Animal-to-human viral epidemics increasing

Four types of animal-to-human viral infections have been increasing at an exponential rate, with epidemics generally becoming larger and more frequent over the past 60 years.

Scientists, writing in the influential BMJ Global Health say on current trends, zoonotic events are expected to collectively kill 12 times as many people in 2050 as they did in 2020.

The findings outlined in a new study come from an analysis of more than 3150 outbreaks and epidemics between 1963 and 2019.

“The devastating impact of contemporary zoonotic spillover-driven epidemics on human health and livelihoods, has highlighted the need to better understand trends in infectious disease spillover,” the authors write in the paper.

Human-driven changes to climate and land use, as well as population density and connectivity, are predicted to increase the frequency of animal-to-human viral spillover epidemics in the future.

But according to the study “the magnitude of its implications for global health in the future is difficult to characterise given the limited empirical data on the frequency of zoonotic spillover, and its variability over time.”

So, the researchers set out to look for trends in historical spillover events that might shed light on future expected patterns. 

They focused on Filoviruses like Ebola virus and Marburg virus, SARS Coronavirus 1 – which causes Severe Acute Respiratory Syndrome(SARS) – Nipah virus, and Machupo virus – which causes Bolivian haemorrhagic fever – because of their potential to pose a significant risk to public health, economic, or political stability.

“We find the number of outbreaks and deaths caused collectively by this subset of pathogens have been increasing at an exponential rate from 1963 to 2019,” they write.

They identified a total of 75 spillover events, occurring in 24 countries and causing 17,232 deaths, during this period. They estimate that the number of reported outbreaks has been increasing by about 5% annually, while the number of reported deaths has been increasing by about 9%.

“If the trend observed in this study continues, we would expect these pathogens to cause four times the number of spillover events and 12 times the number of deaths in 2050, compared with 2020.”

“This study suggests the series of recent impactful spillover-driven epidemics are not random anomalies, but follow a multi-decade trend in which epidemics have become both larger and more frequent,” they write.

“These findings provide additional evidence that concerted global efforts to improve our capacity to prevent and contain outbreaks are urgently needed to address this large and growing risk to global health.”