic in West Africa in 2014 after reaching urban centers, having previously been confined to isolated villages.
Prediction Based on History
Historically, only a few dozen viruses have entered the list of agents associated with outbreaks. Even so, researchers consider this group a strong indication of future health emergencies. Among the viruses initially included are Ebola Zaire, Chikungunya, Zika, and Oropouche viruses—transmitted by insects—and mpox, which has a DNA genome. All of these have caused major epidemics. Other lesser-known viruses have also gained prominence recently, such as the Andes hantavirus, linked to an outbreak on a cruise ship, and the Bundibugyo ebolavirus, which is currently spreading in Central Africa.
Projection of the Next Pandemic Virus
The data from the catalog also allows researchers to project what the so-called 'Disease X' virus will look like, a term used to designate a future unknown pandemic. Covid-19 serves as an example of this prediction. In 2019, the University of Edinburgh team released an analysis indicating that highly transmissible viruses are often close relatives of other viruses already circulating among humans, even if they emerge independently from animal reservoirs. This description fit perfectly with SARS-CoV-2, which showed great similarity to the SARS coronavirus but was acquired independently—and possibly indirectly—from bats. A year before the start of the COVID-19 pandemic, the World Health Organization had already suggested a SARS-like coronavirus as a candidate for Disease X, which contributed to the rapid response of the scientific community to the emergence of Covid-19.
Limitations of Pandemic Potential
The study highlights that not all newly identified viruses possess the adequate characteristics to trigger a global pandemic. Researchers state that neither the Andes hantavirus nor the Bundibugyo ebolavirus presents the necessary profile for an event of this magnitude. On the other hand, they warn that the appearance of a new measles-related virus would have a much more alarming potential, potentially leading to a global health emergency more severe than Covid-19.
Importance of Rapid Detection
Researchers highlight a common lesson observed in various recent outbreaks. Both the Andes hantavirus and the Bundibugyo ebolavirus continued to circulate for weeks before being identified, just like SARS-CoV-2 at the beginning of the Covid-19 pandemic. For the team, identifying and understanding new viruses more quickly would diminish the initial advantage of these pathogens, which could significantly impact the final death toll and the social and economic effects of future pandemics.